New Alternator

[Ned]

I have a d21-87 model and need a new alternator. Mine is a Hitachi but part number is gone. I have figured it is a 60amp but whilst shopping on the net I have found a patrol alternator that is very close in dimension that is 100 amp. does anyone know if the pulley alignmet will be ok and if going from a 74mm pulley up to an 84mm pulley will effect the charging or will it work just as well spinning a little slower?
Thanks,
James

 

[Pinelli]

Any chance you could swap pulleys over?
I think you'll find that at a slower speed, it should still give the same voltage, but at a lower current. I'm pretty sure that the voltage is to do with the number of coils in the beasty, not the revs. There is also the effect where at high load, you may get a lower voltage due to internal resistance in teh regulator and alternator. So at idle you may not quite get the volts you expect if also running the a/c, charging a second battery, running a fridge things like that.
I'm just brainstorming here. Feel free to correct me people, I'm working on theory here, not practice.

If it does work with the larger pulley, then you will never pull the current it is rated for, which should mean it will be fairly robust as it won't ever be stressed.

 

[Old.Tony]

That sounds pretty spot on. The larger pulley will make the alternator shaft turn over slower and that could be a problem, so I'd definitely try to change that over.

At idle, with your headlights on, the alternator should JUST hold its own. One way you can tell: at night, idle the car with your headlights on and turn on your indicators. Your dash lights should dim a little as your indicators come on - it should be nearly imperceptible - but you should be able to notice it. Raise the RPM by a few hundred and that effect should go away. If it doesn't go away with (say) 1200-1300rpm, your alternator is not putting out enough power (or your battery is drawing a lot of power to charge up - check fluid levels).

As for putting that alternator in your car - I have no idea. If it were the last alternator on the planet you'd probably grab a welder and make something up to suit if needed!

 

[Ned]

Thanks guys. I think I will go for the bigger. I would think it would be pretty unlikely that the shafts were different so I was always planning on swapping the pulleys just thought I would see the negatives of leaving it on.
My biggests worry is the offset of the pully but the pictures look like they are the same. I am waiting back from the seller so will let you guys know if there is any difference.
It would be good to have an extra 40 amps as I am running a thermo fan that eats up about 26 amps plus the spotties and some winching. No wonder I'm shopping for a new one!

 

[Old.Tony]

Don't bother budgeting for an alternator for the kind of amps a winch draws. They take 300+ amps on full load - you need a decent battery to do that, not the alternator.

Sure the better alternator helps the battery recover faster and you're absolutely right in considering a larger one running the fan & spotties, but when you're winching, have as much as possible turned off, get someone to hold the car's RPM at about 1500 in neutral with their foot on the brake (no handbrake) and you should be a little better off.

 

[Pinelli]

I'm curious Tony, why no handbrake? Or do you mean that the handbrake isn't enough by itself?

 

[Old.Tony]

Handbrake only holds the two rear wheels and if your tub's empty, your ute will just slide around, so yes the handbrake isn't enough on its own.

 

[Ned]

So I have bought the Patrol Alternator which is the type off the GU, no pump on the back.
Pretty obvious that the screw on terminal on the back will be the one that carries the current to the battery but still working out the two wires labled S and L off my old alternator. I know they will be for the charge light but not sure if polarity matters. i assume these wires will go into the side of the GU alternator. If any of you gurus can help it would be great.

 

[Old.Tony]

A quick search using the ultimate Guru (google) revealed this chart.

Enjoy.

 

[Ned]

Thanks Tony,
I found the info on google also. I like to ask people because they will usually have had first hand experiencs etc.
I put the alternator in tonight and it ran ok. So if anyone wants to know, a GU patrol alternator fits on a Z24 engine. Just had to swap pulleys and a little wiring. Standard belt still fits and plenty of clearance around alternator.
Thanks for the help guys,
Cheers

 

[Old.Tony]

So you got an extra 40A out of it? That's pretty good.

Next test: with the bonnet up and everything in the car switched off, start the engine and as quickly as possible, measure the battery voltage at the battery itself with a digital multimeter.

Five minutes of idling later take the same measurement. What is the voltage?

With nothing switched on in the vehicle, 5 minutes of idling ought to make a noticeable change to the battery. This will determine if the idle speed of the alternator is good.