John Larkin wrote:
------------------------------
> >>
> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> >> > I will be driving it from both sides, but not at the same time.
> >>
> >> Sure, a transformer works either way.
> >>
> >
> >** But makers nominate the primary and secondary for good reasons.
> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> >
>
> Any winding can magnetize the core. The primary is the one you decide
> to put power into and the secondary is the one you elect to take power
> out of.

** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.

> 2-winding power transformers are usually designed for equal copper
> loss on both windings. So are thermally symmetric. >
> Sometimes some windings are insulated better than others.
>
> What other catches might there be?

** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.

You may have to seriously de-rate the transformer in order to use it that way, mains frequency transformers under 100VA are the most affected.

....... Phil

On Sat, 01 Jul 2023 21:27:42 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:

>On Sat, 1 Jul 2023 19:32:12 -0700 (PDT), Phil Allison
><pallison49@gmail.com> wrote:
>
>>John Larkin wrote:
>>----------------------------
>>> Eddy Lee
>>>
>>> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
>>> > I will be driving it from both sides, but not at the same time.
>>>
>>> Sure, a transformer works either way.
>>>
>>
>>** But makers nominate the primary and secondary for good reasons.
>>
>>The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
>>
>>
>>
>>
>>...... Phil
>
>Any winding can magnetize the core. The primary is the one you decide
>to put power into and the secondary is the one you elect to take power
>out of.
>
>2-winding power transformers are usually designed for equal copper
>loss on both windings. So are thermally symmetric.
>
>Sometimes some windings are insulated better than others.
>
>What other catches might there be?

Those (380/220 V), 400/230 V or 690/230 V transformers are typically
used with big three phase motors running with delta feed only (no
neutral available).

If some ordinary small 230 V loads, such as local control panels or
lights, are needed close to the motor, just connect the small
transformer primary between two phases pf the 400 V or 630 V delta
feed. The secondary 230 V feeds low power mains equipment, with
possibly grounding the cold end of the secondary, if local regulations
demand it.

Industrial gear are usually designed for well below absolute maximum
ratings to ensure long lifetime. Swapping primary and secondary should
not be an issue, unless you load the transformer with 100 % or more as
in some consumer electronics cases.

I guess similar transformers for the US market are 480/120 V for three
phase 480 V delta motor systems.

On Sat, 1 Jul 2023 23:07:24 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>------------------------------
>> >>
>> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
>> >> > I will be driving it from both sides, but not at the same time.
>> >>
>> >> Sure, a transformer works either way.
>> >>
>> >
>> >** But makers nominate the primary and secondary for good reasons.
>> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
>> >
>>
>> Any winding can magnetize the core. The primary is the one you decide
>> to put power into and the secondary is the one you elect to take power
>> out of.
>
>** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
>
>> 2-winding power transformers are usually designed for equal copper
>> loss on both windings. So are thermally symmetric. >
>> Sometimes some windings are insulated better than others.
>>
>> What other catches might there be?
>
>** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
>

That's easy to think through. Power transformer models are simple and
easy to reverse.

>You may have to seriously de-rate the transformer in order to use it that way, mains frequency transformers under 100VA are the most affected.

A 100 VA transformer is happy moving 100 VA in either direction.

Mike Monett VE3BTI <spamme@not.com> wrote:

> upsidedown@downunder.com wrote:
>
>> On Sat, 1 Jul 2023 05:07:53 -0700 (PDT), Eddy Lee
>> <eddy711lee@gmail.com> wrote:
>>
>>>47uF 400V cap.
>>
>> If you feed the 220/380 V transformer with something that even
>> remotely looks like 220 Vrms and rectify the output with a bridge
>> rectifier, the idle (no load) voltage will be the peak voltage or
>> about 530 V.
>>
>> I would suggest using a capacitor rated for 600 V.
>
> That hardly provides any margin.
>
> Use two 450 volt caps in series with equalizing resistors in parallel.

Plus two reverse polarity diodes.

--
MRM

John Larkin wrote:
------------------------------
> >> >>
> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> >> >> > I will be driving it from both sides, but not at the same time.
> >> >>
> >> >> Sure, a transformer works either way.
> >> >>
> >> >
> >> >** But makers nominate the primary and secondary for good reasons.
> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> >> >
> >>
> >> Any winding can magnetize the core. The primary is the one you decide
> >> to put power into and the secondary is the one you elect to take power
> >> out of.
> >
> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> >
> >> 2-winding power transformers are usually designed for equal copper
> >> loss on both windings. So are thermally symmetric. >
> >> Sometimes some windings are insulated better than others.
> >>
> >> What other catches might there be?
> >
> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> >
> That's easy to think through. Power transformer models are simple and
> easy to reverse.

** But real transformers are not so simple.

> >You may have to seriously de-rate the transformer in order to use it that way,
>> mains frequency transformers under 100VA are the most affected.

> A 100 VA transformer is happy moving 100 VA in either direction.

** JL has such simple faith in overly simple models.

I wonder why ?

...... Phil

On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>------------------------------
>> >> >>
>> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
>> >> >> > I will be driving it from both sides, but not at the same time.
>> >> >>
>> >> >> Sure, a transformer works either way.
>> >> >>
>> >> >
>> >> >** But makers nominate the primary and secondary for good reasons.
>> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
>> >> >
>> >>
>> >> Any winding can magnetize the core. The primary is the one you decide
>> >> to put power into and the secondary is the one you elect to take power
>> >> out of.
>> >
>> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
>> >
>> >> 2-winding power transformers are usually designed for equal copper
>> >> loss on both windings. So are thermally symmetric. >
>> >> Sometimes some windings are insulated better than others.
>> >>
>> >> What other catches might there be?
>> >
>> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
>> >
>> That's easy to think through. Power transformer models are simple and
>> easy to reverse.
>
> ** But real transformers are not so simple.

The Spice model of a transformer is simple: each winding has ESR,
there's magnetizing inductance, and there's leakage inductance. Ignore
capacitances at line frequencies.

Given a Spice model, you can run it in either direction, with
resistive or diode loads or whatever, and Spice will tell you
everything you need to know. The only gotcha it misses is core
saturation.

I had to take TWO semisters of Electrical Machinery at Tulane, which
was a huge nuisance, but I did learn about the circuit equivalent of a
transformer, which was almost worth the hassle.

>
>> >You may have to seriously de-rate the transformer in order to use it that way,
>>> mains frequency transformers under 100VA are the most affected.
>
>> A 100 VA transformer is happy moving 100 VA in either direction.
>
> ** JL has such simple faith in overly simple models.
>
> I wonder why ?

I design things that work, and verify by experiment if there's any
doubt. And the transformer model IS simple.

One thing that's often worth verifying is temperature rise, with
actual mounting and air flow. Transformer vendors are vague and the
thermals are hard to math out. [1]

If you are concerned about reversing a transformer, just try it.

[1] the affect of air flow and duty cycle on parts is rarely
mentioned.

On a sunny day (Sun, 2 Jul 2023 04:19:47 -0700 (PDT)) it happened Phil Allison
<pallison49@gmail.com> wrote in
<5f09e2f5-5376-44bd-8d95-f299090aad04n@googlegroups.com>:

>John Larkin wrote:
>------------------------------
>> >> >>
>> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
>> >> >> > I will be driving it from both sides, but not at the same time.
>> >> >>
>> >> >> Sure, a transformer works either way.
>> >> >>
>> >> >
>> >> >** But makers nominate the primary and secondary for good reasons.
>> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the
>> >> >secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
>> >> >
>> >>
>> >> Any winding can magnetize the core. The primary is the one you decide
>> >> to put power into and the secondary is the one you elect to take power
>> >> out of.
>> >
>> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
>> >
>> >
>> >> 2-winding power transformers are usually designed for equal copper
>> >> loss on both windings. So are thermally symmetric. >
>> >> Sometimes some windings are insulated better than others.
>> >>
>> >> What other catches might there be?
>> >
>> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the
>> >full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
>> >
>> That's easy to think through. Power transformer models are simple and
>> easy to reverse.
>
> ** But real transformers are not so simple.
>
>> >You may have to seriously de-rate the transformer in order to use it that way,
>>> mains frequency transformers under 100VA are the most affected.
>
>> A 100 VA transformer is happy moving 100 VA in either direction.
>
> ** JL has such simple faith in overly simple models.
>
> I wonder why ?

Because it works, did something for the county here like that to replaces a very complex design..
Used existing transformer models in reverse.

> ...... Phil
>

On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> <palli...@gmail.com> wrote:
>
> >John Larkin wrote:
> >------------------------------
> >> >> >>
> >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> >> >> >> > I will be driving it from both sides, but not at the same time..
> >> >> >>
> >> >> >> Sure, a transformer works either way.
> >> >> >>
> >> >> >
> >> >> >** But makers nominate the primary and secondary for good reasons.
> >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> >> >> >
> >> >>
> >> >> Any winding can magnetize the core. The primary is the one you decide
> >> >> to put power into and the secondary is the one you elect to take power
> >> >> out of.
> >> >
> >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> >> >
> >> >> 2-winding power transformers are usually designed for equal copper
> >> >> loss on both windings. So are thermally symmetric. >
> >> >> Sometimes some windings are insulated better than others.
> >> >>
> >> >> What other catches might there be?
> >> >
> >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> >> >
> >> That's easy to think through. Power transformer models are simple and
> >> easy to reverse.
> >
> > ** But real transformers are not so simple.
> The Spice model of a transformer is simple: each winding has ESR,
> there's magnetizing inductance, and there's leakage inductance. Ignore
> capacitances at line frequencies.
>
> Given a Spice model, you can run it in either direction, with
> resistive or diode loads or whatever, and Spice will tell you
> everything you need to know. The only gotcha it misses is core
> saturation.
>
> I had to take TWO semisters of Electrical Machinery at Tulane, which
> was a huge nuisance, but I did learn about the circuit equivalent of a
> transformer, which was almost worth the hassle.
> >
> >> >You may have to seriously de-rate the transformer in order to use it that way,
> >>> mains frequency transformers under 100VA are the most affected.
> >
> >> A 100 VA transformer is happy moving 100 VA in either direction.
> >
> > ** JL has such simple faith in overly simple models.
> >
> > I wonder why ?
> I design things that work, and verify by experiment if there's any
> doubt. And the transformer model IS simple.
>
> One thing that's often worth verifying is temperature rise, with
> actual mounting and air flow. Transformer vendors are vague and the
> thermals are hard to math out. [1]
>
> If you are concerned about reversing a transformer, just try it.
>
> [1] the affect of air flow and duty cycle on parts is rarely
> mentioned.

There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect..
A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.

On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > <palli...@gmail.com> wrote:
> >
> > >John Larkin wrote:
> > >------------------------------
> > >> >> >>
> > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > >> >> >> > I will be driving it from both sides, but not at the same time.
> > >> >> >>
> > >> >> >> Sure, a transformer works either way.
> > >> >> >>
> > >> >> >
> > >> >> >** But makers nominate the primary and secondary for good reasons.
> > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > >> >> >
> > >> >>
> > >> >> Any winding can magnetize the core. The primary is the one you decide
> > >> >> to put power into and the secondary is the one you elect to take power
> > >> >> out of.
> > >> >
> > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > >> >
> > >> >> 2-winding power transformers are usually designed for equal copper
> > >> >> loss on both windings. So are thermally symmetric. >
> > >> >> Sometimes some windings are insulated better than others.
> > >> >>
> > >> >> What other catches might there be?
> > >> >
> > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > >> >
> > >> That's easy to think through. Power transformer models are simple and
> > >> easy to reverse.
> > >
> > > ** But real transformers are not so simple.
> > The Spice model of a transformer is simple: each winding has ESR,
> > there's magnetizing inductance, and there's leakage inductance. Ignore
> > capacitances at line frequencies.
> >
> > Given a Spice model, you can run it in either direction, with
> > resistive or diode loads or whatever, and Spice will tell you
> > everything you need to know. The only gotcha it misses is core
> > saturation.
> >
> > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > was a huge nuisance, but I did learn about the circuit equivalent of a
> > transformer, which was almost worth the hassle.
> > >
> > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > >>> mains frequency transformers under 100VA are the most affected.
> > >
> > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > >
> > > ** JL has such simple faith in overly simple models.
> > >
> > > I wonder why ?
> > I design things that work, and verify by experiment if there's any
> > doubt. And the transformer model IS simple.
> >
> > One thing that's often worth verifying is temperature rise, with
> > actual mounting and air flow. Transformer vendors are vague and the
> > thermals are hard to math out. [1]
> >
> > If you are concerned about reversing a transformer, just try it.
> >
> > [1] the affect of air flow and duty cycle on parts is rarely
> > mentioned.
> There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.

From my measurement of 250V DC (around 12% higher) out of 220V DC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.

Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.

On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:
> On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > > <palli...@gmail.com> wrote:
> > >
> > > >John Larkin wrote:
> > > >------------------------------
> > > >> >> >>
> > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > > >> >> >> > I will be driving it from both sides, but not at the same time.
> > > >> >> >>
> > > >> >> >> Sure, a transformer works either way.
> > > >> >> >>
> > > >> >> >
> > > >> >> >** But makers nominate the primary and secondary for good reasons.
> > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > > >> >> >
> > > >> >>
> > > >> >> Any winding can magnetize the core. The primary is the one you decide
> > > >> >> to put power into and the secondary is the one you elect to take power
> > > >> >> out of.
> > > >> >
> > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > > >> >
> > > >> >> 2-winding power transformers are usually designed for equal copper
> > > >> >> loss on both windings. So are thermally symmetric. >
> > > >> >> Sometimes some windings are insulated better than others.
> > > >> >>
> > > >> >> What other catches might there be?
> > > >> >
> > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > > >> >
> > > >> That's easy to think through. Power transformer models are simple and
> > > >> easy to reverse.
> > > >
> > > > ** But real transformers are not so simple.
> > > The Spice model of a transformer is simple: each winding has ESR,
> > > there's magnetizing inductance, and there's leakage inductance. Ignore
> > > capacitances at line frequencies.
> > >
> > > Given a Spice model, you can run it in either direction, with
> > > resistive or diode loads or whatever, and Spice will tell you
> > > everything you need to know. The only gotcha it misses is core
> > > saturation.
> > >
> > > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > > was a huge nuisance, but I did learn about the circuit equivalent of a
> > > transformer, which was almost worth the hassle.
> > > >
> > > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > > >>> mains frequency transformers under 100VA are the most affected.
> > > >
> > > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > > >
> > > > ** JL has such simple faith in overly simple models.
> > > >
> > > > I wonder why ?
> > > I design things that work, and verify by experiment if there's any
> > > doubt. And the transformer model IS simple.
> > >
> > > One thing that's often worth verifying is temperature rise, with
> > > actual mounting and air flow. Transformer vendors are vague and the
> > > thermals are hard to math out. [1]
> > >
> > > If you are concerned about reversing a transformer, just try it.
> > >
> > > [1] the affect of air flow and duty cycle on parts is rarely
> > > mentioned.
> > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
> From my measurement of 250V DC (around 12% higher) out of 220V DC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.

You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.

>
> Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.

If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.

On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote:
> On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:
> > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > > > <palli...@gmail.com> wrote:
> > > >
> > > > >John Larkin wrote:
> > > > >------------------------------
> > > > >> >> >>
> > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > > > >> >> >> > I will be driving it from both sides, but not at the same time.
> > > > >> >> >>
> > > > >> >> >> Sure, a transformer works either way.
> > > > >> >> >>
> > > > >> >> >
> > > > >> >> >** But makers nominate the primary and secondary for good reasons.
> > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > > > >> >> >
> > > > >> >>
> > > > >> >> Any winding can magnetize the core. The primary is the one you decide
> > > > >> >> to put power into and the secondary is the one you elect to take power
> > > > >> >> out of.
> > > > >> >
> > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > > > >> >
> > > > >> >> 2-winding power transformers are usually designed for equal copper
> > > > >> >> loss on both windings. So are thermally symmetric. >
> > > > >> >> Sometimes some windings are insulated better than others.
> > > > >> >>
> > > > >> >> What other catches might there be?
> > > > >> >
> > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > > > >> >
> > > > >> That's easy to think through. Power transformer models are simple and
> > > > >> easy to reverse.
> > > > >
> > > > > ** But real transformers are not so simple.
> > > > The Spice model of a transformer is simple: each winding has ESR,
> > > > there's magnetizing inductance, and there's leakage inductance. Ignore
> > > > capacitances at line frequencies.
> > > >
> > > > Given a Spice model, you can run it in either direction, with
> > > > resistive or diode loads or whatever, and Spice will tell you
> > > > everything you need to know. The only gotcha it misses is core
> > > > saturation.
> > > >
> > > > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > > > was a huge nuisance, but I did learn about the circuit equivalent of a
> > > > transformer, which was almost worth the hassle.
> > > > >
> > > > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > > > >>> mains frequency transformers under 100VA are the most affected.
> > > > >
> > > > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > > > >
> > > > > ** JL has such simple faith in overly simple models.
> > > > >
> > > > > I wonder why ?
> > > > I design things that work, and verify by experiment if there's any
> > > > doubt. And the transformer model IS simple.
> > > >
> > > > One thing that's often worth verifying is temperature rise, with
> > > > actual mounting and air flow. Transformer vendors are vague and the
> > > > thermals are hard to math out. [1]
> > > >
> > > > If you are concerned about reversing a transformer, just try it.
> > > >
> > > > [1] the affect of air flow and duty cycle on parts is rarely
> > > > mentioned.
> > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
> > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.
> You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.

Full bridge rectifier and 82uF 450V capacitor. Steady reading of 450V DC. I can try out a different inverter.

I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine.
> > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be e.
asier to adjust input between 20V to 24V.
> If you have that transformer on hand, go for it, it should work just fine.. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.

Ordered a 10W version to test. Will get the 100W version if it works.

On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote:
> On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote:
> > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:
> > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > > > > <palli...@gmail.com> wrote:
> > > > >
> > > > > >John Larkin wrote:
> > > > > >------------------------------
> > > > > >> >> >>
> > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > > > > >> >> >> > I will be driving it from both sides, but not at the same time.
> > > > > >> >> >>
> > > > > >> >> >> Sure, a transformer works either way.
> > > > > >> >> >>
> > > > > >> >> >
> > > > > >> >> >** But makers nominate the primary and secondary for good reasons.
> > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > > > > >> >> >
> > > > > >> >>
> > > > > >> >> Any winding can magnetize the core. The primary is the one you decide
> > > > > >> >> to put power into and the secondary is the one you elect to take power
> > > > > >> >> out of.
> > > > > >> >
> > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > > > > >> >
> > > > > >> >> 2-winding power transformers are usually designed for equal copper
> > > > > >> >> loss on both windings. So are thermally symmetric. >
> > > > > >> >> Sometimes some windings are insulated better than others.
> > > > > >> >>
> > > > > >> >> What other catches might there be?
> > > > > >> >
> > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > > > > >> >
> > > > > >> That's easy to think through. Power transformer models are simple and
> > > > > >> easy to reverse.
> > > > > >
> > > > > > ** But real transformers are not so simple.
> > > > > The Spice model of a transformer is simple: each winding has ESR,
> > > > > there's magnetizing inductance, and there's leakage inductance. Ignore
> > > > > capacitances at line frequencies.
> > > > >
> > > > > Given a Spice model, you can run it in either direction, with
> > > > > resistive or diode loads or whatever, and Spice will tell you
> > > > > everything you need to know. The only gotcha it misses is core
> > > > > saturation.
> > > > >
> > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > > > > was a huge nuisance, but I did learn about the circuit equivalent of a
> > > > > transformer, which was almost worth the hassle.
> > > > > >
> > > > > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > > > > >>> mains frequency transformers under 100VA are the most affected.
> > > > > >
> > > > > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > > > > >
> > > > > > ** JL has such simple faith in overly simple models.
> > > > > >
> > > > > > I wonder why ?
> > > > > I design things that work, and verify by experiment if there's any
> > > > > doubt. And the transformer model IS simple.
> > > > >
> > > > > One thing that's often worth verifying is temperature rise, with
> > > > > actual mounting and air flow. Transformer vendors are vague and the
> > > > > thermals are hard to math out. [1]
> > > > >
> > > > > If you are concerned about reversing a transformer, just try it.
> > > > >
> > > > > [1] the affect of air flow and duty cycle on parts is rarely
> > > > > mentioned.
> > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
> > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.
> > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.
> Full bridge rectifier and 82uF 450V capacitor. Steady reading of 350V DC. I can try out a different inverter.
>
> I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine.
>
> > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be e.
> asier to adjust input between 20V to 24V.
> > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.
> Ordered a 10W version to test. Will get the 100W version if it works.

Correction: 450V DC to 350V DC.

On Sunday, July 2, 2023 at 12:51:41 PM UTC-7, Eddy Lee wrote:
> On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote:
> > On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote:
> > > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:
> > > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> > > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > > > > > <palli...@gmail.com> wrote:
> > > > > >
> > > > > > >John Larkin wrote:
> > > > > > >------------------------------
> > > > > > >> >> >>
> > > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > > > > > >> >> >> > I will be driving it from both sides, but not at the same time.
> > > > > > >> >> >>
> > > > > > >> >> >> Sure, a transformer works either way.
> > > > > > >> >> >>
> > > > > > >> >> >
> > > > > > >> >> >** But makers nominate the primary and secondary for good reasons.
> > > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > > > > > >> >> >
> > > > > > >> >>
> > > > > > >> >> Any winding can magnetize the core. The primary is the one you decide
> > > > > > >> >> to put power into and the secondary is the one you elect to take power
> > > > > > >> >> out of.
> > > > > > >> >
> > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > > > > > >> >
> > > > > > >> >> 2-winding power transformers are usually designed for equal copper
> > > > > > >> >> loss on both windings. So are thermally symmetric. >
> > > > > > >> >> Sometimes some windings are insulated better than others.
> > > > > > >> >>
> > > > > > >> >> What other catches might there be?
> > > > > > >> >
> > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > > > > > >> >
> > > > > > >> That's easy to think through. Power transformer models are simple and
> > > > > > >> easy to reverse.
> > > > > > >
> > > > > > > ** But real transformers are not so simple.
> > > > > > The Spice model of a transformer is simple: each winding has ESR,
> > > > > > there's magnetizing inductance, and there's leakage inductance. Ignore
> > > > > > capacitances at line frequencies.
> > > > > >
> > > > > > Given a Spice model, you can run it in either direction, with
> > > > > > resistive or diode loads or whatever, and Spice will tell you
> > > > > > everything you need to know. The only gotcha it misses is core
> > > > > > saturation.
> > > > > >
> > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > > > > > was a huge nuisance, but I did learn about the circuit equivalent of a
> > > > > > transformer, which was almost worth the hassle.
> > > > > > >
> > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > > > > > >>> mains frequency transformers under 100VA are the most affected.
> > > > > > >
> > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > > > > > >
> > > > > > > ** JL has such simple faith in overly simple models.
> > > > > > >
> > > > > > > I wonder why ?
> > > > > > I design things that work, and verify by experiment if there's any
> > > > > > doubt. And the transformer model IS simple.
> > > > > >
> > > > > > One thing that's often worth verifying is temperature rise, with
> > > > > > actual mounting and air flow. Transformer vendors are vague and the
> > > > > > thermals are hard to math out. [1]
> > > > > >
> > > > > > If you are concerned about reversing a transformer, just try it..
> > > > > >
> > > > > > [1] the affect of air flow and duty cycle on parts is rarely
> > > > > > mentioned.
> > > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> > > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
> > > > From my measurement of 250V DC (around 12% higher) out of 220V AC. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.
> > > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.

> > Full bridge rectifier and 82uF 450V capacitor. Steady reading of 250V DC. I can try out a different inverter.
> >
> > I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine.
> >
> > > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.
> > > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.
> > Ordered a 10W version to test. Will get the 100W version if it works.
> Correction: 450V DC to 350V DC.

Correction again: measured 250V DC out of 220V AC inverter.

250V DC (from inverter) + 170V (from wall) would be perfect. But the wall is not always available.

On Sunday, July 2, 2023 at 4:19:08 PM UTC-4, Eddy Lee wrote:
> On Sunday, July 2, 2023 at 12:51:41 PM UTC-7, Eddy Lee wrote:
> > On Sunday, July 2, 2023 at 12:46:04 PM UTC-7, Eddy Lee wrote:
> > > On Sunday, July 2, 2023 at 12:26:54 PM UTC-7, Fred Bloggs wrote:
> > > > On Sunday, July 2, 2023 at 3:07:52 PM UTC-4, Eddy Lee wrote:
> > > > > On Sunday, July 2, 2023 at 11:00:17 AM UTC-7, Fred Bloggs wrote:
> > > > > > On Sunday, July 2, 2023 at 7:39:31 AM UTC-4, John Larkin wrote:
> > > > > > > On Sun, 2 Jul 2023 04:19:47 -0700 (PDT), Phil Allison
> > > > > > > <palli...@gmail.com> wrote:
> > > > > > >
> > > > > > > >John Larkin wrote:
> > > > > > > >------------------------------
> > > > > > > >> >> >>
> > > > > > > >> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
> > > > > > > >> >> >> > I will be driving it from both sides, but not at the same time.
> > > > > > > >> >> >>
> > > > > > > >> >> >> Sure, a transformer works either way.
> > > > > > > >> >> >>
> > > > > > > >> >> >
> > > > > > > >> >> >** But makers nominate the primary and secondary for good reasons.
> > > > > > > >> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
> > > > > > > >> >> >
> > > > > > > >> >>
> > > > > > > >> >> Any winding can magnetize the core. The primary is the one you decide
> > > > > > > >> >> to put power into and the secondary is the one you elect to take power
> > > > > > > >> >> out of.
> > > > > > > >> >
> > > > > > > >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> > > > > > > >> >
> > > > > > > >> >> 2-winding power transformers are usually designed for equal copper
> > > > > > > >> >> loss on both windings. So are thermally symmetric. >
> > > > > > > >> >> Sometimes some windings are insulated better than others.
> > > > > > > >> >>
> > > > > > > >> >> What other catches might there be?
> > > > > > > >> >
> > > > > > > >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> > > > > > > >> >
> > > > > > > >> That's easy to think through. Power transformer models are simple and
> > > > > > > >> easy to reverse.
> > > > > > > >
> > > > > > > > ** But real transformers are not so simple.
> > > > > > > The Spice model of a transformer is simple: each winding has ESR,
> > > > > > > there's magnetizing inductance, and there's leakage inductance. Ignore
> > > > > > > capacitances at line frequencies.
> > > > > > >
> > > > > > > Given a Spice model, you can run it in either direction, with
> > > > > > > resistive or diode loads or whatever, and Spice will tell you
> > > > > > > everything you need to know. The only gotcha it misses is core
> > > > > > > saturation.
> > > > > > >
> > > > > > > I had to take TWO semisters of Electrical Machinery at Tulane, which
> > > > > > > was a huge nuisance, but I did learn about the circuit equivalent of a
> > > > > > > transformer, which was almost worth the hassle.
> > > > > > > >
> > > > > > > >> >You may have to seriously de-rate the transformer in order to use it that way,
> > > > > > > >>> mains frequency transformers under 100VA are the most affected.
> > > > > > > >
> > > > > > > >> A 100 VA transformer is happy moving 100 VA in either direction.
> > > > > > > >
> > > > > > > > ** JL has such simple faith in overly simple models.
> > > > > > > >
> > > > > > > > I wonder why ?
> > > > > > > I design things that work, and verify by experiment if there's any
> > > > > > > doubt. And the transformer model IS simple.
> > > > > > >
> > > > > > > One thing that's often worth verifying is temperature rise, with
> > > > > > > actual mounting and air flow. Transformer vendors are vague and the
> > > > > > > thermals are hard to math out. [1]
> > > > > > >
> > > > > > > If you are concerned about reversing a transformer, just try it.
> > > > > > >
> > > > > > > [1] the affect of air flow and duty cycle on parts is rarely
> > > > > > > mentioned.
> > > > > > There's nothing to justify the hysteria about reversing the power flow in a transformer. Unless it can be shown that something about transformer operation is compromised by the direction of power flow. There is no such effect.
> > > > > > A very safe bet is taking one of those 220:120 transformers and wiring as autotransformer with secondary aiding. That gives him the 340 V,RMS required for a 450 VDC supply. He can double insulate his hot side load.. The only problem is size and expense of transformer required. I don't think it's going to compete with that 7 lb weight Chinese switcher.
> > > > > From my measurement of 250V DC (around 12% higher) out of 220V AC.. 340V AC would only give around 384V DC. 429V DC out of 380V AC would be better.
> > > > You can't trust a general purpose multimeter to make reliable measurements of those broken waveforms. The 340 VAC has a peak of 340 x SQRT(2)= 480 Vpk. Full wave rectified and capacitor filtered should give you 450 VDC.
> > > Full bridge rectifier and 82uF 450V capacitor. Steady reading of 250V DC. I can try out a different inverter.
> > >
> > > I got 170V DC if i connect my rectifier to the 110V outlet. So, i am sure the circuit is working fine.
> > >
> > > > > Alternatively, I am going to try a 24 to 380 reverse transformer. It might be easier to adjust input between 20V to 24V.
> > > > If you have that transformer on hand, go for it, it should work just fine. That lower primary voltage gives you the opportunity to AC regulate the output with cheaper and more readily available parts too. Watch your HV filter cap selection.
> > > Ordered a 10W version to test. Will get the 100W version if it works.
> > Correction: 450V DC to 350V DC.
> Correction again: measured 250V DC out of 220V AC inverter.
>
> 250V DC (from inverter) + 170V (from wall) would be perfect. But the wall is not always available.

Some of these inverters put out square waves. The RMS of a square wave of amplitude V is V. So if the nameplate says 220V,RMS, its peak is only 220V, which is down 30% from a transformer output. Others put out some kind of stepped waveform, but you'll have the same effect. That would explain the discrepancies you're seeing with them.

John Larkin wrote:
---------------------------

> >> >
> >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
> >> >
> >> >> 2-winding power transformers are usually designed for equal copper
> >> >> loss on both windings. So are thermally symmetric. >
> >> >> Sometimes some windings are insulated better than others.
> >> >>
> >> >> What other catches might there be?
> >> >
> >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
> >> >
> >> That's easy to think through. Power transformer models are simple and
> >> easy to reverse.
> >
> > ** But real transformers are not so simple.
>
> Given a Spice model, you can run it in either direction, with
> resistive or diode loads or whatever, and Spice will tell you
> everything you need to know. The only gotcha it misses is core
> saturation.

** That "gotcha" is the biggie here.

> >> >You may have to seriously de-rate the transformer in order to use it that way,
> >>> mains frequency transformers under 100VA are the most affected.
> >
> >> A 100 VA transformer is happy moving 100 VA in either direction.
> >
> > ** JL has such simple faith in overly simple models.
> >
> > I wonder why ?
>
> If you are concerned about reversing a transformer, just try it.
>

** LOL - of *course* I have and that is why I know about the pitfalls.

........ Phil

On Sun, 2 Jul 2023 18:43:01 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>---------------------------
>
>> >> >
>> >> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
>> >> >
>> >> >> 2-winding power transformers are usually designed for equal copper
>> >> >> loss on both windings. So are thermally symmetric. >
>> >> >> Sometimes some windings are insulated better than others.
>> >> >>
>> >> >> What other catches might there be?
>> >> >
>> >> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
>> >> >
>> >> That's easy to think through. Power transformer models are simple and
>> >> easy to reverse.
>> >
>> > ** But real transformers are not so simple.
>>
>> Given a Spice model, you can run it in either direction, with
>> resistive or diode loads or whatever, and Spice will tell you
>> everything you need to know. The only gotcha it misses is core
>> saturation.
>
> ** That "gotcha" is the biggie here.

With pure AC, just don't run it much above its rated voltage.
Whichever winding you care to call the secondary will be affected by a
net DC load current.

Basically, if you buy two equal-power-rated transformers, one sold as
120:240 and one sold as 240:120, they are the same transformer.

>
>> >> >You may have to seriously de-rate the transformer in order to use it that way,
>> >>> mains frequency transformers under 100VA are the most affected.
>> >
>> >> A 100 VA transformer is happy moving 100 VA in either direction.
>> >
>> > ** JL has such simple faith in overly simple models.
>> >
>> > I wonder why ?
>>
>> If you are concerned about reversing a transformer, just try it.
>>
>
> ** LOL - of *course* I have and that is why I know about the pitfalls.

I haven't heard any real pitfalls so far. What problems did you have?

John Larkin wrote:
----------------------------
>
> Basically, if you buy two equal-power-rated transformers, one sold as
> 120:240 and one sold as 240:120, they are the same transformer.

** But not exactly - see below.

>> >> >You may have to seriously de-rate the transformer in order to use it that way,
> >> >>> mains frequency transformers under 100VA are the most affected.
> >> >
> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
> >> >
> >> > ** JL has such simple faith in overly simple models.
> >> >
> >> > I wonder why ?
> >>
> >> If you are concerned about reversing a transformer, just try it.
> >>
> >
> > ** LOL - of *course* I have and that is why I know about the pitfalls.
>
> I haven't heard any real pitfalls so far. What problems did you have?

** Same as everyone else's !!

When roles are reversed, the previous 240VAC supply winding supplies less under load.
The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.
Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.

This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met.

....... Phil

On Sun, 2 Jul 2023 22:47:47 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>----------------------------
>>
>> Basically, if you buy two equal-power-rated transformers, one sold as
>> 120:240 and one sold as 240:120, they are the same transformer.
>
> ** But not exactly - see below.
>
>>> >> >You may have to seriously de-rate the transformer in order to use it that way,
>> >> >>> mains frequency transformers under 100VA are the most affected.
>> >> >
>> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
>> >> >
>> >> > ** JL has such simple faith in overly simple models.
>> >> >
>> >> > I wonder why ?
>> >>
>> >> If you are concerned about reversing a transformer, just try it.
>> >>
>> >
>> > ** LOL - of *course* I have and that is why I know about the pitfalls.
>>
>> I haven't heard any real pitfalls so far. What problems did you have?
>
>** Same as everyone else's !!
>
>When roles are reversed, the previous 240VAC supply winding supplies less under load.
>The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
>Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.

Sure. That's obvious from the transformer model. A given amount of
core excitation needs N*I, whichever winding makes it.

>Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.

Don't do that!

>
>This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met.
>
>

That's the part I don't see. "Primary" is an application decision, or
a data sheet convenience.

John Larkin wrote:
----------------------------
> >>
> >> Basically, if you buy two equal-power-rated transformers, one sold as
> >> 120:240 and one sold as 240:120, they are the same transformer.
> >
> > ** But not exactly - see below.
> >
> >>> >> >You may have to seriously de-rate the transformer in order to use it that way,
> >> >> >>> mains frequency transformers under 100VA are the most affected.
> >> >> >
> >> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
> >> >> >
> >> >> > ** JL has such simple faith in overly simple models.
> >> >> >
> >> >> > I wonder why ?
> >> >>
> >> >> If you are concerned about reversing a transformer, just try it.
> >> >>
> >> >
> >> > ** LOL - of *course* I have and that is why I know about the pitfalls.
> >>
> >> I haven't heard any real pitfalls so far. What problems did you have?
> >
> >** Same as everyone else's !!
> >
> >When roles are reversed, the previous 240VAC supply winding supplies less under load.
> >The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
> >Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.
>
> >Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.
> > >
> >This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met.
> >
> >
> That's the part I don't see. "Primary" is an application decision, or
> a data sheet convenience.

** It is far more than that, but you will never admit it.

........ Phil

On Mon, 3 Jul 2023 03:45:00 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

>John Larkin wrote:
>----------------------------
>> >>
>> >> Basically, if you buy two equal-power-rated transformers, one sold as
>> >> 120:240 and one sold as 240:120, they are the same transformer.
>> >
>> > ** But not exactly - see below.
>> >
>> >>> >> >You may have to seriously de-rate the transformer in order to use it that way,
>> >> >> >>> mains frequency transformers under 100VA are the most affected.
>> >> >> >
>> >> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
>> >> >> >
>> >> >> > ** JL has such simple faith in overly simple models.
>> >> >> >
>> >> >> > I wonder why ?
>> >> >>
>> >> >> If you are concerned about reversing a transformer, just try it.
>> >> >>
>> >> >
>> >> > ** LOL - of *course* I have and that is why I know about the pitfalls.
>> >>
>> >> I haven't heard any real pitfalls so far. What problems did you have?
>> >
>> >** Same as everyone else's !!
>> >
>> >When roles are reversed, the previous 240VAC supply winding supplies less under load.
>> >The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
>> >Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.
>>
>> >Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.
>> > >
>> >This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met.
>> >
>> >
>> That's the part I don't see. "Primary" is an application decision, or
>> a data sheet convenience.
>
> ** It is far more than that, but you will never admit it.
>
>
>....... Phil
>
>

The word "primary" on a data sheet doesn't stop me from using a
transformer in either direction. Like the Coilcraft PL300-100L right
now. Try and stop me!

On Monday, July 3, 2023 at 7:15:10 AM UTC-4, John Larkin wrote:
> On Mon, 3 Jul 2023 03:45:00 -0700 (PDT), Phil Allison
> <palli...@gmail.com> wrote:
>
> >John Larkin wrote:
> >----------------------------
> >> >>
> >> >> Basically, if you buy two equal-power-rated transformers, one sold as
> >> >> 120:240 and one sold as 240:120, they are the same transformer.
> >> >
> >> > ** But not exactly - see below.
> >> >
> >> >>> >> >You may have to seriously de-rate the transformer in order to use it that way,
> >> >> >> >>> mains frequency transformers under 100VA are the most affected.
> >> >> >> >
> >> >> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
> >> >> >> >
> >> >> >> > ** JL has such simple faith in overly simple models.
> >> >> >> >
> >> >> >> > I wonder why ?
> >> >> >>
> >> >> >> If you are concerned about reversing a transformer, just try it.
> >> >> >>
> >> >> >
> >> >> > ** LOL - of *course* I have and that is why I know about the pitfalls.
> >> >>
> >> >> I haven't heard any real pitfalls so far. What problems did you have?
> >> >
> >> >** Same as everyone else's !!
> >> >
> >> >When roles are reversed, the previous 240VAC supply winding supplies less under load.
> >> >The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
> >> >Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.
> >>
> >> >Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.
> >> > >
> >> >This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met..
> >> >
> >> >
> >> That's the part I don't see. "Primary" is an application decision, or
> >> a data sheet convenience.
> >
> > ** It is far more than that, but you will never admit it.
> >
> >
> >....... Phil
> >
> >
> The word "primary" on a data sheet doesn't stop me from using a
> transformer in either direction. Like the Coilcraft PL300-100L right
> now. Try and stop me!

An exception is for industrial grade "protected" transformers which have either a fuse or thermal cutout embedded in their designated "primary." That really needs to be on the line side of the transformer drive.

https://www.electronicproducts.com/protecting-transformers-with-pptc-devices/

On Mon, 3 Jul 2023 06:23:17 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

>On Monday, July 3, 2023 at 7:15:10?AM UTC-4, John Larkin wrote:
>> On Mon, 3 Jul 2023 03:45:00 -0700 (PDT), Phil Allison
>> <palli...@gmail.com> wrote:
>>
>> >John Larkin wrote:
>> >----------------------------
>> >> >>
>> >> >> Basically, if you buy two equal-power-rated transformers, one sold as
>> >> >> 120:240 and one sold as 240:120, they are the same transformer.
>> >> >
>> >> > ** But not exactly - see below.
>> >> >
>> >> >>> >> >You may have to seriously de-rate the transformer in order to use it that way,
>> >> >> >> >>> mains frequency transformers under 100VA are the most affected.
>> >> >> >> >
>> >> >> >> >> A 100 VA transformer is happy moving 100 VA in either direction.
>> >> >> >> >
>> >> >> >> > ** JL has such simple faith in overly simple models.
>> >> >> >> >
>> >> >> >> > I wonder why ?
>> >> >> >>
>> >> >> >> If you are concerned about reversing a transformer, just try it.
>> >> >> >>
>> >> >> >
>> >> >> > ** LOL - of *course* I have and that is why I know about the pitfalls.
>> >> >>
>> >> >> I haven't heard any real pitfalls so far. What problems did you have?
>> >> >
>> >> >** Same as everyone else's !!
>> >> >
>> >> >When roles are reversed, the previous 240VAC supply winding supplies less under load.
>> >> >The difference is about twice the regulation percentage, so 20 to 30% less in some cases.
>> >> >Imag current ( previously easily supplied by the mains ) goes up by the turns ratio, up to maybe 40 times in a low voltage winding.
>> >>
>> >> >Applying more than rated voltage to the secondary in order to to fix this results in excessive current and overheating the transformer.
>> >> > >
>> >> >This all derives from how transformer makers engineer * real * transformers and rely on specifying which is the primary etc so all specs are met.
>> >> >
>> >> >
>> >> That's the part I don't see. "Primary" is an application decision, or
>> >> a data sheet convenience.
>> >
>> > ** It is far more than that, but you will never admit it.
>> >
>> >
>> >....... Phil
>> >
>> >
>> The word "primary" on a data sheet doesn't stop me from using a
>> transformer in either direction. Like the Coilcraft PL300-100L right
>> now. Try and stop me!
>
>An exception is for industrial grade "protected" transformers which have either a fuse or thermal cutout embedded in their designated "primary." That really needs to be on the line side of the transformer drive.
>
>https://www.electronicproducts.com/protecting-transformers-with-pptc-devices/

Sure, if something is powered off the AC line, there needs to be
protections and the design should be able to be UL and CE certified.
One would always apply 120 volts, or whatever, to a transformer's 120
volt primary.

Fortunately, we electronics guys don't connect to the AC line a lot
ourselves any more; we can buy listed AC switch/filter/connector
things and listed switching power supplies. Or, whenever possible, use
a wart. There are some monster 24 and 48 volt warts and laptop
supplies around these days.

60 Hz magnetics and giant electrolytic caps and primary voltage
switches are big and expensive anyhow. Ancient tech.

I don't want nasty line voltage in my beautiful little boxes!

On Sun, 02 Jul 2023 11:44:20 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

>On a sunny day (Sun, 2 Jul 2023 04:19:47 -0700 (PDT)) it happened Phil Allison
><pallison49@gmail.com> wrote in
><5f09e2f5-5376-44bd-8d95-f299090aad04n@googlegroups.com>:
>
>>John Larkin wrote:
>>------------------------------
>>> >> >>
>>> >> >> >Question is whether they are symmetrical from either side (primary/secondary) in efficiency and load capacity.
>>> >> >> > I will be driving it from both sides, but not at the same time.
>>> >> >>
>>> >> >> Sure, a transformer works either way.
>>> >> >>
>>> >> >
>>> >> >** But makers nominate the primary and secondary for good reasons.
>>> >> >The primary supplies the magnetising current, which can be significant, plus is wound to allow for voltage drop at the
>>> >> >secondary under full load. If the roles are swapped, there are several changes that can catch the unwary.
>>> >> >
>>> >>
>>> >> Any winding can magnetize the core. The primary is the one you decide
>>> >> to put power into and the secondary is the one you elect to take power
>>> >> out of.
>>> >
>>> >** The maker tells you which is which because they have adjusted the windings ( number of turns and wire gauges) accordingly.
>>> >
>>> >
>>> >> 2-winding power transformers are usually designed for equal copper
>>> >> loss on both windings. So are thermally symmetric. >
>>> >> Sometimes some windings are insulated better than others.
>>> >>
>>> >> What other catches might there be?
>>> >
>>> >** As I mentioned, which winding carries the I mag plus the turns ratio have been adjusted by makers to compensate for the
>>> >full load voltage drop. Reverse the makers intended roles and those built in compensations operate in the opposite directions.
>>> >
>>> That's easy to think through. Power transformer models are simple and
>>> easy to reverse.
>>
>> ** But real transformers are not so simple.
>>
>>> >You may have to seriously de-rate the transformer in order to use it that way,
>>>> mains frequency transformers under 100VA are the most affected.
>>
>>> A 100 VA transformer is happy moving 100 VA in either direction.
>>
>> ** JL has such simple faith in overly simple models.
>>
>> I wonder why ?
>
>Because it works, did something for the county here like that to replaces a very complex design..
>Used existing transformer models in reverse.
>

My/our job is to build things that work, and we can use any design
tools, or none for that matter, that work.

Spice has removed the necessity for a heap of classic and tedious
tools and equations and papers. But any non-trivial design, no matter
how derived, will probably be simulated and often lab tested.

It's good to get away from a screen and solder up stuff now and then,
stress some parts and see what happens.

Last week I toasted a bunch of wirewound resistors and blew up a few
solid-state relays, and learned things not on data sheets.

The Coilcraft PL300 planar power transformers are dynamite. They have
6, optionally 7 windings and they call one set "primary", which is
silly; they're just windings. Leakage inductance is so low it can be
ignored.