Making a bipolar cap? (electrolytic? using 2 caps?)

[Myron Samila]

Hi all,

I need a high value Bi-Polar electrolytic (200uF, 132.5uF, etc...), I remember that if you
take two polarized electrolytics and join the positives (? or was it negatives?) I can
basically end up with a non polarized cap (bi-polar).

I just need to filter off some low frequencies from the front speakers in my car, 4ohm
impedance, and I want to cross them over at 200hz at 6db/octave, I'll basically need a
200uF cap, 300hz would be 132.5uF.

Anyhow, fill me in? I can't remember, and now I am so dependant on computers and google, I
forgot how to open a book and read. Sad, very sad.

thanks

 

[Art]

Gov, connect the + terminals together, be advised that the working voltage
should be a consern also. Cheers & have a fine Holiday there in To

 

[CWatters]

Two caps in series = half the capacitance of one.

 

[Myron Samila]

True, it is hard to find high value non polarized electrolytics. Finding two polarized
400uF caps would be much easier and probably a lot cheaper.

Working voltage is quite low, since a 45w car audio deck doesn't put out very much, works
out to 20v at most?

A 1200 watt amp puts out somewhere around (pro amp of course, concert audio) 56-70 volts

 

[DarkMatter]

True, it is hard to find high value non polarized electrolytics. Finding two polarized
400uF caps would be much easier and probably a lot cheaper.

Working voltage is quite low, since a 45w car audio deck doesn't put out very much, works
out to 20v at most?

A 1200 watt amp puts out somewhere around (pro amp of course, concert audio) 56-70 volts

To increase capacitance place two in parallel, and two more in
parallel, connect those pairs in series opposed fashion.

That restores the original capacitance value of the single can.

Remember to use peak voltages for this application, when determining
what cap ratings to use, and don't buy electrolytics from surplus
houses ever.

They dry out with age... badly. That changes there cap value...
badly.

 

[Zak]

Hi all,

I need a high value Bi-Polar electrolytic (200uF, 132.5uF, etc...), I remember that if you
take two polarized electrolytics and join the positives (? or was it negatives?) I can
basically end up with a non polarized cap (bi-polar).

Plus or minus together doesn't matter, as long as it is plus-to-plus or
minus-to-minus.

I just need to filter off some low frequencies from the front speakers in my car, 4ohm
impedance, and I want to cross them over at 200hz at 6db/octave, I'll basically need a
200uF cap, 300hz would be 132.5uF.

A problem may be the tolerances. Bipolar caps should have narrower
tolerances as they are meant for filtering. Ordinary electrolytics are
used for power supplies; I remember -10% +50 % as tolerance bands.


Thomas

 

[Myron Samila]

Tolerances wouldn't be a problem, it could be as far off as 30%, and you wouldn't hear any
difference in the sound.

At a crossover slope of 6db/octave, the only difference between one speaker and another
would be at the crossover point, and then, you'd never be able to tell the difference of a
few percent since this particular slope quickly disappears in the next lower octave.