Charge 2 batts off one stator

[Dm82]

Hello all thanks for reading. So I have a 1968 Johnson 100 hp outboard on my boat. This motor has a 15 amp stator that also charges to battery. So what I need to know is can I run my batteries in series and have the stator charge both. As of right now I have only one battery powering my starter for the motor, bilge pump, nav lights, marine radio, fish find and gps. I want to have the new battery run all my accessories and the battery that is there now just for the motor. Is this possible? I would like to add one nice switch panel for all accessories and have that connected to extra battery.
So I would like to hear your thoughts and suggestions. Anything would be appreciated. I do not know if this is even possible or how to check if this would over load my stator. Thanks for the help

 

[Vic.S]

Re: Charge 2 batts off one stator

No not in series. That would make a 24 volt battery.

Several ways in which you could do this. One is just by switching between batteries BUT you must never switch off the battery while the engine is running or you'll blow the rectifier. when changing over you must switch on the new one before switching out the old one.

Assume though you want an automatic system with one battery reserved for the engine starting etc the other for the other accessories on the boat.

Two solutions but you will have to separate the changing output from the power supply to the motor for starting etc.

Diode splitter. Output from motor goes to the common terminal. the two batteries to the other two terminals. Snag is about 0.7 volts drop across the diodes means you never get the batteries fully charged.

Alternative is a voltage sensitive relay (VSR). Allows the motor to charge the starter battery and then when the volts have risen on that it switches in the other. Advantage is no volts drop.

Just to clarify the business about series connection a diagram I did recently for another forum

 

[F_R]

Re: Charge 2 batts off one stator

There are commercially available battery isolators. Motor homes use them all the time to separate the "house" battery from the starting battery.

Simply wiring the batteries in parallel (not series) will charge them both, but the lights and stuff will discharge Both batteries, still leaving you with a dead starting battery.

http://www.iboats.com/Boat_Battery_...5842762--**********.945910699--view_id.216584

 

[alangf]

Re: Charge 2 batts off one stator

The series/parallel issue has already been covered. Wiring both batteries in parallel to charge both at the same time will work well only if all conditions are perfect. Both batteries would have to be identical and in identical condition for the distribution of the charge to be balanced. Even under ideal conditions you are charging two batteries with an alternator designed for one. There are both manual and automatic switching systems to provide charging for multiple batteries from a single alternator. The good part is they charge the batteries one at a time. With the automatic system the one most in need gets charged first.

 

[Dm82]

Re: Charge 2 batts off one stator

Thanks for the advice!!! This is my first boat so I will probably be asking a lot of different questions. But as far as the battery situation, this is the first thing I want to tackle. Had a bad experience with a friend out on lake erie when a storm kicked up and his boat wouldnt start because the battery was dead.
Thanks for the info on not wiring in series. 24v probably isnt a good thing!!! I am going to look into this switching device you speak of. Thanks again.

 

[alangf]

Re: Charge 2 batts off one stator

Thanks for the advice!!! This is my first boat so I will probably be asking a lot of different questions. But as far as the battery situation, this is the first thing I want to tackle. Had a bad experience with a friend out on lake erie when a storm kicked up and his boat wouldnt start because the battery was dead.
Thanks for the info on not wiring in series. 24v probably isnt a good thing!!! I am going to look into this switching device you speak of. Thanks again.

I understand where you are coming from about the experience of a storm on Lake Erie. My boat looks an awful lot bigger on the trailer in the driveway than it does 65 miles offshore in a storm.

"Good judgement comes from experience and most experience comes from bad judgement."

 

[Dm82]

Re: Charge 2 batts off one stator

Lake Erie sure is a lake you need to respect.

So does anyone know where I can get a voltage sensitive relay at cheap? Or should I say at least cheaper.