Current alternator putting out 12.48 volts so thinking its time to rebuild or replace? Want to confirm if the existing alternator is original so wanted to see if anyone could tell me what to numbers etc. to look for to identify correctly?
1970 Swinger 340 - Alternator
- Thread starter 70GoMango340
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I tested it with a volt meter at the stud and grounded to the housing to to get the 12.48v reading, that would just be voltage from the battery which is fully charged? I use stock gauges. When I'm at idle or low rpm the gauge shows discharge and when I'm in it a little or cruising at 2,500 plus it shows charging.
At first start up, you have to run up the engine rpms to something like 1500 to 2000 rpms to "initially energize" the alternator, then it should charge normal from there when it goes back to idle.
If you don't rev it up some, it's not going to charge, even on a good system.
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If you don't rev it up some, it's not going to charge, even on a good system.
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Post some photos and also look at "Identifying Alternators" in the sticky section of this (electrical) forum.
What you are reading with a voltmeter lead on the output stud and the other other lead grounded is system voltage.
The battery at best can provide 12.8 Volts. When the engine is running the alternator provides power between 13.9 and 14.9 Volts.
The gage showing discharge is an ammeter. It shows whether electrons are flowing into or out of the battery. I know its marked 'Alternator' on the gage but only indirectly is it telling us about the alternator. Discharging while the engine is running indicates something is wrong with the alternator circuit or the alternator itself.
The fact that the ammeter moves to charge when the engine is at higher rpm tells us that in general the system is working. It's possible that a diode has failed or one or even two of the windings in the alternator is open. That's my guess at this point. We can track this down more precisely if you want. There is a slight chance the belt is slipping - so check that. Usually tehy squeal but not always.
The engine does not need to be at 1500 rpm to energize the alternator. That is false. In fact at 1250 engine rpm the alternator should be able to produce close to its 'rating'. That info is right in the service manual.
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One wire alternators do need to hit a minimum RPM to energize, but externally regulated ones energize any time the regulator has power.
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