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Melted Rectifier

J

john_in_oz

New member
"Hi everyone. I'm a new c

"Hi everyone. I'm a new contributor to the board but I've been reading articles here for a while to help me get to know the motor on my new boat. I have a '79 Johnson V6 150HP. I bought the boat from my father in law and it’s almost pristine - motors only done 200 hours.

At any rate, the tacho stopped working the other day so I decided to test the rectifier. It was faulty all right and in fact the epoxy like material that is used to fill the metal housing had actually melted and dripped all down the side of the motor.

What I am curious about is what would cause this. I note that before I took the boat out last I charged the battery in situ but only disconnected the positive lead. I figured this would be OK and there shouldn't be any current flowing through the system. I still don’t understand how this could have caused the problem but its might suspicious. If this wasn’t the cause, I guess I have a serious problem with my charging system. Any help would be greatly appreciated. Thanks, John"
 
"Melted rectifiers, Well in my

"Melted rectifiers, Well in my experience a melted rectifier is caused by either the battery cables being connected the wrong way or somebody charging the battery with the charger leads on the wrong terminals."
 
"I suppose if you have continu

"I suppose if you have continuity both ways through your diode in your rectifier (one way electrical valve) It could also melt your rectifier while charging the battery, if both battery cables were connected while charging."
 
Thanks for your thoughts young

Thanks for your thoughts youngtech. I definitely had the +ve disconnected and the charger polarity correct so neither of these cases would apply.

I’ve got a new rectifier and as a precaution I’ll be making sure I disconnect both leads before I charge the battery in future. My real concern is that there might be a problem with some other components of the charging system.

Does anyone know if there is a possibility of a faulty charge coils outputting enough power to cause this?
 
"On thing often forgotten is l

"On thing often forgotten is lack of engine cooling. Weak impeller, defective thermostats might lead to an air pocket on top and the regulator does not get properly cooled off. Have seen quite some engines that have overheated, got impeller/thermostats changed and short after the regulator is gone."
 
"Moreton, thanks for your inpu

"Moreton, thanks for your input. I hadn't considered the possibility of a thermal conductivity problem. Mine is not one of the water cooled devices, it just bolts on to the side of the motor. All the same, I believe they still need to transfer heat to the motor and it only had a single bolt installed which wouldn't help.

One of the other possibilities that I've been toying with is that the rectifier case itself wasn't earthed. The single bolt holding it in place was installed using thread lock and the motor is painted where it is seated. Assuming mine is actually a regulator as well as a rectified, not being earthed might generate enough heat to melt the unit down (this is just a theory of course).

Mine is one of the simple triangle base units (P/N 583408). Is anyone able to comment on whether this particular unit actually regulates voltage (rather than just converts from AC to DC) and if the earthing theory has any legs?"
 
"It is a simple diode bridge r

"It is a simple diode bridge rectifier, and should be bolted with 2 screws! Heat transfer is important.
A low charged too big battery will ruin it if You run at full speed for a couple of hours. Charging AMP's is close to linear rev dependent."
 
"I once had a similar problem

"I once had a similar problem and it was blamed on sulfided battery ,which happens from being overcharging"
 
"i have seen this a few times,

"i have seen this a few times,..even when all electronics spec out fine,and no indication of why it melted,...it is my opinion,that at times,..they will just short out due to heat.wiring etc,..and go bad....its just an elect part.....they fail.."
 
"Thank you all for your contri

"Thank you all for your contributions. I pulled the battery out the other day. It's one of those with a visual indicator - green is good, clear is add water and black is bad. At any rate, it was black, so it looks like the battery has some problems. It actually still has plenty of charge, but presumably it’s been presenting a high resistance to the rectifier that has caused it to fail (looks like you were on the money with this one hurdy). I didn't check it first because it’s not very old but I guess they are a disposable item, particularly if you don't keep them charged off season.

At any rate, I've bought a brand new 500 CCA battery and a little device called a battery fighter. You keep it plugged in to the mains when you’re not using the boat and it keeps the battery topped up. Unlike a regular charger, this thing senses when the battery is full and turns itself off, then when the charge drops blow a certain level it comes on again. I'll let you know how it turns out. Once again, thank you all for your input."
 
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