Voltage drop due to signals/turnout motors?

[AndrueC]

I just tried an experiment. I found a spare PSU rated at 12v, 1.5 A and connected that. The trains I tried ran slower than 'normal' which is to be expected. But interestingly I didn't see a huge difference between their speed with/without the acc. bus attached. For what's worth the voltages reported by my MM with the 12v supply were:

 

* No acc. bus: 19.7

* With acc. bus: 16.4

 

Not really sure what that tells me but it sounds like a proportional change (13.8 -> 12 = 14% lower). Also it looks like that PSU didn't drop its voltage quite as much. But from what I've been reading PSUs should drop their voltage at all unless you pull too much from them. Do you think it worthwhile measuring the current supplied to track+acc. bus using the multimeter rather than relying on the PowerCab? I do know that the 13.8v PSU never gets warm.

[Crosland]

I would start measure at the input to the PowerCab. Voltage across the input. If it's DC that's straightforward. If it's AC then it will be 50Hz and the meter will be accurate, so also straightforward). Current by putting the meter in series with one connection.

 

If there's no appreciable voltage drop, then the problem is downstream.

 

Next, build a simple bridge rectifier and turn the track into DC volts for more accurate measurement. Use that at various points around the layout and accessory bus. Add a couple of volts to account for the voltage drop across the diodes.

 

See what is the effect of connecting/disconnecting the accessory bus, running trains, ...

[AndrueC]

I've found the answer. It's the cable between the PCP and Powercab. I replaced it with a longer one I bought from Amazon. With the original cable in place my multimeter now reports 22 VAC between the rails and even with two locos + acc. bus everything seems fine.

 

Curiously the Powercab is now reporting higher currents than it ever has before - at one point it was showing just over .6A. The track voltage still drops but even with two locos it was being reported as 20 VAC.

 

https://ncedcc.zendesk.com/hc/en-us/articles/201799499-NCE-DCC-Cables-Explained

 

I'm still mildly curious about why my multimeter - a Rapidtest DM25 - appears to report double the actual voltage whereas all the comments I've found on the web imply MMs are just be 'a bit inaccurate' but it doesn't really matter

Edited October 25, 2021 by AndrueC

[ISW]

31 minutes ago, AndrueC said:

I've found the answer. It's the cable between the PCP and Powercab. I replaced it with a longer one I bought from Amazon.

There were 2 cables with my PowerCab. You HAVE to use the flat flex one between the PowerCab and the PCP, not the coiled one. The latter cannot take the current ...

Ian