2nd rectifier this year

[itsaboattime]

Hey everybody. I am at a loss. I have a 1983 Johnson 50 hp. When I replaced the rectifier first time, in July, I did the tests in the FAQ section and came up with infinate resistance both ways on the red wire. Had the boat out yesterday and noticed that the voltmeter was only at 12.7 volts, and my tach would only get up to 3000rpm. I know the motor was running at higher RPM than that just from the sound. When I got home I tested the rectifier and came up with low resistance on the red wire both ways.

My motor has the small rectifier with the yellow, yellow/grey, yellow/blue and the red wire.

I don't think I am overloading the charging system. All I run is the depth finder, and the running lights after dark. No stereo or anything like that.

What could be making my rectifiers go bad??

 

[Randybeall]

Re: 2nd rectifier this year

Worst thing for a rectifier is to break the circuit while the engine is running. Make sure there are no loose connections on the power or ground side of the charging circuit. Screw on terminals are notorious for corrosion and not making good contact. Make sure both cables and posts are clean and the cable won't wiggle when tightened down.

 

[Al-53]

Re: 2nd rectifier this year

Interesting...will the tach still work with the rectifier bad ?...as I may have the same problem..at WOT my tach just reads 3200 rpm's....but I do 26 MPH with a 17' Sea Nymph Bass boat..I have a 1983 35HP Johnson...ELCTS....I may check my rectifier now to see if its bad....this is my first boat and still learning..I do have the OMC shop manuals

thanks

AL

 

[F_R]

Re: 2nd rectifier this year

If you are using a digital multimeter to test the rectifier, it may give false results. Many just will not test diodes. Mine won't. But a cheap Wal-Mart $9.95 analog one will. Go figure.

 

[itsaboattime]

Re: 2nd rectifier this year

I am using a digital multimeter. I think it is giving me a true reading only because of the issue with the tach. I mean I think the rectifier has a problem because the tach is reading wrong as well as a low voltge on the volt meter.

I will clean all the contacts at the battery as suggested, and I'm going to take the rectifier into the shop and have it tested there.

 

[ezeke]

Re: 2nd rectifier this year

You have to disconnect a rectifier to test it. You can only test a unregulated rectifier properly although the lack of correct tachometer reading and charging voltage are good indicators of a problem with regulated rectifiers.

Rectifiers can be damaged by poor battery cables with high resistance, by failed or failing batteries, by a bad ignition switch, or by any combination of things that can replicate the effect of disconnecting the battery while the engine is running, including battery switches.

 

[itsaboattime]

Re: 2nd rectifier this year

Ok ezeke. I will test the easiest, the battery cables, first. Then progress to the ignition switch and so on. I dont have a battey switch, so that rules that one out,lol.

My ignition switch is somtimes "sticky". Meaning that it will sometimes stick in the "start" position until I manually put it in the "run" position. Could this possibly be the cause of my rectifier troubles???

 

[itsaboattime]

Re: 2nd rectifier this year

I checked my battery cables and they have very little resistance. I am taking my ignition switch an my rectifier in this morning to have them tested.

 

[Randyg123]

Re: 2nd rectifier this year

Interesting...will the tach still work with the rectifier bad ?...as I may have the same problem..at WOT my tach just reads 3200 rpm's....but I do 26 MPH with a 17' Sea Nymph Bass boat..I have a 1983 35HP Johnson...ELCTS....I may check my rectifier now to see if its bad....this is my first boat and still learning..I do have the OMC shop manuals

thanks

AL

Yes the tach can still 'work' if the rectifier is bad. By work I mean give you a reading. Correct reading...now that is a different story. Depending on how the rectifier is shorted or open, you can still be getting a partial signal to the tach, allowing to indicate something. I saw it happen on mine and many other posts here. with my scenario, I was reading low rpms and when I replaced the rectifier, the rpm readings shot up by almost two times which makes sense if half the rectifier circuit was shorting out the tach signal.

 

[Al-53]

Re: 2nd rectifier this year

Randy..thank you for the answer.....I am going fishing in the morning and after I will check the rectifier when I return....

so its best to disconnect the battery and the rectifier leads off the buss bar in the engine...and test that way?...

also on the tach i have a few settings on the switch...I forget what they are right now..but for this engine what should it be set at....the original owner never got the tach to work....and i wired it as shown on a post here and it worked...just need what setting..I think it has like 6....12 and a few other settings...I just left it where it was and never turned it...it may be on the setting P if I remember right....

I have to say..for a 1983 motor...it runs great..just touch the key and it starts..even in the cold weather we have now..I will be out in the 30's in the morning looking for the monster bass or pike...

also the prop on it is either a 11-9 or a 9-11 is this a good prop for this motor....

Thanks so much

Al

 

[Randybeall]

Re: 2nd rectifier this year

Just a note. Resistance is not a good way to test battery cables. You need to do a voltage drop test. That is to put a volt meter between the positive battery terminal and the starter cable terminal. You should show 0 volts, observe the voltage while cranking the engine, you should have no more than .2 volts. Do the same on the ground side from the engine block to the negative battery post, again no more than .2 volts. Battery cables are so large that the tiny current of an ohm meter is no test, only under load will you know how they are doing.

 

[itsaboattime]

Re: 2nd rectifier this year

Hey thanks Randy, Will do that test today. The rectifier tested out bad at the boat shop. surprise surprise. My ignition switch tested good tho. John, the mechanic, said it was a little sticky because the key/lock is wore. He advised replacement within the next year. I am fixin to put the boat up for the winter and probly won't replace it this year.

He couldn't help me with the reason I am going thru rectifiers without bringing the boat in. That presently isn't in the budget.