8 Volt Battery

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Feb 24, 2015 | 01:15 PM

#46

Jolly Roger Joe

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Joined: Jul 2011

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From: Rockingham, VA

Quote:

Originally Posted by ALBUQ F-1

All the tests are covered in the Workshop Manual.

So if I'm reading at that correctly, the test simply bypasses the regulator.

What I don't understand is how I have in the past read 7.4 volts on the battery terminals while running at high idle. That's why I said to test it that way. It would seem to me that would show if the generator and the regulator are working.

Feb 24, 2015 | 01:59 PM

#47

ALBUQ F-1

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From: NM

You're correct, Joe. It "full-fields" the generator, telling it to put out full output. It eliminates (or confirms) the generator as the problem. If it works, then the regulator needs attention, perhaps just an adjustment, maybe replacement.

If everything is working correctly, right after starting the generator will likely be putting out 7.4v to recharge the battery. Your test tells whether the system as a whole is working, but doesn't isolate the problem if you get a low reading.

Feb 24, 2015 | 02:31 PM

#48

Tedster9

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From: Waterloo, Iowa

Testing the voltage output at say 1500 RPM, is a good quick test, tho voltage is only part of it. A generator actually runs full tilt all the time, the regulator itself throttles the voltage and current back as load demands. Full fielding basically indicates that the generator can both handle the current requirement of lights and heater blower and charge the battery as well. Corrosion and rust are the big enemies of a healthy charging system.

Feb 24, 2015 | 03:32 PM

#49

Jolly Roger Joe

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From: Rockingham, VA

Quote:

Originally Posted by ALBUQ F-1

Quote:

Originally Posted by Tedster9

OK, I got it now. I guess I was just lucky everything was working when I checked the voltage. Actually, I did that after I rebuilt the generator. I never read the test procedure out of the Shop Manual. I don't think my ancient Fluke meter will measure up to 50 amps anyway. I'll have to look.

EDIT: I just checked my meter. It is limited to 2 amps.

Feb 24, 2015 | 03:45 PM

#50

Tedster9

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From: Waterloo, Iowa

I ran into the same "problem" and solved it with this: (more tools are always a Good Thing)

Attached Images

Feb 24, 2015 | 05:05 PM

#51

Clint1950f5

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Joined: Jan 2015

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From: McCook, NE

One other quick question. Are these systems supposed to keep the motor running if the battery is disconnected after the motor is started? Sorry if this is a stupid question.

Feb 24, 2015 | 05:18 PM

#52

ALBUQ F-1

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From: NM

A generator will keep the engine running; some alternators will, some won't. Some alternators burn up if you disconnect the battery.

Feb 24, 2015 | 11:57 PM

#53

Tedster9

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From: Waterloo, Iowa

Technically the battery's only purpose is to start the engine, the alternator or generator provides all of the voltage and current required for lights, ignition and accessories. It also acts as a filter of sorts to smooth out voltage spikes or sags. This is one reason why disconnecting the battery while engine is running can cause system voltage to spike dangerously high. A generator is a little different in that it utilizes a low RPM cutout at the regulator, since it cannot produce enough voltage at idle. The truck will draw on the battery then. A battery with good reserve capacity helps here, not just CCA.