Back to Back Polarized Electrolytics

[jclin4]

I'm in a pinch and trying to get to a 26uF cap value. This is the second series cap in a 3rd order electrical high pass. I have a 15uF film cap on hand and want to parallel with 11uF. Local R-Shack has these 22uF polarized axial electrolytics in stock which I plan to put back to back.



http://www.radioshack.com/product/in...uctId=2102482#

Question is do I put the negative ends together, then attach the positives to my filter, or does it matter?

It is just for experimenting this weekend to make sure I am on the right track. Eventually I will replace with film caps.

Thanks in advance!

[PWR RYD]

Re: Back to Back Polarized Electrolytics

I've seen it done negative to negative but it doesn't really matter.

[jclin4]

Re: Back to Back Polarized Electrolytics

Thanks PWR! It is as I thought, but just wanted to check.

[dcibel]

Re: Back to Back Polarized Electrolytics

Like many forum questions, this has been answered many times and google will answer it for you as well.

To make a bipolar cap from two standard electrolytic, you solder the negative terminals together so + is on either end connecting to your equipment. You'll also need 2 caps that are double your required value, so if you want 26uF, two 50uF caps are required. With the 22uF caps from Ratshack you will have a 11uF cap when both are wired in series.

[jclin4]

Re: Back to Back Polarized Electrolytics

Thanks. I intend to wire the two 22uF caps in series, and then parallel that with a 15uF cap I already have on hand.

So (22/2)uF + 15uF = 26uF.

[dcibel]

Re: Back to Back Polarized Electrolytics

Thanks. I intend to wire the two 22uF caps in series, and then parallel that with a 15uF cap I already have on hand.

So (22/2)uF + 15uF = 26uF.

OK, you are good then.

[xxbaker]

Re: Back to Back Polarized Electrolytics

Quick question related to this, if you connect two caps in series does that double their voltage rating? ie two 22uf 50v caps == 11uf 100v cap xor 11uf 50v cap? Seems like it shouldn't change the voltage rating since there won't be any voltage drop over the caps, but just wanted to check.

[Æ]

Re: Back to Back Polarized Electrolytics

Quick question related to this, if you connect two caps in series does that double their voltage rating? ie two 22uf 50v caps == 11uf 100v cap xor 11uf 50v cap? Seems like it shouldn't change the voltage rating since there won't be any voltage drop over the caps, but just wanted to check.

Two 100 volt rated polarized capacitors in series result in a 100 volt rated non-polar unit with half the capacitance. Two 100uf electrolytic caps back to back only gets you 50uf.

This is because non-polars have twice the tension range from the negative of the rated tension to the positive of the rated tension where polarized units only have a range from zero to the rated tension.

[AJ]

Re: Back to Back Polarized Electrolytics

Two 100 volt rated polarized capacitors in series result in a 100 volt rated non-polar unit with half the capacitance. Two 100uf electrolytic caps back to back only gets you 50uf.

This is because non-polars have twice the tension range from the negative of the rated tension to the positive of the rated tension where polarized units only have a range from zero to the rated tension.

In addition, the voltage rating only doubles when the caps are connected positive to negative. This is useful in tube amps for the high voltage B+ filtering. Care must be taken to keep the voltage across each cap close to even, though.

[PWR RYD]

Re: Back to Back Polarized Electrolytics

In addition, the voltage rating only doubles when the caps are connected positive to negative. This is useful in tube amps for the high voltage B+ filtering. Care must be taken to keep the voltage across each cap close to even, though.

To expand on AJ's correct info... balancing resistors are used to ensure that the voltage is even across each cap. We used to do that in 480 VAC AFD's. Large banks of parallel/series caps with balancing resistors. Caps were rated for 450 WVDC, bus voltage could hit 800 VDC in regen/dynamic braking mode.