Battery setup

[Kaladar]

I'm half-way through building my own 16' power boat (with a small cabin). I am planning on using a 30 HP Honda 4-stroke motor. I am hoping to use this motor (10 amp 126 watt) to charge the battery (or batteries) for both the electric start and electronics such as fishfinder, radio, GPS and a few nav light when running at night. I am thinking of using two 6 volt batteries wired in series. Does this sound reasonable? Will the outboard provide enough charging capability? I was also thinking about installing a small solar unit to keep her charged when at dock. Any suggestions? Thanks, great forum.

 

[18rabbit]

Re: Battery setup

For a boat like you have you may be a candidate for a single, 12-volt dual-purpose battery. 6v bats have a lot of advantages but most of it would be lost on an application where the same bats are used for starting and deep cycle. Keep it simple. If you decide on separate battery banks (a bank can be a single battery) for starting (motor) and house (electronic toys) than a couple of 6v for the house bank makes sense.<br /><br />Something else to keep in mind with smaller boats like yours is the weight distribution. Three bats (1 starting and a couple of 6v for the house bank) can be a significant weight issue in a 16-ft’er.<br /><br />For most marine applications I really dislike dual-purpose bats. They don’t do either starting or deep cycling as well as application specific bats, but in small boats with a single bat they are invaluable. If you plan to operate electronics for a long period of time without the engine’s alternator support, separate starting and deep-cycle bat banks is the way to go. With the deep cycle application, you need to compare the cost, weight, and amp-hours of a couple 6v bats to that of a std 12v bat. In general, many (most?) boats with trolling motors would benefit from a couple 6v bats in series.<br /><br />Solar is ok for a trickle charge to keep your bat(s) topped off but that’s about it. And any trickle charge needs to be regulated, especially anything solar, and the cost of regulating solar often outweighs the benefit it offers. Some folks here have had success with small, unregulated solar panels for keeping their bats topped off.<br /><br />A common solution for what you are doing is to have a 12v starting bat is to use a battery combiner to make the starting bat bank the primary recipient of the alternator’s output. The bat combiner will sense when the starting bat is full and then will redirect the alternator’s output to the house bank. This way your alternator is keeping the start bat ready, keeping it the priority that it should be, but also supplying voltage to the deep-cycle bank. Fwiw, if your motor is maintained, very little energy is actually yanked out of a starting battery to get things up and running, so most of the time the alt is supporting the house bank.<br /><br />It is virtually impossible for an alternator to completely charge batteries without the support of some kind of regulating scheme similar to that found in quality multi-stage bat chargers. You may want to consider a multi-stage charger for when you get your boat back to the barn. With a quality charger, you can plug it in and walk away indefinitely, and the bats will be ready to go whenever you return.

 

[Silvertip]

Re: Battery setup

Why two six volts in series when one twelve volt will do. If capacity is your concern, put two twelve volt batteries in PARALLEL to double the capacity. Whether or not the engine will keep those batteries charged depends on how long your wide open throttle runs are. Even a single battery would require several hours of wide open throttle operation to fully charge. Unless you use a "large" solar panel, that too is a painstakingly slow operation.

 

[Paul Moir]

Re: Battery setup

Given the engine he's got, wouldn't just a single deep cycle make more sense? Or better yet, an AGM deep cycle? That 30hp starter isn't going to be drawing thousands of amps, so there's no real need for a dual purpose battery let alone a seperate cranking batt.<br /><br />I think two batteries are a waste & too heavy on the size boat you're talking about. In case of emergency, the outboard isn't going to be too hard to rope-start and it'll power the nav lights just fine. GPS + Nav lights + Fishfinder + Radio don't add up to a lot of power. Something above 50Ah would be good. A quality multi-stage automatic charger is your best investment.<br /><br />EDIT: Honda recommends a 65Ah or better.

 

[Kaladar]

Re: Battery setup

Thanks very much for the responses. I'm not really worried too much about he weight. This boat looks like a mini tug and speed is not a big deal. Much appreciated.

 

[18rabbit]

Re: Battery setup

Ohhhhh! Displacement hull… Welcome to the club. <br /><br />And welcome to the forums. (Sorry, I forgot that in my first reply to you).