Everything that I've read says that you can put a pair of polarized electrolytic caps back-to-back, and achieve an unpolarized cap. It must be true, but I've never understood the theory of it.

When the back-to-back pair has an alternating current across it, one of the caps will be reverse biased during each half cycle, right? Theoretically, I don't understand why this is acceptable. And if it is acceptable, then why is it unacceptable to use a single, polarized cap across AC?

I can't recall ever encountering such a back-to-back pair installed as an OEM component.
Doug

Hi Doug

You can use 2 electrolytic caps back to back for AC use. During one half of a cycle one cap charges. The other acts like a short circuit. During second half of a cycle operation is reversed.

Best to connect a diode across each cap. This prevents reverse bias across the cap. Although caps won't charge in reverse the diode prevents any reverse voltage across the cap.

You can buy non polarized electrolytic caps that are built with 2 caps back to back inside.

Norm

:Everything that I've read says that you can put a pair of polarized electrolytic caps back-to-back, and achieve an unpolarized cap. It must be true, but I've never understood the theory of it.
:
:When the back-to-back pair has an alternating current across it, one of the caps will be reverse biased during each half cycle, right? Theoretically, I don't understand why this is acceptable. And if it is acceptable, then why is it unacceptable to use a single, polarized cap across AC?
:
:I can't recall ever encountering such a back-to-back pair installed as an OEM component.
:Doug

:Hi Doug
:
: You can use 2 electrolytic caps back to back for AC use. During one half of a cycle one cap charges. The other acts like a short circuit. During second half of a cycle operation is reversed.
:
: Best to connect a diode across each cap. This prevents reverse bias across the cap. Although caps won't charge in reverse the diode prevents any reverse voltage across the cap.
:
: You can buy non polarized electrolytic caps that are built with 2 caps back to back inside.
:
:Norm
:
:
:
::Everything that I've read says that you can put a pair of polarized electrolytic caps back-to-back, and achieve an unpolarized cap. It must be true, but I've never understood the theory of it.
::
::When the back-to-back pair has an alternating current across it, one of the caps will be reverse biased during each half cycle, right? Theoretically, I don't understand why this is acceptable. And if it is acceptable, then why is it unacceptable to use a single, polarized cap across AC?
::
::I can't recall ever encountering such a back-to-back pair installed as an OEM component.
::Doug

::Hi Doug
::
:: You can use 2 electrolytic caps back to back for AC use. During one half of a cycle one cap charges. The other acts like a short circuit. During second half of a cycle operation is reversed.
::
:: Best to connect a diode across each cap. This prevents reverse bias across the cap. Although caps won't charge in reverse the diode prevents any reverse voltage across the cap.
::
:: You can buy non polarized electrolytic caps that are built with 2 caps back to back inside.
::
::Norm
::
::
::
:::Everything that I've read says that you can put a pair of polarized electrolytic caps back-to-back, and achieve an unpolarized cap. It must be true, but I've never understood the theory of it.
:::
:::When the back-to-back pair has an alternating current across it, one of the caps will be reverse biased during each half cycle, right? Theoretically, I don't understand why this is acceptable. And if it is acceptable, then why is it unacceptable to use a single, polarized cap across AC?
:::
:::I can't recall ever encountering such a back-to-back pair installed as an OEM component.
:::Doug

Doug:
An electrolytic cap is made by oxidizing aluminum, to insulate it, and putting it in a liquid that conducts, an electrolyte. When the polarity is correct, the oxide acts as an insulator, and the aluminum and the electrolyte act as the two plates. However, there is a little problem with this arrangement, that is if connected backwards, the aluminum oxide acts like a diode, and the cap will conduct very well, getting hot enough in the process to explode at times. To make a large value NP cap, you series two caps in a can. put diodes across them to be more stable than aluminum oxide, and call it non-polarized. But, unlike non electros, the value of the caps will not be halved, as one is shorted out by the diode.
Lewis