antarmike Posted January 18, 2010 Share Posted January 18, 2010 (edited) I am starting to think about a problem. On my way home with the Douglas, my lights started to fail. The vehicle still has a dynamo and has always charged without fault. My wife met me with a spare pair of batteries and I made it home in the dark, but with the lights almost gone again when I arrived home. I have only had the briefest of looks.. sS per common practice the control box has a rotary isolator, and a seperate switch that needs to be thrown before the starter button is pressed. Opening this switch, engine not running, an indicator light should come on. When started, and on tickover the light should stay on, and dim to nothing as the engine is revved to indicate the system is charging. I found that with engine stopped the charging light comes on. when the engine is started it stays on, if you rev the engine very slightly the light goes out, but if you continue to increase revs the charging light comes back on. Were do we think the problem lies if the generator kicks in charging when revved gently, but charging stops at anything more than a few extra revs? Edited January 18, 2010 by antarmike Quote Link to comment Share on other sites More sharing options...
Tony B Posted January 18, 2010 Share Posted January 18, 2010 Could be the bearings have collapsed. So that when you add revs the the commutator is slipping. Quote Link to comment Share on other sites More sharing options...
Rick W Posted January 18, 2010 Share Posted January 18, 2010 Not familiar with your system Mike, but possible bad earth? Quote Link to comment Share on other sites More sharing options...
Grasshopper Posted January 18, 2010 Share Posted January 18, 2010 Had a similar problem with a CVRT (alternator) and found that the cause to be excessive dust on the slip rings. A quick clean out solved it. I know the Douglas has a dynamo, but the problem could be hopefully be a simple one. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 18, 2010 Author Share Posted January 18, 2010 I suspect the regulator. It is still the original but I can't remeber if it is a 2 coil or 3 coil regulator. The simplest explanation for not charging is the main fuse has gone, but then the light would not go t at fast tick-over. so its not that. The cut out that is supposed to isolate the field windings at rest may not be working and this may be falling open, but I can't think of a reason why, or the Regulator is not sending the approriate current to the field windings ( may favoured idea of what is happening. Dirty contacts, burned out resistor, dunno at this stage. I can check the output of the dynamo with in in place, or I could feed my own field voltage into the generator, and see if the output current increases with increaded field winding P.D. But not tonight! Just thinking at the moment. You can't keep everything original on a (nearly 60 year old vehicle, so it may be time to put a modern control box onto the generator. Last time I was inside the electrical box I decided to do away with the mercury switch that was designed to sense braking, and complete the stop light circuit. I just couldn't get it reliable enough, so I put an air pressure switch in circuit in place of the mercury switch. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 18, 2010 Author Share Posted January 18, 2010 (edited) Yes had a quick look the problem lies somewhere with the cut out coil. If I have the engine running at above cut-in speed, there is little output from the Genny. (residual magnetism excitation) but if I manually press up the armature on the cut out coil, the headlights brighten appreciably, and the chargeing light fully extinguishes immediately. If you keep the engine running fast it continues to charge. Let the revs die right back and the cut out coil drops out as it is supposed to, but rev again and it won't cut back in, (unless you push it) I guess the Dynamo is ok and I have to sort (or replace ) the cut out coil. Simms Control Panel Type FR 49/3 24 Volt 40 Amp 100-200 Amp Hour, Comp Voltage Pos Reg to suit Dynamo 724 DH. Any ideas folks? Edited January 18, 2010 by antarmike Quote Link to comment Share on other sites More sharing options...
Tony B Posted January 18, 2010 Share Posted January 18, 2010 What is the gap between the arm and the coil? If as you say it stays in when pushed, I'd wonder if the gap has opened so that the magnetic effect wont pull it in again?. May just be dirt build up? Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 19, 2010 Author Share Posted January 19, 2010 (edited) What is the gap between the arm and the coil? If as you say it stays in when pushed, I'd wonder if the gap has opened so that the magnetic effect wont pull it in again?. May just be dirt build up? If has to be something like that. There are two windings on the solenoid. One seems to be sensing voltage, the other current? I havenot readup or tried to figure it out yet. I wonder if one coil has gone open circuit, and the other is able to maintain the magnetic feild sufficiently to keep the armature in, but not able to produce a strong enough field to pull it in. Edited January 19, 2010 by antarmike Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 20, 2010 Author Share Posted January 20, 2010 What is the gap between the arm and the coil? If as you say it stays in when pushed, I'd wonder if the gap has opened so that the magnetic effect wont pull it in again?. May just be dirt build up? You have to push the armature almost all the way up, until the airgap is far less than it should be. Because there are five contacts on the star, one may actually touch before the coil pulls in. I am just starting to wonder if the Genny has lost residual magnetism, and isn't producing enough voltage (25 volt) to make the cut out contacts close. Once they are closed the field windings are powered up and everything is fine. I wonder if "flashing" the field winding to restore the residual magnetism, might solve the problem. If I am going to try flashing the field windings, does my memory tell me correctly to flash the field with a voltage of the same polarity as the field windings are excited when the cut in closes? Thoughts please? Quote Link to comment Share on other sites More sharing options...
philb Posted January 20, 2010 Share Posted January 20, 2010 Mike, it sounds like the cut-out voltage coil (that brings it in) has gone and once you force the contact to close the forward charging current is enough to hold it in - it's the reverse current through that coil that kicks it out when the dynamo slows down. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 20, 2010 Author Share Posted January 20, 2010 Mike, it sounds like the cut-out voltage coil (that brings it in) has gone and once you force the contact to close the forward charging current is enough to hold it in - it's the reverse current through that coil that kicks it out when the dynamo slows down. I don't want to hear I have an O.C. coil!! I wan't an easy fix! If the Coil has gone, does anyone know a likely source of a replacement, or is it a case of modern regulator box, hidden somewhere out of sight? Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 20, 2010 Author Share Posted January 20, 2010 I can't find a good explanation as to how the cutout actually works. The idea that one of the two windings is to throw out the solenoid hadn't entered my thinking. Do you think it is out of the question to get the voltage coil rewound? It can't be that technical and is the best hope of keeping things almost original? Quote Link to comment Share on other sites More sharing options...
philb Posted January 20, 2010 Share Posted January 20, 2010 I would guess that you would be able to fix it. Get at the cut-out voltage coil terminals while the dynamo is running ( even slowly) to see if the dynamo output is being presented to the coil - it might not be. Either way track down the break in the circuit. I'd be surprised if was actually in the coil, they don't do much work and the innards are usually quite well protected from the elements. Re-winding the coil is more awkward than difficult, you probably have to remove the current winding first. As it's nice and old the connections might be screwed rather than welded - that should help. Is that more up-beat? Quote Link to comment Share on other sites More sharing options...
philb Posted January 20, 2010 Share Posted January 20, 2010 Mike, do you know what make/type of control gear you have, I might have details of it. Quote Link to comment Share on other sites More sharing options...
Tony B Posted January 21, 2010 Share Posted January 21, 2010 Dynamo NOT connected to anything. Flash from live side of battery to F terminal on dynamo. A forgotten black art. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 21, 2010 Author Share Posted January 21, 2010 Mike, do you know what make/type of control gear you have, I might have details of it. Simms Control Panel Type FR 49/3 24 Volt 40 Amp 100-200 Amp Hour, Comp Voltage Pos Reg to suit Dynamo 724 DH. It looks very much like the Cut out fitted to The AEC Matador and illustrated Maintnance manual 101/FW1B as illustration Q39, and drawn in section in Q40. When I get a bit more time i'll scan it in. Except it is slightly later with a back stop screw fitted into the back cross bar. Just found a cross section of one with Back stop screw in my Civilian "Matador" O853 Goods Chassis manual. I'll scan that tomorrow. Cheers That control gear is Simms type CP if that means anything. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 21, 2010 Author Share Posted January 21, 2010 Coil looks like this, can anyone help identify or locate a supplier? Quote Link to comment Share on other sites More sharing options...
Tony B Posted January 21, 2010 Share Posted January 21, 2010 What stae are the connecting pips on the end of teh arm? Might they just need a judicous rebuild? Drill out replace with small BA nut and bolt then file to fit. All the old tricks coming out! Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 21, 2010 Author Share Posted January 21, 2010 What stae are the connecting pips on the end of teh arm? Might they just need a judicous rebuild? Drill out replace with small BA nut and bolt then file to fit. All the old tricks coming out! Pips are silver plated and in good order. its the series winding that has prbably failed. When I get a chance I will pull off the fly leads and to a reststance test on this winding. I guess it wiill be O.C. Quote Link to comment Share on other sites More sharing options...
Tony B Posted January 21, 2010 Share Posted January 21, 2010 As you say not much hope of a rewind. Might be worth giving Charge and Start a ring. They are at Welling near Dartford. An old fashioned workshop very skilled at odd bits. If you could post. The number is 0208 301 3144 Quote Link to comment Share on other sites More sharing options...
philb Posted January 21, 2010 Share Posted January 21, 2010 Mike, I know it's not what you are asking for but - I have the circuit diagram, description, settings and maintenance instructions if you would like them. It's the SHUNT winding (the other end from the contacts) that pulls the armature in. It looks to me as though it would be quite easy to remove that solenoid and repair/rewind it. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 21, 2010 Author Share Posted January 21, 2010 Mike, I know it's not what you are asking for but - I have the circuit diagram, description, settings and maintenance instructions if you would like them. It's the SHUNT winding (the other end from the contacts) that pulls the armature in. It looks to me as though it would be quite easy to remove that solenoid and repair/rewind it. Yes I have mechanical and electrical setting instructions but I have no description of how it works, nor have I maintenace instructions. Would appreciate more info, Thanks Mike. Quote Link to comment Share on other sites More sharing options...
philb Posted January 21, 2010 Share Posted January 21, 2010 I've e-mailed the scanned text but I realise there is not much in the way of description. Going on from what I said yesterday: The dynamo output is always applied to the cut-out shunt winding. When the dynamo output gets to about 25V, the shunt winding pulls the armature in and the contact is made. The load current passes through the series winding. Charging/load current just pulls the armature harder. As the dynamo slows, its output drops below that of the battery and when the reverse current through the series winding reaches about 4A its effect cancels the shunt winding field and the armature is released. If the whole system has been designed correctly, which yours should be, the dynamo voltage at idle is far lower than ~24V and the cut-out works properly. I have come across installations where the dynamo voltage does not fall low enough at idle and the cut-out does not drop out. This can leave a discharge of a few amps through the dynamo all the time the engine is idling. The point of saying this is: make sure the cut-out does drop out properly if you re-build it. Quote Link to comment Share on other sites More sharing options...
antarmike Posted January 21, 2010 Author Share Posted January 21, 2010 I'll start by taking the leads of the dynamo, and check output with no field voltage applied to check (peace of mind) that there is enough residual magnetism to self excite. Then I will feed the field from a variable DC power supply to chack that I get a rising output from the genny. Next I will free one end of each coil and see what resistance reading I have, then I willhave a think! Quote Link to comment Share on other sites More sharing options...
radiomike7 Posted January 22, 2010 Share Posted January 22, 2010 Try Shorts of Swansea, they had all the bits to rebuild my '50s Constructor control box and claimed that it was quite modern for them. Quote Link to comment Share on other sites More sharing options...
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