The Stovebolt Site Forums The Shop Area The Electrical Bay generator cut-out

Got the '37 running pretty good but am seeing sparks in the cut-off mounted on top of the 6 volt generator.
The base is bolted to the the generator so it's grounded. The top part of the cut-off is a little loose and sparks
between it's lower edge and the base. Should there be an insulator between those two pieces or should the
whole thing be insulated from the generator case? Don't want to burn the thing down.
Thanks
John

Nothing about that cutout relay should be sparking. Try removing the cover so you can see what's going on inside- - - -its only function is a dust cover. Brand new cutout relays are on Ebay frequently, and they're not terribly expensive.
Jerry

The cutout relay should be grounded but just because it is bolted to the generator does not necessarily mean it is grounded. I would clean up the mounting hardware and see if the sparking persists. Maybe the unit is just trying to find ground. Also, what is the ammeter doing when the sparking is happening?
Kent

No grounding involved anywhere in the cut-off (see diagram).
Check that the wiring inside the cut-off is not shorted to the cover or case.
There is/are points or relay inside the cut-out cover that open and close.
Maybe the contacts are bad and arcing across?

That terminal marked "G" in the left diagram certainly looks like a ground, unless electrical symbols have changed recently. The right figure completes the point closing magnetic coil circuit by going back to the generator.
Jerry

Buoymaker, I see ground indicated in both figures in the attachment. In figure 35, associated with "V" coil there is ground indicated. In figure 36, if you follow the wire from the "V" coil it goes to ground inside the generator. Also, my 1937 shop manual shows the cutout or "circuit breaker" as it is also called with a ground connection from the coil.

Kent

Yes, there is a ground inside the generator but not under the cut-out relay cover where the sparks are coming from unless I read it wrong.
All the electrical parts inside the cover should be isolated from ground.
The "ground" connection inside the generator is (-) negative AND chassis ground.

The other diagram is for a relay not mounted on the generator.

Does the OP's generator have the built-in thermostat that alters the charge rate according to temperature? There is also another 3rd. brush circuit that incorporates a resistor built into the light switch to change the charge rate from daylight to dark operation. None of the systems can actually charge a low battery- - - -the best to expect is maintaining whatever state of charge the battery is in at the moment. Back in the 1930's, some battery manufacturers had "battery charging stations" to top off their customers' batteries while they were at work.
Jerry

One sure way to crack this nut is to take the cover off and look for a ground connection.

The wiring in the original photo appears to be incorrect. There is a heavy wire leading away from the generator, and another one coming out of the wire bundle, attached to one terminal of the cutout relay- - - -with a tiny wire at the other relay terminal. Wired that way, the charging current cannot be interrupted between the generator and the battery.
Jerry

Attached is a picture of my '37 and the wiring seems to the same as 37Barn Find posted originally. The two heavy wires in my case go into the harness. I finished restoration in 2018 and have put 1400 miles on the truck without problems so I think it is correct. I have also posted a portion of the wiring diagram that came with my harness done by Rhode Island Wiring. You can clearly see that the cutout is placed on the generator and the cutout is grounded. The diagram also confirms the wiring seems correct, at least as we can determine from pictures and diagrams. Many of us have seen examples of poor ground due to corrosion and I still think that has not been ruled out in this case.
Kent

Thanks everybody. I'll take your advice and see what I can figure out tomorrow.
This is the truck that some high school kid was working on over 50 years ago and has been sitting on blocks
in a barn ever since.
It could very well be wired wrong.

So Jerry,
How should the wires be connected?

Look at Lightholder's diagram, (not his photo) and compare it to your wiring. It shows a heavy wire from the generator going directly to the cutout relay, and from there to the battery. That will disconnect the generator from the battery and prevent the battery from discharging through the generator when the engine stops and the generator is at a lower voltage than the battery. Generators do not have diodes- - - -current can flow either way. It doesn't make any sense at all that the generator output would have to flow through a tiny wire when the other one is so big. The only way that would have any hope at all to work would be if the charging current is grounding itself to the governor housing through the relay mounting bracket after passing through the battery.

I have some original Delco-Remy service bulletins from the 1950's with wiring diagrams for 3-brush charging systems. PM me a snail mail address and I'll send you some copies as soon as I get some more printer ink.
Jerry

Looks like I was wrong about the ground at the cut-out. There is a chassis ground. Sorry about that folks.
The changes in electrical design between 1936 and 1939 is crazy.

To me it looks like the wire coming from the hole inside the generator housing going to the cut-out is a coated wire.
The size of the wire coming out of the cut-out is unknown because it runs through a cloth covering but one would think it is a large conductor.
The smaller cloth covered wire, coming from the connector on the generator housing, goes to the lighting switch.

1937 generator with a cut-out is model 948-R (truck?). The generator with a regulator is model 960-G (car?).

Buoymaker,
The labels you have kindly provided on my picture are correct and your wiring diagram agrees with that provided with my harness. So back to '37 Barn Find's original question, do you think it is possible his problem is a poor ground on the cut out? It would be pretty easy to clean up the bolts mounting to the generator housing and see if his problem goes away.
My harness was made by Rhode Island Wiring and is supposed to be a copy of the factory drawings. It comes with factory correct cloth coverings with proper markings. The large wire attached to the cutout is 12 gauge and the wire coming off the generator itself that goes to the field resistance is 16 gauge.
Kent

I would take the cover off and look. Hopefully the OP will provide more info.

I haven't found any information on the original size/gauge wiring was used so I would go by what was originally installed by Chevrolet.
The problem is finding a 37 truck that hasn't been modified.

I have no idea if this is a correct generator. Like I said- the previous owner started tinkering with it when he was 14 so who knows

The noise is my chin hitting the table.

So today I removed the cut-off. I found that there is a plastic (?) insulator between the cover and the base (see photo).
The insulator was intact on the left side (battery side) but was broken on the right side (generator side) so it was arcing
between the cover and the grounded base by the terminal screw. I built up the missing insulator with PC-7 epoxy and
problem solved.
Thanks everyone for the help.
John

Looks like an excellent job of troubleshooting, diagnosis, and repair! I'd love to get some test equipment onto one of these old rigs and document just how much charging current they can produce under different ciccumstances such as lights on or off, medium engine speed, highway speed, etc.

The most recent use of 3-brush generators and cutout relays was on farm tractors, stationary engines such as irrigation pumps, etc. where the engine was started once and ran for hours without being shut down. Bacically a trickle charge system.
Jerry

Appreciate everyones advice.
Yesterday I didn’t know what a cut-off was and now I’ve fixed one. Generator is 4.7v at idle and 5.8v revved up a little. Cut- off is releasing properly when engine turned off

One further tidbit of information- - - -to properly check the output of any charging system, but definitely a 3 brush setup, it must be running againat a fully charged battery. A 6V battery with a full charge will have a terminal voltage of 6.3 with no load on it. In order to keep a 6V battery charged, you need to have around 7 volts at the battery posts with the engine running at highway speed. Chances are you're dealing with a partially discharged battery which will accept a charge at a lower than normal voltage.
Jerry