Finding low-ESR 400V capacitors

[accent]

I'm about to replace all the electrolytic capacitors inside a 30 year old computer power supply and will order mostly Panasonic FR-series capacitors which I understand are ideal for this sort of application (low ESR, 105 degrees C and 10 000 hour life) from Farnell for this.

But locating replacements for the two 400V caps in the PSU proves to be a challenge (150uF/400V and 10uF/400V) as neither are available in Panasonic's FR range and I am having difficulties figuring out if the other brands/types available are indeed low-ESR types. I did find a Rubycon BXW-series 150uF/400V, but I haven't had success in figuring out if they're catagorized as "low ESR" or not. They do appear to be geared towards power supplies, according to a description of Rubycon's BXW-series, but then again in Rubycon's online catalog (scroll down to the "Radial lead aluminum electrolytic capacitors" section) it doesn't list them as low-ESR but they're still recommended for power supply applications....
I'm confused! Are Rubycon BXW-series capacitors rated as low-ESR?

As for the 10uF/400V I haven't found anything suitable at Farnell although there is a 12uF/400V Rubycon BXW capacitor available. Will it do, or should I really find something which is exactly 10uF?
Other than that there's a Panasonic ED-series 10uF/400V, but I believe that's a general purpose type cap, not low-ESR.

[stj]

Re: Finding low-ESR 400V capacitors

mains input caps dont need to be low-esr because the frequency is low (50/60Hz)

and as you noticed, Rubycon is best for high voltage stuff.
for 10uf you may find one intended for led psu's
10uf 450v LLE series - very long life caps
https://cdn.badcaps-static.com/pdfs/...bfcb570360.pdf

[accent]

Re: Finding low-ESR 400V capacitors

Aha! I didn't think of that.
So the high frequency/high ripple part of a switching mode PSU basically comes after the first transformer, and that's where you need low-ESR caps because otherwise their internal resistance will drop the voltage output and also generate internal heat which will in turn wear down/damage that capacitor?
A schematic of the power supply in question is attached here (I've marked the two 400V caps in red)

An online recapping article on how to recap this particular PSU suggests slightly different values from the original ones. Is this considered safe, and might the reason be minor improvements overall (less ripple, more stable output etc?).
The 120uF/400V cap among others is suggested to be replaced with a 150uF/400V instead.


You mentioned the Rubycon LLE-series, but I couldn't find any at Farnell.
But am I understanding it correctly that just about any "general use" quality brand 400V rated capacitor with a long lifetime and 105 degrees C rating will work for this use (before the high frequency section)?

A quick look at Farnell's findings with the above features suggests (for the 10uF cap):

10uF/400V Rubycon BXC-series (10 000 hours at 105 degr. C)
10uF/400V Wurth WCAP-AT1H Series (10 000 hours at 105 degr. C)

[stj]

Re: Finding low-ESR 400V capacitors

yes, generally the low esr is to assist high frequency operation.
as for ripple, it's a selectable value - make sure your replacement for the caps is rated equal or higher than the originals

[stj]

Re: Finding low-ESR 400V capacitors

btw, what computer is it? that's a lot of 12v for a floppy-drive or 2.

----

ok, i checked your Link.
Falcon - i think that had an internal harddrive option.

[PeteS in CA]

Re: Finding low-ESR 400V capacitors

A 30 year old power supply? Those Panasonic output caps might be "too good". The very low ESR (compared to 1987 technology) might cause stability problems. Nichicon PM or PS series might be close to the impedance of the original parts. The PJ series would probably be OK.

In compensating the feedback loop to avoid oscillation, the ESR is relevant, and if the new parts are much lower ESR than the originals, the compensation will be incorrect and oscillation could result.

[accent]

Re: Finding low-ESR 400V capacitors

I didn't know the stuff about self-oscillation (what does that mean and do by the way?).
Were you referring to ALL the replacement capacitors in this respect or just the two 400V ones before the high frequency/high ripple section? I attached a schematic a few posts above.

Apparently this recapping business is a little trickier than I first thought (expecting to just look for the best low-ESR caps I could afford/justify, to replace the old ones with).
So basically, you have to take into account which time period the gear in question came from when choosing replacement capacitors? Does this apply to only switched mode type power supplies or "traditional" type power supplies with a rectifier board as well? I believe a lot of my musical equipment has those. Sorry for all the newbie questions


Falcon was a very close guess, but it's an Atari Mega STe and is probably more like 25 years old as it first came out in 1991.

There's a detailed web page on recapping the various Atari power supplies -here's scrolling down to the PSM-5341 section which is used in my Mega STe. It lists the original and replacement values used.
If you scroll up to the very top of that same page the author explains what it's all about and mentions using Panasonic FR caps, which is why I've added them to my Farnell shopping cart (still not too late as I haven't ordered anything though). Here's a quote (relevant text marked bold by me):

NOTE2: I keep getting asked about part numbers I use for these kits. Unfortunately I do not list them anymore simply because by the time I have sorted part numbers out and updated my site, the part numbers are no longer valid or discontinued. With several PSU's now on this part all needed various capacitors, it would be a huge undertaking to keep updating this page (time I just do not have unfortunately). Generally I go with the Panasonic FR series as they are really good ESR values. Please don't fit "any old capacitor sold around the Internet" as the cheaper capacitors are not suitable for switchmdoe designs and can easily overheat or explode! I am trying to update my store with new re-cap kits so please keep checking there.

This guy seems to know what he's doing (he's even redesigned his own improved replacement Atari power supply (explained in detail here) which he sells through his webstore (click on the "PSU" button at the top) ). Would I still be better off by looking at other low-ESR capacitors for this particular PSU?

[stj]

Re: Finding low-ESR 400V capacitors

i use FR for just about everything - no problems yet.

[PeteS in CA]

Re: Finding low-ESR 400V capacitors

1 Were you referring to ALL the replacement capacitors in this respect or just the two 400V ones before the high frequency/high ripple section? I attached a schematic a few posts above.

2 Apparently this recapping business is a little trickier than I first thought (expecting to just look for the best low-ESR caps I could afford/justify, to replace the old ones with).
So basically, you have to take into account which time period the gear in question came from when choosing replacement capacitors?

1 I was referring to the low voltage caps on the outputs, not the 400V caps.

2 Yes, switching power supplies are deceptively complex. Compensation (e.g. R7-C10 by IC1 and R16-C20 by the PC and SHR) tailor the frequency response of the amplifiers (the SHR and in IC1) to match the output capacity, the ESR, the "output inductor" (the transformer primary, since this is a flyback design) so that the amplifiers don't oscillate. There is margin in compensation designs, so, for example, significantly better output caps may not cause oscillation, but transient response (response to sudden increases or decreases in load current) will be affected, and oscillation is possible.

So repairing older switching power supplies is not always simple, and better performance as a part does not guarantee better performance in the power supply as a whole. Modern parts such as Panasonic FR or FC may work OK - as stj indicated has been his experience. That this power supply is 25 years old rather than 30 is probably a good thing if you go with modern parts.

[accent]

Re: Finding low-ESR 400V capacitors

1. Apologies if I'm not "getting it" as this is all new to me, but I first thought you meant that low-ESR capacitors (such as the Panasonic FR-series) are considered "specialized" so they shouldn't simply be used to replace any aged/expired capacitor (i.e. "recapping"), but ONLY for recapping special, demanding applications such as the high frequency section of a switched mode power supply.
In which case it makes sense NOT to replace the two 400V caps with low-ESR types, but instead to recap with normal type (but quality and long life/high temp rating) capacitors.

Or are you saying that the above is irrelevant (I can indeed use low-ESR capacitors to replace ANY aged/expired electrolytic capacitor anywhere) EXCEPT in electronic designs which are old (i.e. "old" meaning the time period before those low-ESR came into the market) because those designs never took into account the ultra-low internal resistance values of "low-ESR" capacitors available today)?

2. I can totally agree that all this is complex (especially for a hobbyist like me)
Regardless of the above (or me totally misunderstanding the point) I have to take it that the guy who posted the replacement capacitor values for recapping this particular PSM-5341 SMPS knows what he's doing as he also has a webstore and sells recapping kits. If others have had issues after using one of his kits I'm sure I would have heard about it in the related forums.

There's a small photo of his recapping kit at his webstore and I can just make out a red 150V/400uF capacitor. I know he orders from Farnell and the only 150uF/400V I can find is a Wurth branded one rated at only 2000 hours if I'm not mistaken. As I want the hour rating to be the same for all caps (so when it's time to recap there's no second guessing which ones are oldest and possibly resulting in all the expensive Panasonic FR-series caps being replaced (5x longer life) when the culprit is the lower life one), so.... I found a 400V cap with actually a 12000 hour life, but it's at 120uF (which is the old, original value).

So... having said all that (sorry for rambling) I'm wondering:

a) Can I still use the old value for C6 (120uF/400V) even though the recapping guy says to use a new value (150uF/400V) without causing any problems or electrical danger?

or....

b) Must I use the new value (150uF/400V) for C6 because many of the other caps have also changed their values, so they interact with each other, and this person has calculated the new values because of this interaction?
So in case I want to use the 120uF/400V capacitor (because I can't find a long lifetime rating for a 150uF/400V) I also need to replace all the other caps with their original values as well?

I'm enclosing the PSU schematic again (C6 on the upper left section, marked blue), this time with the replacement capacitors written in red/blue and the new values written alongside the parts in bold red or blue. The other components are left as they are.

[Stefan Payne]

Re: Finding low-ESR 400V capacitors

An online recapping article on how to recap this particular PSU suggests slightly different values from the original ones.

From what I've seen so far it seems like Bullshit from a Clueless guy.
Why would you replace the (2A) Bridge Rectifier with 10A parts in this kinda lowish watt PSU? What are we talking about? Something like 25W secondary?? 2A rectifiers for the primary seems more than fine. More isn't always better! Sometimes it's just bullshit and gives you no advantage what so ever....

As for isolated PSUs, too low ESR capacitors can cause problems like oscilation.
And you should replace the original parts with something somewhat equal. That's what that circuit was designed for, that's what the engeneer calculated the parts and designed it...

[Stefan Payne]

Re: Finding low-ESR 400V capacitors

(I can indeed use low-ESR capacitors to replace ANY aged/expired electrolytic capacitor anywhere) EXCEPT in electronic designs which are old (i.e. "old" meaning the time period before those low-ESR came into the market) because those designs never took into account the ultra-low internal resistance values of "low-ESR" capacitors available today)?

No because you need to look at datasheets, the ESR and so on.

There are huge differences between capacitors.
Ripple Current seems irrelevant in these old circuits.

But take 16V/2200uF as an example.
Panasonic FR has 18 Ohms ESR @ 100kHz.
Panasonic FC has 30 Ohms ESR @ 100kHz

You see there are enormous differences between those two...

What I'm saying is that there are rather huge differences between 'low ESR' capacitors so you have to look up the datasheet and take a look at the part you want. Not just put "any low ESR" one in there...

[accent]

Re: Finding low-ESR 400V capacitors

Thanks for your replies. I see I still have a lot to learn about the subject.

I couldn't find anything about replacing the bridge rectifier. Are you referring to some other part of that page, or the section about my PSM-5341 power supply? (the link goes directly to that section).

So a low-ESR capacitor isn't some sort of "perfect replacement" for old/bad/expired/bad quality capacitors then, but the entire circuit needs to be designed for those type of components?
In that case it appears to be a common rumour that "if you have a capacitor problem, replace it with a good quality brand, low ESR-type and everything will be fine".

To conclude, you suggest that I NOT replace the PSU capacitors with Panasonic FR-series (low ESR) capacitors, and that I NOT change the values from the original design (as that guy suggested), but stick to the original values (possibly higher voltage, temperature and lifetime rating) with good quality but "normal" capacitors?
And by "normal" capacitors I still have to find out the internal resistance of the original capacitors so I can find similar (but better quality/longer lasting) replacement capacitors?

The existing capacitors are from some cheap, unknown (to me) brand name, probably cheaply made in Taiwan or China so it could prove difficult to find their original internal resistance. In that case, what should I do?
The capacitors are probably something like 25 years old and I believe they do need replacing so they won't all of a sudden blow up etc. and maybe damage my computer attached to it.

[Stefan Payne]

Re: Finding low-ESR 400V capacitors

I couldn't find anything about replacing the bridge rectifier. Are you referring to some other part of that page, or the section about my PSM-5341 power supply? (the link goes directly to that section).

Yes, for example ** MITSUMI SR98 **...
2A seems fine to me. Others have just the 4 Diode full bridge rectifier...

So a low-ESR capacitor isn't some sort of "perfect replacement" for old/bad/expired/bad quality capacitors then, but the entire circuit needs to be designed for those type of components?

It depends. That's what I was trying to say.
There are low ESR Capacitors with rahter high ESR, there are low ESR capacitors with rather low ESR...

Panasonic FC seems like a better choice, maybe Nichicon UPS.
But we should wait for a comment from PeteS in CA for that...

In that case it appears to be a common rumour that "if you have a capacitor problem, replace it with a good quality brand, low ESR-type and everything will be fine".

That's wrong. You have to look at the datashet. There are so many vaulues of capacitors important that you can't just say it in one sentence.

To conclude, you suggest that I NOT replace the PSU capacitors with Panasonic FR-series (low ESR) capacitors, and that I NOT change the values from the original design (as that guy suggested), but stick to the original values (possibly higher voltage, temperature and lifetime rating) with good quality but "normal" capacitors?

Mostly yes. Some Low ESR capacitors should be fine though.

So you should look at 'bad' low ESR capacitor rather than the best of the bunch.


Something like Nippon Chemicon KY, KYA, Panasonic FC, possibly/maybe Nichicon UPS

The existing capacitors are from some cheap, unknown (to me) brand name, probably cheaply made in Taiwan or China so it could prove difficult to find their original internal resistance.

ESR is only mentioned in low ESR capacitor datasheets but not in 'General Purpose' Capacitor Datasheets. So you should look at the buttom of the line Low ESR/Low Impedance Capacitors of a manufacturer, not the highest end.

In that case, what should I do?
The capacitors are probably something like 25 years old and I believe they do need replacing so they won't all of a sudden blow up etc. and maybe damage my computer attached to it.

Replace the Capacitors with buttom of the line Low ESR capacitors that are recommended in this thread by other people

[PeteS in CA]

Re: Finding low-ESR 400V capacitors

It depends. That's what I was trying to say.
There are low ESR Capacitors with rahter high ESR, there are low ESR capacitors with rather low ESR...

Panasonic FC seems like a better choice, maybe Nichicon UPS.

Individual components in a poser supply can't be treated as just individual components. They were selected to work together as a system. Depending on how carefully each part in the system was chosen, there will be substantial margin to allow for component tolerances and aging. Unless one has the engineers' records, one really cannot know how great that margin is.

One may be able to (and sometimes is forced to) substitute parts of slightly different values or impedances and have the power supply work fine, but the greater the differences, the greater the risks of poor performance or instability. As an example of being forced to substitute, were I repairing a power supply with old UCC RX series or old Nichicon PA series output caps, I would have to substitute. Those simply are not available.

That's an extreme version (10-15 years older) of the situation of this power supply. Given that this power supply is ~25 years old, I would use cap series that was around in that time-frame. Nichicon keeps older series in production longer than does UCC, for some reason. The PM series is the lead-free version of the PL series, which came out in the mid-late 80s; the PS series is the lead-free version of the PR series, of similar vintage. The PJ series, which probably came out in the early-mid 90s should be suitable. I would not try anything lower in impedance than Nichicon's PW, UCC's (NCC's) LXZ series, or Panasonic's FC series unless that's what is reasonably available (in which case Nichicon HE or UCC KY would probably be the lowest risk choices).

FWIW, I'm not a design engineer, but I've worked in power electronics since 1980 and have done stability testing.

[accent]

Re: Finding low-ESR 400V capacitors

Thanks for clarifying further, guys.

Back in the days (80's/90's) when I got into electronics as a hobby and built stuff from schematics, magazine articles, kits etc. an electrolytic capacitor was simply that. If a schematic said 100uF/16V I went out and bought a 16V rated 100uF capacitor. Being quality-conscious I also looked for a brand name (Sanyo, Matsushita/Panasonic, Rubycon, Nichicon etc.) but that was about it.
What happened since then? Has it really become more complicated to get the right type these days, or is it just that the ones marked "low-ESR" are for special purposes and I should stay away from them unless I know exactly what I'm doing and instead figure out which manufacturer series are marketed as "general purpose"?

I'm guessing the latter is exactly what you've suggested in your latest posting, PeteS in CA.


Unfortunately I'm unable to get hold of either Nichicon HE, UCC, UCC KY or PW series caps. It seems they're available in the US from my dealer (Farnell) but not here in Europe. The PM series on the other hand comes up with a variety of caps, so that could possibly work out. Also Panasonic FC. Nichicon PS comes up with just a few values, so I might need to mix caps from different series.

As for the Panasonic FR-series I was suggested elsewhere -I should stay away from these unless I'm asking for trouble? And by recapping with "regular" caps instead (the different series suggested above) I should likely still get improved performance (less ripple, better voltage stability, less noise etc.) over the aged, original capacitors?

[stj]

Re: Finding low-ESR 400V capacitors

what i do remenber about repairing original ST's and maybe STE's back in the day,
the psu i saw fail a lot had a 2A fuse, and a 1A rectifier - the rectifier was a common failure!!

i used to put a 4A one in instead - simply because it was the next size up that was designed for horizontal mounting.

a lot of people just replaced the psu, there was an american company that sold their own replacement higher spec psu's.
infact they specialisesd in everything "ATARI" from the 2600 onwards!!

[Behemot]

Re: Finding low-ESR 400V capacitors

There is the typical 60-100 kHz in active (boost) PFC.

Most of the better HV caps are of long-life type, so the ESR is lower than of standard but still higher than of low-ESR. Also putting too low ESR caps into such old device is usually worse than better.

If you need some, got them cheap from NCC (some Rubycons too), as all the others. Panasonic has insane MOQs and even than they are expensive.

[stj]

Re: Finding low-ESR 400V capacitors

no pfc bullshit in atari stuff, it predates it by decades.

[Behemot]

Re: Finding low-ESR 400V capacitors

You general statement about 50/60Hz on input capacitors is false as I have shown. On the other hand I said nothing about PFC being here in particular, just that are such frequencies in boost PFCs.