RailPro User Group
RailPro => RailPro Specific Help & Discussion => Topic started by: KiloWhiskey on September 16, 2020, 02:27:37 PM
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my Kato -9 suddenly started doing current overload on initiating movement. I checked connections and all seem intact. Any Ideas where to start?
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It's doubtful with a Kato, but any binding in the drive train?
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No binding, smooth and free turning
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Closely inspect the wires between LM and motor.
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If everything in the drivetrain is free and all wires are checked it sounds like a motor that is developing a fault (yes, even Kato motors can go bad). The LM could be developing a fault too so also check that out as well.
To start troubleshooting I'd start the loco moving while watching the info screen and see what current it's drawing (I wish that info screen would give a number and not just a bar meter!). You can then raise the motor load value manually and see if the overload warning disappears. If that works don't just leave it raised though without positively identifying the cause as leaving it raised would just be masking the symptoms which could lead to a much quicker motor death and is not a good idea.
If you can remember what it was set to previously I'd also check and see that the motor load value has not somehow been magically altered or reset.
If you have another Kato you could try and measure the resistance across the windings of each and see if they differ greatly (eg, known good motor was 30 ohms and overloading motor was 10 ohms) but it is a bit difficult to get a stable reading anyway so it might not be much help. I've also read of a convoluted way by measuring current draw and voltage and applying ohms law but that would require removing the motor from the model for testing.
And of course if you have a spare LM around try that too just to rule out the LM having problems.
- Tim
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I removed the module, and tested it with a test motor and it operated fine. The loco, when I removed the
8pin connector, reinstalled the DC pins and put a 9v battery to it and the loco motor started running. I removed the 8pin board, and did a hard wire install, and again it wont run... lighting and sound work fine.
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What is the motor full load current setting?
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When I originally put it on line, it auto set at 180... I attempted to retest but it went straight to overload .
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I removed the module, and tested it with a test motor and it operated fine.
The loco, when I removed the 8pin connector, reinstalled the DC pins and put a 9v battery to it and the loco motor started running.
This would be expected. A 9v battery is only good for testing if the motor actually works by turning over, not if the motor is consuming more current than an LM can safely provide. A battery is not a protected device like the LM is so the motor will just consume as much as it can from it which is limited by the battery make up (eg, the make up of a 9v battery limits it output to about 1A max which is all the motor will get, even if it's trying to consume 2A).
I still suspect that the motor has/is developing a fault (possibly low resistance?). That a test motor worked fine with the LM supports that. You need to find out how much current the motor is trying to draw. Do you have a multi-meter?
- Tim
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If I measured this correctly the suspect motor was about 25 ohms on meter autoset, and a known working kato motor read 308 ohms...
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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
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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?
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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
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I do appreciate the help everyone, my solution to this will be to park the loco and replace the motor.
Kevin
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Per the above, using contact cleaner, what's the best way to clean the motor?
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Per the above, using contact cleaner, what's the best way to clean the motor?
Just give it a little squirt in the brush area. Spin the motor a few times and give it another little squirt from the other side. If you have compressed air available, a light blowing afterwards is helpful. Let everything dry completely before putting juice to it.
Washing away residual carbon dust and cleaning/de-oxidizing the commutator is what you are doing.
Toy train motors use bronze bushings but if you are cleaning a motor that uses ball bearings you should lube the bearings afterwards.
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Thanks for that! I have some trichloroethane but it's 20 years old.
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I was able to swap out motors on the loco, and it now runs fine.
Thanks again
Kevin