Alternator tech in GCC How does the excite/sense wire work? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 07-03-2019, 07:17 AM   #1 (permalink)
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Alternator tech in GCC How does the excite/sense wire work?

I've had a couple of alternator issues lately and wondering if anyone has any knowledge they would like to share.

Two different rigs. 89 Trooper with stock GM V6 and 91 Ford Backhoe.

The backhoe has wiring issues and the 'excite' wire has no voltage. So I wired a push switch from the battery to the excite wire and that worked fine for ~200 hours of use.

The 89 Trooper needed some work done on it and I ended up leaving the excite wire disconnected which resulted in it not charging. Connected the excite wire and now the alternator doesn't work. Napa tested it. Replaced the alternator and it works fine now.

So my question is surrounding the way alternators work. How much voltage should they get to the excite/sense wire and why would they fail if they get no/too much voltage?
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Old 07-03-2019, 07:42 AM   #2 (permalink)
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Old 07-03-2019, 07:54 AM   #3 (permalink)
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The sense wire should be wired to the battery or fuse block close to the battery so the alternator can sense the voltage of the system. Lots of people/some systems just use a jumper to the pos terminal of the alt but that doesn't account for voltage drops. The excite wire is usually wired to the charge light and/or through a diode. Most good alternators can charge without that hooked up by self exciting the windings by spinning the alternator fast enough by blipping the throttle. Yea, might not be the best for the alt because you'll be full fielding it at high rpms but meh. You can't give the excite wire 'too much' voltage as it generates charging voltage on that wire when the field excites. The reason you use a lamp, diode, resistor, is to prevent back feeding of voltage to the system on key off. Then the alternator would be powering the vehicle through the excite wire and will smoke the regulator.
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