Baffled

[DaveB]

Not sure what the problem is or where to start looking.  Hard wired a LM3 in a Scale Trains gevo. It runs great at 20% and under. When you go over 20% it will go 6 to 8 inches and stop (everything,engine, lights and sound) last about a second and does it all over again. It's like turning a light switch off and on. Throttle back under 20% and it runs great. Switched out the LM3 and still does it. No warning signs or problems come up on the controller. I have 2 Scale Trains SD-40's and a Intermountain ES44 that run great. (All have been hard wired) Any ideas?

Thanks, Dave

[Alan]

Been there, seen that. Voltage under load at the LM is dropping below 10V for some reason. Most likely a poor connection somewhere between the truck wires/wipers and the LM power leads.

[DaveB]

Thanks.  Looks like tear down and check connections. 

[Alan]

My situation turned out to be the black wire on the JST plug that connected to the trucks' black wires. The wire had unknowingly been stretched causing all but one of the wire strands inside the insulation to be broken. From the outside it looked fine. I may have stretched the wire when I stripped the insulation. The lone wire strand could pass enough current to run the engine slowly but as soon as throttled up the strand essentially became an inline resistor.

[DaveB]

Problem solved.  Replace the wires from the trucks. Runs great.  Must have been one of those.  Why they use such small gauge wire is beyond me.

Thanks for the help. Dave

[Alan]

Problem solved.  Replace the wires from the trucks. Runs great.  Must have been one of those.  Why they use such small gauge wire is beyond me.

Thanks for the help. Dave

Glad to hear.