49 Merc overcharging

[Marv 49]

The generator on my grandpas 49 Merc is putting out over 9VDC when reving the motor. With the motor off it is 6.5, and at idle around 7.2. This is a new battery only a couple months old. The battery cables were redone with 1/0 cables I saved from wrecking out an old battery backup system at work.

The only change to the charging system was I opened up the generator and used elctraclean to clean all the old grease and grime from the internals of the generator. I assume this is where my issue lies, but can’t find the problem

I polarized/motored the generator and polarized the regulator using the instructions on the cover. I tested the output of generator with the motor running and the field and armature wires disconnected. This resulted in the output of 14-15VDC.

Any ideas on what I need to do check? I would love to drive it 15 min to town today for our local car show, but I also don’t want to mess anything up

[Kurt in NJ]

The regulator controls both the voltage and limits the amperage to safe amounts for the generator and usually can be adjusted.
What happens when the headlights are turned on— that could be good enough to go to the show.

[Marv 49]

Thanks, I will give that a try

[hueyhoolihan]

it's my understanding that generator output voltages vary directly with the speed at which they turn. the faster it turns the more voltage it creates. the regulator is there to protect the battery from voltages greater than that it needs to charge the battery, which is about 6.5 to a bit over 7 volts. too much and it can damage the battery or at least shorten its useful life. voltage regulator designers have used various means to dispense with excessive voltage throughout the years.

i get about 6.3 volts from my multimeter when the engine is not running. i get about 6.5 at idle and about 7 at 2500rpm. the dashboard gauge is there to reflect something similar for the driver.

[38 coupe]

If you are careful, and your regulator is of good quality, you can adjust the voltage regulation down to the factory setting of approximately 7.2 volts output. Adjusting requires very carefully and gently bending the tang holding the spring on the voltage regulation section of the three unit regulator. More spring tension ups the voltage, less spring tension lowers the voltage. This is a very delicate setting, not simply bending things visibly. I have experience this adjustment not working properly on a new lower quality regulator, where a series of small adjustments made no difference and the next small adjustment disabled the regulator from functioning effectively at all.

[hueyhoolihan]

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6v voltage regulators are readily available on the internet. purchased one for my '41 when i found that the regulator was throwing out almost 11 volts! it seems someone had been in there a tweaking it...

it's too complicated to go into why they did it and how i found out, but let's just say there was an 8 volt golf cart battery mismatched with a new 12v starter involved. and things were not going well...

[Anteek29]

My '55 Vic had an 8 volt battery put in by the previous owner who lived in a cold weather area. I replaced that battery with a new 6 volt one and adjusted the voltage regulator to proper charge setting of 7.2 volts.

[rotorwrench]

The old voltage regulators work like a horn vibrator coil only much smaller and more intricate in adjustment. They basically just buzz along maintaining output by rapidly opening and closing the output circuit. It should maintain the voltage to the 7.2 volt mark with a very small range like +0.2 to - 0. A person needs a very good analog de'arsonval type voltmeter with decimal graduations to adjust them properly. The current limiter pole and cut out pole can also be adjusted but a person needs the proper test equipment to do that as well. Digital meters tend to be difficult to read when working with small voltage values but some good ones will work.

An FYI on flashing the field. The field coils will magnetize the generator pole shoes with enough residual magnetism to generate a voltage. The act of flashing the field is to flash it for just a momentary spike of energy to the coils. Since the field is connected for proper polarity of the magnetic gauss, this is the reason the term polarizing is also used so that the generator can have output on the proper polarity for the systems battery connections, ie positive ground for most Ford applications after the model T era and prior to the 1956 model year when the voltage went to 12-volts.