Kveldulf Posted January 22, 2012 Share Posted January 22, 2012 I've been installing some decoders in old DC locos (with 100% success so far). I fear however, that my latest attempt may have killed the motor in my little Farish 04 shunter! Basically, it was tripping my DCC controller each time I put it on the track and powered on. After a good going over with my multimeter revealed no problem with the wheel pickups, I found that it was showing continuity between the two poles of the motor. Is it time for a new motor? Link to post Share on other sites More sharing options...
hollywoodfoundry Posted January 22, 2012 Share Posted January 22, 2012 It would be very surprising if there was no continuity between the poles of a motor, otherwise it would not work. The key thing is how much. The best test is to remove the motor from the model, or isolate it electrically, then connect the motor to a normal DC supply and measure the amount of current it draws when running. If it draws more than about 1 amp, then the motor is very likely faulty. Link to post Share on other sites More sharing options...
Kveldulf Posted January 22, 2012 Author Share Posted January 22, 2012 Thanks - i'll break out my DC controller and give it a whirl. Link to post Share on other sites More sharing options...
Dr Al Posted January 23, 2012 Share Posted January 23, 2012 If it draws more than about 1 amp, then the motor is very likely faulty. For an N gauge Farish 04 if it draws more than about 150mA it's faulty. These motors draw <50mA when running normally. If it draws 1A you'll know. It'll be on fire... Cheers, Alan Link to post Share on other sites More sharing options...
Kveldulf Posted January 23, 2012 Author Share Posted January 23, 2012 Well, it's only drawing 40ma so the motor looks to be fine. Now I just need to work out where the short that keeps tripping the DCC controller is. Thanks for the pointers gents. Link to post Share on other sites More sharing options...
hollywoodfoundry Posted January 23, 2012 Share Posted January 23, 2012 For an N gauge Farish 04 if it draws more than about 150mA it's faulty. These motors draw <50mA when running normally. If it draws 1A you'll know. It'll be on fire... Cheers, Alan Yes, however to trip a DCC supply, the current would have to be in the region of 2A, and if the motor has a short in it, it most likely will not catch fire either. Link to post Share on other sites More sharing options...
Dr Al Posted January 24, 2012 Share Posted January 24, 2012 Yes, however to trip a DCC supply, the current would have to be in the region of 2A, and if the motor has a short in it, it most likely will not catch fire either. Which is why these can be so damaging to N gauge models - no N gauge model I've run (Farish, Dapol, UM, even elderly Minitrix) runs on more than 300mA. A 2A trip is therefore totally useless in N to stop motor damage - at 500mA your motor will be cooking nicely, and yes, I have actually seen such melting, smoking (essentially on fire) motors and burning commutators. You need a fast acting 500mA breaker really - on standard DC controllers also the thermal trip is too slow and too high a current. Or ensure that your system has a series ammeter wired so you know how much current is being drawn and you can see if something stops performing correctly if this correlates to a large current draw. Then you can stop it quickly and investigate! Cheers, Alan Link to post Share on other sites More sharing options...
hollywoodfoundry Posted January 24, 2012 Share Posted January 24, 2012 Which is why these can be so damaging to N gauge models - no N gauge model I've run (Farish, Dapol, UM, even elderly Minitrix) runs on more than 300mA. A 2A trip is therefore totally useless in N to stop motor damage - at 500mA your motor will be cooking nicely, and yes, I have actually seen such melting, smoking (essentially on fire) motors and burning commutators. You need a fast acting 500mA breaker really - on standard DC controllers also the thermal trip is too slow and too high a current. Or ensure that your system has a series ammeter wired so you know how much current is being drawn and you can see if something stops performing correctly if this correlates to a large current draw. Then you can stop it quickly and investigate! Cheers, Alan And if you wish to run two or three locomotives on your DCC system? The OP did indicate he was using DCC, so if it tripped at 500mA then you would never be able to run two locomotives under load. Link to post Share on other sites More sharing options...
Dr Al Posted January 24, 2012 Share Posted January 24, 2012 And if you wish to run two or three locomotives on your DCC system? The OP did indicate he was using DCC, so if it tripped at 500mA then you would never be able to run two locomotives under load. Ammeter is the best tool - I've used it to identify countless N gauge models that could be performing better. Keep an eye on it after knowing what the locos draw individually. 500mA trip would still allow between 3 and 10 modern N gauge locos to be run at once depending on the specific type - only the really older models draw more. Under load there is rarely much appreciable difference in current draw in N gauge. Cheers, Alan Link to post Share on other sites More sharing options...
hollywoodfoundry Posted January 25, 2012 Share Posted January 25, 2012 I bow to your superior knowledge of the DCC requirements. Link to post Share on other sites More sharing options...
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