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-   -   Running DC device off AC (http://www.diychatroom.com/f18/running-dc-device-off-ac-151245/)

Richo 07-23-2012 09:08 AM

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

k_buz 07-23-2012 09:25 AM

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

DangerMouse 07-23-2012 10:24 AM

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.

DM

curiousB 07-23-2012 10:27 AM

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...

ionized 07-23-2012 10:31 AM

Quote:

Originally Posted by Richo (Post 972315)
... 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.

danpik 07-23-2012 10:33 AM

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

Richo 07-23-2012 10:51 AM

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.

DangerMouse 07-23-2012 11:01 AM

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.

DM

J. V. 07-23-2012 11:02 AM

What is the total current requirement? Wattage? Then we can help.

Richo 07-23-2012 11:40 AM

Quote:

Originally Posted by J. V. (Post 972380)
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?

DangerMouse 07-23-2012 11:43 AM

Quote:

Originally Posted by Richo (Post 972406)
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.

DM

Richo 07-23-2012 11:54 AM

Don't have a replacement bulb and I can't even figure out how to get it out of the lamp holder. :mad: Tried pulling and twisting and it doesn't come out. My e-mail to the company included that question as well.

curiousB 07-23-2012 12:39 PM

Quote:

Originally Posted by Richo (Post 972418)
Don't have a replacement bulb and I can't even figure out how to get it out of the lamp holder. :mad: 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.

Richo 07-23-2012 12:53 PM

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 :)

DangerMouse 07-23-2012 01:22 PM

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

DM


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