Outboard to Battery disconnect?

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Aug 4, 2009
Oday 25 Olympia
The most direct answer that I can get from dealers and repair shops, is vague. The question is: Can a 1990, 9.9Hp Mercury electric start outboard be run without being connected to the battery and without harm to it's alternator?
Secondly, Why does loss of the battery connection 'blow the diodes' on an inboard engine driven alternator? I can understand the harm of a current surge into a shorted condition but not into an infinite resistance.
"Is a puzzelment"
Thanks much, Geohan
May 8, 2011
ODay 25 Cambridge
I have an O'Day 25 with a 9.9 Yamaha electric start. I installed a switch between the engine and the battery. I turn off the switch to prevent the outboard from overcharging my batteries as I have solar panels that keep the batteries topped off almost always. I can turn the switch off w/o any damage to the outboard. It only puts out 6 amps charge but that 6 amps is not regulated well for my configuration.
Jun 2, 2004
Oday Day Sailer Wareham, MA
I am not familiar with the setup of the Mercury outboards with battery-charging ability (including those w/ Electric start) ,but I know that Evinrude/Johnson outboards with Electric-Start and/or battery-charging ability can be run OK without hooking the batery wires to the battery as long as the wire ends can not contact each other (a rubber cover was included for the Positive wire). I guess a switch would accomplish the same thing as that cover. I would think that the Mercury setup would be similar to the E/J setup?
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