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Posted by Chris Case [75.36.45.15] on Thursday, October 04, 2012 at 21:23:55 :
In Reply to: OT Delco alternator output posted by Sherman in Idaho [72.47.9.37] on Thursday, October 04, 2012 at 19:35:01 :
Alternators maintain voltage. Usual setting is 14.2v. They increase amps as a way to maintain volts. So, iv you want to know whether the output is adequate for the load, check volts at full load. The yae or nay would be that 14.2v.
Now the problem with one-wire systems is that the internal regulator will make said 14.2 at the alternator. A 2/3 wire system will make the 14.2 at the battery, regardless of how funky the wire harness is.
The 3-wires are:
1) big red one on the back is output. Hook to battery via amp meter.
2)Little white one is for the idiot light and also 'energizer circuit'. It gets some power into a brand new alternator via the idiot light. Old/rebuilts have built up enough residual magnetism to self- energize, so white/idiot light is optional. (I just have to rev mine a bit to get the charging system started.)
3) small red wire in the pigtail with white wire is 'sensor circuit'. It tells the internal regulator what the battery voltage is. It should go as direct to the battery (+) as possible, around any funkiness in the harness.
So much for theory. You my have bad windings or diodes in an alternator. But brushes are the usual wear point, and are cheap and easy to replace. I just did some in-chassis by removing the back of the alternator. 4 small screws and pry the back off - it still has wires attaching it, careful. Didn't even have to loosen the belt. You'll need a straightened paper clip to hold the brushes back in, when replacing back. Then pull out the paper clip wire and snap! the brushes go into place.
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