Jer82Z28

I have been having trouble keeping my alternator charging. I replaced the battery ground wire, and connections going to the alternator. Finally I installed a brand new alternator but the problem hasn't left. The alternator will charge good for the first minute or so. a solid 13 volts or more at the battery, then slowly the the guage will drop as power is drawn from the battery instead of the alternator. If I shutoff all the electronics that I can, it seems like the guage will slowly climb back up. Is it possible that my alternator just doesn't have the capacity to power the car? I'm running 2 extra guages, an MSD coil and 6Al powersource, electric fan. with just those running, I do not have any power left to run my power locks, windows or heater.
I have the stock 60A alt in there now. I just tryed boosting my other vehicle with the camaro and it would not charge the other battery.

Danno

A 65 amp unit should maintain the battery fine. Despite what you read more is not better. Current demand from ignition, guages is negligable in the scheme of things. The electric fan should be no more than 6-8 amps, more on initial turn on but again thats not really an issue. Look at the brown wire on the alt with a meter. That is the "sense" wire. Early third-gens used the 10Si alt and they used a resistance wire in the sense circuit. Pull the plug off the alt and with the key in the run position(engine off) measure the DC voltage at the brown wire. If it is low or missing suspect a problem in the sense line. If the sense wire is OK check the other wire, normally a heavier red one in most cases for 12 volts. There is a school of thought that says mucho amps is the way to go, but is not true. A 65 amp unit will maintain the battery under almost all but the extreme cases. The real current eaters are the heater blower, headlights and power window/rear hatch motors. Since everything but the lights are generally intermittent duty devices 65 amps is plenty. Plus your battery will last longer with a lower output unit. If you want to "fool" the sense line to test take a test light and hook one end of the light to the positive battery terminal and the other end to the "sense" line. The bulb in the test light simulates the resistor. If there is a problem in the sense line the alt should throttle right up to normal output.

Jer82Z28

How do you test the volt sensing wire? I used my guage to check voltage between the small black plug in to a ground..
I got no power coming from my volt sensing wire. Where does that wire go?

Danno

This is one of those times where a Helm manual is helpful. I have generic diagrams but they don't say exactly where it comes from. According to Chilton the brn wire gets fed 12 volts through a resistance wire, or on some models a diode. They both do the same thing. The resistor or diode provides a small voltage drop to keep the sense wire a half volt or so lower than the battery so that the alt will charge. If the sense wire were exactly the same voltage as the battery the alt would only trickle at best. If you don't want to try to trace it, try this. Go to radio shack and buy a 1N4007 silicon diode. Look at the diode, you will see a band at one end. That is the cathode. Attach the cathode end to the brown wire, the other end can go to the red wire in the plug or any 12 line. The diode provides approx. .6 volts drop and should get the alt to start charging assuming the sense line is at fault. If you want you can leave it that way or once you have verified it is now working you can begin to locate the real source of the problem. You mentioned you use your guage, does the car have the stock one or an aftermarket. I am not sure what you mean by that.

formulajoe_2

i am having this exact same problem except my alternators are just taking a crap on me after like 20 mins. PUt a new one on....and 20 mins later it stops charging and wont ever charge again. This is in a project car of mine that i have never even driven, so there is a lot of things in question in my situation, but im leading towards a problem with the sensing wire as well. Keep this post alive i need to get this thing figured out so i can start driving again. Anyone else have any more info on this matter??????? Any help would be greatly appreciated.

Danno

What alt and how is it hooked up.

formulajoe_2

im using a stock ac delco factory replacement alternator from oreilys. It is hooked up with the 2 wire plug (one brown wire and one red wire) along with the big black wire that goes from the alternator post to battery.

86BirdSE

Or perhaps a brain fart....

Can you directly wire the alt to the battery + terminal? That to me seems like the way to keep the battery charged up better. I have the same problem where when the lights are on the whole system dimms and the turn signals won't flash at idle. Once I give it gas it's fine. Everything is stock on the car, new Interstate 600 CCA battery.

formulajoe_2

would a 1 wire alternator solve this problem? Seems like it should. What about installing a resistor inline somewhere with the sensing wire on the stock alternator to show a voltage drop??? Anyone have any thoughts/comments on this?

compcg

My car is kinda acting like that too but if I don't drive my car for like 2 or more days the battery dies. When I start the car the volt meter slowly goes down until it reads a quarter of the way. Another thing is that the only way my air/heater will turn on is when I turn on either my parking or my regular lights. I think it has something to do with the wiring on my alternator. I have an 86 TA with a 92camero engine. My TA had the old style serpentine belt, then I decided to upgrade it with a single serpentine one. I would notice that even with the car off, I could hear a noise coming from the alternator. Of course I had to change alternators being sence it was a different serpentine set up.
So if ANYONE has any clue of wtf is going on please let me know!!!! I need to fix the problem inorder to either drive the car or sell it.

Danno

Sure, you can cut the sense wire and either use a diode or a resistor in the sense line and tie it to the red wire in the plug(key on 12 volts) and it should work fine. I don't like to do band aid fixes, but if you don't care or don't have the time to troubleshoot it is an option. Or you can purchase a one wire voltage regulator, crack the alt open and replace the regulator and you are done. Probably wouldn't hurt to replace the brushes while it's apart.

compcg

Does anyone have a clue about this problem of mine????????

jlbolin

heres my deal, 91 firebird 305 originally but did my 350 swap, after getting changed over and i running condition had to get new alt, had them test this one and it was a new good alt. bring it home and put on ,start car and voltage gage still says between 8 and 12 volt closer to 8, i took it back off and it still test at 14.7 volt. but if i take the bigger red wire on back of alt and hook it sraight up to the battery the gage jumps instantly to 13 but if you kick fan on or any other accessory it will drain battery in about 20 minutes. cant figure this out.

86BirdSE

jlbolin, are you running underdrive pulleys? Try a pulley off a different alternaor

jlbolin

i have no performance parts at all except headers.

gtabadboy

My alternator has the same problem as the original post. I tore my dash apart and built a new one so im guessing that I cut a wire somewhere. How again do you "fix" the sense wire so that it will work properly....assuming that my sense wire is at fault? Also when testing the sense wire as you said

"The bulb in the test light simulates the resistor. If there is a problem in the sense line the alt should throttle right up to normal output."

What do you mean by throttle up? Can I hook the test light up to a positive soure and probe the sense wire. Does the clip have to remain in the alternator. Then what... do I start the car up and check voltage? Thanks

Danno

Basically the sense wire needs to be a little lower voltage wise so that the alt regulator will start to charge. You can temporarily tie the sense to the other wire on the plug which should be key on or switched 12 volts. With the sense wire there the alt will charge about 30% of the time. Throttle up means simply it should start charging.