Paul Smith Posted September 30, 2019 Share Posted September 30, 2019 Hello, new member here who has been lurking for a while but now wishes to be part of the community. I've been building my first largish layout for a while now which is DDC using the NCE Powercab system. My problem is that the trains run too slow which seems to be discussed on here a fair bit, with my system though I have good track voltage with no trains running but it drops significantly as I run trains. All the measurements below were taken from the rear of the panel and correspond with the measurements I see around the layout so I am confident it's not due to a voltage drop across the track wiring. No train = 13.6v 0.01A 1 train = 12.2v 0.21A 2 trains = 10.9v 0.49A 3 trains = 10.2v 0.64A I am using the supplied 13.8v 1.5A psu which remains constant at 13.8v all the time Any thoughts? Paul Link to post Share on other sites More sharing options...
dasatcopthorne Posted September 30, 2019 Share Posted September 30, 2019 16 minutes ago, Paul Smith said: Hello, new member here who has been lurking for a while but now wishes to be part of the community. I've been building my first largish layout for a while now which is DDC using the NCE Powercab system. My problem is that the trains run too slow which seems to be discussed on here a fair bit, with my system though I have good track voltage with no trains running but it drops significantly as I run trains. All the measurements below were taken from the rear of the panel and correspond with the measurements I see around the layout so I am confident it's not due to a voltage drop across the track wiring. No train = 13.6v 0.01A 1 train = 12.2v 0.21A 2 trains = 10.9v 0.49A 3 trains = 10.2v 0.64A I am using the supplied 13.8v 1.5A psu which remains constant at 13.8v all the time Any thoughts? Paul I guess you are using an ordinary meter to measure the voltage. If so, this method doesn't work with DCC. With the speed, what are you comparing it with? Dave Link to post Share on other sites More sharing options...
Paul Smith Posted September 30, 2019 Author Share Posted September 30, 2019 Thanks for you reply Dave, I'm using an ordinary meter which I know isn't accurate but I would have thought that it's proportionate and it's dropping each time I run another train. I'm comparing the speed to DC and I can just about live with the slower speed if I'm only running one train. The problem is that as I add more trains they are reduced to a crawl. Paul Link to post Share on other sites More sharing options...
WIMorrison Posted September 30, 2019 Share Posted September 30, 2019 There is nothing wrong with you multimeter and it is perfectly adequate to display the issue - it will be under reading by an amount that we don't know, but it will under read by the same proportion on all readings. What you describe suggests that your power supply is significantly under spec'd for the task in hand and isn't able to provide the power that you are trying to draw from it. Perhaps a faulty PSU, that is where my money would be put. Link to post Share on other sites More sharing options...
Brian Posted September 30, 2019 Share Posted September 30, 2019 Hi Why not use the built in Amp meter on the Powercab to check current to track? Also, if using your multimeter it needs to be on AC volts or AC Current to read DCC power to rails. Not all domestic/low cost multimeters offer AC current! Link to post Share on other sites More sharing options...
Paul Smith Posted September 30, 2019 Author Share Posted September 30, 2019 4 minutes ago, WIMorrison said: There is nothing wrong with you multimeter and it is perfectly adequate to display the issue - it will be under reading by an amount that we don't know, but it will under read by the same proportion on all readings. What you describe suggests that your power supply is significantly under spec'd for the task in hand and isn't able to provide the power that you are trying to draw from it. Perhaps a faulty PSU, that is where my money would be put. I initially suspected the PSU but I've measured it at the panel and it remains at 13.8vdc at all times so it seems ok? Link to post Share on other sites More sharing options...
Crosland Posted September 30, 2019 Share Posted September 30, 2019 9 minutes ago, WIMorrison said: What you describe suggests that your power supply is significantly under spec'd for the task in hand and isn't able to provide the power that you are trying to draw from it. We are told the PSU voltage is constant so the voltage drop is in the Powercab. The figures given equate to an internal resistance of about 4.5 ohms which seems way too high for a DCC booster. It should be well under 1 ohm and the voltage should remain fairly constant up to the rated current. I would suspect the Power cab. 1 Link to post Share on other sites More sharing options...
Paul Smith Posted September 30, 2019 Author Share Posted September 30, 2019 19 minutes ago, Brian said: Hi Why not use the built in Amp meter on the Powercab to check current to track? Also, if using your multimeter it needs to be on AC volts or AC Current to read DCC power to rails. Not all domestic/low cost multimeters offer AC current! I've used the built in amp meter on the Powercab and it reads:- No train = 0.01, 1 train = 0.21, 2 trains = 0.49 and 3 trains 0.64 Link to post Share on other sites More sharing options...
Paul Smith Posted September 30, 2019 Author Share Posted September 30, 2019 Is there anyone anywhere near South Lincolnshire with a Powercab setup that I could plug mine into to see if it the unit? Link to post Share on other sites More sharing options...
WIMorrison Posted September 30, 2019 Share Posted September 30, 2019 22 minutes ago, Paul Smith said: I initially suspected the PSU but I've measured it at the panel and it remains at 13.8vdc at all times so it seems ok? Apologies - missed that bit, I agree with @Crosland having had my attention brought To this - either way it shouldn’t happen Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted October 1, 2019 Share Posted October 1, 2019 17 hours ago, Paul Smith said: All the measurements below were taken from the rear of the panel and correspond with the measurements I see around the layout so I am confident it's not due to a voltage drop across the track wiring... Any thoughts? But have you measured the track wiring impedance from the location where it connects to the power cab track supply output? (Disconnect power cab, measure the layout wiring impedance.) Your measurements of voltage drop with increasing current draw indicates excessive impedance 'somewhere' in the complete DCC system and track circuit. But measurement at the DCC system outputs with supply to track to apply varying load doesn't give a reading independent of impedance in the track wiring. If the track wiring impedance is negligible, then it's as Crosland suggests, and best course would then be to return the unit to vendor or service agent for repair. Link to post Share on other sites More sharing options...
Crosland Posted October 1, 2019 Share Posted October 1, 2019 I took: 18 hours ago, Paul Smith said: All the measurements below were taken from the rear of the panel To mean the rear panel of the Powercab. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted October 1, 2019 Share Posted October 1, 2019 47 minutes ago, Crosland said: ...To mean the rear panel of the Powercab. So do I. But the complete circuit inevitably includes the track and locos drawing the power, so we cannot locate the undesirable impedance to within the DCC unit. A quick measurement of the track impedance independent of the DCC system will resolve the question. Link to post Share on other sites More sharing options...
NIK Posted October 1, 2019 Share Posted October 1, 2019 15 minutes ago, 34theletterbetweenB&D said: So do I. But the complete circuit inevitably includes the track and locos drawing the power, so we cannot locate the undesirable impedance to within the DCC unit. A quick measurement of the track impedance independent of the DCC system will resolve the question. Hi, If the voltage drop is seen at the Panel the Power Cab connects to then the resistance of the track connections is not relevant. The current has been measured and is proportionate to the number of locos on the track. As to the cause of the voltage drop it could be in the connections between the Panel and the Power Cab. The Panel could be faulty or the cable to the Power Cab. Regards Nick Link to post Share on other sites More sharing options...
Paul Smith Posted October 1, 2019 Author Share Posted October 1, 2019 5 minutes ago, NIK said: Hi, If the voltage drop is seen at the Panel the Power Cab connects to then the resistance of the track connections is not relevant. The current has been measured and is proportionate to the number of locos on the track. As to the cause of the voltage drop it could be in the connections between the Panel and the Power Cab. The Panel could be faulty or the cable to the Power Cab. Regards Nick Track impedance is zero, it does sound like a panel, cable or handset issue. I'm trying to find someone near me in the Peterborough area with a Powercab that I can try to determine the cause. 1 Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted October 1, 2019 Share Posted October 1, 2019 (edited) I'd go straight to sending the unit for service myself with that evidence. Edited October 1, 2019 by 34theletterbetweenB&D Link to post Share on other sites More sharing options...
Paul Smith Posted October 1, 2019 Author Share Posted October 1, 2019 15 minutes ago, 34theletterbetweenB&D said: I'd go straight to sending the unit for service myself with that evidence. Neither Hattons or NCE want to know. I'm told that if I get 13.6v with nothing running then the Powercab is fine and it's an issue with my locos or track. They have advised comparing the results with another Powercab either on my layout or a different layout with the same trains. They also tried to sell me a booster! Link to post Share on other sites More sharing options...
RMweb Gold RedgateModels Posted October 1, 2019 RMweb Gold Share Posted October 1, 2019 (edited) I know it' s a bit of a way but what about popping along to Digitrains? they have a DCC setup that you could plug your handset into to test? or maybe Gareth at @Trains4U could assist? Edited October 1, 2019 by RedgateModels 2 Link to post Share on other sites More sharing options...
Crosland Posted October 1, 2019 Share Posted October 1, 2019 5 hours ago, 34theletterbetweenB&D said: So do I. But the complete circuit inevitably includes the track and locos drawing the power, so we cannot locate the undesirable impedance to within the DCC unit. A quick measurement of the track impedance independent of the DCC system will resolve the question. Sorry, but if the voltage drop is measured at the Powercab then the wiring and the track are irrelevant. Link to post Share on other sites More sharing options...
johnb Posted October 1, 2019 Share Posted October 1, 2019 The OP seems to indicate that the voltage drop is being measured at a panel, not the Powercab itself, so what is between the P'cab and the panel? Could it be a 'dry' solder joint, poor connection in the RJ12 connections, I've had that one where the 'fingers' in one of the female sockets were dodgy. Maybe the cable has partly broken core, is there a kink in the cable, or a poor connection within the RJ12 plugs? Just issues that I have come across over the years. Link to post Share on other sites More sharing options...
Paul Smith Posted October 1, 2019 Author Share Posted October 1, 2019 The voltage is being measured at the panel that the Powercab connects to. I think the cable is a standard network cable, I'll borrow one from my router and test it in my system Link to post Share on other sites More sharing options...
NIK Posted October 1, 2019 Share Posted October 1, 2019 1 hour ago, Paul Smith said: The voltage is being measured at the panel that the Powercab connects to. I think the cable is a standard network cable, I'll borrow one from my router and test it in my system Hi, I don't think its an Ethernet cable. The pin to pin wiring also has to be correct for the Power Cab. I've had the cable type that suits the Power Cab go high resistance in the past. Regards Nick Link to post Share on other sites More sharing options...
Paul Smith Posted October 1, 2019 Author Share Posted October 1, 2019 48 minutes ago, NIK said: Hi, I don't think its an Ethernet cable. The pin to pin wiring also has to be correct for the Power Cab. I've had the cable type that suits the Power Cab go high resistance in the past. Regards Nick You're right Nik, I've just ordered a RJ12 cable from Ebay that is supposed to work with NCE equipment. I'll let you know what happens. Thanks Paul Link to post Share on other sites More sharing options...
Paul Smith Posted October 9, 2019 Author Share Posted October 9, 2019 I think I've got to the bottom of the problem. With thanks to @HLT 0109 and @Edward I've tried my Powwercab on different layouts and they seem to behave roughly the same. All trains slow a bit when multiples are running but my Bachmann type 25 is painfully slow. I put my oscilloscope across the rails and can see the bipolar DCC waveform giving approx 27v peak to peak under no load, when I run a train it drops by about 2 volts and the edges of the trace become quite noisy. The voltage drop is probably inconsequential for most trains but not my type 25. I'll go to Trains4U in Peterborough and try a different make of decoder. I've attached a couple of images that show the trace with no load and with a train running. Link to post Share on other sites More sharing options...
NIK Posted October 9, 2019 Share Posted October 9, 2019 (edited) 6 hours ago, Paul Smith said: I think I've got to the bottom of the problem. With thanks to @HLT 0109 and @Edward I've tried my Powwercab on different layouts and they seem to behave roughly the same. All trains slow a bit when multiples are running but my Bachmann type 25 is painfully slow. I put my oscilloscope across the rails and can see the bipolar DCC waveform giving approx 27v peak to peak under no load, when I run a train it drops by about 2 volts and the edges of the trace become quite noisy. The voltage drop is probably inconsequential for most trains but not my type 25. I'll go to Trains4U in Peterborough and try a different make of decoder. I've attached a couple of images that show the trace with no load and with a train running. Hi, My Bachmann Class 25 are on the slow side. I wouldn't have expected a drop of 2 volts (1 volt once rectified inside the DCC decoder) to have that much of an effect except for top speed. Do the decoders in the Class 25s have Back EMF feedback and if so is it turned on. If it is not then turning it on may help (as the decoder can extend the width of the pulses to the motor to compensate for the lower supply voltage). I would not have expected the voltage to drop by 1 volt rectified when a single Bachmann Class 25 is moving as my Class 25s consume about 250ma at 12V DC. That voltage drop of 1 Volt equates to a series resistance of 1/.25 =4 ohms in the DCC circuit (includes power supply). Which DCC decoders are you using?. Regards Nick Edited October 9, 2019 by NIK SPELLING CORRECTION Link to post Share on other sites More sharing options...
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