RMweb Gold PhilH Posted May 9, 2017 RMweb Gold Share Posted May 9, 2017 (edited) I've just watched online a video of some diesel locos being towed back from the Swanage diesel gala. Now, undoubtedly I'm way wrong on this but I thought if an electric motor was driven it turns into a generator. Traction motors are geared to wheels so if my first statement is correct then the traction motors will be generating current. If that is right what happens to the electrickery so generated. As I say I'm undoubtedly talking out of the place where the sun don't shine.... Edited May 9, 2017 by PhilH 1 Link to post Share on other sites More sharing options...
RMweb Gold big jim Posted May 9, 2017 RMweb Gold Share Posted May 9, 2017 ive never thought about that before! all i can think is if the battery switch is out then the contacors arent energised so it wont generate any current? Link to post Share on other sites More sharing options...
Titan Posted May 9, 2017 Share Posted May 9, 2017 The motors will not generate unless a voltage is applied to the field windings. In a permanent magnet motor you can't turn the field off as it is provided by the magnets, so it will always generate if rotated. However on a traction motor (and indeed on anything other than small motors) the field is created by energising field windings. No field means no generation. 1 Link to post Share on other sites More sharing options...
Ken.W Posted May 10, 2017 Share Posted May 10, 2017 Electricity also has to have a complete circuit to flow. When the power controller's at 'off' the Traction Motor Contacters are open - they're only closed by selecting 'first notch' on the controller, so with no circuit the motors can't generate. Hence you can also coast even when the engine is running Link to post Share on other sites More sharing options...
Nearholmer Posted May 10, 2017 Share Posted May 10, 2017 There is another entire thread about this, with almost the same title. K Link to post Share on other sites More sharing options...
Edwin_m Posted May 10, 2017 Share Posted May 10, 2017 Electricity also has to have a complete circuit to flow. When the power controller's at 'off' the Traction Motor Contacters are open - they're only closed by selecting 'first notch' on the controller, so with no circuit the motors can't generate. Hence you can also coast even when the engine is running I think you'd find volts on the terminals if the motor was turned with the field coils energised and no circuit. In fact I think this might be a risk of damaging the motor by overvoltage. Link to post Share on other sites More sharing options...
jim.snowdon Posted May 10, 2017 Share Posted May 10, 2017 I think you'd find volts on the terminals if the motor was turned with the field coils energised and no circuit. In fact I think this might be a risk of damaging the motor by overvoltage. You would, if that was to be the case. Except that it isn't. With few exceptions (Class 60), locomotives with DC traction packages use series wound motors, so once the supply contactors are open there is no circuit to provide excitation to the field coils, so no volts across the armature terminals. For the few locomotives with separately excited DC motors, all that is required is that the field supply is off. The same principle applies to AC traction motors- no excitation equals no generation. Jim Link to post Share on other sites More sharing options...
RMweb Gold PhilH Posted May 10, 2017 Author RMweb Gold Share Posted May 10, 2017 Thanks for the replies. This new fangled electrickery is puzzling stuff. Link to post Share on other sites More sharing options...
RMweb Gold The Johnster Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 Thanks for the replies. This new fangled electrickery is puzzling stuff. No, it's very simple. You switch the switch, and the light comes on, or whatever is supposed to happen. It might as well be magic beyond that as far as I'm concerned... Link to post Share on other sites More sharing options...
RMweb Gold tomparryharry Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 Thanks for the replies. This new fangled electrickery is puzzling stuff. Stay away from that 3rd rail stuff Phil! You might look at it at Alton, but 'tis the devils work, I say! Link to post Share on other sites More sharing options...
RMweb Gold big jim Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 No, it's very simple. You switch the switch, and the light comes on Don't mention light bulbs, I think I mentioned them once but got away with it (With apologies to the trolls thread) 1 Link to post Share on other sites More sharing options...
RMweb Gold PhilH Posted May 10, 2017 Author RMweb Gold Share Posted May 10, 2017 Stay away from that 3rd rail stuff Phil! You might look at it at Alton, but 'tis the devils work, I say! Funny you should say that...when out on the mainline with various locos the one thing that really, and I do mean really, concentrates and exercises my mind is when I have to step over the third rail. Obviously we look for a break in it to cross but sometimes you have no choice. Again, although we have the 3rd rail guards which fit over it, when you have to water with the hose(s) just above it that makes you think hard too. We spend nominally a full day on it when doing the Sentinel card course, but when you come to do it for real, well, as I say... 1 Link to post Share on other sites More sharing options...
RMweb Gold big jim Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 (edited) i hate 3rd rail! i had to speak to the signaller on the LUL lines outside moor park one day from the spt and that was between the shared NR/LUL main line and met proper lines, had about 3ft wide walking route between both live rails to get to the phone, scary stuff i believe in 'the olden days' as part of PTS you had to get hold of a length of live rail with rubber gauntlets on to pass the course! Edited May 10, 2017 by big jim 1 Link to post Share on other sites More sharing options...
stewartingram Posted May 10, 2017 Share Posted May 10, 2017 Thanks for the replies. This new fangled electrickery is puzzling stuff. It will never catch on.... Stewart Link to post Share on other sites More sharing options...
roythebus Posted May 10, 2017 Share Posted May 10, 2017 Nothing wrong with 3rd rail or 4th rail, I've worked on both long before the elfensafetea days and never got damaged by it, but then I never touched it! Link to post Share on other sites More sharing options...
Edwin_m Posted May 10, 2017 Share Posted May 10, 2017 You would, if that was to be the case. Except that it isn't. With few exceptions (Class 60), locomotives with DC traction packages use series wound motors, so once the supply contactors are open there is no circuit to provide excitation to the field coils, so no volts across the armature terminals. For the few locomotives with separately excited DC motors, all that is required is that the field supply is off. The same principle applies to AC traction motors- no excitation equals no generation. Jim Thanks for the information. I was clarifying the previous point "with no circuit the motors can't generate". Link to post Share on other sites More sharing options...
LMS2968 Posted May 10, 2017 Share Posted May 10, 2017 i believe in 'the olden days' as part of PTS you had to get hold of a length of live rail with rubber gauntlets on to pass the course! Seems a pretty severe test. On the other hand, those who fail presumably don't come back for a retest! Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted May 10, 2017 RMweb Premium Share Posted May 10, 2017 It will never catch on.... Stewart Just wait for a day with no wind or sunshine! Link to post Share on other sites More sharing options...
Swindon 123 Posted May 10, 2017 Share Posted May 10, 2017 i hate 3rd rail! i had to speak to the signaller on the LUL lines outside moor park one day from the spt and that was between the shared NR/LUL main line and met proper lines, had about 3ft wide walking route between both live rails to get to the phone, scary stuff i believe in 'the olden days' as part of PTS you had to get hold of a length of live rail with rubber gauntlets on to pass the course! I had to do the "3rd rail course" when a Traction Trainee, (remember them) at Kings Cross, for the 3rd rail into Moorgate and going across the North London Line. As well as having it drummed into us, "watch were you step" when getting off a loco, we had to go down to Drayton Park station where a short section of 3rd rail track (not live) had been set up so we could show off our prowess with a short circuiting bar. Simples in those days. Paul J. Link to post Share on other sites More sharing options...
Swindon 123 Posted May 10, 2017 Share Posted May 10, 2017 Seems a pretty severe test. On the other hand, those who fail presumably don't come back for a retest! Almost as bad as testing "Stamp on" detonators to check they were in date. Paul J. Link to post Share on other sites More sharing options...
RMweb Gold The Johnster Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 After those overhead warning notices began appearing on everything that moved on BR, I used to get a sort of grim amusement from the mental picture of some hapless soul on the Southern (other live rail systems were and are available but in my head it was always the Southern) looking above him for the mythical overhead wires too avoid and not where his feet were going on the ground... An early example of elf and safetea gorn mad, actually creating a dangerous situation. Southern Region emus which would never see an overhead wire were plastered with the 25kv notices as well! Link to post Share on other sites More sharing options...
Mark Saunders Posted May 10, 2017 Share Posted May 10, 2017 After those overhead warning notices began appearing on everything that moved on BR, I used to get a sort of grim amusement from the mental picture of some hapless soul on the Southern (other live rail systems were and are available but in my head it was always the Southern) looking above him for the mythical overhead wires too avoid and not where his feet were going on the ground... An early example of elf and safetea gorn mad, actually creating a dangerous situation. Southern Region emus which would never see an overhead wire were plastered with the 25kv notices as well! How about the Yards with 650 Volt overhead for the benefit of those locomotives with pantographs! Link to post Share on other sites More sharing options...
Talltim Posted May 10, 2017 Share Posted May 10, 2017 Ok, how do you tow a dead diesel hydraulic? Link to post Share on other sites More sharing options...
RMweb Gold The Johnster Posted May 10, 2017 RMweb Gold Share Posted May 10, 2017 How about the Yards with 650 Volt overhead for the benefit of those locomotives with pantographs! Our hapless soul would have been perfectly sate looking upwards in them, as there was no third rail for safety reasons. Mostly colliery sidings in the Kent coalfield I believe, and made obsolete by the introduction of the E6000 Electro-Diesels, which nowadays would be called 'Bi Mode'... Link to post Share on other sites More sharing options...
Mark Saunders Posted May 10, 2017 Share Posted May 10, 2017 Our hapless soul would have been perfectly sate looking upwards in them, as there was no third rail for safety reasons. Mostly colliery sidings in the Kent coalfield I believe, and made obsolete by the introduction of the E6000 Electro-Diesels, which nowadays would be called 'Bi Mode'... No he would still have the changeover area to trip over! Link to post Share on other sites More sharing options...
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