Fast on DC, Slow on DCC

[Souty Train Guy]

Hi all,

Recently, I have been DCC fitting my locomotives to work with an NCE Powercab, however, all my trains go considerably slower on the NEC Powercab than running on DC.

I have tried changing the speed step mode on the controller to 128 and changing CV5 to the max on all my DCC fitted locomotives, but it made no noticeable difference.

DCC Fitted trains:

- Bachmann Class 150 - Bachmann EZ command decoder

- Hornby Pendolino - Hornby Standard 8 Pin decoders

- Bachmann Voyager - Gaugemaster Omni decoder

The odd thing was that when I had the Voyager running around at a Club on a Powercab, it went alot quicker, yet has not been reprogrammed since...

Any ideas?

[ColinB]

What decoders are you using? I did find some perform better than others. It might be that the DC voltage you are using is higher than the DCC. DC is rectified AC, if the controller does very little smoothing of the AC, as say in the case of a really old H&M or the like then you get a much higher voltage than DCC where the decoder is using a much better regulated supply. The other thing is to remove the capacitor across the locos motor, this can sometimes have an adverse effect.

[Souty Train Guy]

What decoders are you using? I did find some perform better than others. It might be that the DC voltage you are using is higher than the DCC. DC is rectified AC, if the controller does very little smoothing of the AC, as say in the case of a really old H&M or the like then you get a much higher voltage than DCC where the decoder is using a much better regulated supply. The other thing is to remove the capacitor across the locos motor, this can sometimes have an adverse effect.

Decoders are mentioned above...

I did measure the voltage on the DC controllers and it measured 12 volts on full power.

The DCC controller was outputting about 15 volts, but dropped to 13 volts when a locomotive was running

[jane1707819582]

Neither the hornby or bachmann support CV 5 . and altering the cab to speed step to 128 will not work either.so that explains why you saw no difference.so. There are no settings within the power cab that I am aware of which will effect the track voltage. I would suggest checking your track connections .

[ColinB]

Sorry, didn't notice the entry of the decoders. Does the Hornby Pendolino go better than the rest as that was one of the decoders that I found was ok. I think jane2 has a point check the track connections, and also how many locos do you have on the track at the same time? With DCC they are all using the same signal even if they are not moving.

[Flashbang]

Hi

Assuming all your rails are spotlessly clean and the wires feeding the rails are of a reasonable wire size then look at the PowerCabs power supply unit which is normally a Wallwart style plug in unit.  Look at the rating plate information.  What is the rated DC output voltage stated?  The PowerCab can work with up to 15 volts regulated DC being supplied to it.  If your power unit is rated at 12 volts DC this may be the cause.  

Ideal input voltage for a powercab input is 13.5 volts DC.

You say you have measured the rail volts, but what did you use to do this? Was it a domestic multimeter? Was the meters voltage range set to read AC volts? Not DC.   Please remember a domestic multimeter will not read accurate DCC voltages due to the high frequency being used. 

However, on the meters AC volts range it will give an indication of rail volts and that reading should be the same at all places around the layout. To note: To accurately read DCC voltage you would need a multimeter capable of reading on its AC voltage range at 10KHz or use a RRamp meter or an Oscilloscope.  

[Souty Train Guy]

Sorry, didn't notice the entry of the decoders. Does the Hornby Pendolino go better than the rest as that was one of the decoders that I found was ok. I think jane2 has a point check the track connections, and also how many locos do you have on the track at the same time? With DCC they are all using the same signal even if they are not moving.

I currently have one train connected as I am yet to electrify the insulfrog points. All the other have no power when a train is in use.

The hornby Pendolino is quicker than the rest, however, it was still considerably quicker on DC than on DCC and was always quicker than the other trains

[Souty Train Guy]

Hi

Assuming all your rails are spotlessly clean and the wires feeding the rails are of a reasonable wire size then look at the PowerCabs power supply unit which is normally a Wallwart style plug in unit.  Look at the rating plate information.  What is the rated DC output voltage stated?  The PowerCab can work with up to 15 volts regulated DC being supplied to it.  If your power unit is rated at 12 volts DC this may be the cause.  

Ideal input voltage for a powercab input is 13.5 volts DC.

You say you have measured the rail volts, but what did you use to do this? Was it a domestic multimeter? Was the meters voltage range set to read AC volts? Not DC.   Please remember a domestic multimeter will not read accurate DCC voltages due to the high frequency being used. 

However, on the meters AC volts range it will give an indication of rail volts and that reading should be the same at all places around the layout. To note: To accurately read DCC voltage you would need a multimeter capable of reading on its AC voltage range at 10KHz or use a RRamp meter or an Oscilloscope.  

The wall transformer used is the standard one that comes with the NCE Powercab. Unfortunately, I can't see the rating on it

[96RAF]

Take a picture of the rating label and post on here.

[jane1707819582]

13.8 volts at 1.8 amps

[Souty Train Guy]

13.8 volts at 1.8 amps

Exactly that

[Souty Train Guy]

I have also just measured how much each locomotive is drawing and the max on full speed is 0.5 amps, using the built in function on the controller to measure it.

[Rog RJ]

Running slow on NCE Powercabs is a pretty well known thing.  Either get a higher voltage power supply (but within the makers specifications) or learn to live with it.

[jane1707819582]

I have also just measured how much each locomotive is drawing and the max on full speed is 0.5 amps, using the built in function on the controller to measure it.

That appears high to me , i would expect around half that . I would examine your track connections.

[Flashbang]

As a general rule and for guidance, a standard loco not pulling any load will draw around 150 to 250  milliamp (approx 1/8 to 1/4 Amp), add lights and sounds and this may well increase to some 350ma.  There are of course exceptions, such as older locos with Ringfield motors and even new Heljan locos which are known to be higher current consumer locos anyway.

 

Your power supply is correct with 13.8volts and 1.8Amps output.   What did you use to measure the DCC rail volts as per my previous unanswered question?  Is the same voltage being read everywhere too?