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Standard light switch for 12V automotive cable.

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  1. #1
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    Default Standard light switch for 12V automotive cable.

    I want to add an on/off switch to a lamp I sometimes use for reading and sometimes I don't want to get out of bed to get to the battery box. I have several surplus light switches here and while I know that they work for the small loads of an LED I am wondering how much current they could handle at 12V as I don't see a current rating anywhere on the plastic moulding to help me make an educated guess.
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  2. #2
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    Picture to help people understand what type of spare light switches you have ?

  3. #3
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    Just your normal architrave switches, actually when I google them to post a picture rather than taking one I see that the cheap DETA from Bunnings has a 10A rating at 240V.
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    Most of them will be 10A.
    Current rating will be similar with 12v DC.

    What is the lamp?, unless it is really high power (120 W) should be no problem and unlikely you would run such a lamp on a battery.

    Unless it’s a car headlamp.

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    Quote Originally Posted by Moondog55 View Post
    Just your normal architrave switches, actually when I google them to post a picture rather than taking one I see that the cheap DETA from Bunnings has a 10A rating at 240V.
    A lot of architrave switches have 10A stamped into the bottom of the rocker switch, you have to have it turned off to see it.
    Most standard architrave switches are 10A but they also make 15A ones.
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    It's a little 30 watt floodlite; it is plenty bright enough in the big tent
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  7. #7
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    A 240v 10A switch will handle 15A 12V. That is 180W 12V
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    DC switching arcs more so than AC at the contacts therefore de-rate.

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    Quote Originally Posted by phild01 View Post
    DC switching arcs more so than AC at the contacts therefore de-rate.
    When AC is switched, any arcing self extinguishes when the polarity reverses. But for DC with no polarity reversal arcs when they occur persist much longer and burn more metal off the switch contacts on each throw. A switch used for DC will burn out much faster than if it is used for AC at the same current. Best to choose a switch with a DC rating if its for a critical purpose. But to the dog's original question, an architrave light switch or inline 240Vac power switch would be fine for 12Vdc, but if you want the switch to last derate the current rating by at least 50%.
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  11. #11
    Golden Member havabeer's Avatar
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    i'd be more concerned about having exposed contacts and screws at the back of the switch then anything else.
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  12. #12
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    Quote Originally Posted by Marc View Post
    A 240v 10A switch will handle 15A 12V. That is 180W 12V
    That's not how it works. A switch doesn't have any idea of what the load power might be. Switches have contact resistance, and therefore dissipate power. The contact area of standard light switches is quite small. Worse, the power dissipated increases with the square of the current, so your 1.5x increase from 10A to 15A would result in 2.25x the power dissipated in the switch.

  13. #13
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    Quote Originally Posted by havabeer View Post
    i'd be more concerned about having exposed contacts and screws at the back of the switch then anything else.
    I would set it up on a riser and back it with a small bit of ply or something, I have spare risers etc that were not used.
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