12VDC Switches

[bigbendhiker]

When I install electrical in my cargo trailer conversion I would like wall switches for interior lighting and also the porch light.

What recommendations do you have for 12VDC wall switches that could be mounted in a shallow box with a face plate?

Thanks for your help.

[bobhenry]

I took a 1/2 depth blue Carlon box and bought the solid cover plates. As my lights were modified by adding sockets to be AC and DC capable.


I used a bat wing toggle for the ac and a twist type rotary switch for the DC so even in the dark I can feel which one I am using.



There are those on here who will tell you that if you mix AC and DC in the proximity of each other you will die in a thermo nuclear explosion of sparks and fire. 5 years and counting I"M STILL WAITING !

[H.A.]

I

[bdosborn]

I use Carlon NEMA spec boxes and regular household duty switches.

That's fine for 120V circuits but a bad idea for 12V. You should always use 12V rated switches as its actually takes a more robust switch to interrupt a 12V arc than a 120V arc.

Bruce

[8ball_99]

I used switches like this in mine http://www.adventurerv.net/onoff-rocker ... -3966.html I did not get them from there though. I found them on ebay. They have wall plates with them to hide the mounting screws. You do not need boxes for them. Just use insulated connectors when making your connections. I don't have any pictures of mine installed, But they look much better then most of the trailer switches and work very well. They have a nice solid feel and operate smooth.

[H.A.]

I use Carlon NEMA spec boxes and regular household duty switches.

That's fine for 120V circuits but a bad idea for 12V. You should always use 12V rated switches as its actually takes a more robust switch to interrupt a 12V arc than a 120V arc.

Bruce

I should have been more complete with my comment. But for brevity and not over-analise the subject.(what seems to be a requirement here)
Otherwise derating the switch, It can work fine for years. More so on resistive loads such as lighting as was the original question.
There is alot of additional science that is dependant of the specific design of the switch for it, thats not permitted here under the brevity requirement, But a based on seat of pants, 30% is a rule of thumb we follow, So 15 amp 120vac switch works to about 5 amp 12vdc. What can be alot of lighting within a camper.

[bdosborn]

I should have been more complete with my comment. But for brevity and not over-analise the subject.(what seems to be a requirement here)

Feel free to elaborate, we're a friendly crowd. Where did you get the derating rule of thumb and what is it based on? Its the first time I've heard of it.

Bruce

[Engineer Guy]

Boy, this Topic blew off some ancient Mental Cobwebs. I can attest informally to this derating concept; an old one.

WAY back in my Electronic Tech days, the standard Form Factor Relays we'd use in Manufacturing were the clear cover types about the size of several Sugar Cubes stacked together. The DC and AC Load Ratings were stamped in the mold of the clear Plastic Cover. A very typical sort of Rating was 6 or 8 Amps 115 VAC, and for 3 or 4 Amps DC at something like 48 Volts.

My unproven assumption was that DC was '100%' Power Factor, so to speak, in terms of Current. Always on. AC, I recall, is more like ~.707% of the peak-to-peak Sine Wave measured. Perhaps this causes a more robust reaction where the Switch Contacts make/break for a given DC, vs. AC, Current. This, then, leads to the necessity of de-rating. Just a thought; ripe for over-Analysis.

Square D makes a Series of Circuit Breakers that are rated for both AC and DC service. Looking at the differences in those AC/DC Specs [if any] might be insightful for the curious...

[zipz71]

Dc rule of thumb here, about halfway down the page.

http://www.carlingtech.com/amp-hp-volts

[H.A.]

Dc rule of thumb here, about halfway down the page.

http://www.carlingtech.com/amp-hp-volts

If I understand this correctly, Seems my 'rule of thumb' is way too conservative...

But, Others of our engineering staff were on to a 20% derating.
And I thought me being a bit of scofflaw was riding the edge of Zombie Resurection on my stated 30%

Overall point is, these switches will handle DC loads just fine provided one respects its limitations.
A greatest advantage to us small-time camper builders is they are inexpensive standardised product with no need to custom build mounting panels etc.

There is alot of science to the de-rating to be completely precise about it. Thus the 'Rule of Thumb'
Type of contact material, speed of the make-break action are prime considerstions. Also intended lifespan at a given load etc.
Its too easy for some people to go off on a NASA level discussion of a freaking lightswitch.

[pmowers]

I recently spoke with an engineer at Cooper Electric, regarding what type of switch I needed to basically serve as a transfer switch for my conversion. The engineer was thinking that I was switching between 110 AC and 12 VDC, and mentioned that most of their switches were rated for AC or DC at the stated amperage. To me, that sounds like I could use the switches for 12V, 15 A.

Actually, my idea is to have a 3-way switch with the common going to an outlet for my mini-fridge. one side of the switch is supplied by the shore power, the other 110 from an inverter, neutrals tied together, grounds also. If I am on shore power, the switch provides 110 to that outlet, if on battery, flipping the switch will connect the outlet to the 110 output of an inverter (750 W/1500 surge). Basically, it is a mini manual version of a generator transfer switch.

[bdosborn]

The problem with using AC switches for DC is the difficulty in extinguishing a DC arc. AC power cycles through 0 volts 120 times a second so it easier to extinguish the arc drawn by switching action at AC than DC. The resultant prolonged arc time from DC leads to accelerated switch wear or the switch might not extinguish the arc at all. That's why circuit breakers aren't routinely dual rated AC/DC and why you usually see lower DC than AC voltages for dual rated switches (it lowers the arc potential). You *probably* won't have a problem using a 120V switch, but you might if you happen to pick the wrong one. You're going to spend hundreds of hours working on your trailer, do you want to use a device that could jeopardize all that just to save a couple of bucks? Why not use a switch specifically designed for 12V and never have to wonder about it?

The other problem is its just plain bad practice to blur the line between 120V and 12V systems. Electrical code requires complete separation of low voltage and line voltage systems for safety reasons. Using a 120V switch for 12v might lead the person who buys your trailer in the future to think its safe to work on all the switches without unplugging from shore power.
Bruce

[deceiver]

I don't know what type of switches to use but I can recommend that you stay away from switches from Radio Shack. I've tried them in everything from electric guitars to dc motors. Even if rated for such things they will sometimes even break into crumbs when attaching wires mechanically or soldering. The mechanisms seem to die very quickly. After a dozen flips sometimes. Very cheap asian products I'd suspect.

[bdosborn]

Try Del City, I've bought from them and there stuff is pretty good:

http://www.delcity.net/store/Switches/

Bruce

[bigbendhiker]

Try Del City, I've bought from them and there stuff is pretty good:

http://www.delcity.net/store/Switches/

Bruce

I was just looking at their web site. They have quite a few 12 vdc rocker switches to choose from. Some have a LED that illuminates when the switch is on. Once I decide how many I need I'll place an order.