AC wall switch work on 12V DC?

robertglines1 · December 04, 2009, 04:22:41 PM

will a ac wall switch work on dc circuit without draining battery? I checked the switch and it showed no flow.Did I miss something? I feel dumb asking this question but need to be told it won"t by someone who knows for sure.

Len Silva · December 04, 2009, 04:51:19 PM

An AC switch will work but is usually not rated for DC. I would derate it at least 50%. That is, not more than 7-8 amps on a 15 amp switch.

Nick Badame Refrig/ACC · December 04, 2009, 07:25:39 PM

Hi Robert,

Len is correct!

And, you should not feel dumb asking a very important question like this one... This is why we are here! To keep everybody Safe!!

Oh, and also to help save you money with all our wealth on Knowledge..

Glad your here!
Nick-

robertglines1 · December 05, 2009, 03:33:59 AM

Thank you all.In this case it will make a difference,I had assumed that a 120 volt 15 amp switch would handle much more amperage at 12 volts... now will use switch to activate solenoid to supply 12v 30amp to motor...Easy solution now! I understand now

Gary '79 5C · December 05, 2009, 04:08:08 AM

Now I must ask, if I may, Robert what will you be operating with a 12V 30 amp motor ?
Bus A/C ?
Gary

luvrbus · December 05, 2009, 08:18:23 AM

Does anyone hook the 115 volt switches up to the ground to make a circut reason for asking working on a bus a few years ago all of his switches were for 12 V and wired that way and it was a high end coach

good luck

JackConrad · December 05, 2009, 08:37:23 AM

Quote from: luvrbus on December 05, 2009, 08:18:23 AM
Does anyone hook the 115 volt switches up to the ground to make a circut reason for asking working on a bus a few years ago all of his switches were for 12 V and wired that way and it was a high end coach
good luck

Just a guess, maybe to save wire and reduce the overall cost of manufacture. Just a short wire from thhe switch to ground instead of a wire from light to switch and back to the light?

robertglines1 · December 05, 2009, 08:56:06 AM

? was ask what for??for slide motor I have run Thur 115 switch and motor seems sluggish and switch seems hot;have tried different motor and no change have not checked amp delivery or draw..this seems to be a easy change to solenoid to help determine problem..I have 12 volt switch and solenoids on front slide and no problem..Just had my thinking backwards thinking the ac switch would handle more amperage.(have 2 motors on each slide)

luvrbus · December 05, 2009, 09:18:24 AM

Robert, I have a new HWH slide switch with a key and rocker switch on a panel I don't know what amps it will handle but check the HWH site if it will work for you I'll ship it to you for shipping cost. Update Robert I just looked in the manual at the way HWH wires the switch

Switch to a relay
relay to a constant voltage solenoid not a type like a starter uses

good luck

robertglines1 · December 05, 2009, 09:41:37 AM

Have parts just had a wrong assumption...thanks to all...

DaveG · December 09, 2009, 04:59:55 PM

Usually when the voltage goes down the amperage goes up.

buswarrior · December 09, 2009, 06:00:09 PM

We need a current expert...

In broad strokes, with the need for the experts to clarify:

There's something bad about using AC switches for DC if you start pushing the limits.

15 amps, is 15 amps, no matter the voltage.

The limits on the internals are for amps, regardless of voltage.

experts?

happy coaching!
buswarrior

junkman42 · December 09, 2009, 06:50:24 PM

BW, 15 amps at 10 volts is 150 watts,15 amps at 100 volts is 1500 watts. Quite a difference in the load on the switch. Generally switches for DC are not constructed the same as switches for AC. DC tends to arc on switch opening and keeps conducting across the open switch, AC because of the polarity reversal tends to be self extinguishing. Some circuit breakers are rated for both AC and DC but the DC ratings are always lower for the DC rating. High current switches and breakers designed for DC will have a dielectric that gets inserted between the switch contacts on opening the switch. I am not good with words on the keyboard but that is a sort of barney type of explanation. Switches that are used at high altitude have additional problems because of lower air pressure which reduces the dielectric properties of the switch. And before some PHD points out that a vacuum is an excellent dielectric, only when the vacuum exceeds a certain level,IE what is generally known as a hard vacuum. Large switches are sometimes pumped with a vacuum pump system and some are filled with oil and some pressurized with gas such as nitrogen! Home light switches are not intended for use with low voltage DC! Regards John

JohnEd · December 09, 2009, 09:48:07 PM

Cliff,

I think Sean will agree that using the "hull" (frame)for neutral or DC ground promotes corrosion. The frame shouldn't carry current. On ships I have seen as much as 90 VAC measured between the neutral leg and the hull. Every car I have ever owned had the frame grounded near the starter. Now that lets the frame carry current but only intermittently.

boogiethecat · December 09, 2009, 10:50:23 PM

I hate to jump in and start picking on points, but....

Junkman, if I follow your logic "[15 amps at 10 volts is 150 watts, 15 amps at 100 volts is 1500 watts. Quite a difference in the load on the switch[/quote], then I'd be left thinking that 15 amps at 12 volts is a lot easier on any switch than if that switch were used on AC 120 volts. It's not. It's exactly the same.

In fact, Buswarrior is correct, as far as the switch is concerned, 15 amps is 15 amps regardless of the voltage; the switch will have the same "on" resistance and do basically the same work regardless which voltage its' operating on. The wattage you are referring to is what the load is experiencing, not the switch.

For the most part, although you are correct about the arcing problem when a switch is run on DC or at high altitudes, that's not really an issue with a switch -at least in a bus- until you get to around 35-40 volts. At 12 volts it's not an issue (well maybe it might be if it's in a very high altitude plane or spacecraft). Down here on earth, switches specifically designed for DC are usually only necessary when you're over 35 volts. Below that, use what you want to and it'll be fine.

The contact size of a 15 amp 120 volt wall switch is going to be, for all practical purposes, exactly the same as a DC switch. And as far as I'm concerned, and my long experience as an electronics designer/manufacturer has shown, you can use a 120 volt wall switch just fine on 12 volts, a long as you don't exceed the switche's rated current, with no penalty.

And just "what if" it really didn't work and i have my head up my private parts? All that would happen is one day the switch wouldn't turn on because the contacts would be too dirty from arcing, and it'd have to be replaced. But I'm willing to bet a lot that'd never happen. It'll work just fine and be quite reliable.