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Buchu
09-16-2004, 07:31 AM
Hi,

I recently converted my cutlass speedo from the standard to the Rallye Pack. Now that I have a voltage gauge, I noticed my car battery is being somewhat overcharged to 15.5 volts. At first I thought the gauge was inaccturate. I measured the battery voltage with a DVM and and it also measures 15.5 volts

What would cause the battery to be overcharged? Could the problem be a bad voltage regulator? If so, where is it located? My cutlass has a standard 307 V8 engine.

Thanks in advance for your help!!

84ZZ4
09-16-2004, 08:05 AM
It's either the voltage regulator in the alternator or the "sense" wire. If the sense wire sees low voltage, it'll crank the output up to compensate, and overcharge the battery as a result.

The regulator is inside the alternator.

Buchu
09-16-2004, 08:14 AM
It's either the voltage regulator in the alternator or the "sense" wire. If the sense wire sees low voltage, it'll crank the output up to compensate, and overcharge the battery as a result.

The regulator is inside the alternator.

Is the sense wire terminated at the alternator somewhere? I'll check that first before replacing the regulator.

Thanks!

84ZZ4
09-16-2004, 08:23 AM
It should be. I think it's the one wire on the two wire plug that goes back into the harness. I don't have my manual in front of me though...

If it IS, what I'd do is unplug the two wire plug, and turn the key on (don't start the engine). Measure the battery voltage and compare it to the voltage on the sense wire. They should be pretty close. If the battery reads 12.4 and the sense wire reads 10.5 that's your problem.

You can probably also "back-probe" the connector while it's on the alternator to see what the alternator "thinks" the battery voltage is. If you get 15.5 at the battery and 13.8 at the sense wire, that would also indicate the voltage sensing wire.

Keep in mind though, the sense wire itself may not be the problem--if you have a large voltage drop from the battery to the starter, the sense wire will read "low" compared to the battery, but the problem in that case is probably the positive battery cable and not the sense wire. Although, if that's the case, usually you'll have a LOW to NORMAL gauge reading and HIGH battery voltage. High gauge reading usually indicates a bad sensing wire OR bad regulator.

Grimm
09-16-2004, 09:56 AM
Before you spend any money, also make sure you have good ground. I had the same thing on my '68 after I got a new battery (the old one was probably fried because of the overcharging) and after replacing the regulator and alternator with no change, I sanded down to metal a little bit around the mounting holes for the regulator and now it's fine.

Buchu
09-16-2004, 11:30 AM
It should be. I think it's the one wire on the two wire plug that goes back into the harness. I don't have my manual in front of me though...

If it IS, what I'd do is unplug the two wire plug, and turn the key on (don't start the engine). Measure the battery voltage and compare it to the voltage on the sense wire. They should be pretty close. If the battery reads 12.4 and the sense wire reads 10.5 that's your problem.

You can probably also "back-probe" the connector while it's on the alternator to see what the alternator "thinks" the battery voltage is. If you get 15.5 at the battery and 13.8 at the sense wire, that would also indicate the voltage sensing wire.

Keep in mind though, the sense wire itself may not be the problem--if you have a large voltage drop from the battery to the starter, the sense wire will read "low" compared to the battery, but the problem in that case is probably the positive battery cable and not the sense wire. Although, if that's the case, usually you'll have a LOW to NORMAL gauge reading and HIGH battery voltage. High gauge reading usually indicates a bad sensing wire OR bad regulator.

There is only a 30mV difference between the battery voltagae and the 2 wire connector that plugs onto the alternator. It doesn't look like the sense wire is the problem. I have a feeling my voltage regulator is shot.

I ran the car with the 2 wire connector unplugged and of course the voltage droped to near 12V.

71CutlassConvertible
09-16-2004, 12:03 PM
You can run by the local auto parts store and see if they can check it for you. Many of the stores have the equipment and will check your system for free.

Cutlass84
09-16-2004, 12:35 PM
yup, i test them at advance all the time. The bench test will most likely reveal a bad voltage regulator like you suspect..

Buchu
09-16-2004, 01:07 PM
yup, i test them at advance all the time. The bench test will most likely reveal a bad voltage regulator like you suspect..

Thanks for the advice guys. I'll stop by Advance on my way home from work. I'll let you know the results.

Can I replace the regulator only, or will I have to replace the entire alternator? I'm not sure if just the regulator can be replaced. Does anyone know?

84ZZ4
09-16-2004, 01:35 PM
You can replace the regulator alone, but I don't know if you can buy just the regulator. I've taken two bad alternators before and made one good one though (one had a bad rectifier the other had a bad regulator, I think).

Buchu
09-16-2004, 02:20 PM
You can replace the regulator alone, but I don't know if you can buy just the regulator. I've taken two bad alternators before and made one good one though (one had a bad rectifier the other had a bad regulator, I think).

Is it difficult to replace the regulator? Do you have to do a complete alternator tear down?

Smitty275
09-16-2004, 05:34 PM
To get to the regulator you have to totally disassemble the alternator. May as well replace any other suspect parts while your in there. And yes you can buy just the regulator, or the matrix, or the brushes. What ever you need is available seperatly.

Oval Olds
09-16-2004, 06:07 PM
Did you check from ground to each slot in the plug? One slot is tied to the battery, and the other goes to the alt light/resistor combo then to switched 12V. If you changed the dash, the alt light is now missing. You will need a wiring diagram to see where the turn on sense comes from.

Buchu
09-16-2004, 07:13 PM
Did you check from ground to each slot in the plug? One slot is tied to the battery, and the other goes to the alt light/resistor combo then to switched 12V. If you changed the dash, the alt light is now missing. You will need a wiring diagram to see where the turn on sense comes from.

I did check from the alternator 2pin connector to the battery. One side measured the battery voltage. What should the second pin measure?
I didn't get a good reading on the second pin. My charge light comes on when the key is on. The procedure I followed didnt mention anything about the turn on sense.

Oval Olds
09-17-2004, 09:25 AM
For a basic GM 10SI diagram go to: http://www.amphicar.net/darrellgaddy/Delco%2010si%20alternator/Amphicar_GM_10Si_Alt.htm

The top picture shows the minimum needed to make it work. Also run the link back and check out the German car boat.

Wire 1 goes to the alt warning light then to + 12V, if you ground this wire your charge light will turn on. This is also the "turn on sense" wire, it lets the alternator know to wake up. If everything in the car is properly hooked up, disconnecting the plug and grounding # 1 should make the warning light turn on.

Wire 2 goes to +12V, this is the voltage sensing wire so the regulator can do it's thing. If this wire sees a low voltage, the reg will compensate. From this wire to ground you should see battery voltage.

Use a 12V test light for checking these wires, a DVM needs such little current to operate, slight leakage will cause false readings. This will make you think there is 12V available at a wire, but when a load is applied it falls to near nothing.

Since we don't know your voltage readings prior to the gauge change, there is a good chance the reg is failing. Have the headlights been really bright lately? Is the battery damp with acid or bulging at the sides?

Buchu
09-17-2004, 11:23 AM
For a basic GM 10SI diagram go to: http://www.amphicar.net/darrellgaddy/Delco%2010si%20alternator/Amphicar_GM_10Si_Alt.htm

The top picture shows the minimum needed to make it work. Also run the link back and check out the German car boat.

Wire 1 goes to the alt warning light then to + 12V, if you ground this wire your charge light will turn on. This is also the "turn on sense" wire, it lets the alternator know to wake up. If everything in the car is properly hooked up, disconnecting the plug and grounding # 1 should make the warning light turn on.

Wire 2 goes to +12V, this is the voltage sensing wire so the regulator can do it's thing. If this wire sees a low voltage, the reg will compensate. From this wire to ground you should see battery voltage.

Use a 12V test light for checking these wires, a DVM needs such little current to operate, slight leakage will cause false readings. This will make you think there is 12V available at a wire, but when a load is applied it falls to near nothing.

Since we don't know your voltage readings prior to the gauge change, there is a good chance the reg is failing. Have the headlights been really bright lately? Is the battery damp with acid or bulging at the sides?

Grounding wire 1 does NOT make my charge light turn on. Any idea why?

The battery looks normal. No signs of bulging or acid residue on the sides. The lights do seem brighter than normal but i'm sure thats due to the higher than normal battery voltage.

Oval Olds
09-17-2004, 02:54 PM
The alt light should turn on when the key is in the run position and # 1 grounded. There is a small chance your alt light is triggered by battery voltage high/low and not connected to the alternator, but I really doubt it.

Did you notice your lights getting brighter after the dash change or before? If it was after the change, there might be a dash plug problem.

You really need a wireing diagram for your car to compare alt wiring for a light vs guage dash. What year is your car?

Buchu
09-17-2004, 03:15 PM
The alt light should turn on when the key is in the run position and # 1 grounded. There is a small chance your alt light is triggered by battery voltage high/low and not connected to the alternator, but I really doubt it.

Did you notice your lights getting brighter after the dash change or before? If it was after the change, there might be a dash plug problem.

You really need a wireing diagram for your car to compare alt wiring for a light vs guage dash. What year is your car?

The lights seems to be the same brightness after the change. The only reason I noticed a problem was the fact that voltage gauge was reading high. My car is a 1984 Cutlass Supreme coupe.

I don't think there is a dash plug problem, but I guess it is something I could easily check.

Buchu
09-18-2004, 06:17 PM
Didn't find any bad connects behind the dash.....

Buchu
09-21-2004, 03:58 PM
Didn't find any bad connects behind the dash.....

Any suggestions from the experts out there?

Grimm
09-21-2004, 04:09 PM
Did you ever get the alternator tested?

83Cutlass
09-21-2004, 07:47 PM
Geez lets quit jerking this guy around. He needs an alternator. End of story. KISS method. Although I would cry over 15.5 charging volts.

84ZZ4
09-23-2004, 10:41 AM
Yeah, not necessarily. Not doing proper troubleshooting before hand is why I replaced about an alternator a year in my old Camaro. Why? Charging wire was bad, and it would put out 16-17 volts to maintain 14.5 at the battery. They died from being overworked.

Not one mechanic ever thought to check it. I didn't find the problem until about 5-6 years later when I finally learned how to do my own work.

Proper diagnosis and testing is the difference between a mechanic and a part installer ;)

83Cutlass
09-23-2004, 06:56 PM
A true mechanic (actually we prefer Automotive Technician nowadays) on flat rate throws an alternator on the car and it doesn't fix it, then he quickly fixes the wiring problem and leaves the alternator on the car and tells the customer everything is fine now. :) :) :) I kid, I kid. I hate flat rate sometimes. 99% of the time its an alt problem and almost no one is gonna disassemble and repair an alt like that when a replacement one cost like $35.
But I see your point :D .

84ZZ4
09-23-2004, 08:50 PM
Sounds like truth!!! :D

Honestly, I don't normally take apart alternators and repair them either. IF we narrowed it down to not being a wiring problem in the car, then yeah, replace the alternator. (I haven't read some of the more recent responses because I've been busy as hell lately :bleh: )

I just don't wanna see anyone else go through what I did.