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MG MGB Technical - New battery - won't charge

Gentlemen,
My 1977 MGB seems to not be charging the battery. I put in a new battery (Sears Die-Hard WeatherHandler, CCA 465) last week thinking the previous battery had probably worn out after at least 7 years. After starting fine for a week, I noticed that the car hesitated, then started, just like it did when the old battery was low. I put the charger on it and it indicated the battery was "charging".
I took the car to AutoZone and had them check the battery and alternator. Both checked out OK. The battery had just been recharged. The alternator was rebuilt three years ago.
Four months ago all the connections at the starter were cleaned. The connections at the alternator are OK, as are the coil connections. The battery connections are clean and new.
I tightened the alternator belt a little, although it seemed tight already. It could be depressed almost a half inch, which is a little loose. Now it can be pushed in about a quarter inch. (That might have been causing the problem.)
When I drove in to the garage last night, the headlights shown bright on the wall. I turned off the engine, leaving the lights on, and they dimmed slightly, not a lot.
I don't think the problem is a lamp, or radio, that is being left on, because the problem doesn't seem to happen after the car has sat idle for a long time. It seems that when I drive the car the battery weakens.
Any ideas what could be causing the battery to not charge?
Regards,
Randy
1977 MGB
randy olson

Hi,
Have you taken a look at the starter solenoid?? May be in its final stages.

FWIW Alyn
Alyn

You might check for a continuous current drain in your electrical system. Out of 7 MGs I have owned over the years the only one that DIDN'T have some amount of current drain was my 1950 YA! That, along with the somewhat anemic output of the stock alternator, can result in a battery that never gets fully recharged during driving.

I see that you believe that this occurs during driving, not while setting. That would hint to me that something is pulling excessive current, or the alternator that checks out "OK" is actually not producing enough amps to keep the battery "full". I would get it checked for actual output. Good Luck and keep us informed.

Paul Briggs
Paul Briggs

Hi Randy.

I suggest you try starting the car with the headlights on, the headlamps should dim, but not too much. If they don't dim too much the problem is probably either with the starter motor as suggested by Alyn OR the engine-to-body ground strap.

A voltmeter on the dash can be helpful for this kind of prob, an ammeter is even better IMHO, but is more difficult to install properly.

Please keep us informed of your progress.. Don
Don

Randy. I recently had a similar problem and found the root cause of the problem to be the negative battery terminal cable. Over the years, the wires had corroded out internally and, when the starter was engaged, the voltage suppled to the starter was only five volts. I checked this by connecting a jumper wire to the main terminal of the starter, then ran it back so that I could measure the voltage while cranking. Voltage at the starter was five volts while voltage at the battery terminal was 12.5 volts. Hence, a problem with the cables or connections. In my case the negative terminal cable. I have also seen bad positive terminal cables (the one running from the battery directly to the starter).

Any battery will, initially, show a charge when connected to a battery charger. How long it continues to charge, at a higher rate, indicates how depleted the battery is.

A quick check for alternator operation (besides the dash light) is to simply measure the battery voltage, then start the engine and measure the alternator output at the battery terminal clamps. They should be showing 13.5 to 14.5 volts if the alternator is charging.

Les
Les Bengtson

I finally got a chance to work on the MGB and found that the alternator is charging...barely.
As suggested, I checked the battery poles with the car stopped, then with it running.
At 1500 RPM the battery poles read 12.9 V. It is the same at 800 RPM.
With the radio, heater, and headlights on, the reading is only 12.5 V. That's the same reading as the battery has when the engine is off.
So, it looks like the alternator is either not putting out enough power, or there are restrictions somewhere. Obviously another alternator, like Bosch, would help. Is there anything short of that I should check? In other words, what is the next step?
Thanks in advance.
Randy 1977 MGB
PS Is anyone going to the Watkins Glen Vintage Races this weekend?
randy olson

Hi Randy.

A Bosch alternator might help, but you have some other fault that needs sorting first unless the fault is in your existing alternator.

The fact that the car started properly while the new battery still had a healthy level of charge suggests that the battery earth strap, engine earth strap, and battery to starter motor cable are all ok.

The battery voltage with the engine running briskly but without the lights, etc, should be more like 13.5V after a few minutes of running to get some charge into it.

Does your ignition warning light come on as usual before you attempt to start the engine ?.
Is the alternator body actually connected to the engine block through the mounts, as it needs to be ?.
Does the fanbelt squeal, indicating that it is slipping ?.
Have you connected a battery charger to the battery without disconnecting the battery first, this may have damaged the alternator ?. (trickle chargers are ok).

Don
Don

Randy. As Don points out, there may be some other problems involved. However, the only one that will give you the exact problem you describe is a bad alternator. My experience is that while a new alternator will last 20+ years, a rebuilt unit lasts 3-5 years max. I have been able to document this over a period of several years on several cars.

As to various brands of alternators, I have always had good luck with Lucas, so I am still running them on my car. Others have used the Bosch and Delco with good success and a few people are using an alternator off one of the Saturn models. Hence, there are a variety of available replacements. Pick one and replace your existing alternator with one that works. If that solves your problem, fine. If not, you will be troubleshooting a system with a working alternator rather than a non-working one which is part of your current problem.

Les
Les Bengtson

Hi all.

Les raises an important if alarming point about alternator reliability. A failed alternator is not only an expense, it is also a pain having to identify the fault, remove the old one, buy a new / exchange one, fit the new one, not to mention the inconvenience of a car that won't start.
Maybe the battery got 'cooked' too if the alternator's regulator failed in then 'wrong' way, as it did in my only personal experience to date of alternator failure.

In my experience in the UK a refurbished alternator would be cleaned and all parts liable to wear (brushes, bearings, etc) would be checked and replaced or repaired if necessary, as well as the original fault being sorted, and an exchange unit would usually last well.

Was / is this true in the US, is it still true in the UK ?, are we getting exchange units that only have the fault fixed and are not thoroughly refurbished, are they being repaired with inferior parts.. ?

Experiences please... Don
Don

Don. I had one alternator rebuilt at a local rebuilder. A Lucas 16AC for my 68GT. It lasted about a year, then started only putting out 17 amps under load. Paul Hunt gave me directions on how to convert to an 18ACR which I installed and rewired the harness to use. It was an AutoLite rebuild with lifetime warranty. It has been replaced, at about the three year point, and the current alternator is still working.

Replaced the alternator on daughter's 77 and my 79 within the last five years. Both have had to be replaced under warranty since.

There are only two or three major rebuilders here in the US with various companies purchasing their product and using the purchasing companies boxes. Thus, you do not know the original rebuilder and cannot decide if one is doing a better job than another. I have had diode pack failures, bearing failures and one bent main shaft. I have had alternators bad from the rebuild shop.

I suspect that the ability to purchase cheap and sell "at a discount" affect how well the original alternator is inspected and what parts need to be replaced. I also suspect that things like diode packs are being purchased from the lower end of the quality range, thus not lasting as well as a better quality semi-conductor would. Hard to say how long one of these would last for the "average" individual, however. Our cars are daily drivers in a very hot area of the country. Both of which may tend to shorten the use life.

Les
Les Bengtson

Hi Les.

Thanks for the deatils. It is certainly true that semiconductors don't like heat, and the underbonnet temp gets quite high here in the UK, so is probably VERY hot in your part of the world.

I am planning to make a hole in the RH inner wing, roughly where the V8 exhaust usually exits, as it seems that there is a low pressure area under the wing which will hopefully draw a bit more airflow through the underbonnet area.

Don
Don

Don. If you are capable of documenting your experiments, my website is available to post the results. For those if us who live in Arizona, and much of the American Southwest, 100 deg F by 10 Ack Emma, is not unusual during the summer. Thus, if you can document a method of reducing the underhood temperatures, I will be more than happy to post your results.

Les
Les Bengtson

Just replace the dang thing already with a new unit! Alternators USED to cost more relatively, but it's somewhat beyond me why anyone faffs about with dodgy recores and refurbishments when a new, reliable unit can be had cheaply.

Go for a new Bosch Saturn (if you're fortunate enough to live in the US), BXF1255A, or the Ford Fiesta unit (marketed in NZ as the replacement for the 16ACR) and be done with it.
Curtis Walker

I have spent the last two days in Watkins Glen at the Vintage Races, and the MGB has been running well. Not racing, of course! Yesterday I started and stopped it a lot without any problem while getting to various viewpoints to watch the racing at the track.
It may not be an alternator problem that was keeping the battery from being charged. I'm thinking now that the battery post clamp/cable connection may have caused the trouble. I tightened the bolts that clamp the end-of-the-cable connector to the positive battery cable a few days ago, and ever since it's been starting fine. This connector had been replace a couple of years ago when the original was found to be badly corroded.
For now, I'm going to watch and see what happens.
Thanks for all the ideas.
Randy
randy olson

This thread was discussed between 04/09/2005 and 11/09/2005

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