Replacing a capacitor

Question

I have an electronic device that I have had for a good few years meaning that it's no longer in warranty. Recently it has developed a fault where the device will turn itself off when more power is being used. After looking online, I found that the cause was more likely a failing capicitor.

My question is what exactly do I look at when replacing a capacitor? When looking at the spec sheet of the original capicitor (https://www.maxcap.com.my/ht.html ) there are plenty of options. (The one I need to replace is rated 35V @ 47µF)

Would I be right to assume that I need to try and match it like for like? E.g, same voltage, working temprature, load life, capacitance?

I can't seem to find the original capacitor being sold online on RS Components or Farnell. I'd appreciate any advice on which capacitor(s) I can use to replace it and why (if it's not like for like).

Answer 1

The capacitor in your datasheet is a low-leakage type with 0.002CV leakage maximum. That's about 10:1 or 20:1 less than typical electrolytic caps, and really is a red flag to my eyes that this is a coupling capacitor and not some kind of power supply part. The other oddball spec is the 125°C rating, which is either specified because the part is exposed to high temperatures or to get a long life (in theory, anyway since life is supposed to double for every 10°C below rated).

Of course we can't tell from the part datasheet whether low leakage is an actual requirement, but it would be prudent to try to find a low leakage part. Nichicon has a good range of such parts.

For example, check out UKL1H470MPDANA, UKL1J470MPD1AA, UKL1V470MPDANA, UKL1V470KPDANA etc. Unfortunately, none of those parts has a higher rating than 105°C. So you may have to make a judgment as to whether life or high temperature operation is actually a requirement unless you can find one that is same or better in all specifications.

Other than that, it has to physically fit, have the same capacitance, same or better tolerance and same or higher voltage rating. ESR should be similar or less.

Answer 2

If you're not sure which capacitor to choose look for a capacitor which has the same specifications as the one you want to replace.

If you can't find a perfect match look for capacitors of the same capacitance and the same mounting type. After that you should check the size of the component you want to replace and how much space there is around the cap on the board, maybe you can use one that has a larger size (height/diameter). The distance between the two pins should be equal to the one that should be replaced. The voltage rating has to be at least as high as the cap you want to replace, but it can also be higher. (If you know the voltage between the two pins on the board and it is less than 35V you can also use a cap with a lower voltage rating, e.g. the volatge on the board is 20V than you could also use a cap with 25V voltage rating). The temperature rating is similar to the voltage rating, if you don't know the working temperature look for a cap with at least the same temperature rating. The lifetime is well explained by @sphero. The ESR should be similar or less to prevent oscillation. The maximum ripple current should also be similar or higher to handle the AC properly.

With all that in mind I would choose one of these two:

Vishay (The diameter is 0.5mm larger than the one from the Maxcap and has very low ESR)

Nichicon

Both caps have a higher max. ripple current, a higher maximum operating temperature and less leakage current. But the lifetime at maximum operating temperature is only 1000h. Everything else is similar to the maxcap.