petertg Posted December 28, 2013 Share Posted December 28, 2013 Evening all! I am here again with another problem. After an extensive exchange of comments on another forum concerning an old Wrenn City Class locomotive, I got it to run in preparation for conversion to dcc. In its present state it has both brushes insulated but both are appropriately wired. As a result also of comments in other places concerning power consumoption and since I am collecting information relating to a controller upgrade, I decided to test the power consumption. To this end, I prepared a small DC circuit consisting of a simple oval fixed directly to the base board with no underlay. The controller is an old Hammett & Morgan Duette (I have, in fact, only used one controllñer of the pair). I wired my multimeter in series with the system. When I set the loco running, in one direction I got readings with occasional peaks of 2 and 3 amps. When running in the opposite direction it gave peaks of 15 and even 17 amps or more. This loco is fitted with a neodymium magnet and has a replacement armature. I then tested an old Lima locomotive (type RE 620, which I had previously tried to convert to dcc, but it didn't work and was reconverted back to DC). This gave consistent readings in both directions, although it did give an odd 2 or 3 amp peak. Where is the catch? Link to post Share on other sites More sharing options...
corax67 Posted December 28, 2013 Share Posted December 28, 2013 I am not familiar with the loco but could the current spikes in reverse be related to some form of binding up in the running mechanism ? In some models the armature 'floats' to and fro and the pinion may be binding up with a gear or maybe the motion is catching in reverse? Just a thought. Link to post Share on other sites More sharing options...
leopardml2341 Posted December 28, 2013 Share Posted December 28, 2013 .............In some models the armature 'floats' to and fro and the pinion may be binding up with a gear or maybe the motion is catching in reverse? Just a thought. Certainly does on an old HD 2 Rail Duchess I have - similar mechanism............ Link to post Share on other sites More sharing options...
petertg Posted December 28, 2013 Author Share Posted December 28, 2013 Unless I am confused, it wasn't a matter of running forward or in reverse. Whichever way the loco was placed on the track, the high peaks occured when the controller was turned one way. Anyway, to be sure, I will try it again. Link to post Share on other sites More sharing options...
leopardml2341 Posted December 28, 2013 Share Posted December 28, 2013 Unless I am confused, it wasn't a matter of running forward or in reverse. Whichever way the loco was placed on the track, the high peaks occured when the controller was turned one way. Anyway, to be sure, I will try it again. I think Karl (corax67) was trying to explain the differences in the magnitude of the current peaks. These being as you say "..........When running in the opposite direction it gave peaks of 15 and even 17 amps or more......" Whether or not the term used is forward or reverse - the term 'opposite' direction' (controller position away from centre off ?) suggests that the motor is revolving the opposite direction to the first measurement. If the armature 'floats' to and fro, in one direction this will tend to drive the armature into or out of the top bearing, If all is not well in alignment terms then there could well be some mechanical interference, leading to the high spikes you see. The fact that it is a spike of such magnitude, suggests that the motor may be actually stalling for a very short period. A multimeter is not really the best test equipment, though analogue will be better than digital - you don't say which you used; a 'scope would be best. Hope that clarifies ? Link to post Share on other sites More sharing options...
RMweb Premium Ray H Posted December 28, 2013 RMweb Premium Share Posted December 28, 2013 Out of interest, can an H&M (presumed) Duette realistically deliver that kind of current even if for only for brief periods without the thermal cut-out tripping quite quickly? Can the (presumed) average digital multi-meter accurately measure that kind of current value, my meter has a 10 Amp max limitation? Someone has suggested to me that one way to measure the current flow is to use a 1 Ohm wire wound resistor - possibly a 10 watt rated one (or bigger). Connect that resistor in series with the supply to the track and use your meter to measure the voltage drop across the resistor. Because of the relationship between current (amps), resistance (Ohms) and voltage, a voltage drop of 1 volt across the resistor will equate to a current flow of 1 amp through the same resistor and thus through the locomotive. For measuring anything above about 3 amps I was advised to use a 0.1 Ohm resistor and divide the voltage drop by 10 to get the current flow. I don't know if this helps. Link to post Share on other sites More sharing options...
berry120 Posted December 29, 2013 Share Posted December 29, 2013 Out of interest, can an H&M (presumed) Duette realistically deliver that kind of current even if for only for brief periods without the thermal cut-out tripping quite quickly? Can the (presumed) average digital multi-meter accurately measure that kind of current value, my meter has a 10 Amp max limitation? Someone has suggested to me that one way to measure the current flow is to use a 1 Ohm wire wound resistor - possibly a 10 watt rated one (or bigger). Connect that resistor in series with the supply to the track and use your meter to measure the voltage drop across the resistor. Because of the relationship between current (amps), resistance (Ohms) and voltage, a voltage drop of 1 volt across the resistor will equate to a current flow of 1 amp through the same resistor and thus through the locomotive. For measuring anything above about 3 amps I was advised to use a 0.1 Ohm resistor and divide the voltage drop by 10 to get the current flow. I don't know if this helps. I must admit this was my thought as well - even for a motor that's worn and stalling, that is a ridiculously high current consumption (the sort of consumption where I'd expect it to burn out after a few seconds and go up in a puff of smoke!) Even peaks of 2-3 amps for a well running Lima loco is, in my books, very high. Something doesn't seem quite right there. I agree with Ray, I'd try either getting a different meter and seeing if that gives the same results, or use his recommended method to measure the current consumption instead. Link to post Share on other sites More sharing options...
petertg Posted December 29, 2013 Author Share Posted December 29, 2013 I have carried out further tests with my present set-up, since I don't have a resistor. The first test was with a differenrt Lima locomotive and levels were normally under 1A except for an odd peak (3 on one occasion). I then put the Wrenn loco back on the track and verified that the exceptionally high values were obtained when running forwards. I tried it with both outlets of the Duette with the same results. It occurred to me to reverse the magnet (quite a job with the neo magnet) and then the abnormally high results (6, 7 and even over 10A) were obtained when running backwards, albeit there were odd 2 and 3A peaks when running forward.. No smoke or cutting out or stopping at any time. The connections were made with small terminal blocks. Does this situation suggest anything new? Link to post Share on other sites More sharing options...
leopardml2341 Posted December 29, 2013 Share Posted December 29, 2013 It would be a good idea if you could observe the vertical movement of the armature as it takes up 'drive'. That way you will see if the top of the armature is being forced up or down. With your statement '.......running forwards......', IIRC, with a normal cut worm and pinion, this is when the armature will be tending to ride up into the bearing and thus 'bind' if out of alignment as I suggest earlier. Link to post Share on other sites More sharing options...
Grovenor Posted December 29, 2013 Share Posted December 29, 2013 This loco is fitted with a neodymium magnet and has a replacement armature. The way this problem reacts to reversing the magnet suggests that it is not a result of mechanical binding but an electrical problem. The new magnet should reduce current as compared to one of the old magnets that suffer from weak field as they age, or if taken out and replaced. And a weak field gives high current and poor torque. I would suspect the armature, if it has been rewound and the commutator has slipped in relation to the poles this would give an asymnetry resulting in the sort of problems you are seeing. Do you have another you can swap out? If not see if you can get hold of a spare to try. Keith Link to post Share on other sites More sharing options...
leopardml2341 Posted December 29, 2013 Share Posted December 29, 2013 The way this problem reacts to reversing the magnet suggests that it is not a result of mechanical binding but an electrical problem. The new magnet should reduce current as compared to one of the old magnets that suffer from weak field as they age, or if taken out and replaced. And a weak field gives high current and poor torque. I would suspect the armature, if it has been rewound and the commutator has slipped in relation to the poles this would give an asymnetry resulting in the sort of problems you are seeing. Do you have another you can swap out? If not see if you can get hold of a spare to try. Keith But why only in one direction? Doesn't reversing the magnet (polarity) just change the way the motor rotates when voltage is applied ? (Flemings Left Hand Rule) Link to post Share on other sites More sharing options...
petertg Posted December 29, 2013 Author Share Posted December 29, 2013 A horrible thought has just occurred to me. Is all this a sign that I have lost the ball out of the top bearing? This was a point about which I became aware after I had already dismantled the motor more than once although a visual inspection seemed to show something in the bottom of the housing. What size was this ball in case I need to replace it? Apart from that I will check the other points mentioned above. Reversing the magnet does reverse the direction of running. Thus, firstly, the high current occurred when running forward. After reversing the magnet the high current occurred when running in reverse. Link to post Share on other sites More sharing options...
corax67 Posted December 29, 2013 Share Posted December 29, 2013 I wonder if it's a problem with the armature, either a winding or the commutator? This is going to be a tough fix without being able to physically see the loco in operation and get a better handle in what's going on since these current spikes are indeed very high - I am out of ideas I'm afraid - sorry Link to post Share on other sites More sharing options...
Robin2 Posted December 30, 2013 Share Posted December 30, 2013 I would temporarily solder power wires directly to the motor to bypass the pick-up of current from the track (sit the loco upside down in a suitable clamp and use your fingers or an eraser to apply a load). That way you can measure what the motor is consuming without any concerns that there might be poor connections at the pickups. Also, as the loco is stationary you will be able to observe what is happening. As others have said a lot depends on the meter you have. Cheap digital meters (i.e. the sort I can afford) react very slowly and are not suited to measuring short peaks of current or voltage. Analog meters are much quicker to respond. There is also a question of what current range the meter can deal with. Having soldered the wires in place I suggest you measure the resistance of the armature. You should expect a low but not zero resistance. Read the resistance while turning the armature very slowly by hand. The maximum (stall) current of a motor is given by ohms law V = R * I where V = volts, R is resistance measured in Ohms and I is the current measured in Amps. You may also be able to see, while measuring resistance, if there are any places where there is an open circuit. Is there a capacitor attached across the motor terminals? I would temporarily disconnect it and see what happens. I would expect the very high currents to be inrush currents after a brief open circuit - except that I wouldn't expect a digital meter to be fast enough detect that. If the high current is the stall current I can't envisage that happening without there being a very visible hesitation in the rotation of the armature. ...R Link to post Share on other sites More sharing options...
petertg Posted December 31, 2013 Author Share Posted December 31, 2013 I have to say that I am going away for a few days and then I have an impending flying visit to the UK for family reasons, whereby most probably I shall not be able to pay any further attention to this problem before the back end of next week at least. In any case, has anyone any comments on the top bearing I mentioned above? A Happy and Prosperous New Year to all. Link to post Share on other sites More sharing options...
Titan Posted December 31, 2013 Share Posted December 31, 2013 Just for comparison, I have a lego (yes I know) Horizon Express (TGV lookee likey). 2 motors (it needs it), six cars, 8mmish scale, high friction track with sharp curves etc. At full warp speed the combined current for both motors is 600mA at 7 volts. As said before the currents quoted in the OP are pretty much in the instant meltdown territory - if not ball of flames! Another thought is it a ringfield motor? If so has the neodymium magnet been magnetised correctly? If it has been wrongly magnetised during manufacture so that the magnetic field is not correctly aligned, then it might also give the symptoms you describe. Might be worth swapping the magnet for a known good one and see if it makes a difference. Link to post Share on other sites More sharing options...
Grovenor Posted December 31, 2013 Share Posted December 31, 2013 In any case, has anyone any comments on the top bearing I mentioned above? If you are unsure that the ball is in there, then best to check, and while you are at it adjust the bearings for minimal end float. However, the top bearing only comes into play when the direction is such that the armature tries to rise, ie forwards or reverse but NOT both, and you have already indicated that your problem occurs in either direction depending on the orientation of the magnet, hence it is not a mechanical/bearing problem, and since a magnet is essentially just a magnet, all that is left is an electrical problem, and the only electrical component is the armature/commutator assembly, so that is where you need to look. Keith Link to post Share on other sites More sharing options...
smokebox Posted December 31, 2013 Share Posted December 31, 2013 Is the OP certain he's interpreting the meter readings correctly? Many analogue meters are marked 10 20 30 40 etc meaning 1 2 3 4 amps etc depending on the range selected. If his readings are out by a factor of 10 they make more sense. Link to post Share on other sites More sharing options...
petertg Posted January 3, 2014 Author Share Posted January 3, 2014 Hi all! I got back home a day earlier than expected and also I shall not have to travel to the UK before Jan 12 at least, so possibly I can check all the points raised before I go. My multimeter is digital, so I don't think I am out by a factor of 10. By any chance is there any show in the Leeds-York area during that week? Regards. Link to post Share on other sites More sharing options...
leopardml2341 Posted January 3, 2014 Share Posted January 3, 2014 This is always a good place to look for shows etc:- http://www.ukmodelshops.co.uk/events No connection other than user of site. Link to post Share on other sites More sharing options...
leopardml2341 Posted January 16, 2014 Share Posted January 16, 2014 Any outcome yet? Link to post Share on other sites More sharing options...
petertg Posted January 17, 2014 Author Share Posted January 17, 2014 Not yet. I am currently in the UK and will not be back home until Sunday. The first week of the year was occupied with trying to find a flight appropriate to my needs, since there are no direct flights from BCN to Leeds at this time of the year and the following week was occupied with preparing for the trip, booking tickets, both flight and train from Manchester, This has been my first experience on British trains for many many years, A late night trip in a DMU to York. When I get back home, I will getr down seriously to the matter. Link to post Share on other sites More sharing options...
petertg Posted January 20, 2014 Author Share Posted January 20, 2014 Hi all! Back home now I have been able to do a test. I had previously requested informationon another thread on how to test consumption and Keith suggested that I should use Ohm's law to calculate the consumption. I have now done that and since I had tested the DC controller output at around 16.3 volts and the motor resistance gives a lowest reading of 8.7 ohms, the resulting division gives me a reading of 1.87 amps, which still seems rather high (I had to test the resistance with the pole pieces removed or otherwise I wouldn't have been able to get the tips of the meter in). I assume that the disparate readings quoted in my first post are due to the way I set up my test track and connected in the meter, although the different values found when running in one direction or the other are curious. Can this be taken as a definitive result, or is there still something wrong? Link to post Share on other sites More sharing options...
stewartingram Posted January 20, 2014 Share Posted January 20, 2014 If the pole pieces have been removed, that's a remag required then. (Expected loss of magnetism if the magnet is disturbed is 70%). Stewart Link to post Share on other sites More sharing options...
petertg Posted January 20, 2014 Author Share Posted January 20, 2014 My magnet is a neo magnet and from the force required to move and replace the pole pieces, it doesn't seem to have lost any magnetism. Link to post Share on other sites More sharing options...
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