Bachmann Loco - HUGE power draw at low speeds?

[KB02]

I have a Bachmann loco that I have posted about before due to the fact that is was so much slower than my other locomotives. The problem has gotten more involved as I have new evidence to report.

This loco was a DCC ready loco that I dropped a simple TCS decoder board into. When I installed the decode, the instructions were to remove the small resistors on the side of the motor as the decoder would not work well with them in place. Not sure if this has anything to do with my I wanted to add that in here.

I had a drive shaft come off the front truck (this happens from time to time) so I pulled the shell off and fixed the problem, got it back on the track and gave it a test run.  Started out just fine ;(slow but fine) then I twisted the throttle to max and the loco immediately stalled out and I got the motor over current error.  Reset, try again, same thing.  I hit the info button to see what’s going on, and at 50% throttle (half the speed of other locos) it is pulled between 75 & 90% motor current.  If I try to go above 60% throttle, I get over current.

I tested every other loco I have and they all run 20-25% motor current at 50% throttle and between 40 & 60% current at full throttle. What’s up with my little Bachmann? Should I reinstall those resistors from the DC days? Strip the whole thing down and rewire? Is it possible I missed something to cause this constant over current issue? Do you think the over current and speed issues are related?

[Gibs]

I'm betting those "Resistors" you mentioned aren't even resistors but rather a RF (Radio Frequency) Filter. Not so as to filter your loco from stray RF, but to help prevent it emitting any stray RF signals its self (so it wont effect your TV lest say) when running the loco.
So yes they can go, in fact its preferred as they will and do effect any type of Controlling Chip for the motor.
As to your main issue, I'd suggest first off to do a full disassemble and see if any wires are pinched/shorted under or near the motor, see if it spins up fine when stripped down and do a service on all mechanical parts. Most times its just something simple that's been over looked or neglected. Do a step by step elimination of possible causes.

[G8B4Life]

I'd probably do a hardwire myself but...

I can't find any pictures of the internals of a DCC ready Bachmann GP40, so which of these other Bachmann loco's did yours look like internally (specifically the PCB and around the motor)?

Bachmann GP40 (Sound Value) @ tcsdcc.com
Bachmann GP30-2 @ tcsdcc.com
Bachmann GP35 @ tcsdcc.com

Note, TCS also makes the mistake and calls chokes resistors!

Anyway, RailPro really does not like the RF suppression (chokes and capacitors) built into many models so you are correct those components should be removed. There was a couple of discussions here about it ages ago:

https://rpug.pdc.ca/index.php/topic,846.msg6496.html#msg6496
https://rpug.pdc.ca/index.php/topic,295.msg2105.html#msg2105

Both the chokes and capacitors should be removed, not just one or the other. Can you confirm that both the chokes and capacitors are removed?

If you can confirm then I'd definitely try running it with the shell off and making sure nothing is rubbing, stray wires etc.

- Tim

[KB02]

The internals are closest to this one:
Bachmann GP35 @ tcsdcc.com]https://tcsdcc.com/installation/ho-scale/1217]Bachmann GP35 @ tcsdcc.com

I had installed the NCE BACH-DSL decoder (sorry, mentioned wrong company above) NCE BACH-DSL Silent Decoder

And, yes, the chokes and capacitors have been removed.

I took Gib's advice and tore the whole thing down yesterday. When wired up just enough to spin the motor, the motor ran fine at normal (compared to my other locos) current. None of the wires were pinched and nothing was binding in the trucks - though one truck gave greater resistance than the other when spinning by hand. That happened to be the same truck where the drive shaft keeps coming off.
After reassembly and everything lightly hanging out on top, I ran the loco with the same issue - then re-ran the Full Motor Load Current test - and then I was back in business. Slow, but at a normal current when running. With everything properly reinstalled and taped/screwed down, it seems to be working good. I paired it with four other locos and ran them around the track and I could hear wheels grinding - like that drive shaft was slipping off again.

I think that truck and the slipping drive shaft may be at the root of the problem. Perhaps that was effecting the motor load current test when I first set it up? I'm going to tear the truck apart and fully service/rebuilt it and see if that helps the situation.

As far as Voltage/Current goes, I think I've got my issue solved. The overall problems with this loco, continue...

Thanks for your help!