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MG MGB Technical - Amp Guage & Charging??

Hi Guys,

On an early MGB with generator / dynamo, how much should the amp gauge show when the car is idling with no accesories on? Mine is always just slightly to the positive side, but enough that it is easily noticeable.

My old generator went out last week and I just replaced it with a newly rebuilt one. With the old generator, the needle was almost right always right in the middle and not noticeably to one side or the other. However, since I replaced it with the new one, it is always slightly to the charging side.

My concern is, I remember hearing that if your system is overcharging that it can ruin your battery and possibly damage your wiring. Is this consiered overcharging or is this normal?

Anyone have any insite to this?

Danny T.

The dynamo should not be charging at idle speed ( say 800 rpm) . The cut out should be working and the red ign light should be on dimly. Revving to 1000 rpm should see it go out .
I would expect your control box needs setting up . It's very easy to do using a voltmeter , I have the factory manual which is excelent and logical , but there may be an online version as well .
The MGB has a 3 coil regulator which includes overvoltage and overcurent protection .
S Best

An ammeter should be measuring the net inflow to or outflow from the battery, not how much the loads on the car are consuming. As such there will be a net outflow or discharge when the ignition is turned on or the engine is idling with the red light on or flickering. When running there will be a significant charge immediately after starting, or a period idling, dropping to very little charge as the battery become recharged. With the engine running only if the load increases above what the dynamo can supply - either because the loads are too high or the dynamo system is faulty, should the ammeter move into the discharge zone. One problem with the ammeter is that unless something is very wrong the needle is always quivering about the zero position, another is that all the charge and discharge current has to go via the ammeter, its long leads and connections, which are all fault liabilities. A voltmeter is a better indication of charge state, is less of a fault liability and safer. But neither tells you much more than a working warning light, and none of them will tell you if your car is going to start in the morning.
Paul Hunt

This thread was discussed on 29/10/2004

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