Many of us have measured the motor stall current of a locomotive to determine whether the motor needs replacing before installing a DCC decoder. Too much amperage will almost instantaneously fry a decoder if the engine stalls under load.
The procedure we’ve used in the past has been to put the engine on a test track with an ammeter installed between the track and the power supply. Apply full power while holding the engine down to prevent the driver wheels from turning. The peak current measured on the ammeter is the motor stall current. If it is higher than the rated maximum current of the decoder you want to put in the engine then you will either have to replace the motor with a more efficient one or use a higher rated decoder.
Recently, the author came across a different method that is interesting. For those of us who may be math challenged don’t worry this method uses basic arithmetic.
First you would have to remove the motor from the
locomotive. Connect the motor to a 100 Ohm series resistor and twelve Volts.
Measure the voltage across the resistor and the voltage across the motor with
the motor locked so that it will not rotate. See figure 1.
Here’s that upper-level math we were talking
about. Divide twelve volts
by the measured motor -voltage. Divide the voltage across the resistor by 100.
Multiply these two numbers together and you have the full load stall current
measured in Amperes in a safe way.
The reason for doing this is that measuring stall current directly (the old way) may damage the motor. It is a little more work but may save you the cost of a new motor. As the author has said in past posts, your call!
Thanks to Ken Harstine of the groups.io forum
for this new method.
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