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MG TD TF 1500 - 52 TD Battery Generator/Charging

I took my 52 TD out today for a drive since I had rebuilt the rear wheel cylinders. Brakes seem to be working fine. I did jump the battery w/ cables from another car to get it started - it was pretty dead after sitting the winter, and it started fine, and while driving the amp gauge was reading on the negative side the entire time. After returning home and trying to restart, it would not turn over, and seemed even more dead then when I first jumped it. I assume the battery could need a charge after sitting so long, but the amp gauge makes me think there might also be something else wrong w/ the charging system. Anyone have any experience w/ charging issues? Thanks Scott
RSC Scott Cleveland

Scott, I would eliminate the battery itself as being a problem first, it it has some age and was completely discharged.
A quick check would be to install a known good battery and see if the system is charging normally.

If your battery is less than 3 years old, you could remove it and fully charge on the bench overnight, and ideally check the cells with a hydrometer after charging.

Clean the post and battery cable connectors well, and try it.
Dallas Congleton

Scott, this has some of the symptoms of a polarity issue. Are you certain that the battery connections match the polarization of the generator? There are a few simple tests to determine how the generator is polarized. Are you comfortable using an analog voltmeter? Do you have one? If so, remove both wires from the back of the generator and then connect the 2 terminals on the generator together with a short piece of wire. Loosen/remove the fan belt. Connect the positive lead of your voltmeter to ground and the negative lead to the terminals on the back of the generator. Put the meter on a scale wher you can read a few volts. Spin the generator pulley clockwise by hand. If the needle goes upscale a bit your generator is polarized for positive ground. If the needle goes downscale it's polarized for negative ground. The battery should be connected accordingly. Sorry to be so verbose.
Bud Krueger

Does your car have positive ground, and did you jump it with a negative ground car? That might have reverst your generator polarity, causing the ampmeter to read backwards.
DL Rezin

As long as it was hooked up neg/neg and pos/pos it shouldn't have affected the polarity... Someone once mentioned that if stored for a long time unused, the system can go neg ground?
gordon lawson

It sounds like it's not charging. But a new battery is always a good start on the diagnosis.

Scott - Start out by checking the battery electrolyte level (if you have a no maintance battery, you will have to pry the rectangular covers up with a putty knife to gain access to the cells). if the level is below the top of the plates, then you may have a generator that is putting out the wrong polarity or the battery may be shot. If the level in the battery is good, proceed as Bud suggests, by disconnecting the leads from the generator terminals, short the terminals together and connect a meter between them and ground. You should use an analog meter for this test and and first test as Bud instructs. If the polarity is correct by this test, or if there is no indication on the meter, then set it to read 20 volts full scale (you may have to select the 50 volt scale if that is all the meter has to offer). connect the meter leads, negative to the shorted terminals of the generator, positive lead to ground. Start the engine and whilemonitoring the meter, slowly raise the RPMs. The meter should rise rather quickly to 20 volts and continue on up. Don't let it go beyond about 25 volts ou you will damage the generator as the voltage will rise from the 20 volt level very quickly as the RPMs increase. If you get a steadily rising voltage, then the genrator is good and the polarity is correct. The nxt step would be to put the battery on a charger and if you have one, substitute a known good battery and see how the charging circuit behaves with it in place. If Bob Jeffers is listening, he can tell you how to check the regulator for proper operation (he can also take your dead regulator is that turns out to be the case and turn it into a functioning solid state regulator in the original case, but you will never know that i is the original case because he shines it up to look like new). Good luck - Dave
David DuBois

Thanks for all the suggestions. I think I will start w/ checking the battery and generator. I bought the car last year and have only driven it twice, as I have been working on new floorboards, rear brakes and and rear shocks. It may have had this condition (Amp Gauge & Battery) all along and I am only noticing it now.
RSC Scott Cleveland

I am going through the same exercise this week. I already fried a digital multimeter but will try again with an analog one. My generator has been sitting for 40+ year and I believe it is depolarized. I have read that I can polarize it by shorting the negative lead to the D terminal. Is this correct for my positive ground car? I am also probably going to need to adjust my voltage regulator. Should I attempt this or replace it.
Russ Oakley

To RSC Scott and Russ Oakley --- To check out a regulator you will need a good ohmmeter preferably a digital unit but analog is OK. The relays will be reffered to as left hand or right hand when facing the terminal side of the regulator.The first check is measure from the heavy metal bracket that the relays mount on to the E terminal, should get 70 ohms. If you get about 140 ohms one of the voltage coils is open. By unsoldering the two insulated wires on the E terminal and measuring each to the bracket you can figure which voltage coil is open.If one of the coils is open you can stop right here the regulator is not repairable. Second measure from D to F. Should measure the same as shorting the test leads together.If it does not measure zero ohms, clean the contacts on the left hand relay. Second test is measure from D to F and press down on the left hand relay, should measure 63 ohms, if it is up to 75 ohms consider it OK. Third measure from D to A should measure infinite. Press down on the right relay then it should measure zero ohms, if not clean the contacts on the right hand relay.

It would be best if during all this cleaning of contacts etc. you do not change any air gaps. These are critical to the set up and operation of the regulator. Chances are that neither of you have the regulator pictured in the Workshop Manual and the clearances are different for the RB106. If you have an MGA manual you will have the correct air gaps.

If you wind up with a regulator that is not repairable contact me off the BBS. Good Luck, Bob
R. K. (Bob) Jeffers

Before you go to the expense of a new battery, give the old one a nice long slow charge (say 24 hrs) and see how it cranks the car. If it doesn't do that, then throw it away. I used to run a Citroen GS (magnificent car, gave it to my daughter, then to someone else who drove it across one of our northern deserts, and now someone else is driving it around!) and if I needed a battery I would go to the local scrap yard, there was ususally one there that had been discarded by someone who wrongly thought they had a dud battery, when really the problem was something else.
Regards, Rick.
R Payne

This thread was discussed between 21/05/2006 and 23/05/2006

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