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Old 04-08-2009
Roberthussey Roberthussey is offline
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how big should the fuse be ?

I have a trailer sailor and have a Honda 9.9 with a 12 amp alternator on it. I have two group 27 deep discharge batteries with a selector switch for all power on board. I do not have a fuse of any kind on the batteries, they feed a power panel with all marine breakers for each circuit.

It appears from the Honda manual they usually just attach the two wires from the directly to a 12 volt starter battery. I use the deep cycle batteries to start the motor, seems to work fine.

After a survey it was suggested I mount a fuse on the common negative wire very close to the batteries. The surveyor thought 70 amps would be about right. While I do not want it any bigger than required if the starter motor should blow it as the motor starts then it will fry the alternator as it will then be running without a battery. I'm thinking about using a 100 amp fuse. Can anyone provide advice on the max. starter motor draw for a 9.9 4-stroke ?
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