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Rectifier, what am I looking at here

danray35e

Mar 24, 2012
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I have this 1976 outboard motor I am working on, and the rectifier is bad on it. The closest compatible replacement for it is listed as

http://www.sears.com/shc/s/p_10153_...9x00001a&ci_src=14110944&ci_sku=SPM4963893501

Since I was going to replace it, and also had a thought that I might be able to remake it with new diodes etc, I wanted to see what was in it. So after digging out a bunch of rubbery material , knocking out the center part then smacking it with a hammer to break the (epoxy?) holding it in place, I have what you see in the pictures I attached. My understanding of its purpose is to change ac to dc for battery charging purposes. I saw some where it was rated 6 to 10 amps. After getting it opened up I did not see any diodes but just these small connectors which seemed before I smashed it to be connected at the bottom to something that looked like mica. My biggest question is could I replicate its function with something off the shelf from radio shack.
 

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duke37

Jan 9, 2011
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This looks like a three phase rectifier. It can be replaced with three diodes but waterproofing will be the main problem.
There must be a fourth terminal and this could be the case. A circuit diagram would help.

Mica was used to electricaly insulate diodes and transistors whilst allowing heat to pass.
 

danray35e

Mar 24, 2012
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This looks like a three phase rectifier. It can be replaced with three diodes but waterproofing will be the main problem.
There must be a fourth terminal and this could be the case. A circuit diagram would help.

Mica was used to electricaly insulate diodes and transistors whilst allowing heat to pass.

Ok I attached the diagram in the manual. It only had three wires, as do the replacement ones I could buy. For waterproofing I was thinking epoxy. It seemed the attachments were at the bottom of the round part where the mica was, I assume to dissipate heat into the housing and away from the diodes. Would heat dissipation still be a problem with new diodes?
 

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duke37

Jan 9, 2011
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It is a single phase rectifier with four diodes and four connections. The two connections at the side come from the alternator. The case is connected to the bottom and the output connected to the top. The output connection is different from the other two.
The heat dissipation will be the same with the new diodes as with the old ones.
I do not know the current requirement, you should go for at least 20A. 25A bridge rectifiers are available at a reasonable price and are available in an isulating package.
 
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danray35e

Mar 24, 2012
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Thanks for the information do you think I can find what I need at radio shack?
 

poor mystic

Apr 8, 2011
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Hi guys :)
Wouldn't you expect Germanium diodes in this application?
 

poor mystic

Apr 8, 2011
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I do expect Germanium diodes, which could possibly be sourced as motorcycle parts.
 

duke37

Jan 9, 2011
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I do not see the advantage of germanium diodes and they are much more sensitive to heat.
As to what shop sells diode bridges, it all depends on where you live. I get my parts from Bob Potts in Derby, UK. Try the internet for information.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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Yeah, I'd replace them with physically (and electrically) similar silicon diodes.
 
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