Nichicon HE, PW, PS, BT ? to replace bad HT Ser

[JBL]

Hi Guys,

I've just signed up after searching on google.

Has anyone seen failures in around 1990's Nichicon PR Series Capacitors?

But not limited to PR. I replace Capacitors in Toyota Engine Control computers that are around the year 1990 of a certain model that has many defective capacitors, and many of these cars some having done quite low KM's have failed capacitors, most if not all leaking from the base. I have been told it's due to age but there are other cars with much higher KM using different capacitors that have not failed..... so I'm suspecting this was a bad batch of capacitors for some reason, or incorrectly specced caps for the circuits I have no idea?

I'd like to know if anybody else has has seen many cases of bad nichicons around equipment in 1990's ERA.

I would like to know in this application what the best series capacitors are to use

I have read the FAQS on good caps etc and seen a few good Series mentioned, the ones on the list that are avaliable to me are :

PM, PW, HE, PS.... I also have access to BT Series.

On the thread in the FAQ there is a thread with Nichicon series from highest to lowest ESR.

HE is listed in amongst the first so I guess it would not be as good?
Because HE is the ones I mainly use as they seem to be quite popular and they seem to have longer life ratings etc.

I'm just not sure what I should use in my application to replace the old discontinued PR's in my ECU's. So in an engine ECU which Series should I go for that will give me the best results e.g stable accurate readings from engine sensors, precise control of electronic modules and injectors etc.

SO far I have been using Nichicon HE, and where I cant get HE for the capacitance I need, I use PW. The main ones that are avaliable from where I buy in Nichicon brand are HE, PW, PS, PM. Since cost is not that much varied I'd rather get the best, but the shop I shop from doesn't sell the highly recommended Nichicon HZ's, only the ones I listed.

I'd be interested to get some feedback to on the failure occurance if anybody else has experienced this in other applications with these capacitors from the same ERA as I'm keen to know the reason of this premature failure, whether it was a bad batch or something?

My Supplier doesn't carry wide variety of Rubycons especially the high regarded, they do carry some ZL's but they seem to be have a lower lifetime than the Nichicons, Nichicons seem most common from my supplier so I'd rather want to know which are the best Nichicons to go with for my application that I can get a hold of.

I always also try to exceed the voltage rating of the OEM capacitor for longevity reasons.... Is this a good practice most of the times?

One more question, other ECU's I have opened up show no signs of bad capacitors at all, from cars that were running mostly well, but I have found the lid of the ECU to have a light layer of smoke/soot like coating that is easily wiped off clean, could this be gas leakage from capacitors indicating that they will become defective soon?

Thanks guys.

[PeteS in CA]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

Nichicon's PR series was "discontinued", but revived in a RoHS-compliant version, the PS series. The same is true, BTW, of the PL series (discontinued) and the PM series ("new" and RoHS-compliant).

So, if you want a direct equivalent, use the PS series. The PM series, if I recall correctly, is lower impedance than the PS, PW is lower still, and the HE series still lower impedance. Since it's an automotive application, I'd suggest using the PW or HE series (longer life than the PS or PM series). Since the i,pedance and the ripple current capability of the PS series is adequate and the water-based electrolyte of the HE series expands more with heat and has a higher impedance below -20C than the PW, I'd lean toward the PW series over the HE series. But unless it gets well below -10C in winter where you are in Germany, or you get really hot summer weather, the HE vs. PW choice for you is probably more a matter of price and availability.

[JBL]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

Thanks for the detailed reply Pete yeah I too thought PW or HE, HE first and PW if I cant find what I need in the HE series.

The ECU's are sometimes for other countries, Australia where it rarely gets below 0 degrees C but have very hot summer days yes so in that case what would you recommend?

I take it we have narrowed it down to HE or PW but keeping in mind the weather which would be better?

still keeping in mind the weather .... but on the other hand, would the HE be better in terms of the internal functioning of the circuit? should I ideally once i replace a cap, compare the HE and PW replacement model for a specific capacitance, and chose the cap with the highest ripple current rating? I understand this would cause the cap to produce more "stable" outputs?

[PeteS in CA]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

JBL! I'm hampered some by not being able to do the mental math to convert Fahrenheit temps to Celsius temps. If your temps got as high as in Redding, California or Phoenix, Arizona (105F - 115F), I'd definitely go with PW over HE. Between the hot engine compartment and the hot weather, those caps could get really hot.

Whether lower impedance is better depends on how the cap is used. If it's at the output of a regulator, there are components that compensate for the caps' impedance whose values are picked for a certain impedance range. If the new cap's impedance is significantly lower it could make the regulator circuit less stable. If the caps you are replacing are at the output of a regulator, that could be another reason to choose PW over HE, since the impedance of the PWs is closer to that of the original PRs.

[JBL]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

Writing this in a hurry.... actually the ECU is inside of the Cabin so won't be subject to engine bay heat.... nonetheless do you still recommend PW for weather reasons?

As for the impedence, I thought lower impedence is always better e.g a lower impedence cap can replace a higher impedence cap in pretty much all applications without ill effects or is this not true? I thought the impedence of a cap just contributes to heat and aging thus possibly creating problems in operation......... so lower impedence would always be better like I thought?

hmmm... thoughts.

THANKS Pete.

[momaka]

Re: Nichicon HE, PW, PS, BT ? to replace bad PR Ser

Has anyone seen failures in around 1990's Nichicon PR Series Capacitors?

Only one (16V 470uF Nichicon PR), and that one too had leaked from the bottom when it failed.
I'm not sure if it was a problem with Nichicon, though, because I got that cap from an old TV mainboard. When I pulled it at the time (a few years ago), it *looked* fine but after installing it in a PSU and not use the PSU for nearly 2 years, it had leaked from the bottom.
Given my limited encounter with Nichicon PR caps, I can't really say if they had problems or now. The few Nichicon PRs in an old 200W Astec PSU still *look* fine and the PSU works too.

[PeteS in CA]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

IIRC, the PR series was discontinued in 2006 or 2007 in bringing Nichicon lines into compliance with RoHS. By then it was 2 or 3 generations down in the Px type Nichicon low Z caps. But it was still used in a lot of existing designs and the users asked Nichicon to bring it back in a RoHS-compliant form. The same may have been the case with the PL series. The RoHS-compliant parts were the PS and PM series respectively. For some reason, Nichicon chose not to rename the PJ or PW series when those were brought into compliance with RoHS ... maybe because those series were "current" products.

JBL, the R-C circuit formed by the C and the ESR of the capacitor is compensated for in the regulator error amplifier. If that capacitance is changed significantly or that ESR is changed significantly, stability and transient response is affected, and the regulator could oscillate or have significant output voltage ringing.

[JBL]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

Ah I see, so the other components in the circuit are made to work with a cap with a certain Ripple current and resistance rating, And if going out of that threshhold that those other components are designed for then it's bad.... I had read some documents from a cap manufacturer that replacing a cap with lower ripple current rating with higher one is fine, i guess not??

So in this case is it best to stick within the window of what was in there from factory?
How much can it deviate by? e.g Original is PR...... PS is the replacement so any PS range capacitor with same capacitance of the PR i'm replacing is 10000% fine?

Now since PW and HE have higher ripple current ratings, lower resistance...... this could possibly put things out of balance depending on the circuit yes? What "window" of specs should I stay within e.g if PS replacement for PR has "X" Ripple current rating... how much higher can I go? say if I wanted to use a HE or PW capacitor.

I'm wondering how often people can run into troubles when not considering these things I mean people replace capacitors heaps of times and often go with the best regarded cap like mentioned on this site....

I was thinking should I just go PS since they are a direct replacement, but the reason I wanted to go PW or even better HE is for longer life etc.... and better built capacitor by sounds of it?

[momaka]

Re: Nichicon HE, PW, PS, BT ? to replace bad HT Ser

So in this case is it best to stick within the window of what was in there from factory?

Yes. Unless they messed up on the design at the factory, of course.

How much can it deviate by? e.g Original is PR...... PS is the replacement so any PS range capacitor with same capacitance of the PR i'm replacing is 10000% fine?

If two cap series are equivalent in terms of ESR and ripple current, then matching the capacitance and voltage rating should give identical circuit operation.

Now since PW and HE have higher ripple current ratings, lower resistance...... this could possibly put things out of balance depending on the circuit yes? What "window" of specs should I stay within e.g if PS replacement for PR has "X" Ripple current rating... how much higher can I go? say if I wanted to use a HE or PW capacitor.

It all depends on the design of the circuit. Some circuits like the CPU VRM of computer motherboards do indeed favor the lowest possible ESR and highest possible ripple current rating, so going for a lower ESR and higher ripple current rating will be better. Computer power supplies on the other hand, do not follow that. Here, picking replacements caps that are closest to the factory specified ones in terms of ESR and ripple yields the best results. That's because the filtering circuit in a computer power supply closely resembles an LRC tuned circuit. Too high an R (ESR), and you get over-damped LRC circuit that cannot filter all of the ripple from the power supply. Too low of an R, and you get a resonant LC circuit that filters the ripple from the power supply but produces undesirable voltage ripple from its own resonant frequency.

Of course, in your case, the endurance life of the caps also becomes very important, especially if the caps are to be run in a very hot environment near their rating, such as is possible in the ECU.
The PW and the HE caps may produce a bit more ripple (though not necessarily, depending on the circuit in the ECU), but if the rest of the circuits can tolerate this extra ripple, then it's worthwhile to use those caps for their longer life.