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Author Topic:   Operating Outboard without Battery Connected
jkh posted 06-12-2004 10:34 PM ET (US)   Profile for jkh   Send Email to jkh  
I just purchased a new 25hp Merc. for my 13' 1967. It ran great. It is an electric start model but I started it manually because I didn't want to full with hooking up a battery. I get home and start reading the motors manual and it says to never run the engine without having the cables connected to a battery because it could damage the engine's charging system. Is this a real concern? How? Should I be concerned that I have already damaged the motor? How would I check? In the future do I realy need to always have a battery? I have read of others on this post who run their electric outboards without a battery. Thanks, KIrk
brisboats posted 06-12-2004 11:46 PM ET (US)     Profile for brisboats  Send Email to brisboats     
Yes, as the manual says that motor should be hooked up to a battery while running. As an outboard flywheel rotates the stator magnets pass by the stator coils and creates an alternating current. This current is sent to the rectifier where it is converted into direct current to charge the battery. On newer outboards with more charging capacity this current is also regulated by the voltage regulator. If you have damaged a regulated system most often symtoms are an overcharge or undercharge condition. You could hook a battery to your motor and check the charging system's output at the battery terminals with a volt meter. Rectifier in my experience is usually the first link in the charging system to "fry". Hope you are safe for now. Run it with a battery attached from here out .


jimh posted 06-13-2004 07:44 AM ET (US)     Profile for jimh  Send Email to jimh     
In any battery charging system, the presence of the battery has a very stabilizing effect on voltage spikes. Having the battery connected limits the upper bound of voltage transients to only as high as they can pull the battery's voltage. In the case of a well-charged battery in good condition, that will not be very far above 13.2 volts.

If the battery is not connected, much higher voltages may develop. The system was not engineered to operate in that condition, and that is why the owner's manual cautions you against using it like that.

In order to develop enough voltage to push current into the battery when it is connected, the alternator/stator coils are wound so that they produce a fairly high open-terminal voltage. It is probably in the range of 25-30 volts.

jimh posted 06-13-2004 07:47 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed TOPIC; was "manual starting of elec. outboard".]

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