Field generation rectifier

Mike Schweikert

I was wondering how the field generation rectifier is used.

My 3.5E62 is going to get its replaced, but I don't know how it is regulating the field unless it is compensating the field current inverse of rotor speed to keep a fairly constant voltage output in absence of a dedicated voltage regulator?

Need some schooling:D

Kevin K

Do you mean the compounding transformer with it's associated rectifier? Is the rectifier a selenium rectifier with large cooling fins?

In Kohler generators that use this regulator scheme, you have two field windings:

A shunt field and associated field variable resistor that uses voltage from the exciter to produce a magnetic field in the stator. You typically adjust the resistor to give 115 or 120 volts with no load.

An Aux field with an associated compounding (current) transformer and bridge rectifier. The primary of the transformer is connected in series with the load. The secondary of the transformer supplies voltage to the rectifier where it is changed to DC and applied to the aux field. As the load on the generator increases more voltage in induced into the secondary of this transformer, converted to DC by the rectifier, and applied to the aux field. The greater load on the generator, the greater the current applied to the aux field, which keeps the generator output fairly constant.

Mike Schweikert

Yes to both. After reading the dire predictions on the selenium, which BTW is akin to my tube radio projects where I see one, it gets replaced with a diode.:O

That's a interesting way of regulating the field without a dedicated VR.

Thank you for the concise explanation, much appreciated:D


Active member
It’s clever old-school design stuff from back when components were all expensive. Cool stuff.

The usual thing to do is to get a beefy bridge rectifier and use that to replace the selenium. Most people use 25 or 35 amp rectifiers. It’s not really necessary to use such a beefy one, but they’re all cheap and it’s convenient to just mount the big ones with a screw through the center hole and use fastons to connect to the terminals.



New member
Good news the scr heatsink assy has finally arrived.
I did a benchtest and it works as discussed earlier.

So now I have an easy re-assemply question.

in the manual tp-5353 page 7-10. One of the note sections states do not exceed a torque value of 8 in pounds..

in my opinion 8 in lbs is way too loose, it's not much more than basically finger tight

I used a very short 4 inch box wrench and snugged the bolts to basically finger tight in place.
when I checked the torque, I easily exceeded the noted value.

this is your typical 10-24/10-32 grade 2 bolt and according to apendix-d, 26 in lbs is listed.

not sure why the difference i re- torqued 2 of the 4 at 15-20.
I don't trust the torque wrench that much since it's a cheap $25 beam type

hope this is ok since I'm putting things back together.

my values were in the 25 to 30 range.

Is 8 in lbs valid or a typo?
If correct should I loosen the bolts and try to hit below 8?
If I do nothing are there any risks to lose sleep over?

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