battery/alternator question

[Dr DSM]

Heres what happened. i was driving home today and my radio kept shutting off and coming back on. i stopped at a store ran in and came out and the car would start. so i had my cousin give me a jump start and it started up right away. i got the car home and did a voltmeter test on the battery and it was at 10 volts so i went and got a new one. when i installed the new one i decided to test the alternator by starting the car and disconnecting the battery. when i did this the car stayed running until i opened the driver door and passenger door (which triggers the automatic seat belts). what do you guys think? do you think the alternator is draining the battery or if thats normal? my old battery was an optima red top that was completely fine just hours before

 

[luv2rallye]

Disconnecting the alt while running risks damage to the ECU and other electronics in the car: http://www.dsmtuners.com/forums/newbie-forum/211550-battery-alternator-question.html#post1763645

Sounds like the alt is bad but test the alt and battery like this: http://www.dsmtuners.com/forums/new...reeway-electrical-problems.html#post151165661

 

[troppo loungo]

Could be the voltage regulator on the alternator. I would suggest a new or rebuilt alternator. Its not too difficult to replace.

 

[GRAVEDIGGER]

Like previously stated, there is no need to unhook the battery to check the alternator. The easiest way to check it is to have the car running and just check the voltage across the battery terminals. If you're not getting at least 13.5 volts at the battery the alternator is either bad, or in some cases the wiring from the alternator back to the battery can be bad. Ideally you should be seeing anywhere from 13.5-14.8 volts with the engine running on a good charging system. Hopefully this helps you understand what you're looking for a little better. Good luck.

 

[obsidian]

The alternator doesn't drain a battery, it charges it.

sounds to me like you have a bad alternator and don't disconnect the leads while the car is running.

 

[DSM1G90]

Battery runs the vehicle and the alternator just keeps the battery topped off.

 

[Dr DSM]

but couldn't the alternator over charge the battery?

 

[ChiTownHussla]

It should never overcharge it . The only way it could is if the internal voltage regulator was bad. Which I havent ever personally seen.

 

[knewblewkorvett]

Go to a Advance Auto or Autozone. They'll check your altenator for free.

 

[DSM1G90]

No, alternator has to put out the higher required voltage to keep the battery's output of 12 volts.

Simply is: when current (amperage) is being pulled out of the battery, voltage drops as well. Thus, you need an outside source to keep the voltage requirements of the battery at peak...basic why of the alternator's 13.8 V coming out of the end of the regulator.

You disconnect that battery from the circuit and run it straight from the alternator, the car's system isn't designed to run at anything higher than 12VDC - you can blow things pretty bad.. and 100vAC voltage spikes will kill anything in sight if it's not designed to operate that way..as what Steve said in his post in that link.

Look at your battery charger for your celphone: its output is higher than what the battery puts out.

EDIT: on that fuse topic within that one post: I also had charging problems and did an alternator changeout (160k miles on it figured it was time for replacing anywhos), but still no charging was happening.
I took the alternator back to have it checked and it was fine.
I had a new battery on and checked the main 80A fuse, which looked good...or did it?
I took it off, and did a "beep" test with my VOM... It had opened up.
I took the fuse apart and one of the legs had brokened open way down close to the one outside connection terminal(figured that with a lot of vibration and what-not caused that end to break off that one terminal). Went out to a yard and found a few DSM's with their main fuses intact. Snagged a few of them for 5 bucks. Put one in and now good to go.

 

[Dr DSM]

how do i check the voltage regulator. and where is the 80a fuse?

 

[ChiTownHussla]

Cant just check the VR. And the 80 Amp fuse is on the pass side of the car right by the battery. Its a black one on an offset to the rest of the fuses. in the corner

 

[DSM1G90]

..under the cover where the fuse box that is bolted to the passenger strut tower.

Take the cover off and it's the big one right at front and angled inward to the middle of the vehicle.

You have to take it out using a 10mm wrench to the bolts on each side of the fuse to check it...and disconnect the negative cable on the battery first before removal.

 

[1983gsp]

The battery is solely for starting the car. After that happens, the alternator replenishes what energy the battery used in starting the vehicle and produces the power to run all the accessories. Quick way to check if the alternator is bad is to load it up (start car, turn on lights and heater/ac, rear window defogger) and check voltage with a digital volt/ohm meter. Voltage should be 12.6-13.8 volts. If its not within range, inspect for bad grounds, faulty wiring, slipping belt, or bad alternator. Also, check to make sure the power steering pump isn't puking all over the alternator as well.

 

[ChiTownHussla]

The battery is solely for starting the car. After that happens, the alternator replenishes what energy the battery used in starting the vehicle and produces the power to run all the accessories. Quick way to check if the alternator is bad is to load it up (start car, turn on lights and heater/ac, rear window defogger) and check voltage with a digital volt/ohm meter. Voltage should be 12.6-13.8 volts. If its not within range, inspect for bad grounds, faulty wiring, slipping belt, or bad alternator. Also, check to make sure the power steering pump isn't puking all over the alternator as well.

Bro, 12.8 with alternator running means its ###### going out . You wanna see at least 1.5 volts more than when the car is off.