I need to put a capacitor across a AC power switch to keep it from "popping" when I turn on the power.

Question

I don't remember what size to use. .47 micro farad sounds about right, but I'm not sure.

I salvaged a subwoofer that had a missing external power supply. I built a AC to DC power supply, but I get a loud pop in the subwoofer when I turn on the power. I switch the AC side. Long ago I put a capacitor across a power switch on a turntable to cure a similar pop, but I don't remember the size. I think it may have been a non-polarized .47 micro farad, but I'm not sure.

Answer 1

Usually the value I find most commonly used is 0.0047 to 0.010uF, depending on the size of the power x-former. The cap should be rated for at least 250vac. This can be a film or ceramic disk type that is UL approved (recommended). I have seen some as high as 0.047, but in very old equipment. Hope this will help!

Answer 2

I am thinking that a switch that pops needs to be replaced. Putting a capacitor across an AC switch will essentially permanently turn the circuit on a little bit all the time. So even if you switch the circuit off, someone can still get a shock. Not safe.

If you are really having trouble with the popping use a sealed mercury switch, which is available in hardware stores.

Answer 3

You're on the right track - but I suspect the cap you are thinking of is to eliminate RF interference on the AC line.
Turn on surge may cause this concern, so you might want to think about a few resisters in series with the power supply capacitors to slow their initial charge rate a bit.

Answer 4

Any power supply is going to cause a 'pop" when it is first turned on. Either find a circuit that turns off the output until the surge is over, or turn down the gain of the amplifier that drives the speaker.

Answer 5

What you are looking for is called a snubber. It is made from a .47uF cap and a 220 ohm 1W resistor. It is specifically designed to eliminate dV/dt problems. Solid State Relays need these to stop false turn-ons. There are companies that make them in one package. Use google search to find "rc snubber" (include the quotes).