Johnson 70 charging question

[dsweet2010]

I have a 1974 Johnson 70hp with a believed to be bad rectifier. My question is, and I use a 3-wire Kohler lawn mower regulregulatoro the same thing? Considering I tried unsuccessfully I will assume my answer will be no. Appears to be the same concept however the diode check with my multimeter did not show current flow in either direction .
This this thing has me seriously stumped . Upon finding a bad burnt red wire on my old rectifier and having no charging, I automatically assumed to have a bad rectifier . I posted on here and asked if I could use a 4-wire that I had at home in place of a 3 wire on my motor. I was told yes so I taped up the remaining yellow and blue wire and installed it and still did not charge .I then bought a new 3 wire unit from the local Marine store and and did get 13 volts charging temporarily. I then checked all of my accessories and proceeded to flip my battery selector to both and just the other battery to test it . Somewhere in that process, I again lost charging all together. I do not have a DVA meter . I have done numerous checks for AC and DC with my multimeter though . All of my rectifiers and stator check for correct ohms and no short to grounds. With the motor running and the red wire unplugged coming out of my rectifier I show 9 9 AC volts from each stator lead and 20 volts ac between both yellow stator wires. The red wire coming from rectifier shows 22 DC volts .Whenever I hook up the red wire back to the terminal, it reads completely different. With everything hooked back up I then show 20 ac volts from only one stator wire to ground and no voltage from the other . The red wire output shows only the 12 volt battery voltage. I don't know why I get completely correct readings while unhooked but then everything reads wacko when hooked up . My first thinking's want to be that I fried the new rectifier that did temporarily work by switching the battery selector with the motor running . It is also hard to believe that I can be holding three rectifiers that test good on diode checks on my meter and show correct resistance with no shorts and still not have charging from any of them. Thoughts???

 

[F_R]

1. Generally speaking, running it with wires disconnected spells instant death to the rectifier.
2. Battery selector switches built within the last reasonable number of years connect the second battery before disconnecting the first one to prevent situation #1. However, if you switch it to off position while it is running, you have created situation #1. Moral: Never switch it while running.
3. Are you testing your rectifiers correctly? There are 8 tests to do on a three-wire rectifier and it must pass all 8.
4. I can't answer your AC voltage questions because I've never attempted to do them. To me, they are not valid, and even risky, diode-wise.
5. Radio Shack used to have a bridge rectifier that was cheap and reliable. Trouble is, Radio Shack has gone bye-bye. The rectifiers are probably still available elsewhere, but I haven't looked. I still have half a dozen of them from Radio Shack.

 

[boobie]

Get a factory service manual and check out your rectifier according to the procedure in there.

 

[oldboat1]

Would buy an oem rectifier, and make a point never to operate the battery switch with the engine running. You will see only 6 amps max, and not much at idle. Additionally, see if there is supposed to be a ground wire for your rectifier (ground to block).

 

[dsweet2010]

F_R, thx for the response!! I have only done the two tests that I know to do on the rectifiers being the diode test on a Wire and the resistance test, both of which pass. Please elaborate on what all of these eight test consist of as I have spent 3 days trying to find information on tracing this issue LOL .

 

[F_R]

Here is a diagram of a common bridge rectifier (OMC 3-wire). Note that there are four diodes. Each diode needs to be tested to see that current flows through it in one direction, but not the other. That's two tests on each diode.

I prefer an analog multimeter to test them. Yes, you can use a digital multimeter, but you have to know how to do diode tests on yours--they are not all the same. I'm old fashioned, I guess, and don't like digital mms for this use. They do not apply enough voltage to the diode to make it do what diodes do.

First disconnect all wires. Now look at the diagram. Let's focus on one diode. Look at one of the yellow wires. You will see a diode between that yellow wire and ground. Test that diode by connecting your meter between the yellow wire and ground. Should pass current in one direction, but not the other. That's two tests

Do the same two tests between the other yellow wire and ground.

Do the same two tests between one of the yellow wires and the red wire.

Do the same two tests between the other yellow wire and the red wire.

That's 8 tests. Do not go and invent more tests of your own.

Hope this makes sense.

 

[dsweet2010]

Yes, my digital mm had diode mode .I did do those tests, and each passed properly .sorry I though you were consider all of those together as one test .I did those as well as testing each wire to groind to verify no continuity .