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steve s · 08-20-2013, 08:09 AM

Using Ohm's law, V = I R or R = V/I, to get a 6V drop across the resistor if your horn uses 6 amps current, R = 6/6 = 1, so, you want a 1 ohm resistor (adjust accordingly for whatever current, I, your horn draws.

The power dissipated by the resistor would be I-squared x R, or, for this example, 36 x 1 = 36 watts. Probably could get by with less, unless you're planning on continuously laying on the horn or the resistor is going to be located with no ventilation.

The wiper will require a lot less.

08-20-2013, 08:09 AM	#3
steve s Senior Member Join Date: May 2010 Location: Kalamazoo Posts: 1,656	Re: 12v to 6v drop down resistors Using Ohm's law, V = I R or R = V/I, to get a 6V drop across the resistor if your horn uses 6 amps current, R = 6/6 = 1, so, you want a 1 ohm resistor (adjust accordingly for whatever current, I, your horn draws. The power dissipated by the resistor would be I-squared x R, or, for this example, 36 x 1 = 36 watts. Probably could get by with less, unless you're planning on continuously laying on the horn or the resistor is going to be located with no ventilation. The wiper will require a lot less. Last edited by steve s; 08-20-2013 at 08:22 AM.