Alternator Output
 

I've done a bunch of searches, but haven't quite found what I'm looking for. I would like to know what the alternator in my '96 850T should be putting out. I've had some starting issues for a while, so finally took it to the shop today. I was told my battery was really weak (barely holding a charge - it was from 1998), and the alternator was weak too. I replaced the battery, and it seems to be running great. My alternator tested out at 13.9 volts at idle with nothing on. The mechanic put a load on it (how much I'm not sure....enough that it sounded like the RPM's dropped by maybe 1-200) and the output dropped to about 12 volts. Is this in the normal/acceptable range, or should I be looking at a replacement alternator? The shop wanted about $480 + taxes to rebuild mine, but I can get a used one out of a car with 70,000 miles for $50. A no-brainer, but if I don't have to do it all that would be best.
Oh...one more thing. The mechanic also said my battery light should've been coming on in the dash. It has never come on....and it does work when the key is first turned.
Thanks

I was running a battery in my car that had 1 or 2 dead cells. When I went to start the car the volts were dropping to about 7.8. While the car was running, my OBD-II ScanGauge II was reading outputs between 12.4 - 13.7. I finally replaced the battery, that btw was only about 3 years old. (If you had a battery that was older than 5 years your car is awsome). After I put another battery in it the meter reads between 13.2 and 13.9.

When a load is applied it really shouldn't drop that much. You can kinda test it yourself. Park in front of a wall or garage. Start the car and turn the lights on. Then turn on other things like radio, ac, and roll a window up or down (this is a normal load). If the lights dim, your alternator is likely going bad. If the lights remain bright you're probably ok.

The alternator should be capable of putting out about 95 to 100 amps max. The problem with going by voltage is that the alternator may be putting out the proper voltage but still might not be putting out enough amperage to properly recharge the battery when you are running the headlights, wipers and blower motor not to mention heated seats or electric defroster. The alternator can fail in a way where it's only putting out one or two thirds of it's rated output and in those cases since it's still charging it will not turn on the idiot light. Under those circumstances the voltage looks good but the battery never gets fully recharged and depending on what you are running may not even have enough left to start a cold engine.
Where are you located ??
If you're still in doubt almost any auto parts store can retest your battery and alternator for free with a handheld tester so you don't even have to pull it out of the vehicle. You may very well have both bad but I'd have the battery retested and if it still tests weak replace it and then have the alternator retested. It would be a good time to check the belt and tensioner too !!

i got mine rebuilt into 170 amp alt and with big 3 and extra batt i dont drop under 13.4

What exactly is a "big 3" in your world ?
And that would help KENM.10 with his problem how ??

this is big 3

Increase Car Audio Power 25% - How To Install Big Three Upgrade - Easy 15 Volt Stereo System Big 3 - YouTube


dont no just wanted to put it out there stfu and have a great day

Thanks for all the replies. I'll try to get another test done to see if I need to switch out the alternator....

This is a bit grim but if it tests bad in the car and you go through the trouble of pulling it I'd still have a parts store bench test it to confirm it's bad before you sink the $$ into a replacement. Once in a while the hand held in car tester will condemn an alternator and it could be a connection problem where it tests good on a bench. Might save you a buck or two ..... :rolleyes: