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.

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.

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