esr

[goodsguys]

Hi and thanks for taking the time to read this post.

May i ask what the most important capacitor parameter is when picking a replacement capaitor for upgrading an old aging one. Many people talk about esr. Should i purchase a capacitor with the very lowest esr. You see it gets a little confusing with so many brands out there and everyone having their own favourite to recommend.

I want to change an aluminium eltrolytic for aluminium electrolytic Should i look at capacitor esr as of utmost importance alone or is there any other parameter to be considered.

Many thanks in advance. John..

[sq225917]

Mark, what is most important is that it is the most suitable set of values for the location it is used in the circuit. Sometimes this will mean matching the current part, sometimes it will mean matching the nominal part values, but beating them in other measurements.

For example, if you are replacing smoothing caps in a power supply then you need the same value for capacitance, at least, but lower ESR may bring an improvement. If you were replacing a capacitor on the output of a regulator, then you might not want a super low ESR cap. It just depends on what the cap is actually doing.

[goodsguys]

Hi. Many thanks for the reply.

The aluminium electrolytic is for use in the power supply, i may try to bypass it as well with a high quality polypropylene.

Many thanks in advance. John.

[sq225917]

Then swap for the lowest ESR cap you can find with the best ripple, You can higher on capacitance , voltage and temp rating.

[reddish75]

Panasonic fc/fm or nichicon he/pw are the defacto standard in my view when replacing capacitors in powersupplys, and most other parts of the circuit come to think of it.

The thing you will find more difficult is matching the physical size of the originals, do your reasearch on this as the panasonics (maybe the nichicons as well) come in two sizes for some values.

Digital calipers will come in handy in this situation.

Chris

[goodsguys]

Hi. Many thanks for the replies. It is genuinely appreiated.

What do you think of trying to lower esr by using capacitors in parallel. The aluminium electrolytic is 2200uf, if bypassed with say a 10uf film type cap would this affect esr.

Many thanks in advance. John.

[NRG]

It's a good idea but only to make up the value of the original cap IE parallel up two or maybe three 1000uf caps if the original was 2200uf, fitting may be an issue.

Bypassing the caps is a technique to improve the HF performance of a typical 'lyric which usually has a rising impedance at higher freq.



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[goodsguys]

Hi. Many thanks for the replies.

Can you recommend a capacitor type for power supply use. The value i need is approx 10,000uf at 63volts but a slightly higher voltage or capacitance would be okay.

A google search indicates nichicon pw, kg, but i can't find esr values for these two, is there any better. or is it best to get the lowest esr and forget about names.

At the moment i am thinking of two 4700uf in parallel, then 100uf in parallel, then a 1uf polypropylene.

Or would i do better (lower esr) with say 10x 1000uf in parallel, then a 1uf polypropylene.

Many thanks. John.

[NRG]

Depends on the amount of space you have but whatever combination you end up with I'd select Panasonic FC's for PSU use. IE: 5x 2200uF or 2x 4700 + 1x 2200...

[goodsguys]

Hi. Thank you for the reply.

So you think there will be little difference between bypassing 10x 1000uf, versus two 4700uf in parallel then 100uf in parallel then a 1uf polypropylene.

I thought the lower esr of the 10 caps in parallel may have some effect, or do you feel the 4700uf with 100uf with 1uf may ensure each bandwith recieves power.

Many thanks. John.

[NRG]

Not sure what you mean by each bandwidth receives power.

You are trying to lower ESR, have a read of this article:

http://sound.westhost.com/power-supplies.htm

Paralleling the PSU caps will also improve the ripple rating of the supply. Bypassing in theory improves the high freq performance of the main supply capacitor supposedly making the capacitor appear more ideal, however, its debatable wether its really necessary...try it and see.

[Reid Malenfant]

I thought the lower esr of the 10 caps in parallel may have some effect, or do you feel the 4700uf with 100uf with 1uf may ensure each bandwith recieves power.
I think the many paralleled capacitors will likely be better in certain respects, as there is something that you are missing from the equation - ESL.

Paralleling a bunch of capacitors will increase the ripple current capability, decrease ESR & also decrease ESL (equivalent series inductance). It's ESL that will have a much greater effect on higher frequency behaviour of the capacitor as put simply they do have inductance. After all, they are a big winding of aluminium foil at the end of the day.

If you parallel two capacitors you'll halve the ESL, if you add two more to that you'll halve it again. Each time you double the number of capacitors in parallel the ESL will halve. So will the ESR come to think of it :scratch:

[sq225917]

Surely if you double the number of caps you double the ESR but half the ESL. The benefit comes from dropping from 1 x 10,000uf cap which will have quite a high ESR to 10x 1000uf caps which should still potentially have lower ESR and for sure have lower ESL/.

Aren't FM lower ESR than FC?

[Reid Malenfant]

If you put two equal value resistors in parallel what happens to the resistance? It sure as hell doesn't double ;)

I think you'd need to look up each capacitor to find out which has lower ESR, I doubt that just going to FC will always give the same results & in some instances other types may be a better alternative. FC are certainly designed for low ESR & high ripple PSUs in a small size can.

[NRG]

Yes the FM series is lower ESR and has better ripple capability but they don't have quite the range of FC in voltage and capacity. ESL is important as well as ESR, it's important to use the same type and value caps if paralleling them up to get the benefit of doing so.