Capacitor replacement - Lead spacings

[socketa]

Am going to replace the caps on a LiteOn PSU, and noticed that some of the original OST caps have lead spacings that are the wrong diameter, compared to the holes on the PCB.
Would the most likey reason be, that the manufacturer just used whatever was available, rather than caps with a lead spacing that matches the holes in the PCB?

So, in this instance is it a good idea to look for wider replacement caps, rather than matching the original dimensions?

One of them is way off in that respect - a 50v 10uf 3.5mm cap on the primary side, with leads stretched into holes that would suit an 8mm cap.

[budm]

Re: Capacitor replacement - Lead spacings

It will be difficult to find 10uF 50V cap with 8mm lead spacing, the board may have been designed for more than one version of power supply. You can carefully bend the lead to fit the footprint.

[socketa]

Re: Capacitor replacement - Lead spacings

Thanks
And what about the others, for where replacements can be found?
Would you preferably replace them with wider caps that match the footprints, or is that nitpicking?
Wouldn't bigger diameter caps be more durable?

[budm]

Re: Capacitor replacement - Lead spacings

The 10Uf cap is probably not much of critical as filtering cap in the circuit, I would use good brand such as PANASONIC (I use FM/FC/FR series for all my repair works), or other major brand MFG. The size alone does not make better cap, it has more to with how the cap is made and by whom.

[socketa]

Re: Capacitor replacement - Lead spacings

Thankyou,

So, really, the only significant deciding factor of using a 10mm (that fits the footprint), or a 8mm cap (that doesn't fit the footprint), that have same manufacturer and similar suitable specs, would be the price?

Also, just quickly,
near the 5vsb output,
i have an RLP 100uf 25v (0.023/0.46)Imp (290mA)Ripple
Which of the following 2 would be the best replacement, and why?
PW 100uf 25v (0.025/0.50)Imp (290mA)Ripple
KZE 100uf 25v (0.013/0.41)Imp (405mA)Ripple

[budm]

Re: Capacitor replacement - Lead spacings

"KZE 100uf 25v (0.013/0.41)Imp (405mA)Ripple" This one has better spec, lower Z, higher ripple current rating. But too low of the Z can cause problem and make power supply unstable. Is this cap part of the output regulation feedback or part of the output section?

[socketa]

Re: Capacitor replacement - Lead spacings

It's on the 5vsb output

[budm]

Re: Capacitor replacement - Lead spacings

Must be really low current rating if if it is for the output filter.

[socketa]

Re: Capacitor replacement - Lead spacings

i checked the wrong one
the aforementioned capacitor is circled in yellow, in the thumbnail below
and i'm not at the stage where i'm ready to remove the board, so hopefully someone will be able to make an educated guess, as to which capacitor i should order

i.e.,
if [PW 100uf 25v (0.025/0.50)Imp (290mA)Ripple] would be close enough
and if the [KZE 100uf 25v (0.013/0.41)Imp (405mA)Ripple] impedance would be too low

[socketa]

Re: Capacitor replacement - Lead spacings

if it is not on one of the outputs, is it ok to use a cap with an impedance a bit higher than the original?

0.025/0.50 to replace 0.023/0.46?

[Agent24]

Re: Capacitor replacement - Lead spacings

I wouldn't, but that's just me. It's close enough that it should be OK, but I would trace out the board and check to be sure.

Lead holes are often not the exact spacing for capacitors, especially sub-8mm diameter ones.

[socketa]

Re: Capacitor replacement - Lead spacings

Must be really low current rating if if it is for the output filter.

Is there a "typo" in the above sentence?
The datasheets only give ripple current and impedance ratings.
What is "current rating"?
And why do these output caps need a "really low current rating"?

[Agent24]

Re: Capacitor replacement - Lead spacings

I don't think he meant [the capacitor] "must have a really low current rating" (if you are choosing a replacement for it)

I think he means that a capacitor with such a small size and value (the original is only 100uF) will have a small rating, or that the 5VSB rail itself in this PSU probably has a low current rating (perhaps?)

Ripple current is the rating being talked about. The original RCR (ripple current rating) of the original capacitor was 290mA. For the replacement capacitor, do not use one which has an RCR less than 290mA. RCR works much the same as the voltage rating. Unless you know for sure you can get away with a lower rating, do not use a part with an RCR lower than the original.

[budm]

Re: Capacitor replacement - Lead spacings

The power supply output current rating, the cap will have to supply the current during the off time of the rectifier and get recharged again when the rectifier is on.

[socketa]

Re: Capacitor replacement - Lead spacings

Ok
I was asked a question and also given a suggestion.
1.

Is this cap part of the output regulation feedback or part of the output section?

2.

It's close enough that it should be OK, but I would trace out the board and check to be sure.

The cap is on the 5vsb output rail, (which means that it is not part of the output regulation feedback)

So from what i can gather, and using an educated guess, since it is not part of output regulation, then, in this particular instance, using a cap with a slightly lower impedance rating than the original would probably have a negligible detrimental effect. ???

(Sorry for any misunderstanding - it can be hard to get at what folks are saying without audible and visible cues.)

[budm]

Re: Capacitor replacement - Lead spacings

It is a lot more complex than you think.
Read up on the subject.

[socketa]

Re: Capacitor replacement - Lead spacings

With respect,

You asked me if the cap was part of the the output regulation feedback, to which i replied, "The cap is on the 5vsb output rail" (in other words, no it's not)

The first pdf pertains to feedback loop design considerations - so that is irrelevant because it is not part of the feedback loop
The last pdf talks about a too low esr, but the cap in consideration has a higher esr - again that is not relevant.

The 2nd pdf (which, for me, might as well be written in sanskrit) does not appear to be relevant either, as it relates to the supply control loop.

One further consideration is the PSU is for older type motherboards with electrolytic caps. And from my reading on this site i see that there is room for a bit of play, since they are not polymer and not as fussy about inrush currents.

Perhaps as long as the cap does not overheat, and the voltage of the 5vsb remains within spec, then it will be OK

I know that this can be extremely complicated, but feel that there can be a reasonably simple approach to finding a reasonable solution.

The main issue, as far as i understand, is ripple current, which causes the cap to heat up.
And that ESR affects ripple current > heat.

This PDF seems more relevant:
https://cdn.badcaps-static.com/pdfs/...3127f28bdd.pdf

Namely, the first section - it relates ripple to ESR, and the main point is the failure rate due to temperature

[budm]

Re: Capacitor replacement - Lead spacings

"Is this cap part of the output regulation feedback or part of the output section?" I should have been clear about the output, in this case it is the filter cap of the power supply generated by the AUX winding of the transformer for supplying the running Voltage for the SMPS IC once the circuit start running, not the main DC out put for the load.
For example: C807 for low current power.

[socketa]

Re: Capacitor replacement - Lead spacings

Wow!, looks like you are correct.
I was looking the wrong cap again! (which you probably already knew)

I traced it out
One side goes to Earth,
Using the convention: IC pins are numbered anti-clockwise around the IC starting near the notch or dot,
The other side of the cap goes to pin 15 (of a 16 pin IC) with PS224U L05916A2F written on it. (Which lines up with the pin description of Vcc power supply)

This is the function of the chip: "Over voltage protection, over current protection, under voltage protection, and power good signal generating"

The datasheet says Vcc can be up to 16V so i can see why the cap is rated 25V
Typical voltage is 5v, and typical current is 4.5mA - so the typical power supply is 0.1W

What now?
Will this Nichicon PW, with a slightly higher ESR, be acceptable to power this chip?
It's low power, so it seems as if overheating won't be a problem.

[budm]

Re: Capacitor replacement - Lead spacings

"What now?
Will this Nichicon PW, with a slightly higher ESR, be acceptable to power this chip?
It's low power, so it seems as if overheating won't be a problem." That is correct so the PW will be just fine.