What's the difference with VDC vs VAC switches?

[Zero_Enigma]

Ok a bit confused here but I think it's how many AMPS the switch can take but what's the difference from VAC and VDC?

I know one is AC and the other is DC. Is there any power loss between the two? I have plans for a 6-10 LED unit running ~800-1000mA on each LED for testing.

 

[Steve K]

Ok a bit confused here but I think it's how many AMPS the switch can take but what's the difference from VAC and VDC?

I know one is AC and the other is DC. Is there any power loss between the two? I have plans for a 6-10 LED unit running ~800-1000mA on each LED for testing.

Usually it's the voltage rating, I think. The primary issue is what happens when the switch opens and has to stop the current. With high voltages and large inductances, the current really, really doesn't want to stop, and will generate large voltages in order keep it going. This produces arcing across the switch contacts, which can damage them.

The nice thing about AC power is that the current goes to zero amps twice in every cycle (every 8.3 milliseconds here in the States), so it's easier to stop the current. With DC power, that arc across the contacts may go on for quite a while, so the switch has to be more robust, or just move the contacts further apart when they open.

The switch manufacturers probably have some good application notes on this sort of thing....

Steve K.

 

[Zero_Enigma]

I was at a local store (Active Electronics) and they had a switch there with a rating of I think 3A 125VAC/28DC I think was what it said. I do know for sure it gave you a DC rating. Is there some formula to convert VAC ratings to VDC equivlents?

Thanks.

 

[Flummo]

No, there is no formula, or at least none for us mortals.

Another problem with DC is that the small arc you get every time you switch it of moves a little metal from one contact point to the other. Very small amounts ofcourse, but with the same polarity the metal moves the same way all the time. (With AC the polarity changes, so in the end it turn out to about +/-0.) A few relays and switches has even been made for current going in one direction only, with one contact point made of silver (best electrical conductor available), and the other made of copper with a thin silver plating.