1930's generator operation question

[hursst]

Hello,
How is the cut-out switch normally supposed to operate on a stock generator for an early 1930's car, specifically, I have a 1930 Plymouth.   I've been having a lot of problems with my generator recently, but I don't really know what "normal" is anymore, since it's never really worked correctly. From my understanding, the cutout switch will operate when the battery needs to be charged. When the cutout is operating, it should read around 0-1 at idle and up to about 18-20 amps at full throttle. When the battery is fully charged, and the cutout switch is not operating, what should the amperage reading be? Will the cutout come on when headlights are turned on no matter what, due to the large drain on the battery? What is the normal reading for amperage at idle and at full throttle if the cutout switch is off?

I had my generator profressionally rebuilt and tested with a functional cutout switch. When I got it home, it worked for about 15 minutes, then did not work at all. I cleaned all the connections to the bracket where the generator attaches, cleaned the attachments to the cutout, and cleaned some residue off the inner rotor where the new brushes are leaving some black residue t oensure ground grounding everywhere. This made it work again for another 20-25 minutes of driving over 2 trips, now it doesn't work again. When I put the headlights on, the cutout switch does not turn on and amperage drops to around -17 amps.

Is all of this normal and the cutout switch should turn on again later if I drain the battery further, or is this indicative of a problem? I'm not an electrical guy, so I don't know if my system is really functioning correctly or not. Thanks for any advice.

[MCHinson]

It sounds like you need to replace or repair the cut out switch.

[hwellens]

The cut out switch is usually off at idle and kicks in about 700 rpm. It is basically and of/on switch for the generator and has nothing to do with the condition of the battery or whether you have your lights on. The amperage is adjusted by your third brush which looks like it is adjusted to produce 18-20 amps as you stated which I think is the maximum you want.   As stated  above, try another cut out switch. You can try to bypass the switch when it is running to eliminate it if you know how to do it, but, be careful not to bypass the switch when the engine is off. It will make your generator think it is a motor and probably burn it up.See attache from a 1929 Dodge manual.

Dodge generator.pdf

 

[Rusty_OToole]

The cutout is solely to prevent the battery being discharged when the generator is not working. It disconnects the generator from the battery so it cannot drain the battery.

 

It works as hwellens describes. It is supposed to switch the generator into the circuit when it is charging and disconnect when the engine is stopped.

 

The amount of charge is regulated by the 3d brush.

[hursst]

Thanks for the replies.  This helps, now I know that in the past the cutout switch was operating as normal. 

 

Recently, sometimes the switch works, sometimes it doesn't.  Same thing happens with a brand new replacement cutout switch I have, so I know the cutout switches should be good.  I'll have to keep messing with it or buy yet another cutout switch in case the 2 I have are both squirrelly. 

[Friartuck]

A few comments not already mentioned. The cutout is a relay that utilizes the generator's output to pull the internal contacts together and make the connection from the generator to the battery. As mentioned, the generator's charge rate is usually done by adjusting the third brush. The battery's charge level has no effect on the cutout operation. If there is intermittent operation, it could be connection related. Check the wire connections and the ground. If the cap is removable, do so and while the engine is at fast idle use an insulated dowel (like a pencil) and manually close the contacts. The contacts should remain closed. This would be the point where the generator is producing enough voltage to keep the relay closed, but not enough to overcome the spring tension to pull them closed. You may have to manually adjust the spring tension with needle nose pliers to a lighter tension to get the contacts to close under lower RPM (i.e. lower output voltage). What is baffling is that it would work for some appreciable period like 15 minutes and then cease. I'm wondering if there is another problem like maybe there is a circuit breaker in the system or the cutout has a thermal switch that overrides. Cutouts operation is usually fool proof since there is just a relay.  Can you post a picture of the generator and cutout as its mounted in the car?

 

1. Clean the Cutout's contacts with very fine sandpaper (600 grit) or crocus cloth. Even a new unit out of the box may have residual debris.

2. If this Cutout is mounted directly on the generator, check screw connections such as under the mounting tabs which are the ground.  

3. Monitor the voltage level with a Volt-Ohm-Meter (VOM) at the input of the Cutout which is the generator's output. Note the voltage level where the cutout closes. Note the level when the cutout ceases to verify that the generator was still producing voltage. This would verify or eliminate the cutout as the problem.

4. When you do get this charging system working reliably, Run the engine at fast idle (e.g. 1200 RPM) and with all lights on adjust the third brush so that the current is about 1 amp. This is intended to run the lights and ignition at night while not draining the battery and not over charge the battery during day time driving.

[rsb]

Think of the cut-out as a diode or check valve allowing current to flow in one direction. That is, from the generator to the battery. It depends on residual magnetism in the generator to generate enough power to close the relay and get things going. Sometimes getting that adjusted just right is a little tricky but the advice above is REALLY good.

 

In my opinion, the lack of any real voltage regulation on these early vehicles reduces the life of the battery due to over/under charging. There are ways to hide a real voltage regulator that will maintain the battery at the proper voltage. Once you get the original charging system sorted, you might consider upgrading to a regulated system.

[Owen_Dyneto]

Voltage regulation with this type of charging system really isn't the shortcoming, it's amperage regulation.  But if you pay proper attention to your charging rate (3rd brush) and current draw it doesn't necessarily shorten battery life - I typically have gotten 8 years or more from the batteries in my '34 Packard with a 3rd brush system.

[hwellens]

I have cutouts on 3 of my cars and none act like a diode or check valve. If you think current can only go one way through a cutout, try holding the contact down with the engine off. The current will go from the battery to the generator. That is why you need some rpm on the motor before the cutout contacts close to insure the generator voltage is greater than the battery and the current only goes towards the battery.  See attached for a more details.

 

Cutouts.pdf

[cahartley]

Do yourself a favor and replace the mechanical cutout with a solid state cutout/regulator.

 

http://funprojects.com/search.aspx?querystr=regulator&querytype=all

[Curti]

You probably have the same Auto-Lite cutout that Auburn used in the 30's.  I gut the internals  from the cutout and solder in a heavy duty diode. The diode only allows current to flow one way.

Diodes come in positive or negative ground.  That way, you retain the original appearance while using modern technology.