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MG TD TF 1500 - charging light on

Gents
We took the TF out on a pleasure drive this morning. About 60 miles. It was hot, maybe 90 degrees. Toward the end of the drive, the charging light came on and stayed on. The dynamo was not hot. Everything worked and the car ran fine. The ammeter was just slightly to the negative of the zero point. I let the car cool down in the garage and just now started her again. Same thing, light stays on.
The dynamo was rebuilt not too long ago. Wiring all looks good. No blown fuses.
What do you think happened?? I'm not sure what to check on next. Any ideas??

Tom
'54 TF
Tom Norby

tom, i assume your fan belt is in fine order. do you have a volt meter? if so what is thew voltage at the battery prior to starting and what does it read after start?
all the sharp "sparks" guys will chime in soon. regards, tom
tom peterson

Thanks Tom P.
Yes, belt is intact and fine. A nice German made cogged one.
Voltage BEFORE start was 12.6v. Voltage AFTER start 12.4v.
Could something happen to the voltage regularor on a hot day??

Tom
'54 TF
Tom Norby

Check the brushes in your dynamo...make sure they're touching the commutator. If they are then measure the voltage from the dynamo to the regulator. It should read around 14 volts when you rev the engine if I'm not mistaken. If that is all good then your regulator needs adjustment...it sounds like you're running strictly on your battery right now.
Gene Gillam

Thank you Gene
Is it possible to see the brushes contact well enough looking through the end openings? What I mean is, without taking the entire unit out of the car??

Tom
'54 TF
Tom Norby

No, can't see much through that rear opening. I'll have to take the dynamo off after work tomorrow. The commutator looks tarnished and dark. Shouldn't it look shiny and copper-ish??

Tom
'54 TF
Tom Norby

The commutator will look tarnished if it has had much use. As long as it all looks the same colour you are probably OK. If any segment is a different colour then you may have trouble.

Run a business card through the points of the regulator relay. If that doesn't fix it run the card through the cutout contacts. If that doesn't fix it measure the resistance from the "D" to "E" terminals.(wires off). Should be about 70 ohms. If it is twice that, one of the voltage coils has opened up.

Is it an original Lucas or a repro?
Cheers,
Bob
Bob Jeffers

Thanks Bob
I went out this AM and did what you suggested with a card, no change. I'll have to wait until after work to measure the resistance between D and E. I would use the "ohms" setting on my multimeter,correct?
It is a Lucas unit.
Because this happened so suddenly and my dynamo was rebulit at the time of the engine rebuild in '03, I suspect the regulator.
Can I adjust the regulator?

Tom
'54 TF
Tom Norby

Tom,

You can adjust your regulator BUT if you can hold off driving your car for a week or two why not send it to Bob to have an electronic regulator put in place of the mechanical monster. It's impossible to tell from the outside that there's been a change but it's one less mechanical object to go wrong on your car.

http://www.wiltonae.com/articles_reviews/article_GettingAChargeOutOfIt/index.aspx
Gene Gillam

Only time this happened to me was when a brush spring broke.
George Butz

George;
This evening I plan to remove the dynamo from the car and peek inside. In looking it over, I saw that the front lower attachment bolt is missing anyway. The front is hanging on only by the adjuster bar. Maybe the belt is slipping because of this.
I'll keep you'all posted.

Tom
'54 TF
Tom Norby

Tom, I would be willing to bet that the cut-out contacts on your cut out relay are not closing when you start up the engine. It is easily to observe whether they are working are not by removing the control box cover to see if they close or not when you start your engine and slowly raise the speed slightly.
See image. Cheers Phil

Phil Atrill

Thanks for the kind words Gene. Every little bit helps.

Just got a glut of regulators in for conversion. So I'll not have as quick turnaround times as during the summer.

Have found a problem with recent positive ground conversions, if you have one, get it back to me.
Cheers,
Bob
Bob Jeffers

Hi Bob,

Not to hijack this but I have one of your positive ground conversions from last summer. Is it a recent problem or is it a general problem where I should send this back to you?

Thanks,

Dave
Dave Runnings

Hi Tom,

I had the same symptoms as you decribe a few weeks ago. The problem was as mentioned by Phil, that is the cut out contact was not closing. I determined by measuring the resistance across D and E that the coil operating this contact was open circuit. I've purchased a replacement regulator and all is now fine. Matt
Matt Davis

To Dave R. If your printed circuit board has surface mount components then you need to return it to me.
Also positive ground setup. Negative ground setup's are OK.
Sincerely,
Bob
Bob Jeffers

Mine is negative, Bob...
Gene Gillam

Thanks again gents
No need to take the dynamo off...it is the regulator. My TF has the 5 post unit. I have cleaned all the contacts with emory paper and sprayed them with electrical contact cleaner. When running, if I push on the contact nearest the D and E terminals, it sticks there and the light goes out. It looks like I could do a bit of artful bending of the arm. Do any of you have exerpience with the "quick fix"?
In the end I will probably get a new regulator, but would like to keep her running in the meantime.
If no response, I might just experiment a bit.

Tom
'54 TF
Tom Norby

For Bob,

I opened up the control box and I didn't see any surface mount so I guess I'm ok. I did take a photo of the nice work Bob does and it's attached for anyone who wants to see.

Dave

Dave Runnings

I had a similar situation a while back. It drove me crazy. I finally determined that the battery voltage was around 14.5 volts. I think that I had just charged it with a battery charger and the voltage was so high that it caused the regulator to cut out, leaving the light illuminated. I think that this normally happens at around 13.5 volts. After leaving the headlights on for a bit, with car not running, the voltage dropped below the cut-in voltage and everything returned to normal.
Steven Tobias

Gents
Here is the update on my charging system problems.
I took the dynamo out and took it in to my local "old school" auto electric shop. Turns out part of the commutator blew out and tore up the field coil. The unit is toast. The tech thought it occured because of a sudden failure of the regulator. My unit was a Lucas with a stamped date of 1985, so old.
He could not locate any good parts to poach to fix the dynamo, so I have a new one coming from Little British. They had the best price by far.
I also have a new regulator.

Before I put it all together, I'd like to hear from the group. Has anyone experienced a similar dynamo problem? I sure have not, in probably 50 cars in my lifetime.
Second post shows photo of the armature and the commutator end.

Tom
'54 TF

Tom Norby

Second photo showing armature.

Tom
'54 TF

Tom Norby

Hoo boy, that is disaster. Yes, a new dynamo is probably the best answer. But don't throw the old one away. Some person may want to rebuild that thing to have an "original" dynamo.

Replacement field coils are available if you look hard enough. So are armatures.

Now that Holcombe Armature Co. no longer supplies either field coils or armatures. The problem has become more difficult.

The best source I know of now is:-
Star Auto Electric Co.
207 W. Foothill Blvd,
Monrovia, CA.
Contact Mike Martinez

Sincerely,
Bob

Bob Jeffers

Bob, I will definately keep these old parts. Always do.
Thanks for the link to Star Auto.

Tom
'54 TF
Tom Norby

I will probably be installing the new dynamo and regulator tonight (if fedex is on schedule).
What are your thoughts on the theory of a random but sudden failure of the regulator?

Tom
'54 TF
Tom Norby

I have only been working with "T" series since 1958, so I can't comment on commutator failures. But I would suggest that they are rare. This is the first one that I have seen documented.

Let us know what you do to repair it.

I am sorry to report that the repro's made in India (or wherever) seem to only last about 6 mos. I get quite a few to convert to solid-state because they have failed. They are quite good repro's of the original relays in aperance but when I unwound one, the workmanship was very poor(INMHOP). Also the resistance from terminals "D" to "E" was not the same as in original regulators. (45 ohms vs. 70 ohms).
Bob Jeffers

My dynamo saga drags on as the summer driving season comes to an end. I have missed 3 weeks!
As you have seen in previous photos, my dynamo blew. Could not be repaired, as least not by anyone in Southern Oregon. I bought a new dynamo from Jeff at LBCars. Unit looked nice, just like original. Made in India. However, once installed, after 5 minutes of idling, the front bearing holder came apart. The front plate, inner bearing holder came lose from its rivets.
After some photo emailing to Jeff, the unit if back to him for replacement. Apparently the first such unitl to fail like this.
Hopefully in a week I will have the replacement installed and the car running.

Ray W, if you are reading this, I hope you can get your unit rebuilt. That would be much quicker than my journey with a new one has been.

Tom
'54 TF
Tom Norby

Gents;
Finally have the TF back on the road with a new dynamo. As you saw from the above posted pics, repairing my old one would have been very difficult (but I will save the parts). The repro is made in India, and looks very nice. It has a few extra amps at 22. The pulley and the tach drive fit on perfectly.

As it went, my regulator was fine, despite being 25 years old.
Jeff Z. at LBCar was a great help.

Unfortunately missed a great September of driving the MG. Autumn is coming on fast.

Thanks all.

Tom
'54 TF
Tom Norby

This thread was discussed between 29/08/2011 and 07/10/2011

MG TD TF 1500 index

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