I have electric engine fans (LT-1 fans) and I now have the A/C working again. At idle my charging system cannot keep up. With both cooling fans on and the A/C on high the voltage at the battery drops to about 12.5 at idle. When I rev the engine a little everything is ok. This will be really bad at night with the headlights on as well. The specifics are:

Cooling fans 12.0A X 2 = 24A
Compressor clutch 2.5A
A/C blower 8.0A

The total for just these components is 34.5A. At idle I measured the alternator output as I turn each component on. With all of them on the alternator output at idle drops from about 35A to about 27A. When I rev the engine to about 1200 rpm or so I see the alternator output jump up to about 44A. I am guessing what I need is to double up the 10 gauge wire coming out of the alternator and to find an alternator with higher output at idle. Anybody have any suggestions?

Thanks,
Clay

a later model alt will make a huge difference in low rpm charging output.

I used a late 80's early 90's alt.Fits in the same mounting brackets. I forget what they call them 10SI or some such? I think mine was specs from a 89 suburban if I remember right but one from about anything will work as long as the mounting holes are clocked right. it will probably have a surp pully on it although some earlier ones had the v belt pully on it already.

I have a link somewhere that has a good wiring diagram to do this swap. it eliminates the external regulator .

the swap makes a dramatic difference in charging. and is cheap too.

DJ

My car is an '81 and is already running a 3 wire internally regulated 10SI alternator. It started life as a V6 car with no A/C, so it probably has the smallest alternator that you could get. I'll see what I can find for a Suburban or something like that.

Thanks

it will be easier for you then. the late 80's alts work MUCH better. they are slightly smaller but use the same mount. look for the black band around it. my car is efi with electric everything and it does a great job. the old style alts suck.

Yes a 3rd gen alternator will plug right up and put out a bunch more voltage.

I use 1989 IROC 105amp alt.Works great.

Any of y'all update the alternator wiring when going to the bigger alternators?

81,

This site has a ton of very good info on alternators and automotive wiring generally:

http://www.madelectrical.com

a bigger main wire from the alt to the bat is a good idea.

I upgraded my charging system because of my elec fan, fuel pump, and underdrive pulleys.

I went with an early 90's GM CS-130 105 amp alt. I snagged mine off a 91 grand am (I think) at a junkyard for $12. Then I upgraded the wiring as well. 2 ga. battery cables, and a 4 ga. charge wire.

Even with my underdrive pullys, I keep 12.9 volts at a 700 RPM idle with everything running (elec fan on high, fuel pump, headlights, etc)

Grab the plug on the CS-130 alt. too, cause you'll need it

It's an easy swap. Just swap pulley with the one on your 10SI alt. You'll need to put a 47 ohm resistor in line with the "L" wire on the plug, and run the "S" wire back to the charge output screw on back of alt.

I ended up putting in the 170 amp alternator in my 71 RS :
http://www.alternatorparts.com/CS-144_Special_offer.htm

I was pushing out over 1000 watts though with the stereo system in the car. I recommend upgrading all your wiring with 4 gauge unless your running a line more than 4 feet. I had no dimming with that alternator whatsoever but we did have to modify my bracket because I had fuelie heads on the car and they didn't have an Alt bracket mounting hole. I also would recommend buying an Optima battery.

So what great alternator will fit in the original brakets and require no rewiring?

MaTt

Well, I would recommend the 6" case, 140-amp GM versions and use an adjustable heim-end bracket and ditch the fac. bracket. I build them from 140 to 200 amps using a 6" case and that will take care of any problems. I build/modify charging systems to handle any type of requirements, if you have any questions, drop me a line and I'll see what I can do for you. When it comes to a reliable charging system, the devil is in the details-(wiring, junctions, relays, etc.) not just a big 'ole alternator, though that is usually where one must start. -Jabin

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Gmachinz Sales and Performance
"...updating the level of performance..."

[This message has been edited by gmachinz (edited June 30, 2005).]