Generqtor differences

There has been some recent discussion here about 6 V generators with 2 brushs vs 3 brushes and what uses a cut out vs a regulator. What is the difference between the 2 types and if using a regulator why would it matter the number of brushes.

Its much deeper then this but I will toss out a few differences, NOT any complete treatise remember so dont anyone have a calf and cut me some slack if it isnt PERFECT

The earlier gennys and systems had less reliable and cheaper regulation methods to prevent the genny running away with itself and used the simpler cheaper cutout relay and the manual Low High charge control (LHBD light switch and charge control) and the third adjustable brush provided an addition manual method to control charge rate and prevent over current.. The field current (which determines in part the output along with the gennys RPM) was regulated manually

Later on to automatically control the charge rate more complex regulation was accomplished using full fledged Voltage Regulators (they automatically controlled field current) and gennys only had 2 brushes as the better VR automatically regulated and protected the genny.

I have data showing the output versus RPM of 2 versus 3 brush gennys and the more complex engineering differences and Im sure my sparky friends Jim and Bob M do also but Im too lazy to do more and post more stuff for now, the first wife has some chores for me lol

PS they also made some 3 brush gennys that still used the later VR"s and when I converted from a relay to a VR on a 3 brush genny I set the third brush over to max charge sionce the VR would regulate and still protect the genny from over current.......

John T

I believe that current adjustment on a 3rd brush generator is adjusted by the postion of the third brush. There should be a screw on the end plate of the generator which when backed off, allows you to move the third brush one direction or the other to adjust the current flow. On 3rd brush generators, what some of us refer to as the "voltage regulator" isn't really regulating anything at all, it's just a cutout relay tower which, when the tractor is turned off, opens a set of points which stops the battery from discharging through the generator. The charge rate of the battery is actually controlled by the "light switch" which usually has a normal charge position and a full charge position (and then a 3rd or 4th position for the lights when in full charge). If the switch has 4 positions, then the 3rd to 4th difference is low beam and then high beam. I think I'm correct on all of this, but I'm no electrical expert.

Hear is a bit of additional content. In an operating (rotating and producing voltage) two brush generator, a probe could be stuck into the end frame to touch the commutator bars near the Armature brush. This sample voltage would be highest near the position of that brush, and taper to nothing at 90 degrees from the Armature brush.
It is this voltage that is used for the field circuit in a three brush gen. That adjustability allows a farmer (or technician) to taylor charge rate to the use of the tractor. If there were no lights on the tractor (or other equipment like a stationary engine) the field current was unregulated through a fixed resistance wire wound resistor (usually in the same housing as the cutout), and tweaked with the third brush. If the tractor had lights, the charge rate was controlled by a (same resistance) fixed resistor on the light switch, and a direct ground of the field allowing the operator to choose to recharge the battery faster if many starts per hour were being made, or for cold weather operation for better recharging when the battery performance was compromised by low temps. The same switch shaft was used to turn on the lights, and at the same time keep the gen field full grounded. Jim

Here is another little bit on the third brush. The main and ground brushes are 180 degrees apart. The voltage across them is the maximum available for a given field strength and armature speed. The third brush, being in an offset position, is sensitive to distortion of the magnetic field. The faster the armature spins, the more the field distorts. Thus the voltage from the third brush is reduced, if not absolutely less it is at least less relative to the full voltage at the main brush. The net effect, 3 brush generators tend to be self limiting. As they are spun faster, the output voltage approaches a limit rather than running up out of control. A full regulator does the limiting so that type generator doesn't need to limit itself.