alternator problems 300 inline six cylinder

we have a 1965 f100 with a 300 inline six cylinder. my question is why wont it stay running with the battery cables disconnected? we just (today) bought a new alternator, and voltage regulator. still when the cables are disconnected it dies. Any ideahs?

 

alternator is turning to slow at idle to effectively charge.

BTW,, thats not a good way to test an alternator.

 

whats a good way to test it without taking it to a kragens?

 

do you have a multimeter? If so set it for 20 volts and test bettery voltage. bring the rpms up a bit and it should read 13.5-14 volts.

If the voltage doesnt climb above 12 volts just above idle, then you probably burned up your new alternator or regulator trying to run it without a battery.

you can also do this with a test light, (sorta).

Put light across battery and fire up the truck, raise the idle speed and see if light gets brighter, if so its charging, (you dont know how well, but it is charging)

 

quickest way to check alt is when running take screwdriver and touch it to the center of the back side of alt. if their is magnetic draw alt. is working, if not bad alt. simple,easy and quick!

 

X2, fastest way to check.

 

If there is a magnetic field, its charging. (but is may not be charging as high as it needs to). You dont always have a meter with you. And yes the best method is with a meter as then you can check the voltages at the alternator and battery with and without accesories on.

 

It's just a small part of that ol' Darwin thang .....!

 

Damn, you can get a pretty decent multimeter at Sears for under 20 bucks and often less than that on sale. If you are really cheap Harbor Freight has one under 5 bucks.

Yea, all of old farts know the story of how the Chrysler engineers pulled the battery out of one of the first cars with an alternator and drove it several hundred miles but that was a stunt and testing takes real equipment and real known values.
The ideal charging rate for an alternator is 14.2 volts with the engine running at cruising speed. Noticeable lower may not keep up with the accessories and lights and still charge the battery and anything higher than about 14.5 will probably overcharge the battery and cause it to fail earlier along with premature light bulb failure.
If you have a decent or even not so decent multi meter it will be the first thing you reach for when checking out most electrical issues on a vehicle. I constantly use mine to check for voltage drops in circuits and to see if I have continuity in circuits.
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someone told me it could be a short in the return line. does that sound resonable?

 

The first thing u need to know is that an alternator requires excitation current, via the field (or rotor). If there is no current feeding the field, then no charging will be present. The idea of jumpering the A+ to the F terminal and observing the voltage at the battery is a good way of checking. If voltage does not rise with rpm, then the alternator is bad, if it does then the regulator is bad. This of course assumes the wiring is good between all units.

Harbor freight sells multimeters for $2.99.