Capacitors in series

[Tage]

Just wanted to try and confirm something, I cannot seem to find information on.

My question is; Do the ripple current ratings sum or divide when connecting capacitors in series?

[Leo_Gnardo]

I'll take a stab at it. They don't change. All the ripple current that one cap passes also has to pass thru the other(s) in series.

Seems to make sense, but there's times I've been wrong. Any EE's out there?

[Jazz P Bass]

I would think, seeing that the voltage rating does not change, that the ripple rating would remain the same.

[Gingertube]

Ripple Current rating of the 2 in series is the same as each by itself.

Usually you will series 2 caps (with voltage share resistors across each - RIGHT) to handle the voltage.

You series connect 2 caps of double the required value.

In most cases the double size caps will have a higher ripple current rating too so when you series caps you will often get a ripple current benefit as well as the higher voltage withstand. A win win for longevity/reliability.

Cheers,
Ian

[Tage]

Yeah I figured there was no summing effect. I just wanted to check if there was an added benefit beyond the summed voltage handling. I just have noted that some times lower Capacitance capacitors of a similar size can have higher riplle current ratings than higher capacitance capacitors.

Ie a 470uf cap with 5.6A ripple current and a 1000uf with only 3.8A ripple current. I understand that if the 1000uf filter was in a larger can it would have a higher ripple rating, as it could handle more heat right?

Although with higher Capacitance there will be less ripple in the supply for the capacitors to have to deal with.

Also I do always use balancing resistors across series filter caps, so no worries there Ian...

[Gingertube]

Tage,
Ripple Current rating is dependent upon the self heating internal to the capacitor from current squared x resistance dissipation and the ability to get rid of that heat.
The current is the ripple current and the resistance is the ESR. The ability to get rid of the heat is a physical constructioin thing but mostly its just size.
The Current squared thing is important. If you choose a cap rated for twice the expected ripple current it will have 4 times (2 squared) the lifetime of one chosen for just the expected ripple current.
Cheers,
Ian

[J M Fahey]

In fact I think the new ripple current rating will be the smaller of them two.
Think different value fuses in series for an analogy.

Or in: "a chain is as strong as its weakest link".