solar for 12v battery

[808stone]

Any flexible solar suggestions for a 12v battery that needs to power a stereo and a strong trolling motor for a hour or two?

[tommays]

It will be really big to be able to recharge a battery run down from a trolling motor

[MARC2012]

Do not know about big but if small bet it takes a looooooogn time.

[scottyt]

okay stone lets take a little more of a scientific approch

how often do you use the boat ?
how often and how long do you motor?

now for some math and some assumptions

if you just do weekend day sails ( as in sail saturday and sunday ) and use the radio for say 6 hours a day and it draws 3 amps. thats 18 amp hours a day over 2 days 36 hours or almost the 50 % charge on a small deep cycle by it self. then if we add the trolling motor which i just looked is up to about 50 amps depending on size ( its about 1 amp per pound of thrust ). so if you use the motor 2 hours a day on max thats 100 amp hours a day.

you should probably size the batteries for 2 days use, incase you can get no charging. this gives you 2 days of use at about 236 amp hours, so to stay under the 50 % discharge rule you would need close to 500 amps of battery.

now for the charging end, if you went solar, you would need about 350 watts of panel to recharge in one day with 8 hours of sun. now this assumes rated wattage out of the panels with a mppt charger. in reality you will get 250 to 300 watts per hour a day charge.

now if you know you will never be out more than 2 days you should be able to get away with 125 watts or so of panel. this will recharge you fully in about 3 to 4 days with full sun for 8 hours a day, including what you get per day using power.

now you see why a gas outboard works better, because you will sink over a grand in batteries and solar for 2 days of use. now if you have shore power you could just put the 500 amps in battery and not do solar but you need shore power to charge.

the ideal system i would say ( or better i would guess ) would be 4 group 27 or 3 group 31 batteries with a shore power charger and 125 watts of solar. the solar would give you in reality 50 % of your use a day back in charge, or around 75 to 80 amps per day if you have a mppt charger. if you just had a solar controller charger you will get about 50 to 60 amps a day.

now this all assumes you have sun and you dont motor more than 2 hours a day and you dont use any running, interior or anchor lights. you might want to use a d battery powered radio instead of a mounted radio, i use a aa powered radio that gives me 2 weeks on a set of batteries.

sorry for the long winded reply. and i assumed some things so this post may not be right but it should be close

[mitiempo]

scotty
Ever notice that with almost all questions like this the poster never says what size boat and his profile leaves it blank. Best bet is it's a small boat as he plans to use a trolling motor. He may not have the space for the 4 batteries much less the solar panels required. I think your dollar estimate is low for the solar and controller as well as I looked at the prices of a few MPPT controllers and that eats up about half your solar budget. For batteries I'd recommend a bank of Trojan T105 though (4) as I think they'll outlast most others in a deep discharge situation.

[scottyt]

brian i agree its probably a smaller boat 22 to 25 footer, i would also bet he is a lake sailor.

as for price
mppt for 110 here now the morning star mppt is a known name and costs about 250, and i also quoted some numbers for a non mppt

$420 135 watt kyocera here

thats about 600 if you include shipping

that leaves 400 for batteries, and 4 walmart batteries would be about 250 bucks, although he may need to replace them twice as oftern

i know he probably does not have space, but i quoted what it would take and i also discounted that it would be possible. yes it is but a gas outboard would be much better because of the draw, esp at 2 hours motoring. i guess i was trying to say while it would work, that i would not due to the costs and space

[mitiempo]

scotty
I agree a small gas ob would be the way to go. Being green isn't cheap! As far as the MPPT controller I was wrong - the ones I was looking at were the Outbacks at much higher prices.

[808stone]

I guess I should apologize for not giving more information. My boat is a 24' Hawaiian outrigger sailing canoe. Like this: http://www.worldofstock.com/slides/OAC6171.jpg
...but smaller. It's about 400 lbs all together with only a few inches draft and little wetted area. We load from 400-1000 lbs on our outings.

Usually we paddle upwind and sail downwind with a modified sunfish rig. A motor would give me a lot more range but I really want to avoid the noise and stink of a gas motor. Also would like to skip trips to the gas station to fill.

Typically, we are out for sunset sails about twice a week so I imagine we would use the motor for 30 min every 3 days or so. However, I would like to play the stereo for a couple hours. I guess there will be an occasion when I would like to go exploring further abroad so being able to use the motor for 2 hours and stereo for 4hrs would be nice, but not essential. Also, I have the boat moored out on the sunny side of Oahu, Hawaii so I get quite a bit of strong, overhead sunshine most days of the year.

I have looked at the Torqeedo and the Minnkota online. The Torqeedo would be nice to plug the battery into the wall but then I have to swim the battery out with me and I already have to swim out the mainsheet and giant steering paddle. It would be nice to just swim up and have the system all charged up and ready to go. Therefor, I started to look at having a battery with a solar charging system. But, because of the nature of the canoe I want to keep the system to one battery and flexible solar for weight and safety issues.

Thank for all your comments... I am an electrical newbie so any help is appreciated.

-Stein

[mitiempo]

Stein
It doesn't sound like you have the space for solar panels that would do the job.

[808stone]

I have a platform area of 10' x 8' covered in two 8' x 3' tramps. Not enough?