Build a Synchro rectifier for Onan CCK??
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Garden Tractors
Forum Description: A great place to discuss the Simplicity and Allis Chalmers Garden Models
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=206795
Printed Date: 21 May 2025 at 10:54am
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Topic: Build a Synchro rectifier for Onan CCK??
Posted By: Heliarc
Subject: Build a Synchro rectifier for Onan CCK??
Date Posted: 20 May 2025 at 7:48am
I opened up the old rectifier from an Onan. It was epoxy potted. I was able to put it in boiling water and carefully pick the epoxy away. Not sure what I'm looking at exactly. I figure the white wire is an output and the two black wires are inputs. Black wires (AC) go into two diodes, then out (DC) through the white wire?
I figure a guy that knows anything about electronics could build this no problem and for only a few dollars.
If anyone on here knows just what this stuff is I'd love to know as well.
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Replies:
Posted By: Codger
Date Posted: 20 May 2025 at 10:23am
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You have a half wave rectifier there. Two diodes mounted to a metallic plate which serves as a parallel anode connection, and heat sink to pull the heat away from the diodes. Assembly should be mounted in the airstream of the flywheel cooling fan. Replace both diodes with 20A units paying attention to the direction. When you impress more positive potential upon the cathode than the anode, the diode conducts rectifying the output through the white wire into a very noisy output DC voltage; good enough to recharge a starting battery. ------------- That's All Folks! |
Posted By: steve(ill)
Date Posted: 20 May 2025 at 12:57pm
the ones i am familiar with are on the old BRIGGS engines.. ONE WIRE from the alternator goes into the two diodes... One diode changes to DC to charge the battery.. The other DIODE changes to DC to feed the head lights... Head lights dont work off the battery... ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 20 May 2025 at 1:18pm
have also seen Two alternator wire in and ONE 12v DC out put... ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 20 May 2025 at 1:35pm
several variations over the years and depends on size of engine / stator.. ------------- Like them all, but love the "B"s. |
Posted By: Walker
Date Posted: 20 May 2025 at 7:08pm
| At one time, there was a guy on the internet who would custom-build them for less than retail. As I recall, I had him build one for a Yamaha mc. Seems to me he was a first name and rectifiers, something like Ricks Rectifiers or something. I'm talking like 25 years ago, so I can't say if he still does or not. Might be worth a Google experience to see. |
Posted By: Heliarc
Date Posted: 21 May 2025 at 5:39am
I'm not sure how this is done but the mounting plate seems like plastic, yet it's tinned with solder. This entire assembly was mounted to an aluminum plate for heat transfer I'd guess but they don't want it to ground out. Do you figure just any old 20A diodes? Was also wondering if I got both of them reversed as far as direction, would that reverse the output polarity of the alternator? Just curious there. I don't know how useful this particular piece would be for many people, but a lot of this stuff we run is obsolete. There's not much money in it for the big guys to make replacement parts so it's going to get passed off to China and India and a lot of times we're lucky to even have that. I hit the jackpot in that someone found some NOS stuff for this engine. It's priced as you'd expect but for now it's the real stuff and it works great. I figure we ought to get creative if we want to keep things running. NOS and used parts will dry up. In time it won't even be worth it to China and India to make parts. |
Codger wrote:Posted By: ekjdm14
Date Posted: 21 May 2025 at 7:33am
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edited because I'm stupid! The reason for the diodes being isolated from the heatsink on what is probably a silver coated mica wafer is because the common output of the diodes is +ve hence can't be grounded. I should think pretty much any old diode will do the job on this, not really a critical circuit BUT if you were to reverse the polarity then you'd likely melt the stator as you'd effectively be shorting the battery to ground through it.
------------- Stuck Farmer |
Posted By: steve(ill)
Date Posted: 21 May 2025 at 7:40am
you can buy most of these PREMADE in the aftermarket... If you are SURE the two black wires come from the alternator and the WHITE wire is the 12v OUTLET... then i have used one of these... If your WHITE wire comes from the alternator and the two BLACK wires are the 12v ( charge and lights) outputs, then you need a Different type of box... see my drawings in the post above... ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 21 May 2025 at 7:48am
variations.......... ------------- Like them all, but love the "B"s. |