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Getting power from your automobile


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#1 Keneu Luca

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Posted 01 February 2010 - 09:11 PM

How practical is it to use an adapter that plugs into a car to provide AC power for a light?

This would not be the only source of power and light, but an additional source, say, to use a for a night time exterior shot.

Anyone have experience with this?

I know they make some of these adapters that can handle a decent amount of wattage.
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#2 Bruce Taylor

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Posted 02 February 2010 - 01:24 AM

How practical is it to use an adapter that plugs into a car to provide AC power for a light?

This would not be the only source of power and light, but an additional source, say, to use a for a night time exterior shot.

Anyone have experience with this?

I know they make some of these adapters that can handle a decent amount of wattage.


Is the car going to be running? You need to know the output of the alternator or you can fry stuff. A modern car will be a 12 volt system (charging at about 14.5v), and the alternator will put out anything from 40 to 200 amps depending on the specific car. If you look the car up in a replacement alternator parts catalog they almost always give the rating of an alternator if you can't find it easily in the owners manual. Maximum output will be reached at 2000 to 2500 rpms. Do the math to figure out how many watts at 120v you can get, while leaving 20 amps at 12v to run the car itself, while not running any accessories (lights, a/c, etc).

If the car isn't running, you'll be running straight off the battery, so you can't run a whole lot of watts for very long, say 100 to 200. You can keep an eye on the voltage with a volt/ohm meter. Don't pull it down much below 12.4v unloaded or you're going to have trouble starting it again without a jump.

Be careful. Modern cars have a lot of electronics that can get very unhappy if they are asked to run on low or "dirty" (A/C waves in the DC) voltage.

Bruce Taylor
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#3 Keneu Luca

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Posted 02 February 2010 - 01:49 AM

Is the car going to be running? You need to know the output of the alternator or you can fry stuff. A modern car will be a 12 volt system (charging at about 14.5v), and the alternator will put out anything from 40 to 200 amps depending on the specific car. If you look the car up in a replacement alternator parts catalog they almost always give the rating of an alternator if you can't find it easily in the owners manual. Maximum output will be reached at 2000 to 2500 rpms. Do the math to figure out how many watts at 120v you can get, while leaving 20 amps at 12v to run the car itself, while not running any accessories (lights, a/c, etc).

If the car isn't running, you'll be running straight off the battery, so you can't run a whole lot of watts for very long, say 100 to 200. You can keep an eye on the voltage with a volt/ohm meter. Don't pull it down much below 12.4v unloaded or you're going to have trouble starting it again without a jump.

Be careful. Modern cars have a lot of electronics that can get very unhappy if they are asked to run on low or "dirty" (A/C waves in the DC) voltage.

Bruce Taylor


Thanks Bruce.
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#4 John Sprung

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Posted 02 February 2010 - 03:54 AM

The other approach to this is to rent a bunch of batteries and rig them in the trunk. Have one set working while another is charging. But with the high efficiency of KinoFlo's and LED's, this is less likely to be necessary now. In the old days, we'd run incandescents that way.




-- J.S.
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#5 JD Hartman

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Posted 05 February 2010 - 02:59 PM

First of all, nothing that "plugs in" is going to deliver a "large" amount of power. If you thinking the lighter type adapter, think 200-250 watts of AC power. If your looking for 1 to 2k watts, that size inverter needs to be wired permently into the vehicles electrical system and fused just as the primary electrical system is. Without the engine running, you'll eventually discharge (and possibly damage) your vehicle battery.
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