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MG TD TF 1500 - Bad Generator

My battery has not been charging so I keep it on a battery maintainer. I decided to try to find out what the problem was. I checked the continuity on all the wiring, everything checked out. The voltage regulator was transistorized by Bob Jeffers. Reading instructions on a Lucas publication. I disconnected the wires from the back of the generator and put a volt meter between the "D" terminal and ground. At about 1,200 RPM, the numbers bounce very rapidly between 0 and about 17 but won't settle down. Does it need to be rebuilt? The stampings on the generator body are:

LUCAS
(peace symbol?) 22265E 2 59
C39PV2 DA 41 12V

Can anyone recommend anyone here in the states that I can send it to for rebuilding? Thank you.
Bob McLeod TD 5618

Bob - "At about 1,200 RPM, the numbers bounce very rapidly between 0 and about 17 but won't settle down."

A couple of things - firs, let me guess, the meter you are using is a digital multimeter - bad choice for looking at something like a generator, the sampling time of a digital meter is contributing to the erratic display. Second, the way to test a generator is to put a jumper wire between the F and D terminals together, use an analog multimeter (one of the cheap little meters from Lowe's or Home Depot will work fine). Attach the meter lead red to the generator (if car is negative ground) or black to the generator (if the car is positive ground) and the other lead to ground. Set the meter to 20 (or 50) volts, start the engine and slowly increase the RPM. If the generator is good, you should get a increasing voltage as the engine speeds up (don't let the voltage go over 20 - 50 volts). If you don't get that voltage, the generator needs attention. Cheers - Dave
DW DuBois

Thanks Dave. Dug out my old analog and jumpered the two terminals,,, nada. Found two shops in town that rebuild alternators and generators. I'll see if they can fix this one.
Bob McLeod TD 5618

Years ago I had the generator stop working. I try to fix everything myself.

Removing the cover strap from the rear, I found the brushes had worn down and one brush carrier had hung up and the brush was not even touching the commutator.
This was before alternators, when all cars had generators (except Leese Nevil in some police cars, with big Selenium rectifier stacks.)

I went to the local parts store and got a set of off-the-shelf brushes, stuck them and the generator is still running to this day.

Jim B.
JA Benjamin

There is a small outfit doing Lucas regulator conversions again. Digital solid-state. Apparently the guys doing these are long time t-typers. Send them a regulator and they replace the guts with the new, and you hook up wires as before, and cannot tell from the outside. $149, and they match it to your current generator setup.

http://www.vintagemecha-tronics.com/index.php

I have no interest in this venture, but was considering having it done at one time. To my knowledge nobody else is doing this. Anybody got one of these?
D mckellar

Bob. If you do find it is bad and don't want to rebuild it, I have a generator that I just picked up with a bunch of parts. PM me if interested
Bruce Cunha

Bob. Sorry. Email me if interested. cunhab52 at gmail.com
Bruce Cunha

Bruce, you have mail.

Bob
Bob McLeod TD 5618

Hi Bob,

You can test a dynamo by removing the fan belt, disconnecting the wires going to the two dynamo terminals, joining these together and then connecting these to the live terminal on the battery. If the dynamo is OK it will run as an electric motor. If it turns but doesn't spin smoothly the brushes are probably worn and the comultator dirty. Before you pay out for a reconditioned unit you could try striping it down, polishing the comultator, giving it a good clean and fitting new brushes. The best way of giving it a good clean is to use hot water and detergent. It will shift all the muck but will not soften insulation.

Jan T
J Targosz

Well, I took the generator apart and found that the wires connecting the bushes had broken. I replace them both and then tried Mr. Tagosz's suggestion. The generator ran like an electric motor. It is reinstalled and now I will try additional trouble shooting. Thanks all.
Bob McLeod TD 5618

Hi Bob,

Just one extra point which you may, or may not, be aware of. Dynamos need some residual magnetism in their field windings to initiate the charging process. Once current is being generated some of this passes through the field to reinforce this magnetism. The north/south orientation of this field is different for positive and negative earth vehicles. If when you tested your dynamo off the car you connected the case to the car's "Live" rather than "Earth" side of the battery you may have reversed the polarity of the field magnetism. It's easy to remedy this by either pressing the cut out contacts a few times or sparking a wire from the battery live to the large terminal on the dynamo. If their is no charge on the ammeter when the engine is running try pressing the cut out points in by hand. If the meter then shows a charge the regulator is probably at fault. If you need to buy a new dynamo or regulator consider fitting an alternator. I don't know about the States but direct replacements for the a dynamo are available in the UK for just over £100.

Jan T


J Targosz

This thread was discussed between 30/10/2016 and 03/11/2016

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