IMRC HO SD40-2 help! MRC


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wyldmanr8cer

Member
I have 2 IMRC SD40-2's consisted together that have the LokSound decoders in them. I had posted in another thread that they seemed to be fighting each other and it was suggested that I turn off the back EMF by programming cv49 to a value of. 18. This fixed the problem but now if set them at 128 speed steps I have to have it up to about 28 on the throttle before they'll start moving. I have them in an advanced consist and I use a MRC Prodigy advanced2 DCC system. Is there a way to get them to start moving when I first increase the throttle? Nate
 
MRC Group isn't going to be real helpful in tweaking Loksound decoders !

BEMF overcomes rotational resistance by reading pulses back from the motor and applying voltage adjustments to maintain a given throttle setting. With BEMF turned off, you are relying on pure straight voltage input to get the motor turning. What you need to do if you have BEMF turned off is to increase the value in CV2.

It's pretty much trial and error. Keep adjusting the value in CV2 higher until the engine JUST begins to move in speed step 1. Do this adjustment on the engine by itself - with no train attached. Do both engines individually as each may require slightly different values to get them to just start moving on speed step 1.

Mark.
 
I've noticed this with my Loksound-equipped units, and when I turn off BEMF, they didn't run nearly as well. I turned it back on, and simply put up with the occasional bucking. The motors in those engines greatly benefit from the BEMF being on.
 
I would agree that they seem to run better with the back EMF on. I have tried everything suggested in the manual to rid the problem of the bucking. I just tried adjusting cv52 to no avail it's still doing it. Does anyone have any suggestions on what other cv's i can adjust instead of just turning off BEMF? Nate
 
You can try the "auto-adjustment" of the BEMF and see if that helps.

LokSound Select decoders have an Automatic Motor Tuning Feature. This feature will automatically adjust the Back-EMF in most cases. This is not meant to be a “cure all” solution. This will only get the settings close. There still may need to be some manual adjustments made.

In order to use this automatic adjustment you will first need to set CV 54 to a value of 0. Then put your locomotive on the layout and activate F1. Be sure to have plenty of clear space ahead of your locomotive. Your locomotive will quickly take off at full speed and gradually slow down to a stop while reading the motor responses. This will automatically set the load compensation in CVs 52, CV 53, CV 54, and CV 55.

Regardless, BEMF does not play well with engines in a consist, no matter how well it's tuned.

Mark.
 
Yes - Clear each unit out of the consist so it is functioning under its own address to do this.

Mark.
 
Mark, if I use CV54 and the locomotives don't quite match each other in speed and one drags the other or vice versa what is the best way to match them up so that they run evenly? Nate
 
Setting the BEMF has nothing to do with speed matching. Setting the BEMF using the auto feature will just set all the BEMF settings so it is optimized to that particular engine. Once that is set, you can then proceed to speed match them using CV2 (start voltage), CV5 (max speed) and CV6 (mid speed).

Unless both engines are PERFECTLY matched, you will probably still see a bit of fighting between the engines as long as you have the BEMF turned on.

Myself personally, I always turn BEMF off for any engines that will be mu'd together. By adjusting CV's 2, 5 and 6 and then increasing the momentum (CV3 acceration and CV4 deceleration) I can get them to run really smooth.

Mark.
 
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