Help needed with Digitrax Zepher

[Anonymous]

I have a digitrax zepher and while running a three unit MU consist I have noticed that the consist is surging (speeding up and slowing down). My layout size is 16x20 with a 12x8 peninsula in the middle and I only operate a maximum of five locos at a time. I have feeder wires to every section of track and the track is very clean. The locos that run solo (Kato , Proto 2000) do not surge and run fine. The throttles I use are DT400 and the UT1. Would the need for a power booster cause the MU consist to do the surging? All help is appreciated.

[rrinker]

No, you probably don't need an additional booster. My guss is that the engines don't run very well together - ie, same speed at the same power setting. Try this: Consist them together, but keep them apart ont he track, don't couple them up. Watch them move - one or more will lag, and one or more will be faster. You'll have to play around with speed tables to get them all to move exactly the same speed at the same throttle setting, especially if all three are not the same brand of loco and/or have different brands of decoders installed.
It could also be excessive Back-EMF. Digitrax Series 3 decoders (123, 143, and 163 series) have two settings for BEMF, one applies to the loco running seperately and the other applies to running with decoder-assisted consisting. If you nevr changed any settings in your Zephyr, then you are NOT using decoder-assisted consisting and the value for the individual loco is what matters. What happens is that you can never get two or more locos to run 100% the same across the speed range, there always will be a bit of speed variation. With strong BEMF, when one loco shoves on the back of the leading unit, it gets slowed down - BEMF applies more power which shoves the lead unit. The load is lessened, BEMF cuts power to the trailing loco, and it pulls back the lead unit. Over and over again, for the 'surging' and 'bucking' you are seeing. BEMF needs to be reduced or turned off for proper consist operation.

--Randy

[Anonymous]

Randy, I took your advice and adjusted the BEMF and all of the surging stopped. Thanks for your help.

--Bruce Pleasant