6 volt generator output

[deetz]

Working on a '39 Mercury which doesn't hold a battery charge too well, and wondering what the generator output should be. Guessing around 7 volts? Thanks.

[JSeery]

A little over 7 volts. Also need to check and see if anything is bleeding the battery down with the ignition off.

[Charlie Stephens]

Originally Posted by deetz

Working on a '39 Mercury which doesn't hold a battery charge too well, and wondering what the generator output should be. Guessing around 7 volts? Thanks.

I am not sure I understand the problem. Does it go down overnight? Does it go down when driving it like the generator isn't keeping up with the load?

Charlie Stephens

[deetz]

I can jump-start it, and the engine starts and runs fine. Have never driven more than about 45 minutes. After initial start, I can get another start or two. After that, starter begins to turn over very slowly and petty soon kaput. Battery is about 10 years old (have not load tested yet). Generator belt and electrical connections are tight. Just poking around under the hood at this point.

[tubman]

If that battery ain't an Optima, you are seriously pushing your luck.

[fordwife]

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test the battery, 10 years is getting pretty old.

[rotorwrench]

10-years is well past any warranty period and most only have a max of 5-years. I never expect much more than that. I've looked for 6-volt high rate discharge testers and I don't think anyone make them any more. A volt meter and a hydrometer will tell you a lot. A good high rate test is to check it a night. Turn the head lights on and crank the starter. If the lights go way dim after it's been fully charged by a charger then the amp hour capacity is getting very low.

Your generator(should be a 2-brush with 3-pole voltage regulator on the 39 Merc) should put out 7.2 to 7.6-volts or there abouts. At the battery, it should give a volt reading above battery voltage when the engine is running with generator charging.

[fjz]

How do you check a generator?

[jimvette59]

fjz charge it and load test it.

[fjz]

Jim: How do I load test it? I have a volt meter. Thinking of Disconnecting the wires from the generator, starting the motor then touching the terminals with my volt meter. Will this tell me anything?

[russcc]

Most good garages have a way load testing a battery. They charge it fully, and then put a load on it to measure it's condition. 10 years is a long time for an average battery, especially if it isn't used often.

[JSeery]

Originally Posted by fjz

How do you check a generator?

Two recent Koats post:

A quick easy test on the generator only. Join the Gen and Field wires together at the regulator but have them disconnected from the regulator. Connect an analogue DC voltmeter to the two connected wires (NEG voltmeter wire) and the POSITIVE voltmeter wire to ground. This is assuming your Ford is original POS ground. The scale on your meter needs to be 20 to 30 volts DC. Start engine and rev it up to 2000 RPM or so and the voltmeter reading should rise quickly to the end of the scale as the revs rise. IF volts are zero or low as in 6 volts or so then the generator is faulty. Its a bit hard using a digital multimeter set to DC volts to read this. An old analogue type voltmeter is best. Just do that test ONLY and report results. Regards, Kevin.

Get your car hot and up to the point where it is not charging again, leave it running and disconnect the field wire, (middle one ) from the voltage regulator and move/connect it over to the Armature or Gen terminal. Rev engine up and read voltage at generator terminal of regulator which should go to 8 volts plus. This is providing the generator is Ok. We have bypassed the regulator field control here and the generator will charge flat out if it is working OK. If there is still a low voltage reading of 6.25 volts then the generator is faulty. If the voltage is 8 volts plus then the voltage regulator is faulty and requires attention. Also very important that all battery power connections and earths a good throughout the car. Check battery terminals, starter solenoid terminals, ammeter terminals, etc. Should be tight, clean and not getting hot to the touch during operation. Regards, Kevin.

[Tinker]

Charlie and JSeery are hitting on all cylinder here on internet armchair ideas.


Of course if your battery is bad then.... autozone will check crank power for free, but they sell batterys . CCA are something to consider. I'd do the battery separate to isolate the issue.

[Tinker]

Originally Posted by fjz

How do you check a generator?

Volt meter will tell if it's charging when running past 2rpm. A good apm or volt meter in the car is convent. Factory installed.


Along with a good oil pressure gauge, left right water temps and a decent fuel gauge. You can't go wrong. I've added a vacuum gauge just for fun.

[fjz]

Did the Koates generator test. Generator putting out 19.6 volts. Amp gauge reads -2 when running both with my old and new regulators. Took cover off the regulator and can not see anywhere to adjust. How can I check the regulator?

[JSeery]

Regulators are not easy to adjust. I have an article on it I can post later.

[fjz]

Thanks JSeery. Looking forward to it.

[JSeery]

This is not the one I was originally thinking of, but it might help give you the idea of what is involved.

[fjz]

JSeery: Read the article. I am thinking my issue is that I have the ground wire connected to the cover and not under the mounting screw. Will install a separate ground later and try that. Thanks for your help. Frank

[JSeery]

It depends on how the VR is mounted, if it is straight to the firewall with metal to metal contact it should be ok as is. If it has the rubber vibration washers then the ground wire needs to be connected to the firewall. I would make sure that both the VR housing and the generator are connected to a common ground near the VR and make sure that the body (firewall) has a good ground back to the battery.