What's the difference between an AC capacitor and a DC capacitor?

[Billy Mayo]

What's the difference between an AC capacitor and a DC capacitor?

I know that DC capacitors use chemicals that are only One Uni Directional not bi directional

At work they use AC capacitors in DC circuits, but I don't understand why they use AC capacitors

Also I have noticed when using AC capacitors they solder a Diode on the Terminals of the AC capacitor, does this turn a AC capacitor into a DC capacitor?

 

[dougy83]

The polarised electrolytic caps only have one of the aluminium plates anodised. Anodising creates a very thin insulator. Refer to https://en.wikipedia.org/wiki/Electrolytic_capacitor

For the nonpolarised electrolytic caps, both plates are anodised. The capacity will be halved in doing so (ref https://en.wikipedia.org/wiki/Capacitor)

For non-electrolytic capacitors, the structure is symmetric and they are nonpolarised. There is no issue with using them in DC circuits except when a large capacity is required; they will be physically larger in that case.

Can you give an example of the diode on the terminals of the "AC capacitor"? Sometimes a diode will be placed on a polarised capacitor to stop it from being damaged when a reverse current is applied. Sometimes there will be two capacitors and diodes in this configuration put in series to emulate a non-polarised capacitor.

Someone did some sims here: https://electronics.stackexchange.c...tic-capacitor-out-of-two-regular-electrolytic

 

[koolguy]

What's the difference between an AC capacitor and a DC capacitor?

AC capacitor are non-polarized don't have +ve and -ve terminal on it, so, it can be used for AC with low farad in 1/2uF but 400/200V
In case of Dc capacitor are called polarized they have +ve and -ve terminal on them generally have high uF but low voltages .

 

[Billy Mayo]

Sometimes a diode will be placed on a polarised capacitor to stop it from being damaged when a reverse current is applied.

What kind of circuit or what circuits have you seen that uses a AC Capacitor Or Polarized Capacitor that has a diode to protect it for reverse current?

The Capacitor is AC so how can it get damaged from reverse current?

The Diode is placed on the terminals of the Polarized capacitor so the Diode is in parallel, If the current is reversed it still will damage the polarized capacitor right because the diode is in parallel?

 

[dougy83]

What kind of circuit or what circuits have you seen that uses a AC Capacitor Or Polarized Capacitor that has a diode to protect it for reverse current?

I assume you're referring to the diode in parallel with the capacitor; I've seen it done on the input bulk caps of a circuit where the designer did not want to use a series protection diode. There was a fuse in series with the power input. There's also the case of people wanting to use polarised caps instead of non-polarised; the details are on the page I linked above, including simulation.

The Capacitor is AC so how can it get damaged from reverse current?

If it is non-polarised, then it doesn't mind voltage applied in either direction.

The Diode is placed on the terminals of the Polarized capacitor so the Diode is in parallel, If the current is reversed it still will damage the polarized capacitor right because the diode is in parallel?

No, if the diode is connected with the anode to the +ve side of the capacitor, and the cathode to the other, the voltage across the capacitor will not go below the forward voltage drop of the diode.