Cut out relay

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Isn’t there supposed to be no continuity between the terminals of the cut-out relay when the engine is not running?

The generator on my 1930 Mod B isn’t charging and the points don’t close on the relay when the engine is running running. Jim

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With the engine running, the generator is turning, and should be creating current at a volt or so over the battery’s voltage.

Using a voltmeter, check the voltage at the wire coming from the generator. If it is making 7v or more, the generator is OK. it should be pulling down the point arm, and making contact with the other point and sending current to the battery.

The cut out has nothing to do with the function of the generator. I only connects a running, working generator to the car’s wiring and battery.

Greg

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I was concerned about the current going to ground through the brushes when not turning.

Doing some searching the info said to never run a generator without it being connected electrically and when it was first started in a bare chassis it wasn’t connected but I didn’t smell anything like burning wiring or see that I let the smoke out. How long can they run disconnected? It wasn’t over a half hour but it

it doesn’t put out at all. Female?

The info said there is a thermostat inside, can that be tested with just an ohm meter? Jim

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Hi Jim. I don’t think any harm comes from running a generator without a battery hooked to it. I’d be more concerned about a generator trying to charge an internally-shorted battery, and putting out full output for hours.

There is a temperature compensator in the end-cap with the brushes.. I do not recall if it is accessible when a generator is in the car.

Usually if a generator is good, the fields are not shorted or have an open, and the armature is also good, then if a battery is hooked to the generator case, and the output wire, the generator will motor, very slowly and not have very much torque. but will motor. Obviously disconnect the water pump and fan belts if you try this check in the car.

If the generator will not motor, it has internal problems. If there is no spark when you connect to the output wire, then there are open, broken wires inside. If there is a strong spark, then shorted wiring or windings..

Greg Long

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I’ll expand on my above message.

An alternator or a generator with a voltage regulator is ‘looking’ for a signal voltage or circuit voltage to establish a charging voltage to create.

If you take a battery terminal off of a running car with an alternator, the voltage regulator will ‘read’ a very high voltage, and ramp up the charging voltage.. This can and often does destroy the alternator.

A similar scenario can happen with a generator if it has a voltage regulator.

Our pre-1936 [maybe 1935?] Pierce Arrows have the voltage controlled by an adjustable 3rd brush. So this manual adjustment controls the generator voltage. It does not know if a battery is in the system, or if there is anything hooked to the output wire.. it just makes voltage.. if there is some load on the output, then it will make current [amperage].

Greg Long

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This thing getting more confusing. The wiring diagram shows a wire to the CO relay from the generator and I’m assuming that’s from the third brush and that’s a small gauge wire maybe 14ga the other terminal at the CO relay goes to the term at the amp gauge with a 10ga wire. Why the heavier wire to the gauge if the smaller wire can only carry so much current.

I’m thinking there is a wire not shown in the diagram. Jim

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Hi Jim,

Nope, that’s all that there is. The wiring as you described it is correct.

A heavier gauge wire for the longer distance from the CO to the Amp Gauge. Distance creates resistance.

The shorter output wire from the generator to the CO relay is well-cooled by the air from the engine fan. The longer wire is tucked away, or in conduit. It needs to be a heavier gauge.

Your generator should generate voltage when your engine is running, this will close the points in the CO which then will connect the generator to the car’s electrical circuitry. Without the CO, with the engine not running, the car’s battery would be feeding current to the generator, turning it into a very weak motor, with no rotation, the generator gets very hot, often ruined, and the battery goes dead.

Greg Long

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Greg, you are correct. Many people don’t realize you can turn your car into a toaster if the points stick on your cut out!

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Greg how do you feel about replacing the cutout relay with a diode? I understand its not original but is it a safe alternative?

Dave

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Hi David, I’ve heard of people using a diode inside the Cutout relay’s box/cover. so it looks normal. I do not know how well it works. or what capacity diode would be needed.

I’ve been known to make a short jumper and manually connect around the Cutout. Connect after starting, then disconnect when shutting down.. The manual ‘Greg-Cutout’.. does the same thing as the original cutout..

David, if you are able to figure out a good diode, with fairly easy to use connections, let us know the part number for it, and show us your installation.

Greg Long

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If the diode fails, you cook the Generator, and they fail often, as they are not made to handle the amperage. Supposedly there are some nor installed in tandem and they work ok. I purchased a car that had one in it, and the generator melted down, and that’s the first time I have ever experienced that in tens of thousands of miles driving big pre war cars. I won’t use them.

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Thank you Greg and Ed,

To answer Greg’s question i was thinking about the electronic cut-out that The Brillion Company sells. The part number is #B8001-002. Its rated at 25 amps while their conventional cut-out is rated at 15amps. I was going to put a 15 amp fuse in series and also run it through one of the extra contacts that cuts-out the back up diaphragm priming fuel pump like what has been suggested in past bulletins. The fuel pump would also have an manual switch to shut if off but could only run if the key was turned on. I also like your idea of the “Greg” switch.

I have had the generator rebuilt and ran it last fall but want to get the dash back in before I run motor again. As usual I tend to over think this stuff a bit and have to be reined in once in a while.

Best regards,

Dave

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Correction “The Brillman Company”””

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Problem solved thanks to Greg, Dave and Jak.

The generator did spin when I put power to it but I checked the brushes again like Greg suggested. One brush was worn so it just didn’t touch the armature but when I ran emery cloth under it to clean the brush surface the spring pushed the brush down and cleaned the surface so the clearance was less than the thickness of the cloth. I replaced the brush and all is well now. At least as the charging is concerned.

Parts Plus has cut out relays that fit but they sit 90 deg to the original. Jim

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