9v train running times and conditions

[coreyg]

I've had a lot of issues will 9v train motor failures after I designed a train controller using an arduino with a motor controller. I had the motor controller in a Forward/Brake configuration which is common for robotics but for long running motors, it seems to be bad. I've switched to an DC source (non-inverting op-amp and a Buck converter) but I continue to see failures. I think all of the recent failures were motors that were run on the original design but I'm not sure. I have run the trains outside (at a show) for a couple hours at a time on a hot day (98 degrees) and that may have contributed to some failures but I'm not sure what "normal" is.

We've had some long running shows that were 5 weekends in a row and the trains would be running on Friday for 3 hours, Saturday for 10 hours and Sunday for 7 hours. I've been swapping out the trains every hour and now I've gone down to every 30 minutes and that seems to eliminate the issues.

In the past, I've run trains for a couple hours at a time and then trade them out, but I've seen the trains kind of slow down after an hour or two and then they wouldn't reliable start again. Sometimes, I could push them and they'd start, but just applying voltage would not get them to start.

I've been shrinking the length of the trains as well. In general, I have no more than 3 cars for each engine and fewer for the heavier trains (santa fe and horizon express).

When people run 9v trains, how long do you generally run the same train and how often do you swap out the train?

Do you have very many 9v motor issues (ie failures)?

Do you see cases where a train will start slowing down, and you give it a rest and then a hour later or so, it won't start up?

-Corey

[jtlan]

This sounds like the thermistor in the motors cutting out. I've heard that they degrade with age, which could cause the variation you saw. I've also heard that removing the thermistor is unlikely to cause problems; I'm not sure how much I believe that. If you're using a custom motor controller you can try to limit the current to the tracks, which should help preserve the motors.

[Haddock51]

Why would a limitation of current to the tracks help preserve the motors? Whatever amount of current you supply, the 9V engines will not pick up more than approx. 350 mA each at maximum speed, i.e. at a voltage of 9V.

In order to run my Swedish Iron Ore Train with the Dm3 locomotive and 24 loaded iron ore wagons (total weight approx. 10 kg), the train is equipped with ten 9V engines. As a consequence - and allowing to run four trains simultaneously - I invested in a PSU Voltcraft EP-925 (3-15V/DC,max 25A ) to get this train - and other long and heavy trains with multiple engines - upp the 8 percent grades in my new 9V Extreme track. I also modified the lego standard speed controllers with LM350T regulators, outside heatsinks, 3A diodes, minifans and temperature controls.

The tests on the test track have been very successful. I have not experienced any slow down with my engines. However I don't run my trains continously for several hours.

I started with lego trains 9V back in the early 90ies. Today, I have more than 30 trains and never experienced any problems with my 9V engines. I guess one of the reasons for 9V engine problems might be too much load per engine. Most of my trains are equipped with 2 - 4 engines.

Edited November 10, 2015 by Haddock51

[jtlan]

Why would a limitation of current to the tracks help preserve the motors? Whatever amount of current you supply, the 9V engines will not pick up more than approx. 350 mA each at maximum speed, i.e. at a voltage of 9V.

Conditions at shows are different. A motor run continuously will heat up, changing its internal resistance and thus current consumed. In addition, the current consumed by motors depends on their load -- a stalled 9V train motor will draw almost 1A, for example. My suggestion was that an unexpected increase in current draw could indicate overheating or some other problem, at which point it's probably safest to shut the motors down.