GT Jets

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Delco alternator how-to New
« on: August 12, 2008, 10:28:58 PM »
I just thought this would be helpful.

I got into a little debate/argument with a guy from my nephews race crew (dirt circles), he's a hell of an engine builder, but knows nothing about electricity.

The Delco Remy alternator is one of the most simple alternators out there (the internally regulated ones).

Everybody always thinks they need a larger alternator when they have battery capacity problems.

Most times its do to the installation and wiring connections.

There is a small plug on the side of the body of the alt. that is used for a trouble feed back and the other is for the exciter circut, the lower the voltage of the exiter circuit the more amperage it develops.

The exciter circuit is what I would like to explain. A lot of you guys out there are using a self excited regulator making your alternator installation simple (1-wire). The only drawback to this alternator is it only "knows" the battery voltage, not the "system" voltage.

The difference is simple, the battery voltage is just that, the voltage at the battery.

The "system" voltage is the voltage you have at the dash and back to the ignition system, think about this; if you follow a wire that powers up the ignition coil, you will start at the battery, to a circuit breaker (hopefully), to the ignition switch in the dash (16' +/-),  back to the positive side of the coil (another 16' +/-), not to mention the voltage drop through each terminal and switch contact. All said it could be the equivelant of like 100' of 30 year old wire...Huge voltage drop.

Back to the small terminals on the alternator, the exciter wire is the "controller" for charging, in a perfect world this wire should go to the ignition coil positive terminal, but can't because the engine won't turn off....instead it needs to go to the "hot" or "Batt." terminal of the ignition switch, seems silly but that will make a huge difference in how the alternator behaves, (this will remove half of the voltage drop of the harness). The alternator will now see the "lower" voltage do to the drop of the wire and switches. A one wire alt. does not see this drop, the output is internally hooked up to the exciter circuit.

On most of our boats this would not make any difference, but bigger boats and boats that have a lot of electrical draw; hot ignitions (MSD, Jacobs, Accel, etc.), siesmic disturbing stereo's (you know who you are), and other electronics like depth finders and stuff, but if you have a 30+ year old wiring harness like me, it makes a difference, one solution is to upgrade the wire sizes to support the equipment (should be done anyway). Most of us can get away with a 35 amp alt. IMO.

BTW if you use an isolator for multiple batteries, this is a must do because the voltage feedback is weak.

I hope this helps clear up why that plug is there (that's what started the debate BTW).

Here is a crappy drawing of that plug....

« Last Edit: August 13, 2008, 04:32:15 PM by GT Jets »
  • Boat #1: 1992 Carrera 20.5 Elite (I/O bitches)
  • Boat #2: 19' Bubble deck Jet BBC Berkeley
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If i get some free time tonight at work, ill play with it and post it for everyone to see.

Time to man up and yank it John!  :banghead:



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