I recall that someone posted this question earlier, but never received a definitive answer. Is it possible to install a decoder and use its motor control features in the older Bachmann Spectrum 70 and 44 tonners which contain the two separate motors? It was common for one of the motors to hang up when starting up the locomotive at low speed. Has anyone tried it?
I have both the older, two motor version and the newer, single motor version of both the 44 and 70 tonners. My older, dual motor models were tweaked and ran very well compared to some of the new single motor productions. I’d like to put them back into operation.
I’ve never tried to control two motors with a single decoder, so it would be impossible to give you a straight answer.
I think your best bet would be to call DigiTrax and ask for technical support. They may have a decoder with sufficient power for your purpose. 770-441-7992. I’ve used this service many times and they’re always helpful. If no one is available when you call, they will call you back.
Most answers you’d receive here would be “best guess”. The guys at DigiTrax would know for sure.
I’ll take a semi-educated guess and suggest that if the decoder can handle the load from the motors (the amperage draw under a given load), then the decoder should be fine. It will provide the required voltage, since the decoder meters that to the motor, but the increased amperage could be the kicker.
I’ve done this in a Bachmann Spectrum 44-tonner with dual motors and it works just fine. My installation was several years ago using a Lenz LE077FX dime-sized decoder, which does not have BEMF. A TCS M-1 is an equivalent decoder. I’ve never had a problem with one motor hanging up.
I was concerned that the back EMF motor control would be scrambled as the twin motors don’t always have the same resistance or speed. The “kick” rate might be problematic, also.
I use a MRC 1650 wired into the two motors on a Spectrum DD40AX. So far no problems with back EMF and it runs quite smoothly, even at low sppeds. I did run a stall test to check amperage draw before putting in the decoder. The 1650 is rated at 1.5 amps continuous, 2 peak, has BEMF, supports advanced consisting and CV21. I believe the Digitrax DH163 and the 15 series NCE docoders have the same features and should run about the same.
So, if the current draw isn’t too great I’d go for it.
HI: I have two Spectrum 44 tonners that I put decoders in about 5 yrs ago. The ones that have the two motors. The decoders were Digitrax DH121. After tuning the Start, Mid and Max CV they ran really nice, but wouldn’t pull very many cars. If you put a decoder in one of them, use very flexable wire to pick-up the power from the trucks. The first one I did the wires weren’t flexable and it would derail because the trucks wouldn’t turn easily and follow the turns in the track. The second one I did I used different wire and it worked very good, so I rewired the first one with the different wire. “The decoder was a very tight fit”
BEMF motor control circuits are designed to control one motor as they use PID (Proportional, Integral and Derivative gains) to determine how much to increase or decrease the current based on a particular motor’s characteristics. To verify if BEMF is truly working would require testing the locomotive by operating the motors at a particular speed, then place a load on the motors and check the decoder’s output to the motor for an increase in current. The increase should be nearly as smooth and consistent as it is with one motor; otherwise, the BEMF circuit will not work as designed.
MR January 2001 had an article “Installing DCC in a 44-Tonner” and RMC April 2004 had one on a Soundtrax decoder “Modeling a GE 70 Tonner for the Modesto & Empire Traction”. With articles this old, the decoders may not be available any more, but, if they are not, it will give a start on finding a substitute.
Carl is quite correct about testing the functioning of the BEMF circuit…or you can watch the loco pull a load up a grade. If the loco maintains it’s set speed, the BEMF is working. Ditto on the down grade. If the loco doesn’t run away, the BEMF is working.
Installing two decoders would work, I considered it with the DD40 and, if the load was greater would have done so. However, constantly consisting two decoders has it’s own problems such as one or the other of the decoders cutting out or losing it’s memory. Also, it would be best to use higher level decoders that support CV21 consisting functions. Such decoders may not be the smallest. Which brings up the space question. I believe it’s a tight fit for one decoder in the 44 tonner, much less two. However, using two, you may be able to use a smaller scale (N or even Z) decoders so it might be a push for space.
