Battery Hook up for Kicker and Main Engine

[John from Madison CT]

I will be adding a 9.9HP High Thrust Yamaha engine to my boat. A Parker 2520DV. The Yamaha is electric start and requires the hook up to a battery.

Is there any downside to hooking up the kicker and my main engine (Yamaha 250hp Ox66) to the same battery??

What would happen if both the kicker and the main engine were running at the same time? Could one engines charging system get damaged?

[Ken]

John,
I don't see any problem with running both motors off same starting battery. The charging system of each motor is designed to charge the battery up to about 14.5 volts, and each system is (or should be ) diode protected from overvoltage.
But two batteries would be a good idea if you don't already have two onboard. Any battery is subject to failure w/o notice, and hand cranking that 250 would not be an option. A pure starting battery for your big boy, and a deep cycle/dual purpose for accessories and the little kicker. In an emergency, the dual purpose battery could be used to start the 250.
That's the way I would go.
Good luck [img]smile.gif[/img] ,
Ken K

[John from Madison CT]

Ken: Thanks ! My concern was with the potential damage of each engines charging system IF both engines were running at the same time.

[Ken]

John,
Even with both motors running at the same time, there should not be a problem IF the charging system of each is designed properly. But I can't guarantee that.
It's the same scenario you have when you jumper one auto to another when one has a dead battery. You wind up with two motors running at the same time trying to charge the same battery source (in this case two batteries in parallel). The charging system, i.e. alternator-rectifier-regulator, should be designed so that if the source battery exceeds the voltage of the charging system there are blocking diodes that will prevent any damage. This is in the auto arena - I can't guarantee the same design for charging systems in the marine world, but SHOULD be the same.
Bottom line - go with two batteries. You could even use a battery selector switch for the 250 to switch over to the aux. battery in case the starting battery won't do the job - and this usually happens when you are FAR from the boat ramp in rough seas.
Good luck [img]smile.gif[/img] ,
Ken K

[John from Madison CT]

Ken: I have two batteries already and with the dual charging leads off the 250hp Ox66, they both are getting juice all the time, so it's tough to isolate one battery for the kicker.

John

[Ken]

John,
You could use a battery switch to solve your problem. Use the extra battery you are charging with the extra charging leads from the 250 to power the kicker. Run the common of the batt switch (I'm talking about the type that has "common" terminal, "batt1" and "batt2", "both" terminals) to the positive of the aux battery. Connect the pos lead of the 250 charge circuit to "batt1" and the charge/start lead(s) from the kicker to "batt2". Both ground from the 250 and the kicker go to ground of the aux battery.
That's it - you would normally have the switch set to "batt1", in this case that would be the 250. When you want to run the kicker, select "batt2" so that now the kicker starter/charge circuit is hooked up to the aux battery, and the charge circuit from the 250 is floating. Voila! You have your isolation.
Good luck [img]smile.gif[/img] ,
Ken K