Choosing the right replacement cap

[bertnz]

Hi,

Apologies for the n00b and probably repetitive question here. I figure I'd rego and post a question or two to make sure I'm going to get this right first time. I'm going to replace a couple of caps on an IBM server motherboard. They're not part of the VRM (from what I can guess) but I could be wrong.
One cap is bad, it has leaked brown stuff over the green PCB. The other cap ... well it's probably gonna go bad at some stage so might as well "upgrade" that too



I've identified the bad capacitor as a Nippon Chemi-Con 1500uF 10V KZG which according to the specs sheet has 0.021 impedance and 1870mA RMS ripple current.
ref: https://cdn.badcaps-static.com/pdfs/...c7199f48e3.pdf

Reading the forums, the KZG series has a bad rep so I'll replace two caps though only one has gone bad at this stage.

What I've been able to ascertain so far - and please correct me if I'm wrong:

I need a 10V or higher cap.
I need a 1500uf cap.
I need a low impedance cap (0.021 or lower)
I need a rated ripple current that's AT LEAST 1870mA RMS.

I've found a three possibilities in the on-line New Zealand RS catalogue, but I'm not sure which one would be best - well, I can guess, but I'd like confirmation or a "no get this one instead" since this is a motherboard after all.

1. A Panasonic FC (NHG according to the datasheet) - but it's ripple current isn't high enough:
http://nz.rs-online.com/web/p/alumin...itors/4490924/

2. A Panasonic FM - seem's perfect but it's ripple current rating is quite a bit higher.
http://nz.rs-online.com/web/p/alumin...itors/5261137/

3. A Nichicon HE - seems the closest in terms of ripple current rating but twice the impedance.
http://nz.rs-online.com/web/p/alumin...itors/4909620/

Looking in the badcaps shop the closest I can find is a Nichicon HZ or Rubyon MCZ, but I don't really know how to compare them against the Panasonic and Nichicon offerings I can get locally.

Or would a polymer 6.3V polymer cap do? https://www.badcaps.net/store/produc...roducts_id=134

Cheers and thanks in advance.

[ReeceyBurger123]

Re: Choosing the right replacement cap

Unfortunately non of the caps listed are the correct ones. Can you find Nichicon Hm or Hz they will work ? You need to find caps with the same if not lower esr than Kzg.

[bertnz]

Re: Choosing the right replacement cap

Hi and thanks for the reply.

How do you find (or work out) the ESR spec for the KZG series caps? It's not listed on the datasheet.

Mouser electronics only have 6.3V 1500 uF Nichicon HM or HZs.

Am I better off just trying to find replacement Nippon Chemi-Con KZG's?

[stj]

Re: Choosing the right replacement cap

ESR = Impedance.

btw, when your looking for a replacement.
ESR can be lower but never higher.
ripple can be higher but never lower

[budm]

Re: Choosing the right replacement cap

http://www.murata.com/en-us/products...en-20130214-p1



https://cdn.badcaps-static.com/pdfs/...f6d3e3e891.pdf



http://www.gamry.com/application-not...-spectroscopy/

[mariushm]

Re: Choosing the right replacement cap

stj : ESR = Impedance.

Not true, but close enough. ESR is the sum of impedance and something else, and that something else is practically zero at switching frequencies commonly found in computer power supplies, motherboards, monitors etc. So for simplicity, it's safe to assume impedance is equal to ESR when you read the information from the datasheets. Just look at the column named Impedance measured at normal temperatures and 100 kHz.

Note that ESR and impedance also varies with the capacitor's dimensions (height, diameter) so it's often possible to use larger capacitors to reach (or get very close to) the specifications you need.

The ripple value must be equal or higher than the old capacitor.
The ESR should be as close as possible or lower.

Since computers work in general with 3 main voltages (3.3v , 5v and 12v) it's safe to say that capacitor is most likely used on 3.3v or 5v, so it would be safe to use a capacitor rated for only 6.3v in that position.
However, since there is room around the capacitor for a larger diameter one, you could use one rated for 10v or 16v or even 25v - the voltage rating on a capacitor simply tells you the maximum voltage the capacitor is capable of tolerating without getting damaged.

If you go with polymer capacitors, it's generally (but NOT always, depends on circuit) safe to replace existing electrolytic capacitors with polymer capacitors of slightly lower capacitance. For example, i'm about 90% sure you could use a 1200 uF 6.3v polymer capacitor there, instead of an electrolytic capacitor.

Panasonic FR 1500/16 or Panasonic FM 1500/10 or 1500/16 will work but you have to buy pack of 10:
FR 1500/16 : http://nz.rs-online.com/web/p/alumin...itors/7083664/
FM 1500/16 : http://nz.rs-online.com/web/p/alumin...itors/5261294/

While they're not quite matching the specs (ripple and esr), I think Panasonic FR 1500/10 should also work, the specs are close enough and the price is better: http://nz.rs-online.com/web/p/alumin...itors/7083550/

In the polymer capacitors area, you have this 1500 uF 6.3v one, and you can buy it in packs of 2 : http://nz.rs-online.com/web/p/alumin...itors/7955673/

[stj]

Re: Choosing the right replacement cap

Not true, but close enough. ESR is the sum of impedance and something else,

i wasnt looking for a science lesson, i was simply pointing out why he couldnt find "ESR" in the datasheets.

[bertnz]

Re: Choosing the right replacement cap

Hi,

stj: Thanks - that's a clear and helpful pointer RE ESR can be lower, ripple must be higher.

budm: Thanks for the references. While I haven't read through all those docs, I found this particularly humorous in the Tantalum cap section of the CDE.com guide:
Strengths are temperature stability, volumetric efficiency and compatibility with all automated assembly systems.
Weaknesses are the limited voltage and capacitance ranges and a short-circuit failure mode accompanied by catching fire.

I have an old old old XT board that I suspect has some bad tantalum caps on it. Will tackle that once I get serious with some some testing equipment and have a lot of spare time.

mariushm: Thank so much for taking the time finding those options. I hadn't yet thought about trying 16V caps to find a better match for ESR/Impedance. Cheers for that. Interesting to know you figure a Panasonic FM 1500/10 would work, but taking into consideration the impedance is a little bit lower than the FR 1500/16, so I'll go with the FR 1500/16. It's impedance is almost a perfect match and it has a fair bit of ripple current headroom. I don't mind getting 10, means I can frack up 8 of them :-)

RE the polymer option, the Panasonic OS-CON 1500μF 6.3 V has an ESR of 10mΩ (making it 0.01, right?) which is half that of the original cap. Is that really OK?

Thanks again guys.

[ReeceyBurger123]

Re: Choosing the right replacement cap

i wasnt looking for a science lesson, i was simply pointing out why he couldnt find "ESR" in the datasheets.

Haha lol easy now lads