Mercury Generator

[RalphG]

I pulled this Mercury generator out of the spare parts bin today and was surprised to see it rated as "7 volts". its an exact match to the one on my 52 but my tag was damaged and not able to read the output rating.
Mine on the Merc still works fine but I notice the little grooves in the commutator are worn nearly smooth and now wondering what shape the brushes are in. I don't want to pull it apart when its still working ok but might consider fixing up this spare one to have on hand in case its needed.

[JayChicago]

A “6 volt” generator’s output when charging is about 7.0-7.4 volts.

[petehoovie]

Originally Posted by RalphG

I pulled this Mercury generator out of the spare parts bin today and was surprised to see it rated as "7 volts".

[Bored&Stroked]

Good idea on getting a spare ready to go. I always have a spare starter on hand as well!

[Flathead Fever]

A generator or alternator needs to put out more voltage than the battery to charge it. If the voltages were equal, it would not charge the battery. Voltage is the equivalent of electrical pressure, if both pressures are the same the pressure would equalize until the battery voltage was drained lower. We don't want the voltage going below the required operating voltage of the system so the charging voltage must always be more than the battery voltage. On a 12V system the battery is 12.6 volts but 14.2V (pressure) is needed to make those electrons flow back across the plates to keep the battery at 12.6 volts.

My dad always carried a spare generator and ignition parts for his Model A's and the tools to replace them. On one club trip to Death Valley a Model A hit a wild burro in the dark and shoved the radiator back into the fan. That would have been hard to anticipate, you can't carry a spare of everything. The burro was fine, you have to pretty tough to live in Death Valley. Wasn't entirely the burro's fault, he wasn't used to running out in front of 6V headlights and Model A brakes. The coldest night of my life was riding in a rumble seat in Death Valley, at night in the winter. I'm damn near froze to death back there. In the olden day if you loved your kids, you bought a sedan and not a roadster.

[rotorwrench]

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Most of the old standard 8BA generators don't have any tag on them. Ford started adding a data plate late in the 8BA era. They used the voltage regulator output specs on the data plate. They could put out 35 amps but it depended on the voltage regulator that was used. Current limiters were set to 26-amps and the voltage regulator to 7.1 volts or so. They ran in a range so they all vary just a little bit.

[RalphG]

I'm not sure that I've done an actual output test on this gen on the Merc. I know it keeps the battery charged so its doing it's job.