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Old 07-23-2012, 08:08 AM   #1
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Running DC device off AC


Hello,

A friend of mine has a police beacon light that is meant to attach to the top of a car and run off 12V DC from the car battery. He wants to use this as an effect light with his DJ equipment and he does have a large 12V transformer (plenty of amperage) that came out of something else, problem is it's AC not DC.

The police light contains just 2 motors and 2 incandescent lamps all wired in parallel.

Can something simple like this be run off AC?


Thanks

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Old 07-23-2012, 08:25 AM   #2
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Running DC device off AC


For a very short period...then comes the smoke.

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Old 07-23-2012, 09:24 AM   #3
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Running DC device off AC


Just find (practically) any wall wart (adapter) rated for AC in to 12v DC out and wire it up. I've done this many, many times for art projects that required a dc input to run little motors/lights, etc. and I've never had a problem.
IF there is any reason not to do so, or precautions to be taken, the guys here will chime in shortly and correct me, or add to the topic.

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Old 07-23-2012, 09:27 AM   #4
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Running DC device off AC


No but adding a bridge rectifier and a capacitor would turn the AC into DC but probably around 17vdc so that creates other problems.

AC in would be quite a bad thing...
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Old 07-23-2012, 09:31 AM   #5
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Running DC device off AC


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... police beacon lightThanks
There is not enough information here to tell for sure, but I I think that k_buz's analysis is the most probably result.
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Old 07-23-2012, 09:33 AM   #6
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Running DC device off AC


Magic AC smoke and Magic DC smoke usally are not compatible. The best way to get this to work is to use a power converter that converts 120 VAC down to 12 VDC
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Old 07-23-2012, 09:51 AM   #7
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Running DC device off AC


I do have basic 12DV wall warts but I am concerned about amperage since the lamps in this device put off a decent amount of light. Many of them are rated at 500ma which I don't believe is going to cut it.
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Old 07-23-2012, 10:01 AM   #8
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Running DC device off AC


You'd be surprised at how many things 500ma will power in DC.
Give it a test run on a "replacement" bulb that works in the unit to be sure, but I doubt you'll have any problems.

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Old 07-23-2012, 10:02 AM   #9
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Running DC device off AC


What is the total current requirement? Wattage? Then we can help.
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Old 07-23-2012, 10:40 AM   #10
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Running DC device off AC


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What is the total current requirement? Wattage? Then we can help.
The unit doesn't give any details on amperage. I did e-mail the company to ask. Their website doesn't have any details as the new model of this light is LED.

If the wall wart is underpowered isn't that going to overheat it, or be a possible fire hazard with the skinny little cord coming from it?
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Old 07-23-2012, 10:43 AM   #11
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Running DC device off AC


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The unit doesn't give any details on amperage. I did e-mail the company to ask. Their website doesn't have any details as the new model of this light is LED.

If the wall wart is underpowered isn't that going to overheat it, or be a possible fire hazard with the skinny little cord coming from it?
Shouldn't be a problem, but test on a replacement bulb first.

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Old 07-23-2012, 10:54 AM   #12
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Running DC device off AC


Don't have a replacement bulb and I can't even figure out how to get it out of the lamp holder. Tried pulling and twisting and it doesn't come out. My e-mail to the company included that question as well.
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Old 07-23-2012, 11:39 AM   #13
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Don't have a replacement bulb and I can't even figure out how to get it out of the lamp holder. Tried pulling and twisting and it doesn't come out. My e-mail to the company included that question as well.

Hook it up to a car battery with a 10A DC ammeter in series to see what the DC current draw is. I suspect it will be more than a couple amps. I'll bet a 500mA ( 500mAx12VDC = 6W total power out) wall wart won't even come close to working. The bulbs are probably 30-40W each.
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Old 07-23-2012, 11:53 AM   #14
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Running DC device off AC


You're right about the lamps. The manufacturer said they are 35W each so that's almost 6 amps for the lamps alone.

An ammeter would have been my first step if I had one
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Old 07-23-2012, 12:22 PM   #15
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Running DC device off AC


Of course, using full wattage will likely blind your audience, but I suppose that's part of the fun!

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