8ba Shoebox generator

mrlaser

mrlaser

Senior Member
I have a question regarding the proper voltage on a positive ground, 6 volt battery. With the engine off the voltage reading is 6.7. with the engine idling and nothing else on, it measures 10.2 volts across the posts. The generator has been rebuilt, the wiring harness is new, and the voltage regulator is NOS. The car runs well,though I should mention that the amp meter needle is broken. Temporarily hooking up a spare amp meter shows a slight neg deflection when the turn signals flash, with the key in the accessory position. (engine not running) Any advice would be appreciated.
 
That is way too much voltage. The maximum output on the voltage regulator B terminal should be 7.6 volts or less (7.2v is better). This should be the same or less at the battery. There is a VR problem, they can be adjusted but it is not simple to do.

Ford has an approximate bulb life chart:

6.1v 3300 hrs
6.5v 1425 hrs
6.9v 645 hrs
7.3v 322 hrs
7.7v 160 hrs
8.1v 87 hrs

So you can guess at 10.2 volts.

Here is a battery percentage of charge chart.
 

Attachments

  • maxresdefault.jpg
    maxresdefault.jpg
    50.5 KB · Views: 19
Last edited:
mrlaser said:
I have a question regarding the proper voltage on a positive ground, 6 volt battery. With the engine off the voltage reading is 6.7. with the engine idling and nothing else on, it measures 10.2 volts across the posts. The generator has been rebuilt, the wiring harness is new, and the voltage regulator is NOS. The car runs well,though I should mention that the amp meter needle is broken. Temporarily hooking up a spare amp meter shows a slight neg deflection when the turn signals flash, with the key in the accessory position. (engine not running) Any advice would be appreciated.
Click to expand...

I agree with JS, way to much voltage. I don't know if there is a brush
adjustment on your gen or not. Voltage regulators are tricky to adjust.
I would take it to a auto electric shop to get straightened out. G.M.
 
One more question. Can the voltage regulator be adjusted off the car? In other words, could I simply take the regulator to an automotive electrical shop by itself? I don't want to risk damaging the ignition system if possible. Incidentally, the generator is a 2 brush type. It is my understanding that any voltage adjustment is accomplished at the voltage regulator. Is this a correct assumption? Thanks for all the information.
 
You can adjust it on the car, not hard if you know what to do. If you bring it somewhere be sure they are familiar with this old technology. If you can find an appropriate service book you can see what to do. It involves bending the spring tension on the field current section of regulator, pictures make it clearer.
 
I have never adjusted one of these, mainly because people I know and trusted have told me it was difficult and it was easy to have done. As to a shop doing it off the car, if they can't, they're not worth going to. The problem will be finding one. When I lived in the twin cities area, we always used A & B Auto Electric. They were good and they were reasonable. I wonder if they're still around?
 
mrlaser said:
with the engine idling and nothing else on, it measures 10.2 volts
Click to expand...

Isn't 10+ volts at idle quite extreme? Doesn't it indicate something more than the regulator being out-of-adjustment? Doesn't it indicate something in the VR has failed, like the voltage regulator coil has lost continuity, or it's contact points are stuck closed?
 
Last edited:
An auto electric shop could adjust the 3-pole VR unit if they still have an appropriate test stand. Keep in mind that these specialty type shops don't likely repair a lot of 6-volts stuff any more and most vehicles use alternators. A shop that has been around 50+ years could have the needed equipment. A 10-year old shop, not so much.

The old original units are made to be adjusted. The new offshore replacements are not.
 
Jay,
I'm sorry for an unintentional misleading statement in my original post. The 10.2 volt reading was at an RPM well above idle. Unfortunately, I don't have anything to measure the actual RPM.

Thanks everyone for the feedback. I'm looking for someone who will be able to attend to this issue.
 
At that voltage level don't think knowing the RPMs are that important, LOL. I believe the manual states 1200 RPM to take a reading. But the VR output should be fairly steady. At idle a generator output will be low, but as soon as it's off idle it should be outputting what the VR is set at.
 
Well, I just switched the voltage regulator for a spare, NOS American Bosch VR which I had forgotten that I had. The current readings are at idle = 6.5 volts. At a moderate RPM= 7.2 volts. That seems to be much better. Should I do any other testing or assume at least this issue is corrected? Thanks for all of the help that you have all provided.
 
Sounds right on spec, should be fine as long as nothing was damaged from the higher voltage. And I think that would depend on how long it was run at the higher voltage. If it runs/drives ok the coil probably survived.
 
How true. I have to admit to being seduced by an item being NOS. Especially when the alternative is "made in China". I lived in China for 2 years nearly 50 years ago. I came to admire their industrious nature, but for the most part quality control was non existent at that time. Kind of like "made in occupied Japan" after WW 2
 
You must log in or register to reply here.
Back
Top