Quote:
Originally Posted by oil pan 4
I attached the 2 ohm resistor with the wires off the 1 ohm resistor just to see what would happen. It was reading 5.3 volts at 3 amps.
The pump was moving a steady but slow stream of coolant through the bypass. Maybe 1 gallon per minute. That would work fine for cold starts but I worry the pump may bind on start up. That is a little too slow for comfort.
I knew that would drop the voltage across the pump down to 5 or 6 volts. This is with engine off at about 12 to 13 volts.
Now if this were normal 14.4 volts I think it would be fine and be at or above 6 volts, but this needs to work under the conditions of an alternator delete.
I went ahead and ordered a 54 watt 1.5 ohm resistor.
That should drop pump power to about 7 volts at close to 4 amps.
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You can purchase ready made units for not a lot of money and kits come for a few dollars. Pulse Width Modulation allows your DC motor to provide relatively high torque while controlling speed. I use simple model train units driving a larger MOSFET in saturation. You can spec your MOSFET to fit your needs.
The chopper circuit is also much more efficient than absorbing part of your power with resistors.