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MG TD TF 1500 - oscillating Ammeter

Finally was able to perform the first start on my TF today which went well once I fixed a timing problem. Unfortunately I am having a charging problem that I wonder if any of the EE's in the crowd might be able to help solve. The ammeter oscillates between about a volt negative and zero while the charging light remains lite at 1500 rpm. The car has a new old stock regulator and a rebuilt generator from AS. I suspect it is the NOS regulator, does anybody have any thoughts on the subject. Couldn't find a similar problem in the archieve.

Bob
R Brown

Hi Bob,

There's a very strong probability that the contacts in your NOS regulator have corroded whist it was on the shelf. You can clean them with a strip of fine emery paper. The dynamo is easy to test. Remoce the fan belt and the two wires at the rear of the unit and join the two terminals together. Take a wire from this junction and touch the live terminal of the battery. (this is the one that goes to the starter switch) If the dynamo is OK it will turn as an electric motor. Dynamos need a little residual magnetism for them to operate. Since it has been rebuilt it is just possible that it needs repolarising. Maybe the repair shop have set it up for negative earth and your car is positive, or vice versa. Running it as a motor will correct the polarisation but you may have to spin the pulley to get it started -BE CAREFULL If the dynamo motors and the contacts are clean and your wiring is OK the regulator is US.

Good luck


Jan T
J Targosz

Bob, have you ever noticed the flicking of the ammeter when the fuel pump ticks? Or, is your oscillation at a higher frequency than once every few seconds? Bud
Bud Krueger

Bud,
The Pump is a recent rebuild from Dave Dubois with the Solid state conversion.

bob
R Brown

Bob, I think the conversion just replaces the contact points with some electronic goodies. The coil still draws a good chunk of current when it pulses. Are your oscillations more rapid than once every few seconds? Bud
Bud Krueger

Bud,
The pulses are probably once every two seconds. What is your guess about whether the gen light is a sign I have a bad gen or bad regulator, assuming the pulsing is the pump. Funny I never noticed the pump pulsing on the TC.Plan to check the gen out according to Jan's suggestion tomorrow...

Bob
R Brown

Pulses most likely fuel pump as suspected. Do what the guys suggest above (clean points, test gen.), pointless to guess. Dirty points not bad, nor is un- or backwards polarized generator, just need to fix/adjust. George
George Butz

Bob, does the ammeter go up if you goose the throttle? How well charged is your battery? Does the ignition light go out if you goose it? Bud
Bud Krueger

After confirming that the generator will "motor" perform the checks in the WSM manual to ensure that it is outputting correctly. My WSM is up in the shop but it's something relatively easy about checking voltage from the big (or maybe small - I forget)_ wire to earth while slowly increasing engine rpms. Jud
J K Chapin

I have done a couple of things since the last post.
1. successfully ran dynamo as motor
2. swapped out the voltage regulator with an older one I had laying around the shop.No change, gen light still on.
3. Checked F to ground on dynamo 5 ohms
4. Checked voltage output of Dynamo, 23 v.

I guess my question now is whether having the wires reversed on the Amp meter will the gen light light and indicate no charge?? This to me does not some likely..

So still puzzled and appreciate any suggestions.

Bob


R Brown

Are you sure your old regulator is good? Did you try cleaning points on that one too (there are two sets of points usually)? I would think it has to be a wiring or regulator issue as you have proven the generator to be OK, presuming it was polarized correctly (and I'm not sure about this step). Reversed wires on the ammeter would just cause the gauge to move backwards, don't think would effect the light. George
George Butz

Bob - "Checked voltage output of Dynamo, 23 v"
Was that voltage the result of connecting the two terminal on the generator together? If so, would the voltage have continued to climb with the RPM of the engine, or did it stop at 23 volts? If it would continue going up as the engine speed increased, then the generator is good, but if it stops at 23 volts, then something is wrong with the generator. I had a similar with the generator in our TD and found that one of the insulators inside the generator had some carbon dust under it, which was acting as a limiting circuit so that the voltage never got above a set point. Cleaning things up, cured the problem.

"I think the conversion just replaces the contact points with some electronic goodies."
Bud is correct here. The coil still draws a set amount of current regardless of the triggering method. In the case of your pump, the current through the coil is 3.3 amps. Cheers - Dave

D W DuBois

Something to share:

I'm looking at a copy of "VOLTAGE REGULATOR 101" by the late Bob Jeffers, revised Feb. 2014. Bob's writing about development of the solid state regulator and is describing the pulse train for control. He says:
"... early versions running at about 130 pulses per second. Later versions will run at about 500 pulses per second....Even the early versions were fast enough to nearly eliminate the flicker in the ammeter by the fuel pump pulsing." Bud
Bud Krueger

took some additional measurements today and found the following

Battery 12.7v
A4 or brown leads at the fuse box was before start 12.7v and after start 12.2v
The white leads at fuse box was 12.2v after start
Checking D to ground after start was only 2v

Again did the the check with F and D on the generator connected and got 23v

I have to suspect the generator. I momentarily froze during the first start but then ran. Polarity could have been wrong initially and during the start something shorted internally...
R Brown

This thread was discussed between 09/11/2014 and 11/11/2014

MG TD TF 1500 index

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