Loco slowing down when another loco starts

[NIK]

Hi,

 

I've got some data from my Power Cab that might be useful.

 

Tested DC input on Power Cab PCB module and DCC output on same module with and without measured 12.2 ohm 50 watt power resistor across DCC output (through 4 inches of 16/0.2 cable).

 

Power supply output printed rating 13.8V 1.8A max.

 

DC input 14.11V open circuit (no load resistor). 14.01V (load resistor).

 

DCC output 14.33V * open circuit, 9.55V **(load resistor).

* must be an over-read as DC input is only 14.11 and there appears to be a silicon diode protecting the input to the Power Cab.

 

** 9.54V at load resistor, 9.55V on PCB module so output cable not dropping much.

 

Power Cab power meter reads 0 Amps open circuit, 0.82 Amps (load resistor).

 

That 0.82 amps is quite a good match to 9.55V/12.2 ohms.

 

So on my set up it looks like significant volts are being dropped somewhere.

Enough to slow down a loco with a thirsty motor perhaps.

 

I'm guessing the cable between the Power Cab and the PCB module is the main contributor.

I don't know whether I'm using the original cable that came with the Power Cab or one of the 2 metre cables I bought online (possibly from CPC Farnell).

I can't get my DMM probes in to measure the resistance of the cable.

 

(14.33-9.55)/0.82 = approx 6 ohms total resistive loss which is a lot.

 

I will see if I can buy a genuine NCE 6 pin flat cable to see if that makes any difference.

 

 

Regards

 

Nick

[KingEdwardII]

23 minutes ago, NIK said:

I'm guessing the cable between the Power Cab and the PCB module is the main contributor.

Always bear in mind that there could also be problems with bad connections along the way - it may not be the cable itself.

 

The voltage drop you've measured is large - and it will only get bigger as the current draw increases, which is where you came in on this, by adding an extra loco...

 

Yours, Mike.

[Nigelcliffe]

31 minutes ago, NIK said:

..........

 

So on my set up it looks like significant volts are being dropped somewhere.

Enough to slow down a loco with a thirsty motor perhaps.

 

I'm guessing the cable between the Power Cab and the PCB module is the main contributor.

I don't know whether I'm using the original cable that came with the Power Cab or one of the 2 metre cables I bought online (possibly from CPC Farnell).

..........

 

I have a half-remembered memory of the PowerCab primary cable being non-standard.  The full current of the system goes up/down that cable to the PowerCab handset.  A standard bit of "networking patch cable" may be under-specified for that current. 

 

 

- Nigel

[NIK]

8 minutes ago, KingEdwardII said:

Always bear in mind that there could also be problems with bad connections along the way - it may not be the cable itself.

 

The voltage drop you've measured is large - and it will only get bigger as the current draw increases, which is where you came in on this, by adding an extra loco...

 

Yours, Mike.

Hi,

 

I've now tried wiggling the connectors. No change in the measured current. Can't find any hot spots with my infra red thermometer.

 

Regards

 

Nick

[NIK]

7 minutes ago, Nigelcliffe said:

 

I have a half-remembered memory of the PowerCab primary cable being non-standard.  The full current of the system goes up/down that cable to the PowerCab handset.  A standard bit of "networking patch cable" may be under-specified for that current. 

 

 

- Nigel

Hi,

 

Thinking about it six ohms is a lot of resistance for a cable and if it was that high I would expect the resistance to go up with time as it heats up but I haven't seen that yet.

 

Could NCE have built a batch of Power Cabs with a high RDSon H bridge on the output?.

 

I have another Power Cab somewhere. The two were bought new about ten years apart so maybe there will be a difference.

 

Regards

 

Nick

[WIMorrison]

Are you 100% certain that the Power Supply is the genuine NCE original? even 14v is lower than I have seen on all the other systems I have seen and used. Normally I would expect an input of 16-18v which allows for command station losses.

[Nigelcliffe]

7 minutes ago, WIMorrison said:

Are you 100% certain that the Power Supply is the genuine NCE original? even 14v is lower than I have seen on all the other systems I have seen and used. Normally I would expect an input of 16-18v which allows for command station losses.

 

Manuals are here
https://ncedcc.zendesk.com/hc/en-us/article_attachments/200498789/Power_Cab_V_1.65_Manual.pdf

 

Standard NCE PSU described in manual is 13.5v.   Quoted input range is 10-15v DC, 3A.    

 

 

[smokebox]

17 minutes ago, WIMorrison said:

Are you 100% certain that the Power Supply is the genuine NCE original? even 14v is lower than I have seen on all the other systems I have seen and used. Normally I would expect an input of 16-18v which allows for command station losses.

 

That's the same as the one provided in my (Brand new) Powercab kit a few years ago.  It is the upgraded power supply.  I believe the earlier version was only 12v and there were many complaints about slow running locos.

Edited March 26, 2021 by smokebox
Typo

[ISW]

1 hour ago, Nigelcliffe said:

 

Standard NCE PSU described in manual is 13.5v.   Quoted input range is 10-15v DC, 3A.    

My manual states 3A maximum. The power adapter I received in my new boxed NCE PowerCab in 2017 has a moulded UK plug and was made by W&T adapters. It has an input of 100~240v AC @1.5amps, with a stated output of 13.8v @1.8amps. I'm using the standard flat-flex cable from the PowerCab.

 

I have a large (ish) roundy-roundy of the 'folded 8' shape with 2 levels and ramps inbetween of ~1in45 gradient. I've had 2 trains pulling 8 coaches each at the same time, while operating a third on the Upper Level without issue. Even with 2 trains going up the ramps I don't exceed 1amp (according to the PowerCab display) and no slowing down due to loss of power.

 

All my power bus cables (I have 8 districts) are cheap speaker cables from ScrewFix and are 24/02 stranded. Droppers are 7/02 at a maximum spacing of ~1m.

 

Based on what the OP has said, it looks like there might be insufficient number of droppers installed and their wide spacing is causing too much volt drop. Hopefully the OP can advise on the dropper arrangement(s).

 

I hope some of this is of help.

 

Ian

[NIK]

Hi,

 

My power supply for my Power Cab is as Ian described.

 

The OP said the speed drop happened wherever the loco was on the layout so local wiring is unlikely to be the problem although the wiring between controller and the bus is a possibility.

 

Its possible that if there is a voltage drop it may depend on on the loco and the decoder as to how the loco responds.

 

Zimo decoders on default settings measure the track voltage and alter the mark space ratio to the motor to try and compensate.

 

Some locos may have sufficient torque in hand to achieve the desired speed on a lower track voltage or their decoder may be able to compensate via its back emf feedback.

My new style Hornby HST power car takes slightly more current than a TTS decoder can supply just to turn its wheels.

 

The OPs current reading of 0.86 amps is very close to the reading of 0.84 amps so that might not be a coincidence.

 

I've just realised if it is a problem with the resistance of the 6 way cable between the PCB module and the Power Cab there are 4 conductors carrying current - the 2 with DC to the Power Cab and two DCC back from the Power Cab. So if it is 6 ohm resistance that's only 1.5ohms per conductor.

 

I've also realised I might be able to measure the resistance of the cable at least at low current as I have some UTP panels somewhere that I think have 6 way RJ connectors on the back edge that are used to daisy chain the Power Pro cab bus round the layout.

 

Regards

 

Nick

[Clagsniffer]

Hi everyone, apologies for the delay in replying. It’s been a god awful day at work! I’m on call all weekend so might not get to have another look until Monday night.

I have got a lend of a good fluke multimeter so I will do some more voltage tests with that.

 

With regards to the question of droppers, I have these on every single piece of track, I’ve got my frogs switched through a micro switch to eliminate relying on switch blades. On the long sections of track I have got two sets of droppers.

 

Hope that clears things up a bit.

[GoingUnderground]

21 hours ago, melmerby said:

That's quite low for a max input voltage. Many other systems are a lot higher than that.

Not for a N. American system, where some manufacturers seem petrified to go much above 12 volts. IIRC, I have seen the user manual for one decoder, sorry can't remember which one, that says that the track voltage shouldn't be higher than 12 volts.

 

Wheras European manufacturers are more bullish on voltage. often outputting 15 volts or slightly higher even on fixed voltage PSUs. For instance in their ECoS manual ESU recommend 15-16 volts for N, 16-18 volts for OO and H0, 18-20 for 3 rail H0 (Maerklin) (and presumably 0 gauge though its not stated), 18-21 for Gauge 1, and 20-21 for G. However, in their N. American CabControl manual they say to use 15 volts for both N and H0, 18 volts for 0 and S and 21 for G.

 

On many voltmeters, the AC setting is intended for sine wave low frequency 50-60 Hz mains, not square wave DCC where the frequency could be up to 100 times higher. Additionally, if a voltmeter is described as digital, in many cases that means that its readout is digital as opposed to the older moving coil/needle type. So don't assume that a digital multimeter is capable of reading DCC voltages just because it is called a digital multimeter.

 

To measure DCC voltages accurately I believe that you need to use a RRampmeter, or a multimeter specifically designed to read DCC voltages, but that can be expensive, and on ESU's forum some folks report good results using a simple, and cheap, rectification circuit, as shown below (courtesy of K Rainer) connected to the multimeter set to measure DC voltages. 

This will under-read by 1.4 volts because of the voltage loss caused by the bridge rectifier.

[melmerby]

8 minutes ago, GoingUnderground said:

 

To measure DCC voltages accurately I believe that you need to use a RRampmeter, or a multimeter specifically designed to read DCC voltages, but that can be expensive,

 

 

Or a true RMS DMM as noted earlier. The £10 DMM from e-bay wont as it needs to be able to measure higher frequencies and they don't

You could also buy a Picoscope (I have) which can also decode the DCC packets, whilst analyzing the waveforms.

[Derekl]

I have a similar problem to the OP, in similar circumstances. Two modern locos run fine, but older (chipped with Hattons chips) seem to cause a slow down. I also have the NCE with the power supply as described above - the 13.8v (I thought 2 Amp, but may be wrong). I had not really got around to losing much sleep on the issue at this stage, although I checked track voltage with a multimeter (off load) and got 12.5v well away from the track supply location and (curiously) 12.4v adjacent. It occurred to me that it may have something to do with the 13.8v supply being a little mean, as the thoughts above. I notice that DCC Concepts are marketing a beefed up supply for the NCE which they say improves performance (well, they would, I suppose), but that is about as far as I have got.

It does occur to me though, that given the OP set up and mine are similar (mine is in a garage size shed essentially around the walls, with supply to each piece of track) it may have something to do with the standard NCE supply plus higher demand locos. I note the Heljan 47 seems to have similar demand to the older locos I have chipped.

[ISW]

52 minutes ago, Derekl said:

I have a similar problem to the OP, in similar circumstances. Two modern locos run fine, but older (chipped with Hattons chips) seem to cause a slow down.

 

52 minutes ago, Derekl said:

I note the Heljan 47 seems to have similar demand to the older locos I have chipped.

Derek (?),

 

As I've said above, I had no problems with 2 trains, which happened to include a Heljan Class 47 fitted with a Hattons chip, on gradients while operating a third train. Did you happen to note the current draw according to the PowerCab? I never exceeded 1amp.

 

One other thing I will add is that my Heljan Class 47 + Hattons chip had been drawing almost 1amp by itself at one point. I left it running with a good load of coaches up/down my ramps and after a while the BEMF stopped working. It wouldn't 'pull' on the ramps. I checked the CV settings and they were fine. Next day it was back to normal, and it was using much less current as well , ~0.6amp, so I can only assume it was an overload safeguard in the chip?

 

Moral of the story?, maybe the OP has a loco that simply demands more current than 'normal' and it affects the running of others. Just a thought ...

 

Ian

[Derekl]

7 hours ago, ISW said:

As I've said above, I had no problems with 2 trains, which happened to include a Heljan Class 47 fitted with a Hattons chip, on gradients while operating a third train. Did you happen to note the current draw according to the PowerCab? I never exceeded 1amp.

 

I have also not noticed the Powercab taking more than 1 amp - it may have done so when I was not looking. My problem is similar - two modern locos run fine, add an older loco (it is a chipped Lima 37) and everything slows down. One modern loco plus the Lima has a lesser effect, but it seems to be there, although it has to be said that it is difficult to detect fairly small variations is speed. I am still at the construction stage (or would be if I could get Peco points  and track), but there is sufficient for a continuous run in each direction,  so I have not yet worried unduly.

 

The layout at standstill draws 0.19 amp which I guess are the Cobalt point motors. I did note that track voltage from a multimeter set to read AC voltage while two locos (and trains) were running was 10.1, as opposed to 12.5 when stationary.

I will investigate further in due course....

[ISW]

35 minutes ago, Derekl said:

The layout at standstill draws 0.19 amp which I guess are the Cobalt point motors. I did note that track voltage from a multimeter set to read AC voltage while two locos (and trains) were running was 10.1, as opposed to 12.5 when stationary.

Derek,

 

For 'comparison' with 2 Bachmann diesels (a Class 25/3 & A Class 37) on good loads going up ~1in45 ramps I'm getting ~0.7amps on the PowerCab. The track voltage (measured with a multimeter on AC setting) gives 20.2v all trains stationary and 18.9v when the 2 trains are on the ramps.

 

Don't know why I'm getting the much higher voltage figures, but it might be either a different multimeter or the fact that I have MERG short-circuit devices installed between the PowerCab and the track power buses.

 

Ian

[WIMorrison]

I think I would be buying a new power supply that has a higher current rating (e.g. 3A, but similar voltage) and trying that as all the issues described point to a power supply that isn't up to spec and is simply 'running out steam' and unable to deliver the required power.

[Clagsniffer]

Again, many thanks for all the responses so far. I’ve been out on call all day today, but I’m hoping to get back in the garage for further investigations tomorrow. I will report back on anything I find.

[NIK]

Hi Claggsniffer.

 

With access to a DMM you can check if the power supply is causing the voltage drop by setting the DMM to DC and measuring the voltage on the PCB module on the points marked + and - firstly with no locos running and then whilst running the loco combo that causes slow down. If the no load voltage is around 14V and the drop is less than about 0.5V then the power supply is not the problem.

 

Regards

 

Nick

[Derekl]

13 hours ago, ISW said:

Don't know why I'm getting the much higher voltage figures, but it might be either a different multimeter or the fact that I have MERG short-circuit devices installed between the PowerCab and the track power buses.

 

Possibly a different multimeter. I have a short circuit protection device, I think from NCE.

I will run some proper tests as to current draws sometime soon, although 0.7 amps for two locos and trains sounds similar. I don't have any gradients at present.

[Derekl]

12 hours ago, WIMorrison said:

I think I would be buying a new power supply that has a higher current rating (e.g. 3A, but similar voltage) and trying that as all the issues described point to a power supply that isn't up to spec and is simply 'running out steam' and unable to deliver the required power.

 

That was more or less my thought when I noticed the phenomenon, but that is about as far as I have got in dealing with it. The fact that the OP has a similar problem to mine with much the same equipment reinforces that thought. 

[NIK]

Hi,

 

I now know why my set up has a DCC voltage drop that equates to six ohms of resistance.

 

My 6 pin cable has 1.4 ohms of resistance per conductor end to end (including the two NCE sockets I used for testing).

 

So 2.8 ohms resistance in the DC supply to the Power Cab and 2.8 ohms resistance from the Power Cab going to the track via the PCB module.

 

I've yet to find any UK stock of the official NCE Power Cab  cable (NCE Part Number 05240213).

 

Regards

 

Nick

[Ray H]

DCC Concepts sell a curly equivalent to the NCE  - six conductor - flat ribbon cable and I suspect they also sell a like for like ordinary - four conductor - curly lead.

 

The mains power supply should be rated at no more than 3 amps and needs to be regulated - so that the output voltage doesn't vary other than perhaps fractionally. The 3 amp limit is as has been mentioned before the maximum if you don't want the PowerCab to overheat and fail.

 

The output voltage of the said power supply needs to be 15 volts - no more because the PowerCab won't like it and no less if you wish to get the best performance out of the PowerCab.

[Clagsniffer]

So, I’ve finally got round to do some testing with the decent Fluke 179 multimeter and this is what I’ve found:

 

voltage on the UTP panel going to the track is 12.87v

 

resistance from UTP panel to the rails is 0.3ohms on each cable.

 

resistance from the UTP track connections to the furthest point on the layout was 0.4-0.6ohms

 

when running the Heljan 47 on its own, the track voltage reduced to 11.7volts

 

when running the Heljan 47 with a Bachmann 37 track voltage reduced even further to 11.1volts.

 

Does this point to the Heljan dragging voltage/power down?