Alternator charging?

marmon77

Member
Have a 1992 Ford 3930 diesel, put a new alternator on that I ordered from this site. I charged battery put in new alternator now about every 4 days the battery is dead and has to be charged again. I check battery with a multi tester while tractor is running and reading doesn't change even when I rev the engine up. Any other ways to check and be sure alt. is putting out?
 
I say that you have already verified that it is not, otherwise battery voltage would go up during operation, that is assuming that all wiring is correct & good.
 
Battery voltage should be roughly 12.6 or so with the engine off, and rise to the low 14s with the engine running. If it stays at 12
something, it is not charging.

If this thing uses the Lucas (Magneti Marelli) alternator, take a close look at the battery temperature sensor under the battery. If this
and/or the circuit is damaged, it will not charge.
 

Bern is there a way to test the sensor under the battery?
Volt meter stays at about 12.4 even when running.
 
Bern may have something more, but for now, that sensor is a temperature sensitive resistor, so use Ohmmeter to measure it & verify that it is not open circuit.
 
Ok. What exactly does it do? I couldn't find any post or connection on the back of the alt. that was even putting out close to 14 volts, even turned on lights really didn't drop but also didn't increase
 
(quoted from post at 14:39:29 09/08/17) Ok. What exactly does it do? I couldn't find any post or connection on the back of the alt. that was even putting out close to 14 volts, even turned on lights really didn't drop but also didn't increase
attery temp sensor terminal is an input to alternator coming from battery + through the temperature sensing element (thermally sensing resistance) and that signal modulates the alternator output via the internal VR, depending on battery temperature. I believe that connection is a spade connector on rear of alternator and is nearest to mounting ear. If it has no voltage on it, that is likely the reason for no alternator output. Of course there could be other problems, especially since you say that you see no terminal with close to battery voltage! Why? Because the heavy wire alt output terminal should ALWAYS be at battery voltage....running or not.
 
(quoted from post at 14:39:29 09/08/17) Ok. What exactly does it do? I couldn't find any post or connection on the back of the alt. that was even putting out close to 14 volts, even turned on lights really didn't drop but also didn't increase

The role of the battery temperature sensor is to basically shut off the output of the alternator if the battery is too hot, and if the sensor is faulty such that it always behaves as it would if the battery was too hot then the alternator will never put out a charging voltage.
 
Is there any way to by-pass sensor? Work around it?
Thanks for responses, took awhile to get back do to hurricane.
 
(quoted from post at 09:51:00 09/15/17) Is there any way to by-pass sensor? Work around it?
Thanks for responses, took awhile to get back do to hurricane.
ry disconnecting small wire from sensor (lower) terminal and connecting 200 Ohm resistor as in photo.

https://imgur.com/a/GOkkM
GOkkM
 

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