eratic operation

[Michael]

Hello Group:

Background: 

I am building a trolley layout with "live" overhead (positive). The overhead contact wire is 24 gauge phosphorus bronze wire (standard for O scale). Track is Code 100 steel electrically bonded together (negative).

I am using 16 gauge buss with 20 gauge drops. The drops for the overhead are soldered to 1/4" steel rods which hold up the overhead.

I have over 200 feet of rail installed, but only about 20 feet of overhead installed to this point.


Problem:

I have converted 3 trolley cars to RP using the LM2-S module. The cars move about 3 inches, then stop; move 3 inches more than stop; move 3 inches  more than stop etc. Occasionally I receive the fault "low track voltage" but not continuously. The HC-2 shows track voltage at around 13.8 volts. The cars pull less than 1/2 amp. The module always runs cool.

The remaining trolley cars (not yet converted to RP) run flawlessly on DC power.

I want to solve any problems now before I go further with any installation.

Does anyone know what I may be doing incorrectly?

Mike Sullivan

[nodcc4me]

A couple questions, Mike.
Are you using a RP power supply?
If you turn off all sounds, do they still stall every few inches?

[Michael]

Yes, I have PWR-56. I get the problem whether the sounds or lights are on or off......makes no difference.

[nodcc4me]

Do you have another locomotive that you can plug one of the modules into? This would possibly eliminate the trolley itself as the cause of the problem.


On the info screen, does the voltage drop with every stall or does it remain constant?

[William Brillinger]

13.8V is low. The PWR-56 should be around 14.5V.
Do you have a meter to check the voltage on the power bus at the PWR-56?

[Dean]

Is there any arching on the catenary or wheels?

[Alan]

Problem:

I have converted 3 trolley cars to RP using the LM2-S module. The cars move about 3 inches, then stop; move 3 inches more than stop; move 3 inches  more than stop etc. Occasionally I receive the fault "low track voltage" but not continuously. The HC-2 shows track voltage at around 13.8 volts. The cars pull less than 1/2 amp. The module always runs cool.

Mike Sullivan

What you describe is indicative of the over-current protection kicking in and then resetting. Both LM and PWR have protection circuitry. Both permit brief over-current to allow for motor start-up (DC motors are a near short circuit before they begin to spin). Place a test light or multi-meter across the rails. If the light goes out when the trolley stops then the PWR is doing the protection. Conversely, if the light stays on then the LM is doing the protection. Either way too much current is being drawn for some reason. It is also possible your shoe/catenary contact is too high resistance.

The mention of arcing by Dean is a valid concern. Anytime a DC circuit is made or broken there is a voltage spike. Depending upon the inductance of the wiring and catenary the spike can be quite large potentially damaging the LM. Given that catenary will always have some arcing you may want to consider adding a bridge rectifier, capacitor, and zener diode ahead of the LM to protect it from the spikes.

[Michael]

Is there any arching on the catenary or wheels?

Yes, unfortunately there is always arching on the catenary from the trolley shoe especially when it rolls over an overhead frog, or other overhead fitting. Very similar to the prototype. 

I don't think this can be avoided. 

[Michael]

13.8V is low. The PWR-56 should be around 14.5V.
Do you have a meter to check the voltage on the power bus at the PWR-56?

I recently purchased a multi-meter, but I'm not familiar with it's use. (I was absent from physics class the day it was covered). Let me check it out, and let you know.