Volt light charging problem

[Odmckee]

HI need some help here. Been through 3 batteries and 2 Altanator's and im still having problems car charges at 12.3 volts at idle with no volt light on when I drive and step on the gas volt light comes on and after a short drive the battery is down to 10 volts or so. It will charge back to 12.3 or so if I let it idle for a while. Belt's not slipping both alt. And battery were tested good off the car. I'm lost as to why there would be a voltage drop under acceleration. I have not been able to test the voltage at the Altanator wit the car revd up but I assume it's under 12 or I wouldn't be having this problem any help would be appreciated.

 

[565bbchevy]

I would check the condition of your battery cables first but your alternator should be putting out 14+ volts when it is charging.
12.3 volts is low for a charged battery and when you are driving anything that uses voltage is going to draw off your battery voltage
Also check for corroded or missing grounds.

 

[Odmckee]

Yeah I've checked the ground's and cables in the past for other issues I've had. I chalked up the low voltage reading to a crappy volt meter because they both passed when bench tested at the parts store. And it charges the battery at idle. I just can't understand why it would charge at idle and die under acceleration. With no accessories on and the only Change being the rpm what could be pulling more draw on the battery then at idle.

 

[565bbchevy]

You need to use a multi-meter and test your voltage at the alternator and battery and cable mounting points to see where the voltage loss is.
With the car running there should be 14+ volts coming off the back of the alternator and there should be very little drop in voltage taking a reading at the positive side of the battery.

 

[Odmckee]

Yeah that's what I've done I'm not getting 14 volts at the altanator I'm getting the 12.3 and it's like 12.3 -12.1 at the battery at idle. I gess I'll have to take it up to the parts store and have them test it in the car tomarrow. Even if it is low I don't understand what would make it drop that with the rpms raised from what I know if the regulator was bad it would charge at over 14 volts or not at all. And if I had a bad ground or bad connection it's would affect it across the rpm range. Idk Mabey it's another bad altanator for what it's worth its a 94 or 96 amp alt. From what I've seen its what they came with stock. I appreciate the help tho.

 

[somaphox]

ive noticed from various other jobs mostly on the negative side but the lugs themselves are the drop area.get new ones and might go away.you didnt mention getting new cables and they can corrode inside as well.come to think of it check the line going from the postive battery to the alternator for a drop,mine was a kinda thin crappy one from factory i upgraded to a fairly thick cable off a caddy i wanna say and now no voltage issues at all...just to clarify i got a single wire battery cable that goes to the starter and as a lug have a battery lug with a post attached you can hook various things to i found at autozone,this allowed me to hook a different cable size up to the alternator

 

[Odmckee]

I'll have to look into that I never replaced the cables just pulled the bolt from the housing and cleaned them when I was having problems with the starter. if I take a larger gage wire and jump form the alternator to the positive and do the same from the negative to a ground and the problem goes away I gess that would give me the answer to that.

 

[somaphox]

yeah ive tried that to sometimes it works sometimes i still get a drop when i read with the vehicle on.not sure why honestly id imagine quality of the metal lug but sometimes even shined up the battery gives he perfect charge but at the lug it drops

 

[V8 Rumble]

Have you inspected the cable/harness that connects to the alternator. Check it for corrosion or frays. try connecting the exciter wire to a 12v ignition source and see if that works.

I had to do this on my malibu. do you have gauges or the dummy light?

 

[pontiacgp]

it sounds like the alternator is not charging at all and the reading you get is the battery which will drop in volts with the engine running if the alternator is not recharging it