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.
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.
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.. ;D
Glad your here!
Nick-
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
Now I must ask, if I may, Robert what will you be operating with a 12V 30 amp motor ?
Bus A/C ?
Gary
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
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?
? 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)
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
Have parts just had a wrong assumption...thanks to all...
Usually when the voltage goes down the amperage goes up.
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
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
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.
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.
I don't know the answer, but the nice people at BackWooodsSolar.com have told me to never use a house type wall switch with DC, period. I had a long talk with them about this, because the nice Decor designer wall switches just look so much like home, and I want my bus to look like home. He knew of no safe way to use an AC house switch with DC. That website specializes in off grid solar living, so they probably know something. I'm not saying they do, or that this is the right answer... but I thought I should chime in with this point of view.
I just want to switch 24 volt DC fluorescent fixtures, and these don't take much power when running. But he said these fixtures can take 10+ amps on starting and I think he said they can take even more when the bulbs or ballast fail, but I can't recall for sure, as the conversation was months ago. He said the danger is a fire danger from the arching inside the switch. I don't see why I the circuit breaker wouldn't trip before a fire could start. But what do those fancy arc detecting circuit breakers do? Would I need one of them? Do they come in DC rated versions? I do have DC rated normal circuit breakers for the bus conversion.
I decided against using the AC wall switches because I just couldn't evaluate the risks to my satisfaction, and I don't want to burn down my bus.
No data or theory to back this up, just what has worked for us. We used standard house type 120 volt wall switched in our conversion to control interior 12 volt lighting (single throw & 3 way). 10 years and no switch failures so far. We were careful to limit the draw on these circuit to no more than 8-10 amps. Just our real world experience, YMMV. Jack
Boogie, I did not say that cheap home wall switches would not work! And I should have said that resistance in a switch might have a different effect when being used in a low voltage high current circuit, but you are right. Just curious as an EE is it possible that the switch manufactures do not know what They are doing or are They just ripping Us off? Why is it that dual rated switches have a much lower current rating for DC than There AC current rating? In the overall scheme of things it does not matter and I am sure that some people will tell Us that cheap extension cords are just fine for wiring Our coaches. There are also those that believe home wiring products are far superior to Marine and Aircraft products. Run what You brung and if it works for You great. I warned all that I could not use a keyboard properly! Regards John
In reality, there is little risk. The worse that can happen is that the switch will fail, most likely in the open position. There is very little difference in operation when the switch closes, it is on open that you get more arcing than with AC.
I wouldn't worry about it if you keep the load under 10 amps and use good quality commercial rated switches, not the 79 cents ones at HD.
I'm with Jack Conrad, 16 years in the bus and 8+ years in the truck-conversion and no problems on house-type light switches.
I had all "designer" type switches, but in confined areas I would always bump into the switch and turn on the light! So, in the hallway I replaced them with the standard type house switch.
YMMV
Ya, you can usually "get away" with using AC switches on low voltage DC loads of the same current rating, for resistive loads. The original poster was asking about using the switch for an inductive load, which is MUCH harsher duty for a switch (which is why often find horsepower ratings on switches in addition to current ratings).
Switch failure can be either in the OFF (contacts dirty/burned) or ON (contacts permanently welded) positions. Fail-ON is more likely with DC than AC, and a strong indicator you've exceeded the DC capacity of that switch. So always consider what the switch controls. What happens if it fails to turn off, and you didn't notice?
All -
Just sort of a "dumb" question here, but would using an AC wall switch on DC be a problem if all it was switching on/off was a relay?
Regardless of whether it's an inductive or resistive item being switched, the relay would carry the load, not the switch itself.
I would think in that situation that an AC switch would be fine. . .
Or am I missing something? (Other than making a circuit more complex than it may need to be, that is.)
FWIW. . .
;)
A relay coil is an inductive load. But if an appropriate relay is selected, it's likely a small enough load to not be a problem for an 15A AC switch.
We have a common 110 vac house switch in the bus master bedroom at the rear door to operate an outside entry 12 vdc light for 38 years now with no issue...
Hey Bob, since Dan is bringing this post back from the dead, I would like to know if you used the house switch and if it has held up for 9 years ?