Over Amp motor issue with LM-4S-G

[blwloco]

Hello RailPro forum! My name is Nick Bulgarino, and I have a model repair shop that installs dead rail systems. I am new to RailPro, and I am running into an issue with the motor control.

There are two issues I have: the first is low speed control; the second is over amping the circuit.

The locomotive, even if I change the start voltage, will not move until I reach 20% or higher. Then it'll jolt forward. I can bring the speed back down and control it, but that's not very prototypical. I am trying to figure out how to fix this, but the manual does not cover this issue.

The locomotive has a stall current of 3.4 amps. The LS-4S-G is advertised to handle up to 8 amps. I am getting an over current error when operating the engine under medium to long train lengths even after doing the Motor Full Load Current test. The test puts the motor current at 750mA to 850mA. That is well below the threshold I think. In order to operate the engine, I have to limit the top speed to 45%. This is too slow for most operations and lacks the power to pull a train up grade.

My question is what am I missing?

Thank you!

[gregeusa]

Seems that one of your problems is that the motor is "spiking" short term current and trips the decoder.

Try adding a 1/2 ohm power resistor in series with the motor(s) and see if that works... common issue in large scale.

Greg

[blwloco]

I just tried that. The intermittent cuts disappeared, but the decoder still tripped under prolonged load, particularly going uphill. I measured the motor again and it's only pulling 2.9amps with some resistance; 3.5amps stalling. I am not sure the decoder can handle the advertised 8amps. Unless I am misunderstanding that.

The low speed control is still nonexistent. I adjust the start voltage but if I go too high the engine will take off and stop. No low speed control at all.

[gregeusa]

Not surprising... the market is littered with units that don't meet specs... current handling is the big one.

Isn't there some adjustment to lower the threshold of sensitivity to load?

What is the locomotive pray tell?

[blwloco]

Sorry! Should have mentioned that. The locomotive is a Sunset (90's, not modern Sunset 3rd Rail) UP MK-6 2-8-2. Locomotive was factory stock when it arrived at the shop; maybe run on track power once?

There is an adjustment to the lower sensitivity threshold, but when I manually adjust it, the engine jolts. say 0 to 15 scale mph instantly.

I put a competitor's decoder in the engine to see if I am crazy. It's a 4 amp decoder, and it had no issues. I got the same 3.5amp read out for the motor. I am not sure what's happening here and RailPro customer support hasn't given me any help (other than advising I read the manual).

[gregeusa]

Not to disparage RP, but clearly the amp rating is not average, but peaks.

Try the power resistor as suggested... 1/2 ohm should do it, if not 1 ohm.

It will lower the top speed of the loco a tiny bit, but will most likely work.

Get the ones in the extruded aluminum body, and bolt down to some metal to dissipate the heat.