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Converting 110v AC to 12v DC

  1. Feb 17, 2008 #1
    Hello all. First thing I have to say is I don't understand much about power and electricity conversion rates. But I do have a need to have two different motors, each requiring a different power load, to run off of a single source AC 110 house outlet.

    First device: Volts: 12, Amps: 3.3, uses a 12V car cigarette lighter (I assume this is DC power)

    Second device is a 2 speed motor: Watts: 37/27, Amps: 0.57/0.39 and runs off of standard 110v AC plug

    I am looking for a cheap solution that will allow me to power both devices off of household 110v AC power but really have no idea on to go about doing this since this is my first project I have ever done that requires me to toy with power/electrical sources.

    I know I can go buy a 110AC to 12V (cigarette lighter) converter for $5, but thats the kind that plugs into a wall outlet and would require some kind of mickey mouse solution that is unclean and probably not safe. I am looking for a solution that runs off of a single source that feeds both devices. Which means I would need to cut off the cigarette lighter adapter and used the exposed wires to connect directly to this power source.

    Also, how do I determine the watt power level of the first device? I need to understand what the total watt power consumption, of both devices, would be.

    Thank you for your help.
  2. jcsd
  3. Feb 17, 2008 #2
    Watts DC = Volts x amps so in your case it would be 12 Volts x 3.3 amps = 39.6 watts.

    I don't think you are going to find a device that would supply power for both. I would just go with your $5 converter and solder the wires to the terminals of your machine. Then of course, put plenty of electrical tape. The other machine could just plug directly in.
  4. Feb 17, 2008 #3
    So is watts DC math any different from watts AC ?

    Watts DC = Volts x amps (12 Volts x 3.3 amps = 39.6 watts)​

    Would the second device simply be:

    Watts AC = Volts x Amps (120 volts x 0.57 amps = 68.4 watts)​

    The second device "advertises" 37 watts with a pull of 0.57 amps off of a standard 110AC outlet. But the math shows different with 120v AC x 0.57 amps = 68.4 watts. Something isn't adding up right.

    Last edited: Feb 17, 2008
  5. Feb 17, 2008 #4


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    Staff: Mentor

    Perhaps there is an inefficiency such as power factor in the AC device.

    Anyway, I'm not sure what you are really trying to do here. 110V Ac is wall power and 12V is a pretty standard power supply. If you the motor and a 12V power supply into a power strip, then you have it all connected together. I'm not really sure what you could do that would be more complex (or useful) than that.
  6. Feb 17, 2008 #5
    When you buy a 120VAC to 12VDC converter make sure the current rating is atleast 3.3A. That's a decent size wall wart. Using a wall wart with that rating is probably one of the safer options you have, especially if you don't feel comfortable with 120VAC circuits.
  7. Feb 17, 2008 #6


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    Gold Member

    Any time that I've run into a similar situation (quite a few times), I just run a dual outlet extension cord into the device housing and plug the adapter into one of the receptacles. Then a regular cord can be plugged into the other to run the AC stuff. For additional safety, if you're not sure of the power draws involved, use a power bar with an internal breaker.
  8. Oct 23, 2009 #7
    I would like to know if there is an inverter to go from my household current to power my 12 v winch. I have a 4x4 super winch LP 8500 12 v DC 4.5 hp 3.3 kw motor.
  9. Oct 23, 2009 #8
    AC Motors, with few exceptions, look inductive from the ac power lines. The 120v ac x 0.57 amps is 68.4 volt-amps or VA (reactive load).
    Bob S
    Last edited: Oct 23, 2009
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