Blown electronics

StanD

Recruit
Joined
Jun 13, 2008
Messages
2
Hi all,
can anybody help with my problem?
I recently bought a used Mercury 6HP 2 stroke motor, 6ML #OP107187 2001. I have fitted an OEM battery charging kit and have paralleled a remote stop to the boat control panel as the motor is used as an auxiliary engine on a sailing boat and the main stop/run switch is hidden behind the remote control cables.
On fitting the engine to the boat it started first pull and ran like a dream, but at this point I had not finished the wiring on the boat so the electrics were not connected. I used the motor in this way for an hour or so while I completed the boat electrics. The electrics consisted of a 3 pin waterproof plug at the motor end, positive and negative leads to the battery and the remote stop to a switch and then to the battery negative putting an earth (ground) to the motor in the off position.
Once connected the engine was started and the remote stop tested with no problems. The battery was showing a low voltage but with the engine running it was showing 13.5 volts so I concluded that the charging system was running OK. I ran the engine, with several stops and starts for about half an hour. The battery was still showing a low voltage so I removed it from the boat and took it home to charge, once charged I left it for a day and checked again and found 10.5 volts and assumed a dead cell. I had a spare battery which I fully charged and took back to the boat. On fitting this battery I noticed a small arc as I connected the negative lead, the boats main isolator switch was off at this point, so I assumed that there must be a short on the engine. I put the key in the remote stop switch and turned it to run and found that there was now no arc as I connected the negative lead.
The motor would not start. I disconnected the electrics at the plug and it still didn't start. I took the rectifier out and taped the leads, and still no start. An ohms test of the rectifier shows that it is blown. The motor is at the repair shop and I am told the electronics box is dead and the replacement will cost over ?200 plus the cost of a new rectifier.
My problem is how do I stop the same thing happening again. The original battery might have caused the rectifier to burn out but as far as I can see the charging system is separate from the ignition system so why did that burn out as well? I will recheck the boat wires but an initial check shows everything to be correct.

Stan
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Blown electronics

It sounds like your wiring somehow put 12 volts to the ign. system could have been at the plug or switch, it's quite hard to say without seeing the wiring. I would separate the ign. and battery wiring to different harnesses
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Blown electronics

The engine has a mag ignition, ground to kill, open to run.

The charging kit is a totally separate electric system, a fixed stator coil, rectifier wired straight thru a fuse directly to the battery, no switch is needed.

The fact that you had a low battery AND a blown rectifier AND a dead ignition module usually equals a momentary reversed battery connection.

Ooops!!! An expensive mistake.
 

StanD

Recruit
Joined
Jun 13, 2008
Messages
2
Re: Blown electronics

Thanks for the advice guys, it was very expensive 70% of what the engine cost me. The motor now runs fine but I will do a check of the hull electrics before I connect the engine to it.
Stan
 
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