Dual Batteries on a Switch... and a Charging Honda 8HP

[Doolin]

Hey Guys,

I've got a 19' Aluminum Jet Sled with an inboard V8 and a single Starting Battery. I've purchased a 'Guest' 2 way switch and will be picking up the second battery shortly.

I did some reading and found the answer to my first question... that being that it's ok to start the motor on (1) and while the engine is running, switch to (both) so they both get charged. I also found the confirmation of how it should be wired.

My remaining question is about the charging capacity of my 8HP 4-Stroke Honda Kicker. I'd like to hook this directly to battery (2), which will be the deep cycle battery. I was hoping someone that really knows can confirm, that what seems like an ok idea to me, isn't totally stupid.

My thought here is that should both batteries completely die (maybe a motor issue and both batteries get cranked down) that I can start the kicker (it's a manual start) and have it charge the deep cycle to the point that I'd have another shot at starting the main motor.

Thanks in advance for the advice.

 

[Boatist]

Re: Dual Batteries on a Switch... and a Charging Honda 8HP

If the guest battery switch is a make before break then yes you can change from 1 to both without damage. Most switches today are make before break but if it is not and you turn it while running it will blow your alternator.

Never turn thru off to get to both with the motor running. It will blow the alternator.

As far as the 8 hp manual start charging a deep cycle. It all depends on the year but in general a 8 hp is going to have an alternator around 6 amps. If the deep cycle is used for a electric trolling motor then it may not be a good idea.
At high rpms the little alternator would be putting out it max current for hours and may over heat and burn up. At lower rpms it would put out less current and be ok but would take a long time to charge the battery. If the deep cycle is only running electronics like a depth finder and GPS then it would be fine. Big stereo or a electric trolling motor I would be very carefull not to over heat the little alternator.

 

[Doolin]

Re: Dual Batteries on a Switch... and a Charging Honda 8HP

Thanks for the info. The first paragraph on my new 'Guest' switch is that it is a 'make before break'. I didn't know what that meant when I read through the first time.

The 8hp motor is the trolling motor and I don't have any big draw items pulling on the deep cycle. I don't anticipate it being drawn way down under normal circumstances.

Again, I really appreciate the help.
Ben

 

[Boatist]

Re: Dual Batteries on a Switch... and a Charging Honda 8HP

Make before break means when turning the switch form 1 to 2 or both that the second battery is connected before the first battery is disconnected.
This means the alternator allways has a load on it which is good.
If you were to turn thru off the alternator would have no load and the voltage would clime so high that it would blow the alternator diodes in under a second.

 

[Silvertip]

Re: Dual Batteries on a Switch... and a Charging Honda 8HP

If you connect the 8HP engine to the deep cycle which can also be connected to the I/O engine via the switch, you now have a small rectifier/regulator (8HP) being back-fed from the large engine (60 amp or more) which MAY damage the smaller unit. Note that I said MAY!!! Yamaha for example does not recommend having two engines on the same battery which is essentially what you have.