Making non-polar caps using polar caps?

[Orbis_Ignis]

I'm getting some conflicting info on the net when using two polar electrolytic caps in series to make a non-polar cap. I read in one place that using two 2.2uf will equal 2.2uf. But normally and what I've read in other places is in order to achieve approximately 2.2 to 2.3uf I should use two 4.7uf caps. So my question is which way is correct?

Edit: or would it just be better to use two 1uf film caps in parallel?

[stecykmi]

two film caps in parallel might be more reliable and is probably a better option but it depends on the application.

however, it is possible to make a non-polar cap from two polar by putting them in series. you will always get a smaller value than either of the two caps you used, its the same calculation for figuring out the resistance of two resistors in parallel. in the case of using two caps of the same value, you end up with half the original value. so for example two 4.7uF caps will give you: 4.7uF/2 = 2.3uF.

as another example, if you used a 100uF and a 1uF, the smaller cap will dominate and you wind up with something slightly smaller than 1uF.

[Orbis_Ignis]

I ended up using two 1uF film caps in parallel and tested them to get as close to 2.2uF as possible.

I figured that the calculation was the same for the electrolytic caps, but I read it on one of the forums that it ended being the same value as the caps used (like two 2.2uf in series would equal 2.2uF). Every time I've done calculations for any caps I've used the same equations as you normally would. Just figured I'd ask to make sure there was something I missed in physics class, lol

[stecykmi]

to my knowledge, you should wind up with something close to the parallel calculation but electro caps aren't really designed to be used in series so using two film caps is preferable almost every time anyway.

[blearyeyes]

to my knowledge, you should wind up with something close to the parallel calculation but electro caps aren't really designed to be used in series so using two film caps is preferable almost every time anyway.

I think Brian used two polar caps in one LFO, it was two Polar Electros with negatives connected together?

[stecykmi]

ya, they sometimes show up in that configuration in LFOs (the ROG tri-vibe as well). this is a case where an equivalent poly cap would be too big and/or expensive so we are forced to use two in series however they could just as easily been substituted with a single non-polar electrolytic cap.

i suppose i don't trust them because the voltage in between the two caps is hard to determine and its therefore hard to say much about the long-term durability. if it works, it works, i suppose but i can't shake the view that using them is way is a hack