Some time ago I stumbled upon a variable iat control generally used for performance tuning. It was a dash mount unit. Anybody else seen this? I've also seen mention at theoldone.com forum about tuning mixture using such a device.
Okay, now I think I understand what you're asking. It sometimes takes us old guys awhile to catch on. :-) You would have to know in advance what the load(Amperage) of the device is that you're going to power. Then it would be a matter of coming up with the resistor values. A simple way to do 12 down to 6 volts would be to use two resistors of equal value in seies. Then you would tap the junction netween the two resistors and place your item between there and ground. As I said above, you need to know the current draw because if you use to high a value of resistors you won't have enough current available; too low and things get hot.
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Ah, I see now. The resistor method that Larry described is called a voltage divider. It'll only work if everything in the circuit is a fixed constant and the load of the circuit you're connecting is very small. This is generally not the best way to drop voltage. A DC motor for example will consume varying current throughout its RPM band. If the equivalent impedence of the circuit you're connecting to the divider is much higher than the resistors in the divider, then the divider won't work at all as expected. Most of the drop will be across the load. Resistor values too high and you may not have enough current. If you're trying to run an accessory of the 12V the voltage divider will only work for very simple circuits like LED lights. If you were to use this method the formula would be:
Voltage_out = Voltage_source * (R1 / (R1 + R2))
where R1 and R2 are in series and Voltage_out is the drop across R1.
A better way of doing this would be to use a zener diode with specs for the voltage drop you want. A 6V zener diode will always (well almost always) have a 6V drop across it. Better yet would be to just get a voltage regulator (looks like a large transistor) that will put out a constant voltage. Radio Shack carries them for the standard values (5V and 12V). Anything different and you've have to order it online or find an electronics store. As long as you don't try to draw too much current from the voltage regulator the output will remain constant.
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