Loco slowing down when another loco starts

[Clagsniffer]

After finishing laying all my track for my layout I have started running in all of my locos. This evening I started with a Heljan 47. After I fitted a decoder I set it off doing circuits which it happily did, no issues. I then chipped another loco and as I set this one away the Heljan 47 slowed down. I stopped the second loco and the 47 gained speed again. I checked the power usage with my power cab and it was reading 0.86 amps with both locos running. I have droppers on every piece of track and have cleaned the locos wheels and dabbed some oil on the gears. What else could be slowing the 47 down? It’s the only loco to have shown this problem so far, I’m a bit puzzled. Any ideas anyone?

 

Thanks in advance.

[RFS]

What gauge wire have you used for your DCC bus? Does the 47 slow down in a particular place, for example at the furthest point from the command station?

[WIMorrison]

Also, what gauge of wire have you used from the command station to the DCC bus?

 

 

[NIK]

Hi,

 

My Heljan Class 47 draws up to 1 amp so depending on the power supply with your Powercab you could be overloading the control system.

 

Regards

 

Nick

[Clagsniffer]

Thanks for the quick replies chaps much appreciated.

 

I’m not entirely sure what size wire I’ve used for the bus, I think it’s 32/0.2? It’s on a roundy roundy around my garage, roughly 16ft x 8ft. I’ve used the same gauge wire to link the command station to the bus.

 

As for the power supply I’m not sure about that either without checking, I’ve just used what comes supplied with the NCE power cab starter set. Looking at the blurb it’s supposed to be a 1.5 amp system so surely that could handle 0.86amps?

 

Thanks again.

Edited March 24, 2021 by Clagsniffer

[WIMorrison]

If it is 32/0.2 then that is definitely heavy enough and wont be causing the issue therefore it may simply be down to the power supply but the default supply is 2A which should run a couple of trains without issue - even greedy ones

[Clagsniffer]

It’s all a bit strange. It runs happily at decent speed on its own but then slows down when I start a second loco, which in this instance was a Bachmann 37, so it’s not like I’m running two power hungry Heljans. Doesn’t seem to make a difference where it is on the layout either. I’d happily just buy a booster but can’t really afford to fork out another £200 just to run two locos.

[KingEdwardII]

Do you have a multimeter? If so, what is happening to the track voltage when you start the second loco?

 

I'd expect the track voltage to be dropping, to explain what you're observing. If it is dropping then the next task is to work out what is causing the voltage drop...

 

Yours,  Mike.

[NIK]

44 minutes ago, Clagsniffer said:

It’s all a bit strange. It runs happily at decent speed on its own but then slows down when I start a second loco, which in this instance was a Bachmann 37, so it’s not like I’m running two power hungry Heljans. Doesn’t seem to make a difference where it is on the layout either. I’d happily just buy a booster but can’t really afford to fork out another £200 just to run two locos.

Hi,

 

If the slow down happens regardless of where it is on the layout then there is likely to be a problem further back before the output from the Power Cab is split off to the individual pieces of track.

 

Its possible the current meter on the Power Cab is not telling the whole story because if the output voltage is reduced for any reason by the time it reaches the track then the current will be reduced accordingly.

 

My Heljan 47 burnt out its original motor so its possible you may have a very thirsty 47.

Be careful about measuring the track voltage as many digital multimeters do not give a useful indication of the DCC voltage.

 

I don't have a Bachmann class 37 to hand in order to measure the current it draws.

 

However if you measure the voltage on any DMM with an AC range with no locos present and then with locos running and you see a drop below about a volt then that may indicate there is a problem in the control system or the wiring from there to the track.

 

Do you have some form of current limiter between the Power Cab and the track as these can sometimes cause problems?.

 

Regards

 

Nick

Edited March 24, 2021 by NIK

[Clagsniffer]

9 minutes ago, NIK said:

Hi,

 

If the slow down happens regardless of where it is on the layout then there is likely to be a problem further back before the output from the Power Cab is split off to the individual pieces of track.

 

Its possible the current meter on the Power Cab is not telling the whole story because if the output voltage is reduced for any reason by the time it reaches the track then the current will be reduced accordingly.

 

My Heljan 47 burnt out its original motor so its possible you may have a very thirsty 47.

Be careful about measuring the track voltage as many digital multimeters do not give a useful indication of the DCC voltage.

 

I don't have a Bachmann class 37 to hand in order to measure the current it draws.

 

However if you measure the voltage on any DMM with an AC range with no locos present and then with locos running and you see a drop below about a volt then that may indicate there is a problem in the control system or the wiring from there to the track.

 

Do you have some form of current limiter between the Power Cab and the track as these can sometimes cause problems?.

 

Regards

 

Nick

I don’t have any current limiters, it’s literally the track output from the nce panel connected to my bus.

 

I had a Hornby 56 and a Bachmann 37 happily running together the other day. However now I think of it, I did have an older Bachmann deltic running with another loco and seem to to think that slowed down when the second loco started. Could it be that it’s just two power hungry older locos?

 

I’ll do some more running tests tomorrow night and note the current draws of the locos running on their own. I’ll report back with my findings.

[NIK]

10 hours ago, Clagsniffer said:

I don’t have any current limiters, it’s literally the track output from the nce panel connected to my bus.

 

I had a Hornby 56 and a Bachmann 37 happily running together the other day. However now I think of it, I did have an older Bachmann deltic running with another loco and seem to to think that slowed down when the second loco started. Could it be that it’s just two power hungry older locos?

 

I’ll do some more running tests tomorrow night and note the current draws of the locos running on their own. I’ll report back with my findings.

Hi,

 

You could have the lead between Power Cab and the PCAB-PP circuit board gone higher resistance. I had something similar and ended up buying a new lead.

 

My Bachmann Class 37 draws 0.4 Amps @ 12V DC.

 

Some UK stockists of NCE Power Cab provide a power supply than is less than the current rating of the Power Cab. It might be worth trying to see what output current rating and output voltage rating is printed on the power supply.

 

 

Regards

 

Nick

[Michael Hodgson]

Poor soldered connection somewhere en route from the command station perhaps - joint going high resistance ?

[smokebox]

It could be a faulty lead from the Powercab to the connection panel or the "prongs" inside the connection socket.  All power to and from the handset goes via the handset cable and socket on a basic Powercab installation.

[Clagsniffer]

Thanks for all the help everyone, I really appreciate it.

 

First thing I’ll do tonight is check my power supply. I’ll then go through my loco roster and not down their power usage. I’ll then then go through the wiring.

 

I did notice when I took all my locos off the track the power cab was still saying there was 0.26a usage. I did have 3 Bachmann Pullman coaches on the track so must have been the coach lighting.

[Clagsniffer]

Ok so I’ve been in the garage for a couple of hours and my findings are as follows;

 

Firstly the power supply supplied with my system has an output of 1.5A.

 

Track voltage with nothing on it was measure with my multi meter on AC range as suggested and I got a reading of 2.7volts, I’ve no idea if this is right? I then measured voltages at different stages with a mix of locos operating and the lowest I saw it go was 2.3volts. I also measured the resistance of each rail from the command station to the furthest away point on the layout and both measured at 0.8ohms.

 

Next I did some tests on individual locos and the results I got were as follows;

 

Bachmann 37 (with cab lights and headlights) stationary was pulling 0.04amps.

Running it was pulling 0.16-0.18amps.

 

Heljan 47 (with headlights) stationary was pulling 0.04amps. Running it was pulling between 0.16-0.37amps. I did notice that this loco did not move until speed step 15.

 

Hornby class 56 (with headlights) stationary was 0.01amps. Running it was pulling 0.09-0.11amps.

 

Bachmann class 47 (with headlights and cab lights) stationary was pulling 0.03amps. Running it was pulling 0.08-0.21amps. Quite a range?

 

The next test involved running the problem 47 with another loco and I took lap times, averaged out over 5 laps. The 47 on its own was averaging 25 seconds. The 47 running with the Hornby 56 then averaged 27 seconds. Definitely slowed down. I timed the 56 on its own and then with the 47 and it was a consistent 30 seconds, no change in lap time. I made sure that the speeds for each test were the same.

 

During all of this testing I never saw the current on my cab go anywhere near 1 amp, I think the highest I saw it was 0.8 amps.

 

So after all that I’m not really any the wiser other than the problem seems to be with the Heljan 47’s. They’re fine on their own but slow down when running with any other locos.

 

 

[norman]

If you really do have only 2.7 volts then locos will barely move if at all.  The output from the transformer should be circa 15 volt AC so you should be measuring above 12 volt AC on the track.

You need to check and make sure you have the correct range set on your meter.

[RobinofLoxley]

Just so as everyone knows, what decoder did you fit to each loco?

[Clagsniffer]

The power into the PCP panel is 13.8V dc from the power supply. I then test track voltage on AC setting of my multimeter via the Track terminals on the PCP panel which comes at 2.4V AC.

 

Power supply voltage.

Track voltage

 

Locos are definitely running, maybe my multimeter is dodgy?

 

The 8 pin decoders in the locos are either gaugemaster omni BPDCC29 or Hattons originals. The 21 pin decoders in the Bachmann locos are Hattons originals.

[WIMorrison]

Unfortunately there is absolutely no relationship between these 2 voltages. The 13.8v DC is probably accurate (though I would consider it to be too low an input voltage) but the AC ‘voltage’ is completely meaningless.

 

[melmerby]

8 minutes ago, WIMorrison said:

Unfortunately there is absolutely no relationship between these 2 voltages. The 13.8v DC is probably accurate (though I would consider it to be too low an input voltage) but the AC ‘voltage’ is completely meaningless.

 

If it's a true RMS DMM (it says it is) and has a reasonable frequency response (say to 20kHz) it should be close to DCC track voltage. (mine is 14.4v using a Fluke True RMS DMM.)

However if it is true RMS only at mains frequencies (50/60Hz) it could be pretty useless for DCC.

 

Agreed DC input votage is too low, I would expect 16v-19v DC

Edited March 25, 2021 by melmerby

[WIMorrison]

Keith

 

i am assuming that is true rms for mains not multifrequency hence the totally inaccurate reading. I haven’t seen a ‘proper’ meter that really reads true rms which looks the same as the cheap eBay offerings (and this meter looks like dozens you see on eBay, just with a different name  )

Edited March 25, 2021 by WIMorrison

[NIK]

Hi,

 

Many digital multimeters give very low readings with DCC. However the fact the voltage went down from 2.7 to 2.4 volts indicated when the load was at its highest may indicate something is up.

 

If the resistance to the loco is  2*0.8 ohms that might be enough to explain the class 47 slowing down by 5 seconds (from 25 to 30 seconds). 0.8 ohms from controller to each rail is quite high and is like what I saw when my NCE cable became faulty.

 

I vaguely recall the Power Cab current meter under-reads the DCC current. I've bought some power resistors so I may be able to check if that is so (I have a DMM that reads the DCC voltage fairly accurately).

 

Regards

 

Nick

 

 

[NIK]

7 minutes ago, melmerby said:

If it's a true RMS DMM (it says it is) and has a reasonable frequency response (say to 20kHz) it should be close to DCC track voltage. (mine is 14.4v using a Fluke True RMS DMM.)

However if it is true RMS only at mains frequencies (50/60Hz) it could be pretty useless for DCC.

 

Agreed DC input votage is too low, I would expect 16v-19v DC

Hi,

 

According to the Power Cab manual the maximum input voltage is 15V DC.

 

Regards

 

Nick

[Crosland]

16 hours ago, Clagsniffer said:

I also measured the resistance of each rail from the command station to the furthest away point on the layout and both measured at 0.8ohms.

 

Remember the current flows there and back so the resistance is 1.6 ohms. You can check this by disconnecting the controller, shorting the track at the farthest pint and measuring the resistance between the two rails where the controller would be connected.

 

Did you add lost of droppers from the bus to the rails?

 

1.6 ohms sounds a bit high for 32/0.2. At just 1 A it will drop 1.6V which is not ideal.

 

Having said that, if the 47 is slow over the whole layout, the problem is closer to home.

 

You can also take measure the current by connecting the DMM in series in the power supply connection. Use AC or DC as appropriate. If it's AC it will be mains frequency and your DMM will still give an accurate reading. The PowerCab itself should not be taking a great deal of current.

[melmerby]

15 hours ago, NIK said:

Hi,

 

According to the Power Cab manual the maximum input voltage is 15V DC.

 

Regards

 

Nick

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

 

BTW

Don't forget when checking resistance the leads of the DMM can be a significant factor with low resistances.