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MG MGA - charging problems

This is a continuation of my starter problem.
Checked my starter and it's fine.
Next thing was to charge the battery and the car started fine.
The ignition light is now on indicating that the battery isn't charging.
Checked the voltage at the battery at 1500rpm and got a reading of 12.5V.
Linked the connections at the gen. and got 15.5-16V.
Checked voltage at starter switch with car running and showed 12.5V same as at battery.
Would this indicate that the voltage regulater isn't working properly. Is there a definative test for this.
Thanks
Kris Sorensen

This page has step by step instructions for checking the generator and regulator. http://www.vintagemg.com/ArticlePDFs/Tech103.pdf

Jeff Schultz

Kris...I didn't want to mention this before, not knowing more about the existing conditions...

I had a starter fail on me, which gave no indications of trouble earlier. Upon inspection, I discovered the charging system was fine and the starter spun when voltage was applied. What I didn't know was that it was failing RAPIDLY and had developed a ground through the field coil(s). It turned the motor over slowly, but just couldn't get her started. So out the starter came for inspection/disassembly.
I also noticed some burn-indicators at the rivets for the brush brackets on the rear casting, which allowed shorting past the insulation. So make sure there is no shorting going on before reinstalling the starter, unless you actually enjoy doing so. Mine would still spin when it was ruined, so "spinning" is NO indication that the starter is fine...just as "clicking" doesn't mean that a fuel pump will actually pump.
Jon Bachelor

Kris
My "A" wasn't charging. Did all the tests in the workshop manual as you appear to have done and so the dynamo was OK. I got onto Lucas and described what I had found, they thought it sounded like the regulator. I bit the bullet, got a new one, put it in and everything worked just fine. Good luck.
Peter
Pete Tipping

It's most likely the regulator.

But bewrae, even new ones need setup. I'd reset the cutout voltage on teh old one first before going to a replacement. See the manual for details of how to do this, or look at Barney Gaylord's site
dominic

I am going to try to take my car to an auto electric shop and get them to sort it out. Hate to buy something to find out it's not what's wrong.
Kris Sorensen

Sorry Kris...I really do need to read better. I see you got her started fine after charging the battery.
Your generator is sending a full charge but the regulator isn't giving it to the battery. This overworks the generator! It is the regulator...but why take it into a shop? It'll cost you double for no good reason.
It probably just needs a little cleaning and adjusting. C'mon Kris...dig in...it really isn't that bad. It's probably a little build-up between the contacts that needs clearing and a tiny (if at all) adjustment as Dominic wrote. The tech steps are clear and fairly simple, if you have a service manual that is...if you don't have a manual, you will save more than its price on your first diagnosis/repair. You and your A will be happier if you do it.
Jon Bachelor

Since we're on the subject of MGA voltage regulators I find it dissapointing that the contact points for the regulators seem to be unavailable as a separate part from our suppliers. If you need to replace a burnt set of regulator points (usually the result of a failed generator) they're happy to sell you a new reproduction voltage regulator. The original Lucas parts catalogs listed the regulator points with their own parts number. -M.S.
Martin Straka

Kris - if you link the 2 connection on the dynamo, it should put out 40-60v DC, if yours is only 15-16, then it is faulty, obviously disconnect the wires from the loom before carrying out this test. I have purchased an alternator that is built into the body of a dynamo, very trick but expensive! If anyone is interested, let me know and I will find out who the manufacturer is.
Terry Drinkwater

Terry - When running the test that you describe in your posting, you should keep the revs down such that the voltage doesn't go much over 20v DC or damage to the generator can result. Cheers - Dave
David DuBois

Kris
Yes you can do it!
Part of the thinking in replacing my regulator was the cost of auto electricians (who were all too busy to see me at the time) who would probably have charged 50 PSTG to fit it, plus the cost of a new regulator!
Here in UK the reg. was around 39 PSTG and dead easy to do, (which is free) and just needs a flat blade screwdriver. Just systematically change each set of wires under each terminal from one reg to the other. Then fix new reg in position. (2-fixing screws)
Don't think it took 30 minutes and it looks nice and new too! Satisfying too, when the lights brighten up as the old dynamo charges again AND you did the job!
Peter
Pete Tipping

Ok here we go again. I replaced the regulator with a used but untested one. The only change was that the ingition light now burns brighter. Still getting 14.5V from generator and 12.2V at the battery. Just picked up my MGB gen. from my 1800(that I havn't had a chance to install yet). I will put that in Sunday morning and see what happens.
Kris Sorensen

Kris...I don't understand why you are doing this. You can not simply exchange an untested regulator and expect to solve the problem. The untested one WOULD most likely NEED TO BE Cleaned and ADJUSTED too!! Do you understand that?
Hey...it's your time and labor...do what you want, but please acknowledge that you HAVE or HAVEN'T performed the cleaning and adjusting of the original regulator (which probably only needed the contacts cleaned using a points file or emery paper.
If you have the old one out(and haven't done so yet)...it's easier to clean and confirm/do the basic settings of the contacts. Put it back in and test/adjust. It really is that simple...
Jon Bachelor

Jon
I did clean the points on both regulators but was a little cautious about doing any adjustments quit yet. I still believe the voltage from the gen. should be above 14.5 before I go about adjusting the reg. Thought I would try a few different things first just to see what differences it made. I will see how it goes Sunday morning and report back.
Thanks
Kris
Kris Sorensen

Kris...throw caution to the wind! just kidding
Thanks for confirming you cleaned the contacts. Some people will just run out and buy new regulators and generators, so you are to be commended for sticking with this. If the generator is getting the 12v supply it needs...it should be putting out more than 14.5v running wild. You may get lucky with a simple cleaning of the generator's brushes and the contact surface, but you'll be removing the generator in any case. You might as well install that spare. The early MGB's (18G/GA/GB) generator should work and may well be your best bet to get going right now. You may want to perform the flash-bit for field polarity to match your setup.
Jon Bachelor

This thread was discussed between 26/10/2004 and 31/10/2004

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