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Will this switches work with DC?

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  • Will this switches work with DC?

    I'm an electronics newbie, but learning. I bought a toggle switch today that says it's rated or 5A at 120V AC or 2A at 250V AC. I want to use it for in my carPC setup. The line it'll be on is 30A at 12V although I'll probably never draw more than 10A. If I compare 5*120=600 with 12*30=360, I think the switch should work. Is there such thing as an AC only switch?
    My worklog.
    Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

  • #2
    no way, switches are rated in current it can break at a given voltage.

    and there are no AC only switches, but AC is easier to break at a given voltage

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    • #3
      Originally posted by greenman100
      no way, switches are rated in current it can break at a given voltage.

      and there are no AC only switches, but AC is easier to break at a given voltage
      I don't understand the whole answer.

      - "Switches are rated for current it can break at a given voltage"
      So, even at 12V, I really need a 30A (or 20A or whatever) switch? I was at the local Fry's Electronics saw nothing remotely close to that amp rating, I'm looking for a small-ish switch.

      - "AC is easier to break at a given voltage"
      Do you mean it's easier for the switch to do it's job at a given AC voltage than the same DC voltage? This shouldn't really be a problem for me though, right since I'm at 12V DC in the car.
      My worklog.
      Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

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      • #4
        Originally posted by greenman100
        no way, switches are rated in current it can break at a given voltage.

        and there are no AC only switches, but AC is easier to break at a given voltage
        when he says there are no AC Only switches he means that a switch can work w/ AC or DC not just one or the other

        your switch will proably work



        http://www.the12volt.com/ohm/ohmslaw.asp
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        • #5
          Originally posted by kbyrd
          So, even at 12V, I really need a 30A (or 20A or whatever) switch?
          BIG difference in amps and volts. amps have nothing to do with the volts.

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          • #6
            amps are the rate of the current, volts are the amount of power given.

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            • #7
              I've seen switches and relays rated at 120VAC and 28VDC. The current is still the same. So your switch will still only be able to handle 5A. You can find relays that will handle the current that you require.

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              • #8
                and try to keep it above your requirements...

                -a fuse, you want to crap out.
                -a switch...you paid a lot of money for and dont want it to crap out.

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                • #9
                  A switch thats designed to handle AC current would work alright with DC. But defently not vise versa.

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                  • #10
                    Originally posted by wsurritte
                    when he says there are no AC Only switches he means that a switch can work w/ AC or DC not just one or the other

                    your switch will proably work



                    http://www.the12volt.com/ohm/ohmslaw.asp


                    your switch will blow up in your freaking face.

                    DC does not extingush very well. I have seem 1 inch arcs from 120VDC. 120VAC will only jump like an eighth of an inch.

                    use a relay bud

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                    • #11
                      That is a lot of amperage to run through a switch. You ought to use that switch to control a relay rated for that amperage.
                      Originally posted by ghettocruzer
                      I was gung ho on building a PC [until] just recently. However, between my new phone having internet and GPS and all...and this kit...Im starting to have trouble justfiying it haha.
                      Want to:
                      -Find out about the new iBug iPad install?
                      -Find out about carPC's in just 5 minutes? View the Car PC 101 video

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                      • #12
                        Originally posted by greenman100
                        your switch will blow up in your freaking face.
                        DC does not extingush very well. I have seem 1 inch arcs from 120VDC. 120VAC will only jump like an eighth of an inch.
                        use a relay bud
                        Ok, bear with me here. Thanks for the help.
                        I understand how a relay works. If I use a relay it would work like this (right?):
                        - Wire A is what powers my car PC, it's got a 30A fuse on it. I'm currently drawing a max of about 3.5, but the PSU I've got will probably draw 10-15 before it's own fuse craps out.

                        - Wire B, some other random constant 12V line in the dash.

                        So, I buy a relay and I with it I control Wire A with Wire B. I then put my 5A switch on Wire B. When the switch is closed, current flows thru wire B to the control terminal on the relay, which closes it's contact and allows current on Wire A, which can be 30A. This sound right?

                        If the above is right, I still have a question. What controls how much current is drawn on wire B to the relay's control terminal? What prevents that wire from carrying more current than the switch can handle? How does the relay's control terminal limit the current it uses to do it's job?
                        My worklog.
                        Status: VM GTI sold, got out of the CarPC tinkering hobby, but I still think about getting back in.

                        Comment


                        • #13
                          Originally posted by greenman100
                          your switch will blow up in your freaking face.

                          DC does not extingush very well. I have seem 1 inch arcs from 120VDC. 120VAC will only jump like an eighth of an inch.

                          use a relay bud
                          Umm...it takes 10,000 volts to arc 1"
                          95 Mazda Protege LX
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                          • #14
                            Originally posted by gameboy
                            Umm...it takes 10,000 volts to arc 1"



                            it takes 10,000 volts to break down / ionize 1 inch.

                            once air is ionized, its resistance is much lower.

                            If you start a 120VDC arc at 1/100th of an inch, it will stretch to about an inch before it breaks. I will not arc again untiul you bring the electrode very very close.

                            I have seen it done.

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                            • #15
                              Originally posted by kbyrd
                              Ok, bear with me here. Thanks for the help.
                              I understand how a relay works. If I use a relay it would work like this (right?):
                              - Wire A is what powers my car PC, it's got a 30A fuse on it. I'm currently drawing a max of about 3.5, but the PSU I've got will probably draw 10-15 before it's own fuse craps out.

                              - Wire B, some other random constant 12V line in the dash.

                              So, I buy a relay and I with it I control Wire A with Wire B. I then put my 5A switch on Wire B. When the switch is closed, current flows thru wire B to the control terminal on the relay, which closes it's contact and allows current on Wire A, which can be 30A. This sound right?

                              If the above is right, I still have a question. What controls how much current is drawn on wire B to the relay's control terminal? What prevents that wire from carrying more current than the switch can handle? How does the relay's control terminal limit the current it uses to do it's job?

                              you do know this has been covered before, right?

                              do this:
                              +12v--->switch--->relay coil
                              other end of relay coil---> ground
                              +12v--->one side of relay contact
                              other relay contact ----> inverter +12v


                              the fuse you should have at the beginning of the +12vrum from the battery will protect everything downstream.

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