Alternator Issues?

[dternst]

The battery was completely dead this morning on my 95 530i (the 530i has been setting in the garage for the past several months). Jumped the battery (just purchased in November '04) and it started with no problem. I drove it around for about 30 minutes and put the trickle charger on it.

Decided to take the BMW to O'Riely's to have them check the battery. The guy told be that the battery needed to be charged. Tourned the car over to determine readings at idle: 12.5 V and 30 amps. He said the battery should be reading 14 V and the alternator reading around 60 amps.

What should the alternator be reading at rest and idle? What and where do I need to check to ensure the issue is stemming from the alternator?

On a scale from 1 to 5 (5 being the most difficult), how difficult is it to replace the alternator?

Thanks in advance,

David

[Kalevera]

David....Well, it should read about 13.6 volts at the battery with the engine running.

It could simply be a bad battery; I'd check the voltage regulator just to be sure it's okay. Leaving a battery to sit in a car for a few months without being connected to a charger will kill it. After its discharged, the plates will start to go. This is especially a problem if you're in a warm climate.

best, whit

[dternst]

Lowell,

This happened last year and I replaced the battery. Damn Texas summers.

Thanks Lowell. As always, you're a fountain of information.

David

[Paul in NZ]

put it n on a trickle charger and or timer next time you leave the car for a long period.

[BobHarris]

Get yourself an Optimate or similar charger.

www.optimate.co.uk

HTH

Bob

[Javier]

save a battery.

http://www.bimmer.info/forum/showthread.php?t=9966

Javier

[SRR2]

The 12.5 sounds a little low, but may be due to battery undercharge. 30 amps at idle is in the ballpark. The alternator is running at only about 1500 rpm at idle and just can't put out its full current rating at that low a speed.

If this car were mine, I'd put a 2A trickle charge on it for at least a day and then check the SG of the electrolyte before condemning the battery.

Lead acid automotive batteries are not designed to deep cycle. Once or twice might be all they can handle before the plates are damaged. If you're going to let the car sit idle for any period of time, say greater than two weeks, you should use a battery maintainer designed for that application.

As far as the alternator goes, you haven't done enough to condemn it. I don't offhand know what the speed/current spec on your alternator is, but in general terms the current rating of alternators is the maximum output under optimum conditions at a specific (high) rpm. Your output will be less. How are you measuring the current, BTW? DC measurements without breaking the circuit to install a shunt are dodgy to say the least.

If you would like to try a simple go/no-go test try this: with the battery fully charged according to your hygrometer, turn on the high-beams, the a/c on high, and the rear defroster. Hold the engine RPM at 2200-2500 and read the battery voltage. If it's 13.5-14, your alternator is OK.

Unless you have some particular reason to trust the dealer, don't trust the dealer. You can do these tests yourself to determine whether you need a battery and/or alternator.

[winfred]

the alt is only going to output what the car needs, the more stuff you turn on the more power/amps it's going to push, the easy way (if you have a meter/amp clamp) to measure the alt's amp output is to hook a inductive amp pick up to the main wire comming directly off the back of the alt, then start motor and turn on everything and rev the motor, most of then will push 50-70 amps at idle and then step up quickly with higher rpm, a couple weeks ago i was testing a 94 525 that was pushing around 67 amps at idle and peaked out at 128 amps at a couple grand, i think that's all the car was drawing and the alt had more to give

[SRR2]

67A at idle and 128A at XXXX? Holy cow. What kind of equipment in that car was consuming that much current? What are you using to measure the DC current, and how do you know it's accurate?

[winfred]

i was using my inductive snap on amp clamp, it's a atachment for any multimeter (most of which can't handle more then 10-15 amps on their internal circuitry) it clamps around the wire that you want to measure the current in and takes a reading and sends it to your multimeter set to mv and what it says in mv what you got in amps, mine reads 0-400 amps but they make bigger and smaller units, it's pretty accurate down to about a 1/4 amp, at that point you can just hook up directly. on the 94 525 i just turned on everything, lights ac blower back window heater radio..... everything except running the windows up and down and standing on the brake, these cars have some big draws ac with aux fan on high and full blower pulls a good 50-60 amps

ps that car i had just put in a brand new battery and was testing the system so that's not charging up a **** battery, it had allready died and was the reason the car was at my shop

67A at idle and 128A at XXXX? Holy cow. What kind of equipment in that car was consuming that much current? What are you using to measure the DC current, and how do you know it's accurate?