dennisr

I have dual 11" Spal fans on my 71 Vette. When the fans are on it reduces my idle almost to the point of dying. Obviously it's a big load on my electrical system. What can I do to fix this. I currently use a 1 wire chrome alternator but I'm not sure if it's an 80 or 90 amp. It was only $99.00 so I assume it's no higher than 90 amp. Can I just put in a 100 amp alternaotr or is there somehing else that may be the problem?

Also is there a way I can verify what my alt puts out?

Thanks in advance



[Modified by dennisr, 9:33 PM 12/19/2001]

A C

That may or may not be the problem. Check the rated amp draw on the fans. I believe for my Flex-a-lites it is something like 20A, which is a lot. Yours may be even more. You could bring your alternator into most parts places and the can test it for you, or if you have an amp clamp, you could check the amp draw on the alternator. Mine used to do the same thing, but that was with the wimpy 69 alternator (40 something amp). I just installed a 100 amp unit, but haven't started the car yet to tell if solved the problem. Will let you know tomorrow hopefully :smash:

AC

daily_driver

well the problem is the output at idle!!!!

a 100 amp alternator doesnt just put out 100 amps at idle!!!

i upgraded to 100 amp and if i turn everything on and the fans and blower motor and headlighrs r goin itll still do it a little bit at idle....

paso

That's exactly the situation I concur with Daily_driver Those alternator are great above idle and you don't need to do anything as long as you realize that it is not putting out 100 amps at idle. It's annoying maybe but not a big deal.

SteveG75

Seems like you got an alternator that has no low speed charging capability.

I rebuilt my 42 Amp unit into an 80 Amp with a kit ($24.95) from http://www.alternatorparts.com . The fans have no problem at idle (dual Spals as well). Shows 20-25 amps charge at idle with fans on which jumps up to 40 amps by 1500 rpm.

FYI: I connected the 12V+ supply side for the fans to positive battery terminal on the starter vice the alternator. That way, the battery takes the load instead of relying on just the alternator.

Ingar, Norway

I think your problem is regulator related. A 80 amp alternator should have no problems is the regulations is correct.

(You can check the maximum output of your alternator by applying 12V directly to anchor. I'm pretty sure that will be sufficient to drive the fans at idle...
A regulated output significantly lower than during this test calls for a better regulator.)

You say you have a 1 wire regulator. I assume this is sensing the voltage directly at the alternator output?

If so, go for a regulator that sense the voltage externally, at the starter, (or even better at the battery) which is the original setup in my 1980.
This will drive the alternator much harder that a internal sensing regulator.

An less desirable alternative is to use a very heavy gauge wire between the alternator and starter, which will reduce the voltage loss. (all load is connected at the starter)

An ideal system will have 14.4V at 70oF at the starter (within the max alternator load range) , anything significantly less that will leave you with a partially charged battery.
In my experience a good externally sensing regulator will drive the alternator at full output at around 1500rpm.

I have an article on the charging system in the technical section of my page.

SteveG75

Got the answer. Should have read more carefully.

The problem is the fact that it is a one wire alternator.

Copied from the http://www.alternatorparts.com site.

Self-Exciting Alternator:
Is an alternator that uses a special voltage regulator that doesn't need an ignition wire to activate it.
This type alternator only requires a battery wire hooked to it. The voltage regulator contains circuitry that uses the residual magnetism in the alternators fields to determine when to turn the alternator on. The regulator does this by sensing the RPM the alternator is turning, when it gets to a certain rpm the voltage regulator "turns on". Typically you startthe vehicle, rev the motor slightly then alternator starts charging. This type alternator is
commonly used on custom cars & trucks, tractors and other non standard applications when wiring is a factor. In choosing this type alternator you must consider, do you want to rev your motor slightly to get the alternator to turn on. Also when using the self-exciting alternator on tractors or other slow turning motors does the engine have enough RPM's to start the alternator charging. This can be overcome by using a smaller pulley or by adding an ignition wire.

One-wire Alternator:
Is another name for the Self-Exciting Alternator mentioned above. You only need connect the battery wire (one-wire).

Two-wire Alternator:
Most standard and all self-exciting regulator alternators will work using the two wire setup. Two wire means that you use the battery wire and an ignition wire to activate the alternator. With this setup the alternator starts charging as soon as the engine is running.

Therefore, that old one wire setup is not charging at idle. Go get a quality 2/3 wire alternator.

427V8

I think you guys a re answering the wrong question.

It seems his motor doesn't have enought horsepower to turn the altenator so it is slowing down when the fans come on.

My 434 doesn't even notice the fans coming on :D:D:D

I think he needs a bigger engine ! :yesnod:

Sigforty

Is there any wiring problems involved in upgrading the alternator amps??

Mark B.

dennisr

I think he needs a bigger engine ! :yesnod:

.
Thanks Steve, I'll swap back to my old alt and see how that works.


My engine is a 383 with 431hp and 440 lb's torque. Not a big block but will give one a pretty good run.

Dennis


[Modified by dennisr, 5:02 PM 12/20/2001]

A C

There are also alternators from car audio companies such as Stinger that put out as many as 270 amps, as well as versions that are specifically for high performance at idle speeds (for sound off competition). These are not going to be cheap alternators though.

AC

Techno

747 watts / 12 volts = 62 amps Or 1 hp = 62 amps at 12 volts

I have an accesorries rich cadillac?(forgot which) alternater in my car I think its 280 amps and much cheaper than a "stereo" alternator. Being a GM product it bolted right in. Wiring didn't seem to be a problem.

A fix for the low idle if nothing else works. Get one of those late model electric idle solnoids that dropped the idle to nothing when shut off. Hook it up off a relay from the fans, this increases the idle and when the fans switch off the idle drops back down to normal. and they're adjustable too.

467-Ratman

I had the same problem with my 71 coupe this summer, then we direct wired the fans to the starter terminal and bingo no problem. My alternator was rebuilt this August and puts out 80 amps. The twin Spal fans do eat a lot of power but should not be a problem with a good electrical system.