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MG TD TF 1500 - Testing Dynamo

On page N4 of the shop manual section N2 where it describes how to test the dynamo on the vehicle. Under "to test on vehicle" statement (d) Connect the two terminals with a short length of wire. Certainly they don't mean to connect the two terminals "F" and "D" to EACH other do they.
Also in item (f) Clip the negative lead of a moving coil type voltmeter', I have a voltmeter but how do I know if it's a moving coil type?
Greg & Grimm
G.J. Cenzer

G & G - If you don't feel comfortable hooking the wires from D & F together, just disconnect the wires from the terminals on the generator's terminals and jumper the two terminals together. This accomplishes the same purpose. What the test is doing is to connect the field windings directly to the armature (or generator output) without the regulator in between them as it is normally run. The field poles have a small amount of residual magnatism in them when the generator is not running. This smal amount of magnatism is enough to give the generator a small output voltage when it starts turning. When this small output voltage if fead directly to the field coils, it reinforces the existing magnatism and cause the output voltage to increase. If the generator is good, positive feedback will cause the generator to continue to climb until something external (the regulator in normal operation) limits it. This is why the manual warns to insure that the voltage not be allowed to exceede 20 volts. As long as you heed the warnig to not allow the voltage to climb above 20 volts (by keeping the reves down to the point that the voltage rises quickly) nothing will be harmed. Keep in mind that above 20 volts, the voltage of the generator will rise VERY rapidly with further increase in revs.

The manual calls for a moving coil voltmeter because it has the best response to follow the rise in voltage. Other types of voltmeters have more damping and they cannot follow fast changing voltages. A moving coil voltmeter is just the D'Arsnoval (sp?) type meter movement found in the majority of analog voltmetrers or the more popular multimeter. Digital voltmeters did not exist when this procedure was written, or the procedure would probably warned against using them also. Most digital meter do not show the smooth rise of the voltage the way that a analog meter does.

This is a very good test to check out the generator, in that it removes everything external that could cause any problems, but leves everything in place int he car, making it a relative simple test.
Good luck - Dave
David DuBois

David,
I guess what I don't understand is ,if I jumper between the two terminals, where do I hook up the volt meter. Greg & Grimm
G.J. Cenzer

G & G - The voltmeter is hooked up with the negative lead to either of the two terminals jumpered together and the positive lead to ground (unless your car has been converted to negative ground, in which case just reverse the conections). Good luck - Dave
David DuBois

Dave,
Thanks for the help. Yes my car is converted to negative ground. I do not have a moving coil voltmeter, what I do have is an ACTRON III Diagnostic Analyzer Model 628. I have used this in the past on Rover 3500S (P6B) to check Tachometer reading, dwell and points, however I never did any volt checking with it as Rover had an alternator. In their intructions they say to hook red clip to pos. on bat. and black clip to neg. on bat.. Then set the amps-other tests switch tp volts. Start engine allow to run a few mins. then observe the reading on the 0-16 volt scale. Pointer should be between 13.8 and 15.2 at 1500/2000 RPM. So tomorow I'm going to try that and see what I get. Greg & Grimm
G.J. Cenzer

Well that meter didn't do any thing good. It read 13 volts as soon as I connected it to the battery and never changed whilst I ran the engine. With the engine running my amp gauge wiggles towards the + sign and when I turn on the headlights with out increasing RPM the needle goes way over to the + side which tells me that the AMP gauge is installed backwards for a NEG. GRD.
I guess I better remove the Generator, clean it up, check the commutator, check the brushes, reassemble and then do the big test as you described David.
Greg & Grimm
G.J. Cenzer

Have you flashed the field . It may be as simple as taking a small jumper wire, attach it to the positive terminal of the battery and quickly touching it to the field terminal on the generator. (small yellow with green tracer)Then connect the two wires together asnd do your generator check. The terminals on the Amp. gauge can wait til later. They have zero effect on the charging aspect.
Sandy
conrad sanders

G & G - Use your diagnostic as described for the battery, only substitute the two jumpered generator terminals for the positive post of the battery and ground as the negative post of the battery and run the test as described in the shop manual. The amp meter was probably never reversed when the polarity of the car was changed, so no would be a good time to do it while doing the work on the generator. Just be sure to disconnect the battery when you swap the leads on the amp meter - you wouldn't want to do any unintentional welding in the processo f changing leads. If you are not getting any voltage at all from the generator, or if it is the wrong polarity, then flashing the generator field windings, as Conrad suggests would be in order. Good luck - Dave
David DuBois

OK I took generator to place that fixed my starter on my Rover 3500S a few yrs back. They tested it for free and he guarenteed my it is in fine oreder and output is proper polarity and at proper levels.
I revesed the amp wires and rewired the selinoid (been fitted with American car type sol) and push/pull starter switch. Car starts fine and runs fine IGN light goes out now but AMP never shows + only shows -.
Gen guy says it's probably regulator. I cleaned points with 1500 emery paper but still no luck. Geg & Grimm
G.J. Cenzer

Sounds like the generator shop understands Lucas and British. Why not take the car to the, with shop manual? Most of those auto electric shops diagnose stuff like this.
George Butz

Well is what I did was to install a new (from LBCC) regulator. Now evrything related to running and charging is working fine. IGN warning light goes out at about 1500 RPM and amp gauge shows slight charge at idle and bumps up to a good charge with headlights on at about 2000 RPM. @ problems left, 1 turn signals don't work, and 2 brake lights don't work. Gonna install a kill switch for fuel pump (like I used to do in old days for theft protection) and then go thru and see where I getting/not getting juice for brake lights turn signals. Hopefull I can figure it out.
Greg & Grimm
G.J. Cenzer

G & G your brake light and turn signal problem are probably going to be related since the brake light circuit goes through the turn signal relay. It is all laid out rather clearly in the shop manual, but if you need help getting through the print, send me an e-mail and I'll try to walk you through it. Good luck,
Dave
David DuBois

This thread was discussed between 07/05/2004 and 13/05/2004

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