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Answered 2010-04-11 07:23:09

Any device that adjusts resistance will inevitably adjust current by means of lowering voltage on the exit side of the resistor as dictated by Ohm's Law.

Ohm's Law states:

Current (Amperage) is equal to Voltage divided by Resistance, therefore, as Resistance increases, Current decreases under a constant Voltage supply.

Given that both rheostats and potentiometers adjust resistance, I would have to say that it would be impossible to lower your current draw to .5A without manipulating voltage via the two devices you mentioned.

It should be noted that the supply voltage on the feed side of the rheo or pot would remain the isn't changed until it passes through the variable resistor. The output current would be lower under the same load because the load would have a new, lower supply voltage.

Suggestion: If you wanted to set the current draw to's easy to accomplish that...or close to it. Just take an amp draw on the device running at it's nominal operation. Then record your supply voltage to the device....I assume that's 240V..but measure it to be sure. Then divide your voltage by your current...that will give you the resistance of the device. Now...divide your voltage by .5...that will give you your desired resistance. Subtract the desired resistance from the actual device resistance. Now...purchase resistors that will add up to calculated difference then wire them in series on the supply voltage. See if this doesn't get you close. You might have to fudge around a bit since there are variable I cannot account for.

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