Tim+ <tim.downie@gmail.com> wrote:
> FWIW the old caps are reading about 830uF. Would this be enough out of spec
> to stop it working?

That sounds within tolerance. What can happen with bad caps is the
Equivalent Series Resistance goes too high. If the cap is being used to
smooth a voltage rail, this makes a problem when something tries to take a
big gulp of current. ESR is analogous with battery internal resistance. A
low ESR cap would be able to fulfill the current demand, but a high ESR cap
can't and so the voltage sags.

You can't measure that on most multimeters, you need a specific ESR meter
(they can be had for £10 from China).

It is possible to buy specific low ESR caps for this application but, in the
absence of a spec for the old ones, we don't know what the ESR is supposed
to be. If you have a choice of replacement, worth picking the one with the
lowest ESR.

Theo

On 08/08/2023 23:11, Theo wrote:

>
> It is possible to buy specific low ESR caps for this application but, in the
> absence of a spec for the old ones, we don't know what the ESR is supposed
> to be. If you have a choice of replacement, worth picking the one with the
> lowest ESR.

Select one with the lowest ESR from the list of zero found ?

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

Theo <theom+news@chiark.greenend.org.uk> wrote:
> Tim+ <tim.downie@gmail.com> wrote:
>> FWIW the old caps are reading about 830uF. Would this be enough out of spec
>> to stop it working?
>
> That sounds within tolerance. What can happen with bad caps is the
> Equivalent Series Resistance goes too high. If the cap is being used to
> smooth a voltage rail, this makes a problem when something tries to take a
> big gulp of current. ESR is analogous with battery internal resistance. A
> low ESR cap would be able to fulfill the current demand, but a high ESR cap
> can't and so the voltage sags.
>
> You can't measure that on most multimeters, you need a specific ESR meter
> (they can be had for £10 from China).
>
> It is possible to buy specific low ESR caps for this application but, in the
> absence of a spec for the old ones, we don't know what the ESR is supposed
> to be. If you have a choice of replacement, worth picking the one with the
> lowest ESR.
>
> Theo
>

Measured ESR is 0.29 ohms.

Tim

--
Please don't feed the trolls

On 07/08/2023 22:08, Tim+ wrote:
> I’m struggling a bit to find replacements that are 100V, 1000uF, 85C and no
> more than 20mm high and 25mm in diameter.

100v seems an odd choice for a PSU. Nowhere near mains, but far too high
for anything intelligent.

Or is it just I don't know enough about PSUs?

Andy

Vir Campestris <vir.campestris@invalid.invalid> wrote:
> On 07/08/2023 22:08, Tim+ wrote:
> > I’m struggling a bit to find replacements that are 100V, 1000uF, 85C and no
> > more than 20mm high and 25mm in diameter.
>
> 100v seems an odd choice for a PSU. Nowhere near mains, but far too high
> for anything intelligent.
>
> Or is it just I don't know enough about PSUs?

It appears to be a motor control board. Not unusual for motors to take 60V
DC or more.

Theo

On 09/08/2023 12:21, Theo wrote:
> Vir Campestris <vir.campestris@invalid.invalid> wrote:
>> On 07/08/2023 22:08, Tim+ wrote:
>>> I’m struggling a bit to find replacements that are 100V, 1000uF, 85C and no
>>> more than 20mm high and 25mm in diameter.
>>
>> 100v seems an odd choice for a PSU. Nowhere near mains, but far too high
>> for anything intelligent.
>>
>> Or is it just I don't know enough about PSUs?
>
> It appears to be a motor control board. Not unusual for motors to take 60V
> DC or more.
>
> Theo

Yes. at high power it often makes sense to push up towards 100V, which
is the sort of cliff edge for cheap transistors, and it keeps currents
down and avoids massive wires.

Above that your transistors tend to become more pricey. A 100v supply
rail is just enough to get 125W into 8 ohms, give or take...we used to
use that pretty much all the time in medium power audio.

Not much point on going much higher since the loudspeakers to take it
didnt exist.

--
“it should be clear by now to everyone that activist environmentalism
(or environmental activism) is becoming a general ideology about humans,
about their freedom, about the relationship between the individual and
the state, and about the manipulation of people under the guise of a
'noble' idea. It is not an honest pursuit of 'sustainable development,'
a matter of elementary environmental protection, or a search for
rational mechanisms designed to achieve a healthy environment. Yet
things do occur that make you shake your head and remind yourself that
you live neither in Joseph Stalin’s Communist era, nor in the Orwellian
utopia of 1984.”

Vaclav Klaus

In article <jwb*Q9knz@news.chiark.greenend.org.uk>, Theo <theom+news@chi
ark.greenend.org.uk> scribeth thus
>Tim+ <tim.downie@gmail.com> wrote:
>> FWIW the old caps are reading about 830uF. Would this be enough out of spec
>> to stop it working?
>
>That sounds within tolerance. What can happen with bad caps is the
>Equivalent Series Resistance goes too high. If the cap is being used to
>smooth a voltage rail, this makes a problem when something tries to take a
>big gulp of current. ESR is analogous with battery internal resistance. A
>low ESR cap would be able to fulfill the current demand, but a high ESR cap
>can't and so the voltage sags.
>
>You can't measure that on most multimeters, you need a specific ESR meter
>(they can be had for £10 from China).
>
>It is possible to buy specific low ESR caps for this application but, in the
>absence of a spec for the old ones, we don't know what the ESR is supposed
>to be. If you have a choice of replacement, worth picking the one with the
>lowest ESR.
>
>Theo

Haven't got the cheapie from China but this one is excellent as is their
back up and service!

https://www.peakelec.co.uk/acatalog/esr70-capacitor-esr-meter.html
--
Tony Sayer

Man is least himself when he talks in his own person.

Give him a keyboard, and he will reveal himself.

Theo <theom+news@chiark.greenend.org.uk> wrote:
> Tim+ <tim.downie@gmail.com> wrote:
>> FWIW the old caps are reading about 830uF. Would this be enough out of spec
>> to stop it working?
>
> That sounds within tolerance. What can happen with bad caps is the
> Equivalent Series Resistance goes too high. If the cap is being used to
> smooth a voltage rail, this makes a problem when something tries to take a
> big gulp of current. ESR is analogous with battery internal resistance. A
> low ESR cap would be able to fulfill the current demand, but a high ESR cap
> can't and so the voltage sags.
>
> You can't measure that on most multimeters, you need a specific ESR meter
> (they can be had for £10 from China).
>
> It is possible to buy specific low ESR caps for this application but, in the
> absence of a spec for the old ones, we don't know what the ESR is supposed
> to be. If you have a choice of replacement, worth picking the one with the
> lowest ESR.
>
> Theo
>

Gah! I’ve been duped. I feel such a fool.

I should have prodded the tops of the capacitors a bit more firmly. Turns
out the “bulging” was just the plastic cover on the end of the cap that
bulged, not the capacitor can itself.

https://photos.app.goo.gl/kDMM8zJBh3EdpqtE6

Tim

--
Please don't feed the trolls

On Tuesday, 8 August 2023 at 12:28:07 UTC+1, Tim+ wrote:
> Theo <theom...@chiark.greenend.org.uk> wrote:
> > Theo <theom...@chiark.greenend.org.uk> wrote:
> >> Another thought is to study the circuit and see if you really need that
> >> voltage or capacitance rating. eg if it can get away with a 63V cap then
> >> you can probably find one to fit.
> >
> > Is the board this one:
> > https://www.ebay.co.uk/itm/404337086224
> > see the third picture, direct link:
> > https://i.ebayimg.com/images/g/ddcAAOSwqoZkjGd~/s-l1600.jpg
> Yep, that’s it.

Maybe I'm misunderstanding, but it looks like there's loads of room to add other caps, lying them onto the low profile parts.
You can connect Cs on long leads, but when doing so do have at least some capacitance in the original position. Fix your Cs mechanically in anything that shakes or moves.

On Tuesday, 8 August 2023 at 23:12:00 UTC+1, Theo wrote:
> Tim+ <tim.d...@gmail.com> wrote:
> > FWIW the old caps are reading about 830uF. Would this be enough out of spec
> > to stop it working?
> That sounds within tolerance. What can happen with bad caps is the
> Equivalent Series Resistance goes too high. If the cap is being used to
> smooth a voltage rail, this makes a problem when something tries to take a
> big gulp of current. ESR is analogous with battery internal resistance. A
> low ESR cap would be able to fulfill the current demand, but a high ESR cap
> can't and so the voltage sags.
>
> You can't measure that on most multimeters, you need a specific ESR meter
> (they can be had for £10 from China).
>
> It is possible to buy specific low ESR caps for this application but, in the
> absence of a spec for the old ones, we don't know what the ESR is supposed
> to be. If you have a choice of replacement, worth picking the one with the
> lowest ESR.
>
> Theo

830uF is ok, but
a) if they're bulging they're failing or failed
b) you need to also measure ESR & leakage (Vloss) to see if they're bad.

On Wednesday, 9 August 2023 at 15:43:39 UTC+1, tony sayer wrote:
> In article <jwb*Q9...@news.chiark.greenend.org.uk>, Theo <theom+news@chi
> ark.greenend.org.uk> scribeth thus
> >Tim+ <tim.d...@gmail.com> wrote:
> >> FWIW the old caps are reading about 830uF. Would this be enough out of spec
> >> to stop it working?
> >
> >That sounds within tolerance. What can happen with bad caps is the
> >Equivalent Series Resistance goes too high. If the cap is being used to
> >smooth a voltage rail, this makes a problem when something tries to take a
> >big gulp of current. ESR is analogous with battery internal resistance. A
> >low ESR cap would be able to fulfill the current demand, but a high ESR cap
> >can't and so the voltage sags.
> >
> >You can't measure that on most multimeters, you need a specific ESR meter
> >(they can be had for £10 from China).
> >
> >It is possible to buy specific low ESR caps for this application but, in the
> >absence of a spec for the old ones, we don't know what the ESR is supposed
> >to be. If you have a choice of replacement, worth picking the one with the
> >lowest ESR.
> >
> >Theo
> Haven't got the cheapie from China but this one is excellent as is their
> back up and service!
>
>
> https://www.peakelec.co.uk/acatalog/esr70-capacitor-esr-meter.html

Generic cheap chinese component testers will tell you if a cap's faulty, ESR meters sometimes do, sometimes don't.

Tim+ <tim.downie@gmail.com> wrote:
> If that’s the only thing wrong with them it seems reasonable to change them
> before the second of the two dishwashers dies. (It’s a “twin-drawer”
> machine).

How do you get on with the dishdrawers by the way? They seem like an
interesting solution to having to unload the dishwasher before putting dirty
things in it.

How does detergent work? It mostly comes in tablet form nowadays. Do you
split tablets or just use a whole tablet per drawer?

I'm assuming the drawers are the same size? Does that mean less space for
pans, tall plates and similar?

Is everything duplicated - two pumps, two salt reservoirs, etc, or are some
parts shared?

Theo

Theo <theom+news@chiark.greenend.org.uk> wrote:
> Tim+ <tim.downie@gmail.com> wrote:
>> If that’s the only thing wrong with them it seems reasonable to change them
>> before the second of the two dishwashers dies. (It’s a “twin-drawer”
>> machine).
>
> How do you get on with the dishdrawers by the way? They seem like an
> interesting solution to having to unload the dishwasher before putting dirty
> things in it.

With hindsight, I’d say one of the best appliance purchases we’ve made.

>
> How does detergent work? It mostly comes in tablet form nowadays. Do you
> split tablets or just use a whole tablet per drawer?

Designed to work with powder but we generally just chop Aldi tablets in
half and toss it in the machine and ignore the soap dispensers.

>
> I'm assuming the drawers are the same size?

Yep, identical.

> Does that mean less space for
> pans, tall plates and similar?

A bit I guess. No problem with 99% of things we put in.

>
> Is everything duplicated - two pumps, two salt reservoirs, etc, or are some
> parts shared?

All duplicated. Might sound like overkill but in practice it’s proved very
reliable.

Tim

--
Please don't feed the trolls