Quick Alterator Wiring Question??

[jrork]

We found out the hard way that our boat didn't have fusing.
Since then weve been rewiring and everything is up and running except for the alternator.
I wanted to fire off the motor and measure output of the alternator without it being wired in to verify that it was working.
When I did so, my handheld voltmeter showed 23volts! I did a quick swap with another one I had in the garage and it was similar (actually higher) to the first.
It's your typical GM rig with one terminal screw marked "Batt" and then a small plug in the top that has two terminals.
I took the reading directly off the "batt" terminal. Are these high readings due to no load being on the system and the Alternator freewheeling on the engine? I've read that I can attach the No.2 termial to the batt terminal. Sound correct? I'm reluctant to plug the wiring in with the reading I was getting. The possiblity of copying the existing wiring is not an option as that was part that got smoked......Thanks for the help.

[MikeF]

Are you running 2 batteries in series? I think that is the only way to get 23 volts.
Check out the liquidaddiction.net site for the wiring schematic. It is set up correctly :cool: .

[BrendellaJet]

Jrork-yes, connect the #2 terminal with the batt terminal. Last summer my alternator was registering 17 volts. The gauge was a cheap one, so who knows if it was right. I ran it all weekend like that-thats the last time I ran it. Didn't experience any problem, although I was concerned and figured a pulley change was in order to slow it down. Seems like that would help you too? I think there are others here more qualified to confirm this. Let us know what happens...
One more thing, the liquid addiction diagram is an excellent reference, let me know if you cant find it, I'll post a pic of it.
[ July 22, 2003, 10:43 PM: Message edited by: BrendellaJet ]

[Old Guy]

I can't tell you how to check your alternator but I can tell you what can happen if the built in (in the alternator) voltage regulator doesn't work. If you have an ammeter on your instrument panel, your wiring will probably melt. Mine did. I think that's why they started using a voltmeter instead of an ammeter. The ammeter requires all the current that's charging the battery to go through the meter. If the alternator voltage is too high, the charging current will be too high. The wiring can't handle that much current and gets red hot thus melting the insulation and causing a fire unless you get lucky or quick and disconnect the battery. Last year that's what happened to my Sleek Craft. I was able to get the battery disconnected before I had a fire (it was very close to being a fire). When I rewired the boat, I found that the wiring harness had melted almost through the vent hose on my gas tank. A few more seconds and she would have gone boom. I now have a volt meter.

[Havasu Hangin']

jrork:
I wanted to fire off the motor and measure output of the alternator without it being wired in to verify that it was working.Uh...not sure I would do that. I'm not sure the regulator will work properly without a load. Also, if you disconnect the battery, the diodes will probably fry shortly (pardon the expression) thereafter.
Better consult an alternator shop.

[jrork]

Thanks guys,
I am only running one battery and I have 12 volts going throughout the system WITHOUT the alternator hooked up.
I purposely mounted the alternator but didn't hook up the wires into the system so I would have a way of accurately measuring the voltage output. This is where I read the 20+ volts.
I realize that the voltage should range between 13.8 and 14.2 volts and this is the reason for my question.
That and the fact that the other alternator I have and mounted up for a test was providing equal or greater voltage leads me to believe that these alternators must have their built in regulator activated by running a jumper up to the No2 terminal.
I would love to see that diagram but I have to admit, I can't find it. If you could provide the link on their site or post it here that would be much appreciated.
Thanks again everyone........John

[malcolm]

The Alternator needs to be hooked up to a battery to work right. If you can get it to charge without a battery it will go wide open. Is that what it's doing?

[Havasu Hangin']

jrork:
I purposely mounted the alternator but didn't hook up the wires into the system so I would have a way of accurately measuring the voltage output. This is where I read the 20+ volts.
I realize that the voltage should range between 13.8 and 14.2 volts and this is the reason for my question.You can put a voltage meter on your battery (when hooked up), and it should give an accurate reading.
Running it without a load is asking for trouble. You might want to call an alternator shop & verify.

[HOSS]

Dunno if this helps but I ran 1 wire to bat+ and post on alt. If I remember correctly 1 from ignition to alt in GM plug+

[Chris J]

In simplest terms, one of the two small wires is used to excite the alternator and the other is used to sense the voltage and adjust the voltage regulator accordingly. With no voltage on the sense wire the voltage regulator will keep increasing the voltage until it is maxed out, This is what you are seeing.
Some alternators are internally excited and do not need a wire running to the ignition, Others also have a built in fixed voltage regulator. If your're shopping for new alternator get one that has both. Then you'll have a simple one wire hookup, works great, easy to wire and looks cleaner. Any auto electric rebuild shop will have one or can convert your current one.

[BrendellaJet]

here is the liquidaddiction.net wiring diagram...
http://www.***boat.com/image_center/data/500/212ignitionandgage-med.jpg