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Alternator is HOT!

Posted by thommy2000

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Alternator is HOT! #1
thommy2000 Thom Tuttle Iowa, USA 1977 MG MGB "LIL TEES"	Posted: August 03, 2012 05:09AM Registered: 3 years ago Posts: 6

I replaced the alternator on my 77 MGB and the next day the battery was dead. I checked everything from the battery up to the engine compartment and when I touched the alternator it was super hot. I have since then taken the battery out while I check to see what's up. I made sure the ground strap was in good shape and ensured that the 3 prong plug was not damaged. Is there anything else I should look at to make sure the sucker doesn't melt?

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Re: Alternator is HOT! #2
hunter1951 Dwight Hunter Anchorage, Alaska, USA	Posted: August 03, 2012 08:11AM Registered: 7 years ago Posts: 1,102

Well, if you have the old ALT. I would hook it back up and see if that cures the issue, there may be some kind of a low grade short in the new ALT.

Dwight

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Re: Alternator is HOT! #3
ingoldsb Terry Ingoldsby Calgary, Alberta, Canada 1971 MG MGB	Posted: August 03, 2012 10:16AM Registered: 9 years ago Posts: 9,764

The fact that the battery is dead seems to indicate that current is flowing through the alternator when the car is off. I would suspect a bad rectifier pack.

Does the ignition warning lamp behave normally? I.e., Off when key is off. On when key is in ignition position (but engine off). Continues to glow when engine is started until about 1000 RPM and then goes completely, 100% off (check in the dark). Most alternator faults cause some misbehaviour in the warning lamp.

Terry Ingoldsby
terry.ingoldsby@DCExperts.com

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Re: Alternator is HOT! #4
gclifft Greg Clifft Dardenne Prairie, MO, USA 1974 MG MGB	Posted: August 03, 2012 08:20PM Registered: 10 months ago Posts: 81

x2 on checking the lamp. While it may seem like just a lamp, that lamp circuit is needed to energize the alternator's field windings. This is really essential on new alternators that don't have any residual magnetism.

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Re: Alternator is HOT! #5
ClayJ Clay Johnston Mt. Olive, MS, USA 1972 MG MGB	Posted: August 03, 2012 09:21PM Registered: 7 years ago Posts: 7,364

Its always amazed me how much information can be gained from one warning lamp; if you pay attention.

I would also have the battery tested. What caused it to need charging?

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Re: Alternator is HOT! #6
pinkyponk Adrian Page Nova Scotia Canada, Canada 1971 MG MGB GT 1973 MG MGB MkIII	Posted: August 03, 2012 09:35PM Registered: 2 years ago Posts: 2,737

It would seem that your alternator is shorted to ground and the windings are acting as heating coils. What was wrong with the old alternator?

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