On Fri, 3 Mar 2023 20:13:46 -0800 (PST), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

>On Saturday, March 4, 2023 at 2:04:20?PM UTC+11, John Larkin wrote:
>> On Sat, 04 Mar 2023 01:23:17 -0000, "Commander Kinsey"
>> <C...@nospam.com> wrote:
>>
>> >On Sun, 26 Feb 2023 16:13:19 -0000, John Larkin <jla...@highlandsnipmetechnology.com> wrote:
>> >
>> >> On Sun, 26 Feb 2023 09:45:26 -0000, "Commander Kinsey"
>> >> <C...@nospam.com> wrote:
>> >>
>> >>> Can I put a diode BEFORE a step up transformer so I can use a lower voltage diode for half wave rectification?
>> >>
>> >> Ah. Humor. Thanks for the laugh.
>> >
>> >I thought current always flowed the same way in primary and secondary.... You know, phases and all that.
>> Assume a loaded bifilar transformer, both dots up, and draw the
>> winding currents.
>>
>> The reason that loading a transformer doesn't make it saturate is
>> because the primary excitation flux and the flux from the secondary
>> load current cancel. Loading a transformer reduces the core flux.
>
>No exactly. The core flux has to keep increasing to generate the voltage the drives the current into the external load. Because you drive transformers with AC the voltage eventually reverses, ideally before you saturate the core.

Bill, I think this assumes that the voltage is regulated with
feedback.

Driving the transformer with, say, just grid voltage would do what JL
is talking about because the IR drop when loaded, reduces the
volt-seconds imposed on the core which is what causes saturation.

Pretty sure that's it anyway.

boB

On Sat, 04 Mar 2023 23:36:56 -0700, boB <boB@K7IQ.com> wrote:

>On Fri, 3 Mar 2023 20:13:46 -0800 (PST), Anthony William Sloman
><bill.sloman@ieee.org> wrote:
>
>>On Saturday, March 4, 2023 at 2:04:20?PM UTC+11, John Larkin wrote:
>>> On Sat, 04 Mar 2023 01:23:17 -0000, "Commander Kinsey"
>>> <C...@nospam.com> wrote:
>>>
>>> >On Sun, 26 Feb 2023 16:13:19 -0000, John Larkin <jla...@highlandsnipmetechnology.com> wrote:
>>> >
>>> >> On Sun, 26 Feb 2023 09:45:26 -0000, "Commander Kinsey"
>>> >> <C...@nospam.com> wrote:
>>> >>
>>> >>> Can I put a diode BEFORE a step up transformer so I can use a lower voltage diode for half wave rectification?
>>> >>
>>> >> Ah. Humor. Thanks for the laugh.
>>> >
>>> >I thought current always flowed the same way in primary and secondary.... You know, phases and all that.
>>> Assume a loaded bifilar transformer, both dots up, and draw the
>>> winding currents.
>>>
>>> The reason that loading a transformer doesn't make it saturate is
>>> because the primary excitation flux and the flux from the secondary
>>> load current cancel. Loading a transformer reduces the core flux.
>>
>>No exactly. The core flux has to keep increasing to generate the voltage the drives the current into the external load. Because you drive transformers with AC the voltage eventually reverses, ideally before you saturate the core.
>
>Bill, I think this assumes that the voltage is regulated with
>feedback.
>
>Driving the transformer with, say, just grid voltage would do what JL
>is talking about because the IR drop when loaded, reduces the
>volt-seconds imposed on the core which is what causes saturation.

Yes. Shorting the secondary will drop the core flux about in half.

>
>Pretty sure that's it anyway.
>
>boB

Sloman has lectured us hundreds of times about how we should design
and not buy transformers, so it's hilarious that he doesn't understand
the basics.

boB wrote:
----------------
>
> Driving the transformer with, say, just grid voltage would do what JL
> is talking about because the IR drop when loaded, reduces the
> volt-seconds imposed on the core which is what causes saturation.
>
> Pretty sure that's it anyway.
>

** Yep, magnetising current is a function of applied (AC) voltage - becoming exponential as full saturation is approached.

This is very noticeable with small transformers ( ie in wall warts) that run near full saturation when off load.
When rated load is applied, magnetising current drops due to *primary IR voltage loss* so it matches or falls below that due to supplying the secondary. The two are easily distinguished on a scope as the peak values are 90 degrees out of phase.

Unlike load current, mag peaks close to zero applied volts.

..... Phil

On Mon, 6 Mar 2023 01:35:41 -0800 (PST), Anthony William Sloman
<bill.sloman@ieee.org> wrote:

>On Monday, March 6, 2023 at 4:09:22?AM UTC+11, John Larkin wrote:
>> On Sat, 04 Mar 2023 23:36:56 -0700, boB <b...@K7IQ.com> wrote:
>> >On Fri, 3 Mar 2023 20:13:46 -0800 (PST), Anthony William Sloman <bill....@ieee.org> wrote:
>> >>On Saturday, March 4, 2023 at 2:04:20?PM UTC+11, John Larkin wrote:
>> >>> On Sat, 04 Mar 2023 01:23:17 -0000, "Commander Kinsey" <C...@nospam.com> wrote:
>> >>> >On Sun, 26 Feb 2023 16:13:19 -0000, John Larkin <jla...@highlandsnipmetechnology.com> wrote:
>> >>> >> On Sun, 26 Feb 2023 09:45:26 -0000, "Commander Kinsey" <C...@nospam.com> wrote:
>
>><snip>
>
>> >>> The reason that loading a transformer doesn't make it saturate is
>> >>> because the primary excitation flux and the flux from the secondary
>> >>> load current cancel. Loading a transformer reduces the core flux.
>> >>
>> >>Not exactly. The core flux has to keep increasing to generate the voltage the drives the current into the external load. Because you drive transformers with AC the voltage eventually reverses, ideally before you saturate the core.
>> >
>> >Bill, I think this assumes that the voltage is regulated with
>> >feedback.
>> >
>> >Driving the transformer with, say, just grid voltage would do what JL
>> >is talking about because the IR drop when loaded, reduces the
>> >volt-seconds imposed on the core which is what causes saturation.
>> Yes. Shorting the secondary will drop the core flux about in half.
>> >
>> >Pretty sure that's it anyway.
>>
>> Sloman has lectured us hundreds of times about how we should design and not buy transformers, so it's hilarious that he doesn't understand the basics.
>
>Joh Larkin's reading comprehension is down there with Flyguys. I'm all in favour of buying off-shelf transformers if you can find one to do the job.
>
>The problem is that you rarely can.
>
>As to why he thinks I don't understand the basics of transformer design, the answer has to be that he doesn't, and thinks that boB does, which is hilarious.

That's OK, Bill. But at least we know what works for transformer
design in a product.

There may be some confusion between inductor magnetics and transformer
magnetics design going on down there. It's all the same thing in the
end.

Try operating a transformer designed for 50/60 Hz operation with
decreasing frequency and watch the magnetizing current rise as it
startes to go into saturation. Lower frequency means higher
volt-seconds.

You have to reduce the exitation voltage as you decrease the frequency
to keep the V-S from increasing and saturating the core in a
transformer.

boB

On Tuesday, March 7, 2023 at 4:10:26 AM UTC+11, boB wrote:
> On Mon, 6 Mar 2023 01:35:41 -0800 (PST), Anthony William Sloman
> <bill....@ieee.org> wrote:
> >On Monday, March 6, 2023 at 4:09:22?AM UTC+11, John Larkin wrote:
> >> On Sat, 04 Mar 2023 23:36:56 -0700, boB <b...@K7IQ.com> wrote:
> >> >On Fri, 3 Mar 2023 20:13:46 -0800 (PST), Anthony William Sloman <bill.....@ieee.org> wrote:
> >> >>On Saturday, March 4, 2023 at 2:04:20?PM UTC+11, John Larkin wrote:
> >> >>> On Sat, 04 Mar 2023 01:23:17 -0000, "Commander Kinsey" <C...@nospam.com> wrote:
> >> >>> >On Sun, 26 Feb 2023 16:13:19 -0000, John Larkin <jla...@highlandsnipmetechnology.com> wrote:
> >> >>> >> On Sun, 26 Feb 2023 09:45:26 -0000, "Commander Kinsey" <C...@nospam.com> wrote:
> >
> >><snip>
> >
> >> >>> The reason that loading a transformer doesn't make it saturate is
> >> >>> because the primary excitation flux and the flux from the secondary
> >> >>> load current cancel. Loading a transformer reduces the core flux.
> >> >>
> >> >>Not exactly. The core flux has to keep increasing to generate the voltage the drives the current into the external load. Because you drive transformers with AC the voltage eventually reverses, ideally before you saturate the core.
> >> >
> >> >Bill, I think this assumes that the voltage is regulated with
> >> >feedback.
> >> >
> >> >Driving the transformer with, say, just grid voltage would do what JL
> >> >is talking about because the IR drop when loaded, reduces the
> >> >volt-seconds imposed on the core which is what causes saturation.
> >> Yes. Shorting the secondary will drop the core flux about in half.
> >> >
> >> >Pretty sure that's it anyway.
> >>
> >> Sloman has lectured us hundreds of times about how we should design and not buy transformers, so it's hilarious that he doesn't understand the basics.
> >
> >Joh Larkin's reading comprehension is down there with Flyguys. I'm all in favour of buying off-shelf transformers if you can find one to do the job..
> >
> >The problem is that you rarely can.
> >
> >As to why he thinks I don't understand the basics of transformer design, the answer has to be that he doesn't, and thinks that boB does, which is hilarious.
>
> That's OK, Bill. But at least we know what works for transformer design in a product.

In the sense that they haven't blown up recently. John Larkin's problem is that he really doesn't want to design a transfomer to a do a specific job or go to the trouble of getting it made, and doesn't want to admit that he is avoiding a task that he finds difficult.

> There may be some confusion between inductor magnetics and transformer magnetics design going on down there. It's all the same thing in the end.

Obviously, but only up to a point.
> Try operating a transformer designed for 50/60 Hz operation with = decreasing frequency and watch the magnetizing current rise as it starts to go into saturation. Lower frequency means higher volt-seconds.

Obviously.
> You have to reduce the excitation voltage as you decrease the frequency to keep the V-S from increasing and saturating the core in a transformer.

That's one option. If you feel the need to do the experiment, you can't have grasped the theory
--
Bill Sloman, Sydney