[BILTIT]

So i have a boat with a 455 pontiac. It had an ext reg alt which is toast so i bolted on my 12si int regulated alt. Trying to figure out the wiring, have heavy wire for ''batt'' terminal (goes to ammeter on dash and back to battery) and a sensing wire for term 2? Do i need to connect anything to terminal 1? I have no voltmeter or idiot light so unsure what to do with term 1.

Pic is of previous setup and boat.

[george kujanski]

The purpose for connecting to terminal 1 on a 12SI is twofold; a bulb is typically used in that circuit to excite the alternator and give an indication when the alternator is not providing enuf voltage.

Connect a 1895 bulb from an ignition source to alt term 1 or use a 75 ohm, 3 watt resistor since you have an ammeter already.

George

[BILTIT]

Thanks George, that is the answer i was looking for.

[jwcfbd]

I can't help with your problem but who doesn't love a boat powered by PONTIAC. Very nice.

[BILTIT]

Thanks, i was very lucky to find a previous owner who wanted to keep it pontiac powered.

[BILTIT]

George, if the ammeter gauge fails can it effect the alternator? I noticed my gauge died the other day (to the max position but stays there when shut off too) and a day or so later the alt. fried. I pulled it out and tested the batt and it was at 4 volts so the alt couldn't have been charging for a while.

I just replaced the alt, charged up the batt and going to test. I haven't looked at the gauge yet but will shortly.

[BILTIT]

Looks like the needle just let go of the sensor shaft. I have 12.5v on each post of the ammeter when shut off. I cannot rev up the engine without it being in the water (rubber impeller in the water pump) so I will wait until it calms down and get it the water to see if the alt. is charging. It was working before I know as the ammeter was working.

[LATECH]

The current from the alternator all passes through the amp gauge.They gauge very well could have fried because it couldn't handle the current.Or it was getting old and the insulators broke or something along those lines.
Best to get a new one.
As allways George is spot on...LOL

[stellar]

On the original setup, the little square box connected to the alt is the regulator. It is used to make the alt similar to a one wire alt. It takes the place of the larger external reg and all the extra wiring. If you connect a 12SI with just the positive battery wire and #2 connected to power it will act like a 1 wire alt and work without an excite wire.

[george kujanski]

To add: if the ammeter is open (no circuit thru it), the alt will not charge the battery. The best test is to run the engine and check the battery voltage, it should be about 14 V. If the ammeter is open, just connect the two terminals together to allow the alt current to pass to the rest of the system.

Alts used on boat engines, (at least engines in a confined engine bay) need to be designed for marine use, primarily the slip rings and brushes are in a sealed chamber to prevent sparks from igniting fuel vapors and causing an explosion.

If your engine is open to the air you should be ok with a automotive 12SI.

George

[BILTIT]

Yup all open.


I have voltage on both terminals but I realize I may still not be able to get enough current through it. I was monitoring the batt voltage but I think I need more rpm to excite the alt.

Hoping to get it out on the water tomorrow.

[BILTIT]

The alt is direct driven, no pulley. Same speed as engine. You can see it off the back of the crank in this pic. Pretty sure I just need more rpm to get it to start charging.

[george kujanski]

Without a connection on term1, you may need to spin it to 1000 + RPM to get it to excite.

You also need to move the steering wheel to the right side...

George

[Bill Hanlon]

Given that the typical belt driven alternator spins 2+ times engine RPM it may take a bit more than 1000 RPM to get the direct drive alternator to self excite.

[BILTIT]

Yes I think it takes 2-3000rpm.

I do have the resistor on term 1 like you originally suggested. I never checked it though after the alt died.

[Blued and Painted]

IMO a volt gauge is safer with less output wire routing (with less voltage drop). As long as the volt gauge is up around 14, it's doing it's job. I dont recall many cars using amp gauges since the 60's. They were always problematic.

[BILTIT]

I agree but to find a gauge to match these old ones is tough. I pretty much have to change them all,

[BILTIT]

It is charging just fine, had it out ripping today. Good times !!

[LATECH]

Pontiac boat...coolest thing under the sun.