My Test Mule

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dibbons

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La Paz, B.C.S., Mexico
I have what was advertised (at time of purchase) as a daily driver '65 Valiant Signet convertible in my stable. It shall become the "hero" by the end of this story (see foto #1). I believe the voltage regulator to be the original factory-style points driven in a black plastic case, not electronic (see foto #2).

In storage, I have a pair of alternators (see foto #3). One is from the complete but hodgepodge 340 I purchased which bears some yellow paint that inscribe the word "Good" (see foto #4). The other is from my '65 Formula S that has been stripped the past two years for restoration. It is a rebuilt that I installed myself.

Curious as to the condition of the two alternators, I tossed them in a box and headed to the nearest Autozone. They could not help me, said the test equipment was "out of service". Went further into downtown to a second Autozone, where an employee there spent about 30 minutes fooling around and "testing". Looking in a drawer full of various wire looms, looking up for fotos to find a similar alternator in the computer database, comparing the display foto with my alternators, consulting an instruction screen on the test unit, talking it all over with a second employee. Finally he finds a belt short enough to spin the alternators and hooks up a couple of wires. He closes the lid and things begin to spin inside.

A large red rectangular box on the tester screen flashed in large print "FAILED". The Autozone guy runs the second alternator through a similar test routine with the same results "FAILED". Then he re-tests the first alternator again, maybe switching some wires around, I don't know. For the third time in a row: "Failed". We place the alternators in my box, I thank the guy and tell him I will advise my mechanic (a white lie).

I come back home and fire up the convertible. It's putting out 13.8 volts at idle and 14.2 volts at a fast idle. I install the two alternators that just failed at Autozone. They both test out at the same 13.8 volts and 14.2 volts. I am pleased with myself and pop open a can of V-8 to celebrate my triumph over ignorance and incompetence. Oh, did I mention this is Autozone Mexico? Don't believe USA stores are much better though.

Note: Last foto below for effect, not a screen image from alternator test bench!

test mule 1.JPG


test mule 2.JPG


two alternators.JPG


Alternator good.JPG


failure.jpeg
 
Good for you.

Now. If you really want to check the alternators, bring the rpms to 1250 and put some load on them.
Since you don't have a carbon pile, turn on the parking lights, then the headlights, and finally add the heater fan.
Check the ammeter at each step. If at any step the meter shows discharge, the alternator output has been exceeded.
Also measure the voltage at each step. You can measure at the battery or at the alternator. I think alt output voltage would be better in this case as it won't be effected by the voltage drop changing with increasing current.
 
PS. Both of those have been rebuild but I can still make out a part number stamping.
It's possible that the with the part number, the original application and rating for each alternator can be figured out.
 
What I did do, was turn the headlights on and off, and then the turn signals. The needle on the ammeter gauge on the dash kept to the right/charge side of the gauge in both cases.
 
If you ever decide to use the one that says "good" on it, swap in a good insulating washer on the main post. The one it has looks cracked. If that washer fails, all hell breaks loose when the post grounds against the case.....think fire and brimstone! It's nut is one of those "tighten, but, don't overtighten" items.
 
Unless you can load the output to full rated current, you are not fully testing them. For example, a "let's say" larger maybe 50A alternator with just one open diode will still output enough to run an older car.

A bad diode CAN cause big problems especially with solid state devices because it causes a lot of AC ripple on the output, as well as a nasty whine in any audio systems.

"In a previous life" in the Navy, my 69RR failed I think it was 2 diodes. This was in the later part of "before payday" so I just pulled it apart and cut loose the two bad ones, and went ahead and ran it. This turned a ?37? A alternator into I don't know, a ?15-20A? alternator. This was in San Diego, so I avoided the heater, did not drive much at night, and a 69 383 RR does not usually have much in accessories. You would not get away with that trick with today's EFI systems............

On the other hand, your test method is likely as good (bad) as these parts stores. Most these parts store testers do NOT fully load an alternator
 
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