Locomotive speed dependent on voltage

[Andrzej]

Recently I did some tests with BiDiB modules. I think there are some interesting observations on changing power supply voltage and locomotive speed, which are worthy to share. It could happen with any command station, my tests were done using BiDiB. I used variable power supply, so the voltage can be precisely adjusted. After all headaches with speed measure devices I use straight track 3,6 meters long with track occupancy detectors.

The results for Roco 72221 steam locomotive Ty2 (BR52) with factory installed sound decoder (Zimo MX645), CV5=136, and acceleration/deceleration delay turned off, are as follows:
17V max speed 110 km/h
16V max speed 101 km/h
15V max speed 94 km/h
14V max speed 87 km/h

Of course, higher speeds are more affected on voltage than lower speeds. Our precisely calibrated locomotives need the same voltage in every corner of the layout. Some track occupancy detectors cut down 1,4V of voltage, sometimes poor wiring lowers voltage. If many boosters are used, all should be calibrated to the same voltage.

[Stefan Lersch]

Hi Kuba,

correct observation! This is indeed true. Fortunately the loss of power over the tracks is usually not very big. That means that our eyes don't see a difference in most cases.

[Adrian L]

Oh this is a nightmare.. I have just upgraded from an eCos 1 with a fixed power supply output voltage to the eCos 2 with the adjustable power supply voltage. It means that I need to re-calibrate over 60 locos and make sure that no one fiddles with the power setting on the power supply.  7-9 km/hr is a significant variation..

Then there is the boosted sections.. 

Thanks for the excellent research Kuba - even if it means rework for me..