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Charging boat battery from two outboards at same time

AEROMAN-grog

New Member
Merc 135 and trolling Merc 9.9----I was cautioned when I bought the boat not to run both engines at same time, as the alternators charging could interfere with one another and possibly damage them .
any comments??
 

crutschow

Well-Known Member
Most Helpful Member
Merc 135 and trolling Merc 9.9----I was cautioned when I bought the boat not to run both engines at same time, as the alternators charging could interfere with one another and possibly damage them .
any comments??
Not sure why they said that. :confused:
If one alternator has a higher output voltage, the other alternator should just shut down.
The alternator output diodes will prevent any reverse current from flowing to the low voltage device.
(See typical alternator schematic below:)

1609573135995.png
 
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