Cap in series or parallel

rknucklez

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please refresh my memory...

say you need a 1000uf 35V and you have a bunch of 1000uf 25V 's but no 35Vs.

should you piggyback them? (parallel?)
negative to negative in negative hole
positive to positive in positive hole

or line em' up (series)
negative on c1 in negative hole positive on c1 to negative on c2, positive on c2 to positive hole

maybe a noob question but good to document nonetheless
 
you need a 1000uf 35V and you have a 1000uf 25V

you cannot go down in voltage. you can go up in voltage.

my first question is the one you are replacing original?

consult the schematic as the 25V might have been originally installed and someone else has installed a 35V since. then you'd be ok to install the 25V
 
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In series you'd halve the capacitance to 500uF. In parallel you double to 2000uF. So it looks like you're screwed. :D

Why not just order the correct part?
 
Electrolytic Capacitor Increased Voltages

Hi,

You can use electrolytics in series to increase their operational voltage but.... There are a lot of variables and capacitors in series have decreased capacitance. Usually there are balancing resistors used in parallel with each cap and the value of those resistors is based on the leakage current of the caps and assumes identical caps. You can usue the caps in series and pray that the equivalent resistance of each cap is close enough to work until you can get the right one, but that is unlikely as they usually have tolerances like +/- 20% or +80%/-20% or +/-50%.....

Long story short... Wait until you can buy the right ones.

Kenneth
 
In series you'd halve the capacitance to 500uF. In parallel you double to 2000uF. So it looks like you're screwed. :D

Why not just order the correct part?

Which is why you take 4, put 2 pairs each in parallel, then put the pairs in series, and you end up with a big ugly 1000uf 50V cap...
 
Thanks guys,
yeah, after a web search I found a site with all the formulas.. I guess I am a waiting for a K4600 cap kit to arrive.
 
You could also just stick in the 25V and hope they over-rated the original design, or under-rated the part ;) . I'm just kidding of course, unless you're in a real pinch and don't mind re-doing it when it fails prematurely (though 25V to 35V isn't a huge jump), or if you look at the schematic/waveforms and can be sure it won't exceed 25V.

DogP
 
You could also just stick in the 25V and hope they over-rated the original design, or under-rated the part ;) . I'm just kidding of course, unless you're in a real pinch and don't mind re-doing it when it fails prematurely (though 25V to 35V isn't a huge jump), or if you look at the schematic/waveforms and can be sure it won't exceed 25V.

DogP

That's true. I usually take 2 to 2.5x the max possible voltage on the cap and use that to select the rating. YMMV.
 
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