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Old 02-12-2009, 17:14   #1
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Electrical Weeds

I am trying to get my electrical system sorted out on my boat and am totally in the weeds.

I have a Toughbook CF 18 that I want to run as a chart plotter it produces between 26 watts and 40 watts. Other than that all I am running is navigation lights, VHF, one Interior light, and a dinky hummingbird depth sounder. This is a very spartan set up.

I want to get a small solar panel (somewhere in the 20 watt) range and use the alternator of a small outboard, probably anywhere between 6 and 12 amps (haven't bought outboard yet- whiny thread coming soon). I currently have two Trojan 605s rated at 120 amp hours in the boat but will probably be replacing them with 12 volts.

My dilemma is this: I have filled out West Marine's little "Electrical Budget Work Sheet" ten times now and it keeps telling me "No". It looks like I would need to run the motor 8 hours a day just to get by. Am I totally screwed here? What else can I do?
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Old 03-12-2009, 03:18   #2
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Get a bigger solar panel. I am surprised the outboard keeps any charge in the batteries but... what is the output from the outboard? If you don't use the boat during the week then maybe the batteries will survive the day or two on the weekend but I would be dubious about that.
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Old 03-12-2009, 04:51   #3
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normal small outboard electrical power is 4 amps. Might get as high as 10 on a big motor! I always had battery problems when I had a 30hp outboard. I added a decent solar panel, and life got a lot easier!
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Old 03-12-2009, 10:28   #4
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Quote:
Originally Posted by Masquerade View Post
what is the output from the outboard?
4 to 8 amps

Quote:
Originally Posted by Talbot View Post
normal small outboard electrical power is 4 amps. Might get as high as 10 on a big motor! I always had battery problems when I had a 30hp outboard. I added a decent solar panel, and life got a lot easier!
What do you mean by a decent solar panel? How many watts?

Jeez should I just get a generator?
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Old 03-12-2009, 11:13   #5
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A lot depends on what you are using the boat for. I assume that your power budget is about 75 amp-hours/24hr day if you are sailing, 25amp-hours/day at anchor. If you are living aboard on the hook, solar panels make sense, and you will need about 100 watts of panel to keep the batteries up. If you are only weekend sailing, you can deplete the batteries and recharge either on the dock or with a smaller panel, say 40 watts. A Honda generator is another alternative, especially if you are carrying gas for the outboard already.
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Old 03-12-2009, 13:07   #6
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We will be actively cruising the boat this spring for a month or two but will be living very close to the bone. I think between running/anchor/instrument lights we will be clocking about 18 Ah/24hr day. Does this sound right? Then when you tack on the computer that would add another 12/18 (2-3 Amps @6hours), for a total of 30-36AH/day.

As you can see our power needs are very limited. What would I need to replenish that?
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Old 03-12-2009, 13:55   #7
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Have you considered an onboard wind turbine? I see boats down here in Annapolis with them all the time. I'm certain you can get various sizes (outputs). It would compliment your solar panel nicely durning the dark days of winter. You can continue to generate power after the sun goes down.

The short answer though, is yes you need a larger (or more) solar panels for the amount of power you are consuming than a single 20w panel. 20w is "optimal", you won't even be generating that much power all day, every day due to cloud cover, impedence in your electrical circuit, etc.
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