battery ground (-) connection generator to motor ?

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Senior Member
Nov 30, 2019
Vessel Name
Lady Penelope
Vessel Make
Trader 54 sunliner
Hello, at the moment the battery of the generator (onan) is only connected to the generator

I put a new battery charger in withs support 3 battery groups with kommen -
for the service and starter battery the - is connected to a star point on one battery.

to connect the generator battery , i need to connect the + to the charger group 3 point and the - to ?
i can easy connect the - to the center point of the starter / service battery but in the onan manuel
they say its a bad idee the - schould be connected from the body of the generator to the body of the motor
with a heavy wire the same size of the one on the starter motor

it for the situation that the - of the motor is getting bad contact then when starting the main engine the current can flow bij the fuel and demange the motor of the generator.

i my boat the generator is connected to a sepperat fuel tank so no electrical connection,
can i connect the - of the generator to the cental - point of the battery ?
can i connect the - of the generator to the cental - point of the battery
Well, since what you are trying to do is charge the battery, YES.
The question becomes should you also ground (-) to all other (-) of the other batteries. A negative from the charger taken to each battery does connect all the batteries on a too small wire for other purposes.
The cables going between the generator and the batter need to be the same size and connected per the manual.

To add the generator battery to your charger you will need to run a wire from the battery (-) to the DC negative buss for which the charger is using.

Since I am unfamiliar with the charger you have, I cannot advise you on whether this is an appropriate set up.

Personally, I like to keep my generator system completely separate. I use an inverter/charger for the house, I have a back up charger for the house and the generator battery has its own charger.
i think that i also put a fuse of 50A in the (-) line that go from the gen to the central (-) point so if i have problems the fuse will blow.
I have not fused a negative wire, only positive near the batteries, then positive to each device.
ABYC requires that the two engines and battery systems have interconnected negatives with enough current carrying capacity for full engine cranking. This can be done by a cable directly between the engine and gen blocks in your case, assuming grounded (thru the engine block) starters on both engines. If your batteries are wired with a negative bus bar like in many larger boats, the bus bar can act as the interconnect point. In all cases the interconnect needs to be able to carry the largest full cranking current.
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