ronny 204 Posted March 2, 2014 Charging system help Ive got an AC Delco alternator that is a 80-120 amp (variable) I put the voltmeter on the back of it and it showed 12.2 volts at idle (not enough) Its turning twice as fast as the crank so the alt is doing 2000-13000 revs This is not enough for what the car is drawing Water pump, fuel pump, fans and ignition have a max draw of 65A It would seem the alt should do the job guessing total draw from everything is say 100A How much minimum output from the alternator do I need to run my car? Do I need to turn it faster? Could it be a poor alternator? Share this post Link to post Share on other sites
ronny 204 Posted March 2, 2014 Ok a bit more history... First alt was a chrome AC delco (had no idea of which alts were any good) I made custom brackets with the p/s and alt on the same belt The problem was not enough belt touching the alt pulley (approx 30%) so when revved the belt would fry To overcome that I put a bigger pulley on the alt which solved the belt issue Output was poor so went to buy a new alt Was a bit of mucking around to change to Bosch, so after being told AC delco is ok I stuck with them Got a new one that needed an exciter, so hooked up a little light to do that The guts was moving and was pushing the bearing out the back so got given a new one (the current one) Now this one has held together for a while I can't remember what output was when it was new but I needed a good battery for the car to last a whole day I put it down to the bigger pulley not turning the alt fast enough Having a fresh battery would get me through the day until I got back to a trickle charger It time I sorted this out so did the test and added up the draw to work out what I need Ive always wanted to change to serpentine belt so I can turn an alt faster Share this post Link to post Share on other sites
gerg 10,871 Posted March 2, 2014 You could see by simply revving the engine up to say 3000 and watching the volts. That should be well and truly enough rpm to see if you have a drama with alt speed or not. Sounds to me like the alt is cactus. Share this post Link to post Share on other sites
Outback Jack 6,352 Posted March 2, 2014 Alternator should be charging that battery to around 14.4 volts. It almost sounds like ya don't have it hooked up right. Oh, and on my XG it's a Mitsubishi alternator, and seen as they the same sort of set up, I'd look at that. Just at a guess, i'd be looking at the regulator, the alternator just spins and produces power, it's the regulator that tells it when to supply that voltage to the battery and when to stop topping up. If your battery is dying over a day, you have a voltage leak. Also don't tighten the alternator up too tight , leave ya 10mm flex in the belt or you will kill bearings in alternators. jack. 1 Jim Rebel reacted to this Share this post Link to post Share on other sites
ronny 204 Posted March 6, 2014 I took the alt back and they checked it out It was working, just wasnt exciting cos the little globe i use as the exciter had popped, newbie error by me Anyway they opened it up and it had heat damage pretty bad which means it was working too hard So i bought a new bosch alt 120A which produces less at low revs so i will need to turn this one a bit faster (changing to serpentine at last...) Below is the output of the 2 alts as tested while i watched 1 Outback Jack reacted to this Share this post Link to post Share on other sites
