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Kohler 6.5 KW 240V AC transformer symbol question

Kenny Crenshaw

What type of transformer is this? The two legs of the AC run into the center of the transformer and lools like a lower voltage AC goes off into the selenium rectifier. I would like to know the name of this type transformer. Thanks



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I've always referred to it as a compounding transformer, but I don't know what Kohler called it. Thinking about it further, I think Kohler would have referred to it just by it's part number, which has to be looked up based on the set's spec number.

It functions more as a current transformer. The two heavy windings are not across the 240 volt output, rather they are in series with it such that all load current passes through the transformer. These windings have few turns. The other winding has many turns. In this way, the heavy load current is dropped to a few amperes for the rectifier and auxiliary field winding, but they are always proportional to each other. Thus, as load increases, so too does excitation, such that output voltage is held practically constant across the load range.

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If your generator still has the selenium rectifiers, replace them immediately! They will fail and in doing so will cause a cascade of failures of other components, mainly the transformer you're asking about.

A standard 25 amp bridge rectifier will do the job, and it's probably a god idea to put a stout MOV across the AC side of it to protect it.



What is a MOV?
Metal Oxide Varistor. It’s basically a special type of resistor that normally doesn’t conduct, but very rapidly changes to heavily conducting above a certain voltage. In this way, an MOV serves to “clamp” (short out) high voltage transients.

MOVs are commonly used in small surge protectors. In larger surge protectors, gas discharge tubes (GDTs) are more useful. Sometimes both are used to combine the properties of both types of devices.



Do I just loosen up A1 and A3 and screw the MOV in there with the leads?

Or do you mean across the AC side of the recifier?
First get rid of Selenium rectifier. When it blows, toxic fumes come out. Replace as LWB suggested. If you use a high PIV bridge, don't need MOV. Bridges are so inexpensive, because of environment, I usually go double amps and 500 volts or so.

Kenny Crenshaw

I ordered a rectifier kit from Kohler. I think it comes with the proper resistor to make up for the lower resistance of the silicon diodes. It was $25, but it is coming to my house and I won't have to hunt for one. I hope it comes with instructions.