1979 Johnson 70HP Rectifier overheating.

[Powdershredder]

I’m having trouble with the rectifier on my 1979 70HP Johnson Outboard. The rectifier is overheating and melting the epoxy out of the back side. It seems to be charging the battery excessively at high RPM’s 15-16volts. The flywheel also seems to be pretty warm after use at higher RMS’s which makes me think the stater is also overworking. All electrical connections and grounds have been cleaned and secured tightly and the motor is connected to a marine starting battery. I’ve had this issue with two rectifiers. Does anybody have any ideas. I don’t know where to go beyond good clean connections.

 

[F_R]

Sounds like it is normal to me. Except for melting the epoxy. Don't know what to say about that. You might try one of the new CDI regulator/rectifiers to control the voltage.

 

[Powdershredder]

I was looking at those. Think that might be my next step. 15-16volts pushing to the battery seems quite high to me. Do you know if rectifiers normally run hot on these engines? It’s just strange that I’ve had two heat up to the point that the epoxy started to drip out of the back side.

 

[F_R]

Well sure, they do get quite warm. But melting sounds odd. Most of that heat should be dissipated through the mounting.

 

[oldboat1]

What's the battery condition? Good shore charge before leaving, and charge holding?

 

[Bosunsmate]

Mine of that vintage gets to just over 17V which concerns me but its never melted.
I agree with FR that the heat should be going out through the mounting.
Check its contacting the crankcase properly. You could put some thermal grease on the bolts.
I turn my lights on to try and lower the V when it gets up to those levels.

 

[Powdershredder]

Right on, thanks for the info. Hopefully a regulated rectifier will fix the issue. I’m hoping it’s not a problem that will affect my stater down the road.

 

[Powdershredder]

Battery condition is good. Actually it’s brand new. Full charge before heading out.

 

[flyingscott]

You have an unregulated system so those voltages are normal. It uses the battery as the regulator. So you must make sure all your connections are tight and clean.

 

[Powdershredder]

Flyingscott.. I went through the entire electrical system on the engine including all grounds and made sure they were clean and tight after the first rectifier overheated. Also made sure the connection to the battery was solid as well. It seems the rectifier is still getting hot enough for the weatherproofing epoxy to start to drip out of the back of the rectifier. I was hoping cleaning and tightening the electrical would solve the issue.

 

[Crosbyman]

try these …. 50 amp capacity metal casing 4 way bridge rectifiers ..not expensive easy hook-up AC in… DC out

https://www.amazon.ca/10pcs-Single-..._rd_t=40701&psc=1&refRID=07EPPPHQB1DWBW9B9ZNJ

 

[Powdershredder]

Crosbyman... I’ll have a look. Thanks.

 

[F_R]

I have used those with success. They do need to be screwed to a heavy metal part for heat dissipation, and they do not cure the overcharging situation. The specs are far superior to the OEM. And they certainly are a good price, 10-for.

 

[juno pierrat]

new battery? what kind, old style flooded or maintenance free?

 

[Powdershredder]

Juno. It’s a new battery, flooded lead acid non-maintenance free marine starting battery.

 

[Powdershredder]

Thanks for the help everybody. I ended up purchasing the CDI regulated Rectifer for the engine and all seems well now. Thanks.

 

[F_R]

Thanks for the report. The CDI regulated rectifier seems to me like a product we should take seriously.