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Generator or Alternator?

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RedTR3

RedTR3

Jedi Trainee
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Ealier this week I posted about converting from generator to alternator. The reason I am considering this is that I installed a large Spal fan (solved my overheating!) but now the electrical system shows discharge at idle when the fan is running.

Now I am wondering, instead of converting to alternator, what is the harm of leaving the Gen and just accept that maybe I have to replace the battery every couple of years? I only drive the car a little on nice weekends.
 
I don't think it is uncommon to have a slight discharge state at idle even w/o the electric fan, especially if headlamps, wipers &/or heater are in use.

So long as you drive some in a charge state (day time, cruising RPMs) I wouldn't expect you'll kill battery much sooner than anyone else unless the fan's draw is quite high.
 
Just throw a battery tender/trickle charger on it if you are really concerned about battery longevity.

Alternator is nice if you don't mind the change and some hassle in making the change.

Are you keeping up with fan and lights on?
 
I'm running the same configuration at the moment (electric fan plus stock generator). So far it's been no problem except in stop-n-go traffic with the headlights on. The generator will keep up with both headlights and fan (at higher rpm); but there isn't a lot left over to recharge what was lost while you were idling or creeping forward. Few months ago, I spent about 1.5 hours going 15 miles after dark; and after dinner there wasn't enough left to start the engine.
 
Alternators are better at low rpm charging while the car is idling. But they need to be in the 2,000 to 4,000 rpm range to do that. So choose the pulley accordingly to match your driving style. And when choosing the pulley keep in mind that the top rpm for an alternator is usually in the 15,000 to 18,000 range.

And be sure you have the correct fan for your alternator. The rotation direction will determine that. The fan should draw air through the alternator from the rear.
 
tdskip: I don't need to run the fan all the time, only when outdoor temps are relatively high. The fan is controlled by a toggle switch and thus I never run the fan at night when the lights are on.

So another question - should I connect the fan directly to the battery output or at the fuse box so that the discharge shows on the ammeter? The fan wire does have an in-line fuse of its own.
 
Skip, I belive if you hook fan to battery you will see charge increase on amp gauge for fan load.At the fuse box will show increase discharge if alternator/generaator cant keep up.if I keep my ammeter,I am wiring to fuse block,so ammeter functions as original.
Tom
 
I agree it shouldn't be directly to the battery, but I wouldn't connect it to the fuse box either. The horn fuse is on the battery side of the ammeter (causing the problem Tom mentions, of the ammeter reading backwards); while the other fuse is powered through the ignition switch. The stock ignition switch is a relatively low-current device, and IMO won't last long trying to carry the fan current as well. (Peak current for the fan can be over 25 amps, even though normal running current is much lower.)

So, I have a relay that gets fed through a fuse from terminal A1 on the control box. (Rather than using an in-line fuse, I added a 4 fuse Lucas fuse box next to the control box.) Then the control circuit gets fed from the ignition switch, so the fan stops when I turn off the key.

You might want to consider adding some sort of automatic control as well. I tried the manual switch route, but I was forever forgetting to turn it on or off.
 
tomshobby said:
So choose the pulley accordingly
Click to expand...
FWIW, I ran for nearly 20 years with the original generator pulley on my 60 amp alternator. While Tom's point about reduced output at idle is certainly true, the high capacity at higher rpm more than made up for it.

Overall, the setup worked very well for me even with all the loads I added (electric radiator fan, 100 watt headlights, 100 watt stereo, MSD6 ignition). My only real complaint was that it was hard to change the belt, even after I notched the alternator case. And the modified case made it difficult to exchange the alternator for rebuild.
 
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