Uh oh...is it the batties or alt...?

[Davecubs14 10+ year member]

Ok. Went to my first comp on sunday, Didn't push my system hard imo. But yesterday, the alt started making a rattling sound. Like change in a jar everytime I hit the gas. I let go, it'll go away. Played a little music, no voltage drop.

Working in my car today, played my music on low for about 30 minutes. I think the air was on as well. Oh well. Usually I can go for hours with my air on full blast while the engine it off.

Bottom line, my car wouldn't turn on after 30 minutes while the engine was off and music volume on like 5. Because I looked over at my voltage, it was in the low 11s.....Wouldn't turn on..

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[bjude1 10+ year member]

You have a bad battery. make sure that the alt. is charging the battery when the car is turned on. If your dmm is telling you that your battery is sitting at 11v's and it wont even turn over than your battery has a bad cell.

 

[Davecubs14 10+ year member]

So use the dmm now, read the batts and jump off the car, and see what they go up to?

 

[mylows10 5,000+ posts]

exactly ,if you check the voltage of your battery and it at 11 volts,then start your car and see if the voltage will rise,check at the battery and then at the alt its self

 

[-01limited- 10+ year member]

Sounds like a dead battery.

 

[Davecubs14 10+ year member]

Ok. Checked both before jumping off.....1400 was 11.6 and the 2400 was 11.75.

Got jumped off, they jumped up to around 13.6 then after a minute, 13.8. Turned the car off. Now they are resting at 12.2 and 12.3.

How do I check the alt with a dmm?

 

[LosIsATool 5,000+ posts]

They should be fine.. Check it again in a few hours

 

[Davecubs14 10+ year member]

Yeah, then we'll know.

 

[Davecubs14 10+ year member]

Ok. Well I checked it twice over the night, kept falling. Both batteries are hooked up atm and both of them read 11.8. I believe it's the 2400. It's the oldest. Has DB drag stickers on it. So....What now? Lol. Switch to XS power and mechman. That's what!

 

[subzero 5,000+ posts]

bad alt that is killing the batteries, or you have a power drain some where. MAybe a bad battery. you neet to take it to have tested at auto zone or shop.

 

[audiolife 5,000+ posts]

If your state of charge of your cells is below 12.7 volts the alt is not keeping up for one of several reasons. To measure State of Charge on a battery it should be measured after the car has been turned off for a few hours so the surface charge has left the battery. Alternators put out voltage of 13.8 volts or higher and this will stay with the battery for a few hours not letting you see the real resting voltage of the battery. Batteries that are as low as yours also should not be "charged" from an alternator as an alternator is not an intelligent battery charge,r it is a bulk maintainer that was not designed to charge a low battery. That would eventually damage an alternator and or battery. If you leave lead acid batteries sit at a low state of charge you will also ruin them as well. Allow them to get hot and continued prolonged use while being under charged speeds up the process of failure. When the batteries discharge they sulfate and the longer they stay sulfated the closer to an insulator that sulfation is becoming making the battery charge slower to the point they wont take a charge. I have rung quite a few new car audio power cells through the ringer and they all sulfate and get to a point where they will not recharge if you do not recharge them correctly. Take a power cell thats rated for a couple thousand watts under the hood where it gets hot hook it up to a car with a 80 amp alt with a 2000 watt rms system and sooner or later you can have a rather large mess if you do not pay attention to how the power cell is charging.

 

[Davecubs14 10+ year member]

If your state of charge of your cells is below 12.7 volts the alt is not keeping up for one of several reasons. To measure State of Charge on a battery it should be measured after the car has been turned off for a few hours so the surface charge has left the battery. Alternators put out voltage of 13.8 volts or higher and this will stay with the battery for a few hours not letting you see the real resting voltage of the battery. Batteries that are as low as yours also should not be "charged" from an alternator as an alternator is not an intelligent battery charge,r it is a bulk maintainer that was not designed to charge a low battery. That would eventually damage an alternator and or battery. If you leave lead acid batteries sit at a low state of charge you will also ruin them as well. Allow them to get hot and continued prolonged use while being under charged speeds up the process of failure. When the batteries discharge they sulfate and the longer they stay sulfated the closer to an insulator that sulfation is becoming making the battery charge slower to the point they wont take a charge. I have rung quite a few new car audio power cells through the ringer and they all sulfate and get to a point where they will not recharge if you do not recharge them correctly. Take a power cell thats rated for a couple thousand watts under the hood where it gets hot hook it up to a car with a 80 amp alt with a 2000 watt rms system and sooner or later you can have a rather large mess if you do not pay attention to how the power cell is charging.

I think I understand. So since I tried to charge the batteries for about 15 minutes. They read 13.8 afterwards. After 6 hours, dropped down to 11.8. Does that mean it's my alt?

 

[tenbux1970 10+ year member]

Odds are if you were hearing a noise when you revved the engine there is probably a bearing going out in the alt.Take off the belt,and see if there is ANY wiggle in the shaft of the alt.

Give the batteries a good charge before you judge them.

Take your meter,and measure the voltage you have before you start.Then start the car,and see if it goes up.

(just so you know) Just because your alt puts out normal voltage DOES NOT MEAN it is putting out the right amperage.

 

[audiolife 5,000+ posts]

I think I understand. So since I tried to charge the batteries for about 15 minutes. They read 13.8 afterwards. After 6 hours, dropped down to 11.8. Does that mean it's my alt?

It is going to take longer than 15 minutes to charge 2 almost totally dead batteries. I would get a Ctek MUS 7002 charger and charge up the cells independantly to see if you can bring them back. Even if it doesn't you have a good charger to help avoid this type of situation as a low battery is hard on an alternator anyway. Chargers like this charge more complete than an alternator as well that will mean longer battery life and better performance over the lifespan.

 

[CRXBMPN 5,000+ posts]

my alt died when I pulled into work yesterday... stock original 90a alt from Acura... I have my DMM with me and got about a 15 minute "jump" to give my four c&d tech's a little juice for the ride home. I started my journey sitting in the 12.4 range and when I got home (40 miles and 50 minutes later) the DMM said 12.12v. Not bad imho. BUT I did have MY alt tested and its dead, nothing at all... getting a new one put in tomorrow. Good luck though. I'd turn my car on and wouldn't gain a single tenth of a volt, that is a bad sign :laugh;