Mercury rectifier test?

[jeff-register]

Yes it is easy to test,Connect your analog meter to positive lead on rectifiers & the black to the mounting stud of the diodes, Record the test results. Oh set on 200,000 ohm scale. flip meter leads to opposite leads & record again. The ratio between first & second test should be a ten to one ratio. Now put meter leads on the two red leads that go to the stator or alternator leads. Again flip the leads polarity & results should be a ratio that is 2:1. In the drawing it shows 4 diodes & to test each diode would be put meter leads on each end, then flip the leads it will pass current one way & almost stop it going the other way. Being built together it is hard to test as a guy can’t get at all 8 leads & isolate. Check while running too on a 25 volt D.C. scale to see if you are charging, Next change the meter to A.C. If you show charging in the AC mode the bridge rectifier has faulted. On AC the meter should show no charging.

[jeff-register]

P.S. You should know the metal of the engine is of negative terminal so you have a 4 wire bridge diode[ & not to confuse but Mercury or any other alternator has a wire that goes to the ign switch to turn it off while the motor is off. If that switched wire had an issue the alternator would not charge. Check your manual for which terminals to check to see if that may be an issue. Without switching the alternator off would allow current to reverse & discharge the battery while sitting. /size]

[frankr]

The trouble with a discussion of this type is that everybody has their own understanding and or methods. Do what I said and you will not go wrong.

OK, along with what jeff R. just said, yes Mercury does run the charging circuit through the ignition switch. That is because selenium rectifiers are lousy at completely blocking reverse current, and leaving it connected will discharge the battery over time. Motors with newer, silicone rectifiers do not have that problem, so the charging current does not go through the ignition switch. Makes no difference when testing the rectifier because you have disconnected the wires, remember? FYI, selenium rectifiers look like a stack of wafers (like yours). Silicon rectifiers can have a variety of shapes.

Here is your wiring diagram.

upload images

[gdcarpenter]

FYI, and it doesn’t affect the rectifier testing since the rectifier should be disconnected from the circuit for testing, but old Mercs with magnetos connect the mag circuit to ground in the "OFF" position to "KILL" the engine.

Do not leave the ignition in the "ON" position if not running the engine!

[wiscoboater]

OK, first of all, thank you to everyone who has replied. I can’t tell you how much I appreciate the knowledge and professionalism members of this site have and share with others. Please forgive me, but some of this has gone completely over my head. I understand the wiring diagrams, that far with electronics I have gotten. My game plan is to purchase a multimeter this weekend and try to figure out how to use it. My background is building construction and automotive mechanics. If you want to know what’s wrong with your home wiring, I can help you. If your Chevy or Ford wont start, I’m good with that as well. Building a boat wiring harness from scratch,…not so much. I will try to the best of my abilities to follow the procedure Frank laid out for me. I’m sure I will make some mistakes and have more questions. Thank you all for your patience and guidance. Joining this site is one of the best things I have ever done to continue to learn about these outboards and their functions and sub systems.

Wannabe

[gdcarpenter]

If you have an automotive background as I do wiring a boat should be easy, it’s DC, just that you need to ground every component individually as there is no ‘ frame per say.

As for checking the diode like effect of the rectifier, the key principal is that current should be able to flow through the diode one way (low resistance) and not be able to flow backwards the other way (high resistance).

[crosbyman]

lots to read and learn if you google or utube volt ohm meters lots of videos to learn from

Joining AOMCI has priviledges 🙂

[jeff-register]

Gents,
I figured the best way was to copy the troubleshooting in the Merc-O-Tronic service manual, so that is what I did. Then broke it down to test a single diode, then complete the circuit by adding the anti reversing switching. This I added so a guy would know to trouble shoot as well if no charge was shown, All part of the charging circuit. Frank, Wasn’t inclusive of the bridge test but completing the charger circuit testing if this wasn’t known. We need to remember the early bridge was light years better than was on the market at the time as an alternative rectifieing full wave circuit.
If it was me I would not even test. I would get a new bridge silicone diode set for reliability. Then again I have a selenium bridge in my Merc O tronic built in Canada & it functions well. But no heat or vibrations to deal with.
It’s all so elementary! electricity will pass one way & not the other, basically. Reverse the leads & the diode reverses output…..It’s a one way valve. But then we could get into ripple voltage & add a cap to smooth that out. Mercury charging has no regulation with the older units & no frequency blocking for the radio either. All in the eyes of the beholder I would agree, I love a debate discussion. 😀

[frankr]

Yes, there is something to be said about just slapping in a silicone bridge. They are more efficient, work better, and wiring it up is simple. And cheap if you know where to get them. I have some if you need one.

free photo upload

[crosbyman]

IF your local Radio Shack has not folded yet they had cheap ones around $5 good for 50 volts and 25 amps

These things are all over the internet

Joining AOMCI has priviledges 🙂

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