ken via EV wrote:
AC switches are built lighter duty, to save on cost, so using the ac power plug for swithcing current is a better way.
It's not really that the switch is cheap; it's just that it was only designed for AC. An AC switch can open relatively slowly, because the duration of the arc is limited by the time to the next zero-crossing of the AC line. Bill had a good explanation of the problem.
Bit AC/DC rated switches are still fairly common. 120 volts *DC* was a standard in the US for a long time (in the days of Edison). You can still find old switches in basements and garages left over from the time. They have a loud, distinctive "click" when switched.
Pulling the plug to turn something off on DC is also a poor way to do it. You still get substantial arcing, which will damage or destroy the plug and outlet.
If you really must use an AC-rated switch on DC, one band-aid is to add a resistor-capacitor "snubber" across the contact. See <http://www.sunrise-ev.com/LeesEVs.htm#snubbers>. A snubber substantially reduces the amount of arcing.
Even though you can run these devices on DC, the switches on these appliances are not suitable for DC, only AC. You risk a fire. You can close the switch just fine on, say, your hairdryer, but when you attempt to turn it "off", the DC will often simply arc across the switch, and current will continue to flow. This arc will start a fire. AC turns off and switches polarity 120 times per second, which extinguishes the arc when switches and fuses open. DC is steady with not breaks or reversals. You get a small warning when this happens. The switch will make a small "hiss" and the appliance only partially shuts off. Turn the switch back on and pull the plug. There will be an arc at the plug and you may avert a fire. The switch is typically toast, however.
-- If we knew what we were doing, it wouldn't be called research, would it? -- Albert Einstein -- Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)