Parallel vs. series vs. one filter cap

[Chris333]

Is there any electrical advantage to using either two parallel or two series filter caps instead of one, assuming the total capacitance and voltage handling is equal for all three options?

For example, 2 X 100uf-250V series vs. 2 X 25uf-500V parallel vs. 1 X 50uf-500V (please correct me if these don't each come out to 50uf-500V!).

[Rob S]

Is there any electrical advantage to using either two parallel or two series filter caps instead of one, assuming the total capacitance and voltage handling is equal for all three options?

For example, 2 X 100uf-250V series vs. 2 X 25uf-500V parallel vs. 1 X 50uf-500V (please correct me if these don't each come out to 50uf-500V!).

Hi there,

This is a view and an opinion only and I'll probably contradict myself...

Electrloytics used to have a tolerance of something like + or - 50 to 100 per cent or +150 -50 per cent or something like it - don't know what it is now but say it's much better...

To me, that still means that two capacitors together in series or parallel would combine to be in the worst case nearer to the values they're supposed to be.

Two series capacitors might share an unequal voltage load because of differences in tolerance which could put one of them under overvoltage stress.

Two parallel capacitors would appear to be the best solution but...
then you have two components with twice the possibility of failure and twice the expense.

On a build or a repair, I would use what I've got - on a design you would use what fits or what's cheap and if it's high frequency then you'd need to use low e.s.r. things.

Presumably the capacitors are for a valve amp power supply and in this case (here's the opinion) I don't think it matters - stick a .1 cap bypass across with a 100k resistor and the audiophiles & electricians will be happy

I make it up you know,

Rob.

P.S. On restoring an antique piece of gear I wouldn't use an antique capacitor cos to me it's daft.

[Enzo]

The reason we use two caps in series is to get higher voltage rating. If you can even find 40uf 600v caps, they will be expensive, but a couple 100uf 350 volt caps will be a snap to source at reasonable cost. That is why an amp maker does that. And those two caps might be smaller than the one 600v cap.

I see no particular advantage to doubling them in parallel unless you need more capacitance than is readily available at a price.

Pretty much keeping it simple works best. One cap instead of two works for me. WHen you see multiple caps where one would work, it is almost always done for economic reasons.

Look at Marshall and those 50+50/500v can caps. They but them by the truckload and no doubt get a great price on the volume. They can probably jump the two halves of one of those together for 100uf/500v cheaper than they can separately get a 100/500v cap. Plus the size of the holes and stuff would remain the same as the other caps, keeping tooling cheap.

Even in my shop, if I need a 40/500 axial cap, I might use two 22/500 caps instead becasue I already stock them and get them at a good price. That of course depends upon what I am doing.

[markbul]

In TUT3, K. O'Connor claims that "lead inductance, internal resistance and leakage capacitance" work against the suppression of noise and amplifier stability. "These commodities are smaller in lower value caps than in high capacitance units, so several low-C caps will outperform one high-C cap of the same net value."

His words, not mine. Discuss among yourselves. :)

[kg]

generally, he's right--the equivalent ESR of multiple, smaller value, paralleled caps will be lower than the ESR of a single larger cap.

whether or not this makes an audible difference i will leave to the ear of the beholder. :)