Chris Stransky Posted November 7 Posted November 7 I have recently started trying to use a Lego 9v motor on metal track to run trains. I use a MRC 1400 power pack and speaker wire to get power to track. The track is an oval with the round ends being brand new FX Bricks R56 curves. The straight sections are used track with three sections on each side. They looked like they are in good shape. No green corrosion and I wiped them down with alcohol before assembly. I verified that electrical to the track is working with a multimeter. The train will start to run but after 10 or so laps the motor slows to a stop and won’t run. The motor was supposedly new/.unused original Lego and looked that way when I got it. Any ideas what my issue might be? This is my first experience with rail powered Lego motors and i was expecting it would either work or it wouldn’t. Kind of surprise at the behavior. Quote
Toastie Posted November 7 Posted November 7 Welcome to EB! Does the train run again, after some motor cool-off time? Maybe an hour or so? Or is it entirely dead? Best Thorsten Quote
L-Gauger Posted November 7 Posted November 7 I noticed you are using an MRC power pack, is that a 12V DC model railroad power pack? I am not an expert on 9V Lego trains by any means, but I remember an N scale modeler who had a similar issue. He had made the mistake of wiring part of his layout to an 18V power supply instead of the N scale standard of 12V, and this caused one of his locomotives to overheat and stall after a short running time. Lego train motors are designed to run on 9V, so is it possible that a 12V power supply is causing your motor to overheat after a few minutes? If the MRC 1400 is a "pulsed-power" pack, it would be supplying 12V power to the track regardless of speed setting. I guess the cheapest way to test this theory would be to replace the MRC 1400 temporarily with a 9V battery. If the problem goes away, the MRC power pack is your culprit. You could either spend the money on an official Lego power pack, or wait until Fx Bricks releases their power pack and buy that. Quote
Toastie Posted November 7 Posted November 7 48 minutes ago, L-Gauger said: I guess the cheapest way to test this theory would be to replace the MRC 1400 temporarily with a 9V battery. If the problem goes away, the MRC power pack is your culprit. You could either spend the money on an official Lego power pack, or wait until Fx Bricks releases their power pack and buy that. This is absolutely true! My pitch was more targeting the "thermistor" TLG put into their 9V motors. These may degrade over time to the extent that they "go off" way too early. I took them all out in my 9V train motors suffering from a similar behavior - with no harm so far (10+ years). It may be a bit risky, but TLG always takes the super save route. And they never know about such devices degrading over literally decades ... Best Thorsten Quote
dr_spock Posted November 8 Posted November 8 Maybe connect a volt meter (or multimeter) to the output of the power pack and don't let it run above 9V? Quote
JopieK Posted November 8 Posted November 8 Yes I guess @Toastie and @dr_spock make some good points. Maybe an IR thermometer could also give some insights? Quote
SD100 Posted November 9 Posted November 9 (edited) Toastie is 100% right about your problem being the thermistor. My LUG thought all our motors were toast (see what I did there) but after thermistor surgery they're all back in service and going like mad, all day long at shows. Also, they take 12V with absolutely no issues, which is why FX Bricks has shown that as an option on their theoretical controllers. SD Edited November 9 by SD100 Quote
Chris Stransky Posted November 9 Author Posted November 9 Thanks for the insight. Any advice on removing the thermistor? Quote
Toastie Posted November 9 Posted November 9 @SD100 has sure much more experience! On most of my motors, they were "tagged in" (just pull them out), on others, they were soldered (just desolder them). In any case, you have to open up the motor; there are numerous recipes of how to do that. You have to carefully cut the lids on the bottom parallel to the bottom plane using a >sharp< knife. Reassembling was never a problem for me, I just pushed everything back in place, they never fell apart after surgery. As said, @SD100 may want to chime in, as this was done for much tougher environments compared to my personal layout. All the best Thorsten Quote
SD100 Posted November 10 Posted November 10 I cut the tabs off with an exacto knife, the thermistor is a small disc next to the actual motor. I pull it out with tweezers and replace with a square of copper tape. Afterwards I secure the cover with clear tape in case of derailments. I'm supposed to be showing some people the process up at Bricks in the 6 this weekend, I'll take some pictures then. SD Quote
dr_spock Posted November 12 Posted November 12 On 11/10/2025 at 4:56 PM, SD100 said: I cut the tabs off with an exacto knife, the thermistor is a small disc next to the actual motor. I pull it out with tweezers and replace with a square of copper tape. Afterwards I secure the cover with clear tape in case of derailments. I'm supposed to be showing some people the process up at Bricks in the 6 this weekend, I'll take some pictures then. SD Cool, see you at BITS. Quote
SD100 Posted November 13 Posted November 13 Heck yea, I'll be the guy in the BuffaLUG shirt with all the hair, come on up and say hi! SD Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.