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MG TD TF 1500 - Charging... then *not* charging...

Had been keeping a little suspicious eye on the ammeter last couple of weekends... Was on the highway approx 4000RPM when suddenly the reading went to zero.

I turned on the headlights (was bright daytime in sunshine) to create some current drain. Reading went negative.

Touched the pedal to tickle the brake lights, current became even more negative.

So no charging at all, all the way. Ended 10 mins later at a set of lights, engine back at idle. Blipped, and the charging came back on - needle only goes as far as max +10 for a while before it plops back to zero. (Later on the battery tested at 12.5V with no load.)


Is this just "normal" operation of the voltage regulator?

Or is something amiss... time to check out the generator? New battery?
Will

Hi Will,

Sounds like an intermittent problem. I would dismantle and clean the generator and check the brushes.

The genny should act exactly as you describe after the stop at the lights. The genny at that stage was putting back what was used previously. 10 amps is right until the battery was full again then it goes back to near zero.

You do not say whether the red ignition light was on when you thought it was not charging. This is another indicator.

Cheers,

Paul.
Paul van Gool

Thanks Paul - no, the red light didn't come on at all.

Think I've done more MG miles (~650) this year alone than in my last 25 years... guess its first time I've ever seen the regulator kick-in!! :-)

Might find a handy spot in the wiring to keep my multimeter plugged in next time... to try work out which point the regulator starts charging again.

Or did the PO leave me a hint by throwing in a whole brandnew regulator wrapped in wax paper??? 8-)
Will

Hi Will,

If you pull the cover off the regulator and idle and then rev the engine you can easily see the points open and close, in fact watch how the whole thing works.

At idle, the points should be open and then as you slowly rev the engine they should close around maybe 1000 rpm. At this stage the genny will not be charging much, but as the revs increase it will start charging.

Back to idle, if you can get it to idle slowly enough, the points should slowly open again, and the red ignition light should come on as well.

Cheers,

Paul.
Paul van Gool

Thanks Paul... might try that sometime, just need to work out the logistics. Carbies on 1 side, blackbox on the other - might have to take the bonnet off!!

Or I could drag in a helper on the go-pedal... but that would be too easy. :-)
Will

You could try cleaning the points of the regulator with some very fine emery or polishing cloth.
Henry


Just send instructions on how to test and set the Lucas voltage regulator to Ron Zander but may be of use to others.

If anyone wants them send an e-m to my personal address and I will send you an attachment


Jan T
Jan Targosz

Had this problem with my recently purchased second TD. The PO had installed a new battery negative ground (backward)and then discovered and corrected his error. This left the generator fields polarized backward. It would still charge but at a max of 10 amps and drop to zero under load (headlamps). Flashing the field coils (see elsewhere on BBS) solved the problem. Now it behaves as did my earlier TD back in the 50's.

Regards,

Jim H.
Jim Haskins

Will, I had a similar thing happen on a few occasions and the first time I took my generator apart and had the armature checked-afterall, I had just replaced it with a rebuilt (armature). It checked out okay-and this check needs to be done by a generator specialist with a "growler"; a mysterious beast that somehow checks the resistance, etc. What I have found is that on a long run the battery voltage slowly climbs to about 13.5 volts and the high limit on the regulator (I believe that you would call it the control box) shuts down and won't kick back in unless you shut down and restart after that "glow" in the battery dies off to a more normal voltage, say 12.8 volts! The way I determined this is, after trying to turn the ignition on and off a few times with no charge, I switched to another battery and it fired right up! You can raise the high limit if you think that it would help-You might find that your is set too low. Good Luck
Steve Tobias

Steve:

Your voltage regulator is set to low.

Battery voltage with the engine off will always be 12.65 volts (new battery) or slightly less.

With the engine running at 2000 RPM or above, the voltage should be set to about 14.5 volts. Connect a VOM meter between the D terminal of the dynamo and ground. Speed up the engine until the meter needle flickers and settles down at one reading. It should read between 14 and 15 volts. If it doesn't then adjust the control box as given in the shop manual.

Blake
Blake J.

This thread was discussed between 22/10/2002 and 29/10/2002

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