This is the longest discussion I have ever seen on a very simple topic. I think that there were some inappropriate terms used earlier on that caused confusion. Here is a sample:
red58
Extreme Gabster
Stovebolter # 2136
posted 02-13-2006 12:47 AM
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easy: I [current draw of motor]=E [12V]/R [the resistance of the motor windings] translates to P=IxE
power in watts [like yer portable electric heater, which is just a resistance wire element], is what makes heat, and that's determined by the current the motor uses to run times the voltage you have - the slower you run the motor, the more current has to be dumped someplace else, which is the resistance unit on the back of [or inside] the switch, and that piece is quite small, hence can get red hot
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Obviously, current is not"being dumped someplace else". This is a series circuit here and the current through the control is the same as through the motor.
Also, the total current does go down as the control is changed to slow down the motor. The voltage drop across the motor also goes down and the control now dissapates energy as heat. This energy exists because the control now has inserted resistance into the circuit and current is passing through it.
I also take exception to the term "juice" because it does not define anything and people use it to describe voltage, current or power flow.
On another note, it was good to see some information on rotating DC machines. Although the affects shouldn't be considered too significant in this discussion, the current flow through the motor with a stalled rotor is different than with a spinning one and even blocking the air intake or output will change this. If you look at the of the specifications for the Chev starters of the fifties you will see a current draw test with the rotor blocked.
Finally, yes the resistors in these controls get hot enough to easily burn skin.
