RailPro > RailPro Specific Help & Discussion
Sudden motor overload errors
G8B4Life:
Hmm, I'm not sure either of those numbers are correct for the Kato motor or not, I can't even make a comparison to what you've measured as I can't get a stable reading using my Multimeter, and from what I've been reading directly measuring the resistance across the motor terminals isn't the correct way to measure our small hobby motors. I've tried measuring another way I've found online but that's just raising more questions as the results don't make sense (still experimenting with it).
Perhaps the easiest thing for you to do would be to put the DC blanking plug back in, put your multimeter in between the power supply (presuming the PWR-56) and the track and measure the current draw (starting, running and stalled and don't forget to subtract the current used by any lights that are lit when it's running). This would tell you if the motor is drawing too much for the LM.
- Tim
Alan:
Measuring a brushed DC motor with an ohm meter won't tell you much, certainly nothing conclusive. Too many variables - armature position, brush-to-commutator resistance, etc. You will get wildly varying measurements as you turn the shaft to various positions. Brush and commutator is not a reliable connection for measurement devices that use micro amps of current (your multimeter). That said, a typical field winding in our little train motors is 10 - 30 ohms if you can manage a good solid direct reading.
There are any number of ways to test a motor. All of them have the same first step - thoroughly clean the motor with contact cleaner (real contact cleaner) before proceeding. You would be amazed how many times this fixes everything. Then start with the simplest test. Wire the suspect motor directly to your power supply. Does it get hot and go up in smoke? Does the power supply circuit breaker flip? Do the lead wires melt? Do the brushes look like arc welders?
If it passes the first test then measuring the current flow is the second easiest test. Set your meter to DC amps on a scale of at least 5 amps. 10 amps is a popular multimeter scale. Some meters have special jacks for measuring high amperage DC. Put your meter in series with the suspect motor and the power supply. Is the current less than 100mA under no load (other than the drivetrain) and well under 1 amp when you squeeze the shaft or flywheel to add a lot of load?
G8B4Life:
Alan,
Thanks for chiming in and confirming what I had written was correct, that measuring resistance directly across the terminals isn't the way to do it (apparently it is the way to do it with much bigger motors, like 110 / 240v and three phase motors). I was going to send you a PM on the method I found for measuring the resistance of our small motors to see why I couldn't make heads or tails of what I was seeing it but I think I worked out why (it's simply Ohm's law on the running or stalled motor but they added resistor in series which I think was throwing out the calculation they gave).
Anyway, without easily measuring the resistance to compare against a good motor to see if it's going bad (which I hoped would be the easiest test for KiloWhiskey to do, why I suggested it) measuring the current draw, which is ultimately the number that matters to an LM is probably the best next thing.
Tim
KiloWhiskey:
I do appreciate the help everyone, my solution to this will be to park the loco and replace the motor.
Kevin
ON28:
Per the above, using contact cleaner, what's the best way to clean the motor?
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