What does a Cutout do?
Posted by John Regan on January 27, 2002 on the MTFCA forum.
In Reply to: 27' Generator "Cut out" posted by Rick Rodgers on January 26, 2002 at 21:17:01:
The mechanical cutout has the purpose of disconnecting and connecting the battery from the generator. Whenever the generator is putting out over about 7 volts the cutout contacts should close and battery charging begins. Unfortunately there is nothing that regulates that charge amount and the battery is quickly hurt by overcharge. The generator has to work pretty hard too even though most of its power is being used to destroy the battery. Henry said to adjust the generator output to match your normal driving. OK - I give up - how do you do that exactly??
When the cutout sticks closed like yours is doing the battery is essentially trying to "motor" the generator when the generator has stopped spinning and this is the load current you are seeing on your ammeter when the engine stops. Unfortunately this will run your battery down if you don't notice it but you are also discharging your battery during idle when the cutout would likely be open because the generator is not putting out enough to charge the battery and the battery again would be trying to spin the generator as a motor.
When cutouts begin to stick closed they quickly soon also stick OPEN which means the points don't close when the engine is running and that has catastrophic results for the generator since the Model T generator must NEVER be spun without a good cutout and battery wired to it since the generator REQUIRES the battery as a load or it will destroy itself because it is a shunt field generator and with no load there is nothing to limit the field current. Thus the cutout based system does have a few problems but the biggest offender is the mechanical cutout. If you intend to drive the car, do not use a mechanical cutout or you likely will destroy your generator at some point. There are fairly cheap diode type cutouts on the market as well as our voltage regulator. I do not wish to appear commercial so I cannot speak to you about the voltage regulator here on the forum but do replace the mechanical cutout if you intend to drive the car at all.
I added a link to John's Voltage Regulator Page at FunProjects.com.