Which battery and circuit set-up?

[Wiggy]

I'm now going to venture into the land of electronics in my little boat but want to hear what the experts think first.<br /><br />All that I'm running is one white light on a rod from the back of the boat and a fish finder. These will used max 5-6 hours in one go.<br /><br />Now I'm also thinking about using my 25hp Merc to maybe recharge the battery (pull start but has alternator and 12v output). Is this advisable? And which battery should I look at buying? How big a battery?<br /><br />Also how should I wire it all up. I have a plate with various switches on and a battery level meter on it. <br /><br />All advice is greatly appreciated.

 

[vipzach]

Re: Which battery and circuit set-up?

First thing, I am no expert! How big is your little boat? I don't think your motor will recharge the battery very fast, but I don't think it will hurt to hook it up. How are you powering the lights and fish finder now? The bigger the battery, the better, as far as run time. You also have to consider the weight though, that is why I asked how big your boat is. If you are going to only run the light and fish finder, than a group 24 battery would last you a long time. I would get a deep cycle and hook it up to a charger when you get home.<br /><br />Does that plate have any switches that are unused? That would be an easy place to be able to turn off the light and fish finder.

 

[Wiggy]

Re: Which battery and circuit set-up?

The boat is a 14 footer. The plate has all three switches unused. Fish finder and light are yet to be installed!<br /><br />How big a battery should I buy? What's a group 24 battery? Obviously money being a boundary, a cheaper battery would be great (e.g. less Ahm). Just need a battery that'll do the job great. And what capacity should I be looking at?

 

[jtexas]

Re: Which battery and circuit set-up?

You only need the white 360º stern light for night running in Norway - surprising there's no nav light requirements.<br /><br />Get a series 24 marine deepcycle...a 12-watt bulb draws 1 amp of current - and the fishfinder draws a very small fraction of an amp - I doubt you could find a battery so cheap that it wouldn't keep you going all night. Wait, you guys have some really long nights there, right? <br /><br />I don't see any real downside to hooking it up to the motor's alternator, but it doesn't seem necessary. Especially since you don't need the batt for cranking the engine. Which you can think about adding electric start now that you're carrying a battery anyway. <br /><br />Your fishfinder won't switch on from the switch panel - after you shut off power to it you'd have to press the on/off switch on the unit to turn it back on anyway. Manufacturer will recommend a separate power line to avoid noise, but I've heard that's not always necessary.<br /><br />You need a wire from the battery (+) to the switch box, probably 10-gauge, with an inline fuse, and from the battery (-) to ground bus (if you have one). Then smaller wire (14 should be fine) from switch to device, and from device to ground bus (or back to battery (-) if you don't have one). The fishfinder will want it's own inline fuse. Wouldn't hurt to put a 5A fuse on your light as well.<br /><br />Might want to think about a bilge pump.

 

[Paul Moir]

Re: Which battery and circuit set-up?

A Group 24 battery is about 75Ah, and about 25kg. You might even consider smaller than that. My brother uses a 50Ah battery (18kg) on his sailboat running just the navigation lights (2 bulbs) and the VHF radio, as well as occasional courtesy lights. It serves it's purpose very well, and only ends up needing to be recharged occasionally. The smaller battery allowed for the investment in an AGM battery, and is light enough to carry.<br />14 gauge ~= 1.6mm and 10 gauge ~= 2.6mm wire.

 

[Wiggy]

Re: Which battery and circuit set-up?

jtexas - Nights can be long, but as long as there's liquor and women.......<br /><br />I have got a bilge pump too, so I thought of hooking this up too. My idea was to run the battery through this switch panel (which has individual fuses per appliance/switch) and then obviously out to the respective appliances. <br /><br />What I'd love someone to tell me is the exact Ahm battery I need. I've now understood it's best with a deep cycle, does a lead/gel/NiCD make any difference?

 

[Paul Moir]

Re: Which battery and circuit set-up?

Lead acid batteries give you the best bang for your buck as far as capacity goes (Ah). There are three forms:<br />Flooded Cell - Cheapest power. Downsides are they need maintanance (occasional water added), must be kept upright, and leak acid if punctured. They can supply lots of current quickly if needed.<br />Gel cell - Medium cost. Downsides are they leak gel if broken, and cannot deliver a lot of power quickly. Advantages are no maintanance, can be operated in any orientation.<br />AGM - Highest cost new kid on the block. Downside is price. Upside is they don't leak if broken, can be operated in any position, can deliver very large amounts of power quickly (better than flooded deep cycles), no maintanace, and can last longer and survive deep discharges better than any other. Self-discharge rate is also low.<br /><br />NiCd is very expensive compared to any form of lead acid, but is very light for the amount of power it can deliver. It's got all the advantages of AGM, except it self-discharges fairly rapidly. You can expect a life of around 600 cycles.<br /><br />I think AGM is really the ideal battery for what you're doing, and flooded is an option if price is the issue. I really don't see gel as being a very useful battery anymore. It's really old technology.