What if both motors can charge the battery?

[Jerry900]

I just recently got an 8 HP Honda kicker that has a 12 volt output for charging batteries. My main motor is wired to two batteries through a switch with "off", "1", "all", and "2" positions. Should I just connect the new motor in parallel with the 90HP Mariner so they both go through the switch?

My concern is: When the switch is turned off so there is no current draw, my kicker can output more than 20 volts average. Will this hurt the Mariner? Can the Mariner hurt the Honda?

How should I do the wiring?

 

[CharlieB]

Re: What if both motors can charge the battery?

Ideally, both motors would have their own separate battery switch.

The rectifier on the small motor can be damaged by the higher amperage charging system of the larger motor.

The smaller system should be disconnected any time the larger system is running.

If you are running a single battery you could use one battery switch but with motors connected to the battery poles, one and two, and the battery connected to the common lug. Off would be Off, One could be the main engine, Two the Kicker. Both would connect both engines and then you would have the possibility of smoking the smaller rectifier, so Do NOT use the two position whenever the main engine is running.

 

[j_martin]

Re: What if both motors can charge the battery?

I'll have to disagree with Charlie on this one. There should be no danger to either charging circuit if they are connected to the same battery. One system isn't going to overpower the other in any way. Current doesn't flow from one power supply to the other, only from each to the sink (battery). The very nature of the rectifier, or regulator blocks reverse current.

The one caveat is if it is hooked up so that it is possible, even for an instant, for both to be connected together AND not be connected to a battery, then a simple rectifier only system (like probably on the kicker) can exceed the reverse voltage specification of the other one, causing it's demise. Open circuit(no battery) on either one at any time can cause that system's demise. They sometimes (frequently) rely on the voltage regulating properties of a lead=acid battery.

I would connect the main motor to the batteries through the switch, with the switch normally in position A. Connect the kicker to battery B directly. The "Both" or B position on the switch would only be used for charging or emergency starting. There's no way this setup would hurt anything, and it allows either engine to charge both batteries, or start from either battery. The kicker could potentially be hooked to a completely fried dead battery that is so bad it can't be jumped (by switch position "both"), but the probability is very remote, and it can be easily rope started anyway.

hope it helps
John

 

[Jerry900]

Re: What if both motors can charge the battery?

Thank you John. The kicker rectifier was dead so I replace it with a rectifier from All Electronics for $2.50. It has a rating of 400 piv so I I am hoping it will be ok. I hooked the two motors in parallel through the switch.
Thanks again.

Jerry