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MG TD TF 1500 - Over Charge Ammeter

The first problem was a dead battery. New battery was installed. Auto store said the old one was ok. The next step was to remove the generator to be checked. The shop said the generator was working ok but recommended it be repaired because of worn bushing, work completed.
The five post regulator was replaced with a new one. Now comes the problem. When you run the RPM up to 2500 the ammeter in the car go to 30+. With old voltage regulator we get 0 amps. We put a Multi meter on the car at the regulator with an external shunt and get only 8 amps at 3000 rpm.
Removed the gauge installed a very old 2" gauge it seamed to work closer to the 8 amps.
Original gauge checked at ADT no problem found. They gave Jim a new gauge to take home and try. That gauge go to 30+ when installed Running at 2500 RPM.
The generator is Positive ground and putting out 16.5 volts.
Any Ideas would be great.
Thanks
Gary and Jim
Gary Krukoski

Hi Gary, the voltage regulator probably needs to be adjusted in the car with the engine running. I have always had this done by an auto electrician in the years before alternators were introduced.

Cheers,

Paul.
Paul van Gool

Gary - "The generator is Positive ground and putting out 16.5 volts." The generator will put out a voltage far in excess of 16.5 volts, it is the regulator that keep the voltage where it should be. 16.5 volts is an excessive voltage and is probably the reason you are seeing such a high charge indication on the ammeter. for modern batteries, the generator voltage should be limited to around 14.5 volts, which is a function of the regulator. The shop manual for the car has an adjustment procedure for the regulator, but it is quite involved and requires careful attention to all of the dtails. Perhaps Bob Jeffers will weigh in on this subjects with some of his expertise in the area of regulators (and correct any mistakes that I have made in my above explanation). Cheers - Dave
David DuBois

Does anyone have the specs on the Lucas generators? I thought them maxed out at about 15 amps or something? Maybe try a 3rd ammeter? At least the smoke hasn't leaked out yet. George
George Butz

To Gary K. Yes the first thing to do is reset the regulator to put out 14.5 to 14.6 volts( or have a shop reset it) Beware of the setup procedure in the shop manual it is for a 9 post regulator not the usual 5 post regulator. The relays are different and the air gaps have to be set just so or it won't function as it should. Also the voltage adjust procedure has you temporarily disconnect the battery from the charging circuit and then set it about 1 volt higher than it will run in the car with the battery reconnected.

There is no current limiter in the original regulators. So it is possible to burn up your battery and/or your generator because the regulator is letting the generator put out unlimited current.

You say you just bought a replacement regulator. If it doesn't say Lucas on the cover it was made who-knows-where. I get them about 15% of the time, they still look real good but don't work. I've never taken the trouble to see what fails. Maybe the next one I get I'll do that so I'll know what the weak spot is. The replacement regulators are close enough copies of the original Lucas regulators that conversion to solid-state with them is not a problem.

Hope this helps!!
Bob
R. K. (Bob) Jeffers

George Butz I have some of the specs, which ones are you interested in?
Bob
R. K. (Bob) Jeffers

TO All
Thanks for your help in solving this over charge. I believe the regulator came from Moss. I have two used Lucas regulators from MGA's that we will try next week. The MGA manual also has instructions on setting the regulator. Will they be the same as the 5 post T type Regulator?
Thanks
Gary
Gary Krukoski

Gary, an interesting article on generators and regulaors:

http://chicagolandmgclub.com/techtips/general/585.html

dave
Dave Braun

I too have been consulted on this particular car's maladies and have been stumped. I thought I knew a thing or two about TD electrics, but am starting to doubt myself.

Dave Dubois: I want to challenge your statement that the regulator putting out too high a voltage will cause excess charging current. Electricity 101 says that for any given load, an increased voltage will results in a REDUCED current. Besides, the apparent current surge comes on suddenly, not slowly increasing.

I agree that if the ammeter is not bad, that the problem would seem to be in the regulator (as the points close), but I can't fathom why. Especially as 3 different regulators have been tried, all with the exact same results. Current is drawn, not supplied. A short to ground would seem to be shown by an ammeter discharge, not an increase.

So what am I missing?

Cheers,
Lew Palmer
Lew Palmer

Lew P. I am afraid you just failed Electricity 101. I=E/R so if R stays the same and E rises then I must also rise.(lets hope you did better in algebra than electricity).

If the regulator is set too high then the charge current will also be too high and you stand a chance of burning out the generator.

Lew don't take my correction too hard I get all screwed up trying to troubleshoot positive ground systems. My brain is so used to voltage sources being plus that I just about have a heart attack every time I have to deal with positive ground.
Sincerely,
Bob
R. K. (Bob) Jeffers

In my books, if you even use E, I and R in an equation, own a voltmeter, or probe live sockets with anything other then a screwdriver...your magical electrical gurus!!!!!
I make sure all my bulbs are tight so the juice doesn't drain out and stain the carpet!!!!
gblawson - TD#27667

Bob, Regarding my specs question, I was just generally curious as to whether the generator could actually put out 30 amps under any circumstance. From the above posts I guess it could with the reg. set wrong. George
George Butz

George B. Yea 30 Amps is a bit much, but at 16.5 volts not impossible.

The TC generator was a C45YV and was rated at 13 Amps.
Early TD's Service P/N 22257 were rated at 17 Amps.
late TD & TF Service P/N 22268B were rated at 19 Amps.
Some late MGA's and Early MGB's had C40 cases and were rated 22 Amps.
Moss replacement generators are rated at 22 Amps according to Moss.

All the above generators will put out considerably more current than they are rated for. The problem is that when the under hood temp. is up and the system is drawing Max. current the armature gets too hot and the unit fails. Thats one of the jobs for the regulator that Lucas doesn't do, limit the current. With a change in wiring it would be possible to let the generator put out Max. current till the generator temperature got too high then cut back the current output to hold the temp. to some reasonable value. But this would require installing a temp. sensor in the generator, adding terminals to connect it. Then adding terminals to the regulator to connect the temp. sensor and the wiring between the generator and regulator. Sure would not be a stealth conversion.

I guess I've said enough.
Cheers,
Bob
R. K. (Bob) Jeffers

Bob Jeffers, you are absolutely correct. I don't know where I lost my memory, but it's here somewhere. <grin>

However in thinking about it, if I assume a constant load (DC resistance), to have the current jump from say 10 Amps charge that I might normally expect, to 30 Amps, would by Ohm's Law require triple the voltage. if E=IR and E=16 volts and I = 30 Amps then R must = 16/30 or roughly .5 Ohms. Then if we were to drop E to a more reasonable 14.5 volts and R remains at .5 Ohms, I would only drop to 29 Amps (14.5/.5 = 29). At .5 Ohms load, to drop the current to 10 Amps, we would have to drop the regulator output to 5 Volts (E=IR, thus 5 Volts = 10 Amps * .5 Ohms)

I simply don't see how the regulator adjustment can be the problem.

Cheers,
Lew Palmer
Lew Palmer

Gordon,

Make sure you separate the electrical juice from the oil in your drip tray, they do not mix too well!!

Gary, Lew,

Sounds like you have been round this loop quite a few times - worth double checking some basics - all the wiring is connected correctly + all earths are sound + ignition switch sound. Agree with Dave and Bob, most likely to be regulator adjustment, but sometimes folks pull the regulator when the root cause is a wiring fault.

Hope you get it sorted.
Graham
TD/C 7822
G.D. Smith

Lew P. Your algebra is absolutely correct. It's your starting assumtion that is the problem. The load does not stay constant. As you force more and more voltage across the battery it's resistance changes.

BTW if you maintain a 10 Amp charge rate you will soon cook the battery. In a properly operating system the ammeter should go to the max the generator is rated for right after the engine has been started. Then as the battery absorbs the charge it's terminal voltage will rise. The regulator should be holding a constant voltage from the generator so the current shown on the ammeter will decrease. With a healthy battery it will probably get down to 3-4 Amps. In fact that is one way an impending battery failure can be seen before it happens. The current will not decrease to a low value but will stay up high.(10 is high in my opinion). Now of course this drop off in charge current depends on the regulator holding the voltage to some reasonable value, say 14.3-14.6 volts. If the regulator allows the voltage to go to 16.5 the current will never come down to a reasonable value and the liquid in the battery(acid) will bubble away exposing the top of the plates to air. That destroys the plate area that has been exposed to air. Now we have a situation where the plates may short together and you will have a 5 cell battery. Then getting a reading of 30 Amps on the ammeter would be very possible.

I'll get down off my soapbox now!
Cheers,
Bob
R. K. (Bob) Jeffers

OK, I agree that there is no other possible explanation. Off to adjust the regulator we go...

Cheers,
Lew
Lew Palmer

All
The car is back on the road after a second session in the garage. The replacement non Lucas regulator was so far off the correct setting we did not use it. The regulator that was in the car from the start was adjusted to the correct value. After sorting through the manual the fix was fairly simple. Thank you to all that waded in on the problem.
Gary
Gary Krukoski

Gary K. Don't throw that replacement regulator away! It will convert to a solid-state regulator very well. Just put it on the shelf and when the need arises get it converted to solid-state.
Cheers,
Bob
R. K. (Bob) Jeffers

I have been trying to contact R. K. (Bob) Jeffers, New Hampshire, USA, bobj50@comcast.net to see if he can convert my TD voltage regulator to electronic but had had no luck. I sent my messagesto the address above but they are returned because his anti-spam program does not admit my message. HELP!

Thank you,

Stuart
Dr. Stuart J. Ramos

Dr. Ramos,
I'm terribly sorry you have been having a problem getting an email to me. I have just changed my whole security system. I hope it was the old system that rejected your messages. I will email you off the BBS and see if that will work.
Sincerely,
Bob
R. K. (Bob) Jeffers

This thread was discussed between 24/08/2007 and 30/08/2007

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