Testing alternator voltage in car

[dragnix 5,000+ posts]

How would i do this with a DMM? Do i put the dmm on the pos and neg of the battery while the engine is running? And should i have it on AC or DC voltage? Help me out because i just want to make sure the alt is charging the battery.

I just changed battery and now it won't start up unless jumped. The battery is reading 10.xx and i just got it and there's nothing in the car that could be draining the battery, i have no system connected.

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[dragnix 5,000+ posts]

bump, need help

 

[SomeDonnieDude 10+ year member]

Dmm on DC, just connect it right to the battery pos and neg. If the battery won't stay charged on the vehicles electrical, try charging it on a batt charger.

Try this at your own risk: pull the positive cable on the battery while the car is running, it is dies then it's probably time for a new alt. Reason I say try at your own risk is due to possible voltage spike.

 

[dragnix 5,000+ posts]

Dmm on DC, just connect it right to the battery pos and neg. If the battery won't stay charged on the vehicles electrical, try charging it on a batt charger.
Try this at your own risk: pull the positive cable on the battery while the car is running, it is dies then it's probably time for a new alt. Reason I say try at your own risk is due to possible voltage spike.

I tried that, the car didn't die. Does that mean my alt is good?

 

[andrew2944r 10+ year member]

Pull Alt of and take it to Napa or wherever and have it tested 1st

Alt sounds bad...

 

[dragnix 5,000+ posts]

If the battery is new and reading 10v out of box, go get a new battery!

not out of the box, i've had it since saturday, but i'm thinking i do need to get a new battery

 

[GreenBook 10+ year member]

Sounds like it's time for a new battery. If you have a Checker Auto parts around you out there in cali they can test your alt/starter/battery while they are still on the car. Thing is you have to drive it up there and be able to start it on its own in the parking lot.You could possibly have a short somewhere draining the batt; but odds are it's just old and needs replacing.

 

[jco1385 5,000+ posts]

if i read this right...

your battery is resting at 10v. time for a new battery

 

[audioatg 10+ year member]

How would i do this with a DMM? Do i put the dmm on the pos and neg of the battery while the engine is running? And should i have it on AC or DC voltage? Help me out because i just want to make sure the alt is charging the battery.
I just changed battery and now it won't start up unless jumped. The battery is reading 10.xx and i just got it and there's nothing in the car that could be draining the battery, i have no system connected.

So the battery is new. And only reading 10 volts? Sounds like you got ripped off.

 

[alotofbang 10+ year member]

yeah reading of a new battery should read between 12.3v-12.7v but you can check if it is charging when you start the car use the dmm to see your voltage if it is below 14v bad alt. ooh and it should be on dc. What kind of car

 

[GreenBook 10+ year member]

So the battery is new. And only reading 10 volts? Sounds like you got ripped off.

I guess I didn't read well enough. A little tip I learned from working at an autoparts store is that they are supposed to check the voltage on all their batteries in stock once a week and charge them if nessecary; but most places don't. Having them sit on a shelf with no charge long enough can make them crap out. I'd take it back up there.

 

[audioatg 10+ year member]

I guess I didn't read well enough. A little tip I learned from working at an autoparts store is that they are supposed to check the voltage on all their batteries in stock once a week and charge them if nessecary; but most places don't. Having them sit on a shelf with no charge long enough can make them crap out. I'd take it back up there.

Humm. If you thought I was saying somthin against you. I hope you didnt. nothin there was ment for you. I just read his thing saying it was new and only reading 10volts.

And your right places do mostly check the voltage here and there. At my shop I work at we sell napa batteries. They made us install a battery tender in. I thought was a very good idea.

 

[GreenBook 10+ year member]

Humm. If you thought I was saying somthin against you. I hope you didnt. nothin there was ment for you. I just read his thing saying it was new and only reading 10volts.

And your right places do mostly check the voltage here and there. At my shop I work at we sell napa batteries. They made us install a battery tender in. I thought was a very good idea.

Not at all, I usually read these forums in the middle of the night before I goto bed so I don't always read everything right, thats all.

 

[SICCMAD3 10+ year member]

once you get the car running, with the dmm set on dc, test at positive and negative on the battery and you should see somewhere between 13.5v and 14.5v. if it is like 12.5 or lower the put the positive lead off the dmm onto the charge wire connection at the back of the alternator, leave the neg. on the batt. ground, while the motor is still running. see what the reading is. again it should be somewhere around 13v-14v. depending on what your reading's are determines where the problem lies.

but more then likely you've got a shit battery, was it brand new or new to you