Drain on Battery

[rov1200]

If a plug in device to the cigar lighter consumes 3 amps how much drain on the 12V battery will it take if the car is stationary.

[Buenchico]

What type of measurement are you looking for? The only 'scientific' answer to your question is '3 Amps' but that obviously doesn't help very much ;-)

As a guide, let's suppose you leave your sidelights on. Each of the 4 bulbs is (typically) rated at 5W, so that's 20W of power. Using 3 amps at (a nominal) 12V means 36W of power. So you'll be draining the battery at roughly twice the rate that you would do if you left your sidelights on.

Chris

[Hymie]

To my mind, you have answered your own question � it will draw 3 Amps from the cars electrical circuitry. Should the engine be idling, the alternator will comfortably handle this load.

Should the car engine be off, based on a car fitted with a 40 Amp/Hour battery, the device could operate for around 13 hours before exhausting the battery. But after around 10 hours, there may not be enough charge left in the battery to start the car.

[rov1200]

Thanks when I said the car was stationary I meant that the alternator was not charging the battery. My problem is that I have a coolbox used for camping which plugs into the cigar lighter which is permanently live. It said on the box rated at 3 amps. Your answer of about 13 hours for a 40 Amp/hour battery gives me the clue.