AC Capacitors

[garrypm]

Hi all,

I can say that I think I understand how a DC cap functions.

We can create and then store a charge in that a DC cap (polarised) and, if it
is not leaky, we can hold this voltage and discharge it at will.

Can someone please explain the fuction of AC caps? Say for example, the
1.0uf 2100v cap found in microwave ovens.

Thanks, Garry

[Armagdn03]

Hi all,

I can say that I think I understand how a DC cap functions.

We can create and then store a charge in that a DC cap (polarised) and, if it
is not leaky, we can hold this voltage and discharge it at will.

Can someone please explain the fuction of AC caps? Say for example, the
1.0uf 2100v cap found in microwave ovens.

Thanks, Garry

An ac cap is simply one which is not polarized. What is stored within is still a DC potential, however it can be charged either way.

[LetsReplicate]

Capacitors have several uses in AC circuits. To a DC circuit, a capacitor looks like an "open circuit" that can store a and source a charge. In an AC circuit, a capacitor reduces in impedance (resistance) as the frequency of the AC increases.

So the ways a capacitor can be used in AC circuit are:

1. DC energy storage - usually using a diode to "rectify" the AC into DC. Usually used for power supplies.
2. DC blocking - allowing high frequency AC to pass while appearing "open" to DC. This is very common in audio amplification.
3. Create a resonance - when an inductor (coil) is added to the circuit. These are most commonly AC frequency filters.

The capacitor in the microwave could be any of these 3 but given the high maximum voltage, it's likely number 1. Non-polarized capacitors can have a much, much higher maximum voltage than polarized ones.

[garrypm]

Thanks guys

[boguslaw]

How a DC electrolytic capacitor can be placed in resonant RLC circuit ? I thought it is impossible but it's not so. I found at least two example when electrolytic capacitor works in resonant circuit giving nice low frequency.
For example Scott McKie -- PODMOD Over-unity power generator

[citfta]

One more purpose for ac caps

There is one more use that is common for ac caps. They are also used as phase shifting devices in ac circuits.

Carroll

[Armagdn03]

How a DC electrolytic capacitor can be placed in resonant RLC circuit ? I thought it is impossible but it's not so. I found at least two example when electrolytic capacitor works in resonant circuit giving nice low frequency.
For example Scott McKie -- PODMOD Over-unity power generator

This works sometimes yes, but it is not optimal because the polarized capacitor will react differently during the two parts of the AC cycle. Unless this is what you are looking for!