3 replies to this topic

[mylow2010]

Hi guys, im new to the forum but been checking out the forum for the last month. Your help will be very grateful.

Mini Sprite:
1995:
Okay I just got my 45amp alternator (brand new) replaced. Whats happing now is the battery is not charging. BUT when I take off the positive terminal - on the battery tester it says the alternator is charging fully 14v+ but when I connect the postive terminal back on the battery it does not charge. Could I need a new battery? :

[dklawson]

Are you saying that you disconnected the alternator from the battery by pulling the positive cable while the engine was running? If you did that... there is a very good chance that you have now damaged the alternator. Pulling cables off with the engine running is something that was done in the days of dynamos but it is a good way to damage the diodes built into an alternator.

Your voltage test method should be to connect a voltmeter across the terminals of the battery with the engine "off". Write down the voltage. Start the engine and repeat the voltage measurement across the battery (with both cables connected). You should see a 1 to 2 volt increase when the engine is running.

Something to keep in mind is that the charge warning light in your gauge cluster is more than just a warning light, it is part of the circuit. The warning lamp must be there and it must work. The red charge warning lamp must work as follows:
1) The lamp must be "off" when the engine is off and the key is out of the ignition.
2) The lamp must be "on" when the engine is off and the key is in the run position.
3) The lamp must be "off" when the engine is running.
If all three of these conditions are not true you have an issue to iron out.

Also keep in mind that batteries only have a finite life and varies according to what you buy (how much you spend). A battery can last anywhere from 2 to 6 years. If you battery is old or you doubt it, you may want to have a shop load test it.

[bmcecosse]

I agree! You must NEVER disconnect the leads to the battery when the engine is running - sure fire way to wreck the alternator, and a few other things too, since the volts can go sky high! It's likely a dud battery - beg/borrow/steal another one and try that.

[1977 Loud_Mini]

I have a 1977 mini and it has the starter solenoid mounted on the inner wing. One of the spade connectors wasn't a tight fit on the terminal and therefore the battery wasn't getting charged properly. If your mini is fitted with the solenoid in the same place then it might be worth checking.