Altenator conversion now overcharging help
 

I converted my altenator tonight to the modern internal regulator from an 81 caprice. I followed the instructions posted in 2004. Now the battery is overcharging 17 volts at battery at high choke idle and the ammeter on the dash is on the high charge side and goes up with rpm. Just 20 minutes of test drive had the battery sizzling. The level goes down to 15.4 at low idle. Any ideas? Thanks in advance for any help. Truck is a 71
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Re: Altenator conversion now overcharging help
 

New alt or used?

Smitty

Re: Altenator conversion now overcharging help
 

It was a used one. I had in mh garage from a car I used to have.
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Re: Altenator conversion now overcharging help
 

I would get it tested. Also check your grounds.

Smitty

Re: Altenator conversion now overcharging help
 

It sounds like the internal regulator is stuck. This is the only thing I know of that will cause an overcharge situation like you have. Even 15.4 is too high.

Re: Altenator conversion now overcharging help
 

Pull the plug in the side of the alternator and check the voltage on the no.2 terminal wire usually the red 12 gauge wire. It should have 12 volts on it with key on or off. This is the voltage sensing wire that tells the regulator what the state of charge is on the system. If it has low voltage or no voltage the internal regulator will allow full charge to the system. Check the other wire for 12 volts with the key on and zero volts with the key off.

The large wire also provides field voltage for the alternator fields so I doubt that it has no voltage or the alternator wouldn't charge or would have low charge. It is most probably the internal regulator. While you have the small plug out, check the battery gauge for neutral charge. If it's still overcharging then there is an internal leak in the alternator circuits and it will have to be replaced.

It is also possible that there is a dead cell in the battery that is causing the alternator to overcharge but that is not as common as the regulator going bad.

Replace your alternator with a 12 SI model from a mid 80s camaro or cadilllac if it's bad. The 12 SI is more reliable and gives better output at idle.

Re: Altenator conversion now overcharging help
 

I did the voltage checks and that looked ok 12 V with key on. I picked up a new 1985 Camaro altenator and installed it. I am using the method referenced in a lot of posts where the brown and blue are cut and joined at the plug for the old regulator and the blue wire goes to the terminal on the altenator farthest from the engine and the jumper goes from the main power stud to the terminal closest to the engine. It does not seam to be working. Now it does not appear to be charging -- 12.2 V at battery with engine running. The altenator and battery are new. I cleaned the ground contact surfaces between the altenator and the mounting bracket.

Re: Altenator conversion now overcharging help
 

This is how the wires are jumpered at the old voltage regulator.

Attachment 1148689

It's brown and white together and red and blue together.
The white wire continues on to the alternator to the no.1 terminal and
the blue continues on to the no.2 terminal on the alternator.

I just eliminated all that and ran the brown wire straight from the firewall plug
to the no. 1 on the alternator and then ran a 12 gauge red wire from the alternator, battery, junction to the no, 2 terminal.

Attachment 1148687

The wires with the fuses are for the battery gauge and they have to be connected on each end of the battery feed wire for the battery gauge to work.

Re: Altenator conversion now overcharging help
 

I don't think that chart is correct. Should be brown to blue. Then white to red.

Don't get caught up in the color of the wires. The diagram is correct. Electrons don't care what color coat they are wearing.

The confusion probably comes from this thread in the FAQ by Toddtheodd.
..... http://67-72chevytrucks.com/vboard/s...d.php?t=119379

He connects the blue and brown wires together in post four and cuts the white wire out of the circuit. Then he connects the blue wire to terminal one of the alternator and he says the blue wire is just an extension of the brown wire.(post 6).

Then he eliminates the red wire and the white wire and just loops the short red wire over to the large post on the alternator from the no. 2 terminal on the alternator.

Now look at the diagram. The white wire is just an extension of the brown wire. The blue wire is just an extension of the red wire which joins the large red wire from the alternator at the junction on the bottom of the diagram, and it connects to the alternator at terminal 2.

Now you have the same wiring connections as the diagram and what Todd shows. The main difference is that the blue(red) wire on terminal 2 is now connected down stream of the alternator and it will send voltage sensing information to the regulator away from the alternator output and compensate for voltage drops in the circuit loads to allow the regulator to adjust for greater alternator output.

The white wire is also the same gauge as the brown wire and the blue wire is the same gauge as the red wire, which is another reason to connect them like the diagram shows.

Re: Altenator conversion now overcharging help
 

OK, I see what you are doing. Bottom line is that #2 gets 12V hot and #1 gets the wire to the light.

Re: Altenator conversion now overcharging help
 

Does there not need to be a ground wire on the 12 SI? Also, how do I differentiate between terminal 1 and terminal 2?

I'm trying to figure out how the PO had the alternator in my truck wired up, and am kind of at a loss. It's an internally regulated, from the position of the tabs (- -). but the only things hooked to the alt when I got the truck was a red wire 12ga to a post and a melted black 12ga to large bolt in the back of the alt that was also spliced to a small black jumper wire to one of the tabs.

Re: Altenator conversion now overcharging help
 

That is correct for the 12v wire. The brown wire will come from the light if it's an idiot light dash and from the key switch if it's a gauge dash. The brown wire has to have at least 10 ohms of resistance in it to protect the diode trio in the alternator and it gets that from the light or the wire in the gauge dash. It is a resistance wire from the key switch to the inside of the cab at the firewall connector block.

The alternator only needs to be grounded to the engine block, as long as the block is grounded to the battery negative cable no separate ground is required.

This should answer the second part of your question.

Attachment 1148799


Look at my post above for the wiring diagrams.

Re: Altenator conversion now overcharging help
 

Thanks for the help VetteVet, really helped a lot! Turns out that I do not have a 12si but a 10si on a 9:00 assembly. I was having such an issue with it because the two look different from the back. I never actually compared the front of the two alternators, if I had, I would have quickly been able to tell that I had something different. For my first go-round with an alt, I've learned a lot already.

I managed to make my way to http://www.madelectrical.com/electri...elcoremy.shtml and learned the visual differences in the two, and which wire will be going on which terminal.