Measuring Alternator Output - Team Camaro Tech
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post #1 of 12 (permalink) Old May 5th, 15, 06:20 AM Thread Starter
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Measuring Alternator Output

Hello Everyone! I have an issue with an electric cooling fan setup that I am told inadequate alternator output may be the issue. Specifically, the 40 amp fuses blew. The alternator that is currently in my car is chrome, at least 10 years old and is internally regulated. Thats all I can tell you. It was something given to me by a friend who does not remember anything about it. There are no numbers, manufacturer name, logo etc. anywhere on it that I can find. Is there a way to test how many amps it puts out? Will a clamp on amp meter be any help? Im told that when they are tested at auto parts stores, its only voltage being measured. Thanks!

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post #2 of 12 (permalink) Old May 5th, 15, 06:37 AM
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Re: Measuring Alternator Output

I would suspect the fans or the wiring to the fans. Seems that something in that circuit drew more than 40 amps and blew the fuse.

"Inadequate alternator output" would just cause them to run slowly.


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post #3 of 12 (permalink) Old May 5th, 15, 07:22 AM Thread Starter
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Thanks for the reply. The wiring harness is brand-new. I've checked all the connections. Everything is tight secured nothing loose or arcing - nothing like that going on. I called Entropy Radiator tech support. This is what they said they commonly see when their fans are exposed to an alternator not putting out the amperage that fans combined demand. - John
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post #4 of 12 (permalink) Old May 5th, 15, 08:18 AM
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Re: Measuring Alternator Output

Where are these fuses wired in the circuit?
Overnight problem or always happened this way?
I agree with Mr. Entropy, wattage is proportional. If voltage goes down, current goes up providing the electrical load remains the same resistance and temperature.

If the fuses are fan fuses, if the fans are two-speed, are both windings wired to the same relay terminal when a speed is selected?
Do the fans spin freely with no power at their operating temperature of hot?
How long has the present alternator been in service?
Is Camaro harness wired for an internal reg'd alt?
Harbor Freight sells a 50 amp ammeter for $10 and I use a strip of 1/8 inch thick copper and mount the ammeter onto the strip and bolt the combo directly onto the BATT stud.

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post #5 of 12 (permalink) Old May 5th, 15, 10:18 AM Thread Starter
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Re: Measuring Alternator Output

The fans and installation are brand new. I previously logged about 15 miles post install before yesterdays incident. The wiring harness and the position of the fuses are provided by Entropy. I am beyond confident this is not and install issue or fuse location issue as its all "plug and play". And, I have so say, Entropy does an amazing job in fabricating its harnesses in addition to their radiators. It is clean, neat and practically a work of art. Given the quality of there work, their tech support as well as my install, I am 100% confident in the explanation for the blown fuses. I would just like to measure the alternator output if that is possible before shelling out whatever the cost is for a high output alternator.

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post #6 of 12 (permalink) Old May 5th, 15, 10:31 AM Thread Starter
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Re: Measuring Alternator Output

Answering the other questions ...the present alternator has been in service for 7 years, and as such, the car has been wired for an internally regulated alternator and the fans spin freely at operating temperature.

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post #7 of 12 (permalink) Old May 5th, 15, 02:35 PM
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Re: Measuring Alternator Output

A very simple 'test' to see if the alternator out put is big enough for the car.
Turn engine on, and turn on the head lights...and interior light.
These are your 'test' lights
let the engine warm up, choke off (or do this after a good run)
increase the rpms a little.. watch the brightness of headlights and interior light.. there should be be very little change to no change at all.
Now let idle, and start to turn stuff on...start with electric radiator fan on... should be no change in brightness.
Now turn on other stuff like windscreen wipers... one at a time, and heater fan, a/c, radio.
At max u should at idle have a very slight dim of headlights and interior IF the alternator output is marginal...and if increase rpms a couple 100 rpms, no dimming.

Generally if running electric fans or a/c this requires bigger alternators getting up to the 100amp... both the 120/ 140 amp mark.
A non a/c basic with clutch fan a stock 64amp just makes the grade.

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post #8 of 12 (permalink) Old May 5th, 15, 03:32 PM
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Re: Measuring Alternator Output

Quote:
Originally Posted by JohnnyD View Post
Hello Everyone! I have an issue with an electric cooling fan setup that I am told inadequate alternator output may be the issue. Specifically, the 40 amp fuses blew. The alternator that is currently in my car is chrome, at least 10 years old and is internally regulated. Thats all I can tell you. It was something given to me by a friend who does not remember anything about it. There are no numbers, manufacturer name, logo etc. anywhere on it that I can find. Is there a way to test how many amps it puts out? Will a clamp on amp meter be any help? Im told that when they are tested at auto parts stores, its only voltage being measured. Thanks!
Yes...simply place an "amprobe" clip over the heavy wire from the alternator output connector to the battery + with the engine running...The meter's current function measures the flow of electrons through the magnetic field surrounding the cable. Typically, the current draw is dictated by the overall diameter of the blades, number of blades, CFM rating, etc. (1) single 16" diameter fan w/ 10 blades rated at 3000 CFM can draw 15 amps by itself. Your old chrome alternator is most likely a 45-50 amp dinosaur of yesteryear and not designed for electric fans!

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post #9 of 12 (permalink) Old May 5th, 15, 04:31 PM
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Smile Re: Measuring Alternator Output

Just make sure that you use a DC amprobe. Most of them out there are for household AC and not for automobiles.

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post #10 of 12 (permalink) Old May 5th, 15, 05:10 PM
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Re: Measuring Alternator Output

Quote:
Originally Posted by TJS69 View Post
Just make sure that you use a DC amprobe. Most of them out there are for household AC and not for automobiles.
You're right...however, the vast majority of quality meters include both AC/DC functionality.

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post #11 of 12 (permalink) Old May 5th, 15, 08:05 PM
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Re: Measuring Alternator Output

John, if the alternator has been wired for an alternator with an internal regulator you can get a SI alternator from any auto parts store. Order it for a 1985 Camaro. It 's an a SI alternator. Or you can get a later model 100 amp CS alternator by purchasing this conversion harness: http://www.oreillyauto.com/site/c/de...1559&ppt=C0243 Here is the website explaining what to do. http://www.novaresource.org/alternator.htm
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post #12 of 12 (permalink) Old May 5th, 15, 10:33 PM
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Re: Measuring Alternator Output

Is your current alternator 3-wire with remote sensing? If it isn't you should replace it with one suggested by Doug above. Using MadElectrical.com improved charging system is a good way to upgrade and add accessories.

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