Scratch_6057
Apprentice Modder
GA USA
56 Posts 
Posted  09/15/2006 : 07:04:59

If you are evaluating motors / doing motor testing and you want to determine how many Amps a motor draws under load, the thing to do is to use a LOW Resistance HIGH Wattage SHUNT as shown in the picture.
The Resistors (R1, R2) are 1 Ohm 25 Watts each, wired in parallel for a total of 0.5 Ohm 50 Watts. (mine actually came out 0.6 ohms) These resistors cost $0.99 each. Measure the VOLTAGE across the RESISTORS (points A, B) and divide that voltage by the resistance of the resistor pair to obtain a current thru the ENTIRE circuit.
In my particular case, with 12 volts applied to the circuit 1.76 Volts (across resistors) / 0.60 Ohms (measured resistance of the pair)  2.866… (amps thru the circuit) No Load
As you increase the load on the motor, you’ll see the current increase.
I wasn’t thinking the other day, (in a hurry) set the meter to read AMPS and placed the meter in series with the motor. Loaded the motor down, read a 47 Amp peek and blew an $11.00 fuse in the meter (20 amp, 600 Volt) BUMMER! Not only was the fuse expensive but it was hard to find locally.
4.71 KB 
Edited by  Scratch_6057 on 09/15/2006 07:10:27 
