New alternator not getting excited

[FabBighorn]

Hi everybody, and thanks for all the useful info posted in this forum. I have problem with the charging system on my 96 bighorn and I was wondering if anybody out there can help me figure it out. My old alternator burnt out after driving in sea water (dumb huh) so I purchased a brand new Oex alternator from ripco but it doesn't start charging unless I rev up the engine to about 1200revs. Alternator belt is tight and not slipping. Abs 4wd water trap and charge idiot lights also stay on until I rev up the engine and the charge relay clicks in. When the relay clicks in the alternator starts then charging correctly and all lights on dash go away. I have tried with 3 different brand new blue relays (one was a Oex brand relay same as alternator) but none of them solved the problem. Seems like the alternator doesnt excite until it starts spinning fast enough to create its own magnetic field. There are 3 wires in the car's wiring (ig, s and l) but only 2 wires on the actual alternator (ig and l). Both wires get 12 volt. Does anybody know how can I get this (600 $) alternator to get excited and start charging without revving up the engine as it used to before? Any wiring trick? Any help is much appreciated. Thanks a lot.

[isuzurob]

Thats just how they are, lots of people have the same issue as you, i have to rev mine to just over 1000rpm to get it to start charging

[stardog]

$600 for a alternator holey doley it must be gold plated or something.
Mine don't show any charging until about 14-1500rpm as well then it shows 13-14v and they are both 120amp alternators in both Isuzu's.

[FabBighorn]

Yeah I got stuck in the middle of the road in Taupo with a broken alternator and a flat battery only place in town that had an alternator was repco. Yeah bought from repco it must be gold plated! Anyway I cannot understand why aftermarket alternators don't work as the factory standard ones.... so why do they even have the L wire if it then just work as a one wire alternator? Just for the idiot lamp?

[geeves]

I did fix this for a short time on my old bighorn but then burnt out another alternator and relay and back to square one. It was the relay but how to find a good one is luck. Both my current isuzus do this and not going to pull my hair out trying to fix

[FabBighorn]

How did you fix it for that short time? At least I would know what not to try. As I dont think wire L is getting enough current to magnetize the alternator, I was thinking about adding a resistor or a diode inbetween wires IG and L... has anybody tried that? Would that create more problems? I red somewhere that even adding a smsll light bulb inbetween the wires might help? Any opinions? Thanks again everybody

[geeves]

some blue relays work better than others

[FabBighorn]

I have tried two different kind of Jideco blue relays and an Oex one same brand of alternator with no results. Also tried with one of the black ones but no win. I am just so frustrated of the fact that a 600 $ alternator doesnt work as good as the old one did...

[geeves]

Dont know why this is but its pretty much par for the course. You might try 50 relays and find one that works or just put up with it as the new normal. Even a new battery may help but its hardly a reason to change a battery

[FabBighorn]

I will try to put a diode in the circuit and see what happens... thanks again for your help

[FabBighorn]

Hi guys the other day I bridged the wires "L"and "ig" using a 14v 3w light bulb (yes 14v) and that fixed the problem. Now the lights go off, the relay clicks and the alternator starts charging straight away as it should. Seems like the "L" wire wasn't getting enough current. As I dont want to leave a light bulb hanging in there I was thinking of using a diode or maybe a resistor instead of the bulb. Does anybody know if a few 12v 1w zener diodes in parallel would work as good as the light bulb? Will the 12v diodes burn out if the "ig" wire will supply let's say 13.5v when alternator is charging? Any advice would be awesome. Thanks

[geeves]

light bulb has a voltage regulating effect but I would experiment with a 5w 5 ohm resistor. If that doesnt work put a 4 ohm one in. The catch is that a bulb draws a lot more current until it heats up so if that start current is the trigger a resistor wont work

[FabBighorn]

Yes you are probably right. I will see if I can find some resistors and try them to see what happens. Thanks again for your advice