# Self Excite Rotating Rectifier Polarity Genset



## nrp3

The one I have in the garage is I'm assuming two diodes, and I can't see how that is arranged as the diodes are buried. What brand and model does this go to. They don't give us a lot to go on for this type generator though the capacitor regulated type are fairly common.


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## Trailboss

nrp3 said:


> The one I have in the garage is I'm assuming two diodes, and I can't see how that is arranged as the diodes are buried. What brand and model does this go to. They don't give us a lot to go on for this type generator though the capacitor regulated type are fairly common.


Two diode are a very common ckt, the excitation stator/capacitor winding is a standard as well.
The interaction of the stator/capacitor winding and the rotating field provides the voltage regulation as you stated.
The common two diode arrangement has two seperate windings each with a single diode across each winding. 
Unfortunately there are no manufacturer markings or any numbers or anything on the unit.
The only thing I know is the unit was sold by Walco Electric in Providence RI. They may have built the gen head. I am waiting to here back from them. The unit was built circa 1988 - 89 judging from the serial number on the Briggs motor. 
Indecently I worked for Walco briefly in 1977 as an apprentice electronics technician. I never spent much time in the motor shop, as on the electronics side we were doing a lot of DC drive motor controllers and some 400Hz military generator controls.
Thanks for the comeback.


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## telsa

I've never fiddled with such a beast, but there's this:

http://generators.tpub.com/TM-9-6115-644-24/css/TM-9-6115-644-24_271.htm

The brushless exciter is actually an AC generator with its output rectified through a full wave bridge circuit. This type of brushless exciter will provide the necessary excitation current. The generator set field flash circuit, activated during each engine start, applies voltage to the exciter stator to begin the voltage build-up process to energize the generator field.

&&&

This device is only a step away from an automobile alternator, a device that generates 3-phase asynchronous power -- that is promptly rectified before it even leaves the alternator chassis. It has a feed back circuit that regulates the excitation so that the voltage is held sweet.

In your case, the asynchronous alternator is integrated with the prime mover.

You can easily figure out which way the diodes must face when you think BACKWARDS. Start from the DC bus. (Hint)

If necessary, grab a four-diode bridge rectifier, or the schematic of same, to realize which way the diodes MUST orient. 

( The current in the DC circuit can only have its one polarity. )

Poke around, you'll get it.

BTW, there is a schematic at the above link that should also give the game away.


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## Trailboss

Hi Tesla,

That's a bit different than the one I have. That is the common full wave three phase ckt that drives the field. It has it's own separate three phase winding and six diodes for full wave rectification. 
It is used in the majority of gensets without AVR.

The one I have the rotor only has the four field windings and four diodes, there is no three phase winding and diode plate with six diodes.
This thing boot straps it's self up by the residual magnetism in the rotor poles tickling the exciter stator, builds a small charge in the capacitor which in turn the discharge current flows through the exciter stator and induces current into the field coils creating a stronger magnetic field created by the rectified current etc....

I believe the diagram I posted has the correct diode orientation now that I have looked it over again. But if not someone pls correct me.

Thanks for the comeback Tess,

Vin


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## RePhase277

It's odd for me to see all the diodes on a single plate. Often the plate is split into positive and negative halves. Is there another plate on the other end of the shaft?


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## Trailboss

RePhase277 said:


> It's odd for me to see all the diodes on a single plate. Often the plate is split into positive and negative halves. Is there another plate on the other end of the shaft?



Nope, just what you see in the pictures and the schematic I drew. 

The diode split plate (3 and 3) is what you normally see in most mid size heads, using a three phase winding to excite the field, the smaller heads will have just 2 diodes, one across each of the two field windings.

Here is another common design. Similar to the the 3 phase in layout, it just uses a single phase winding and a bridge rectifier.


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## MDShunk

Seems like a phonecall to Walco is in order. lain:


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