Simple 12v system

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woowoo2
woowoo2 Registered Users Posts: 13 ✭✭
in Solar Beginners Corner #1
Thanks in advance for the help.

I have on order a 8' x 10' above ground storm shelter.
I am purchasing the following devices and I want to power them.

2 ea.12 volt fans .8 amps each want to use them 24 hours a day
3ea. cold cathode lights .3 amps each want to use them for six hours.
1 ea. portable TV 3 amps used for five hours.
1x3 auto cigarette lighter plugs lets say 2 amps at five hours.
And a lighted 12 volt meter.
Each load has a switch and a fuse upstream of it.
I am using 12Ga. stranded wire to the load switch panel.
The panel would be about 30' from the shelter.
No inverter planned for this system.

So that's about 70ah right?

I bought a no name 10a charge controller.
Now I am looking at batteries and a panel to charge the system.

Do you all think 150ah of FLA batteries and a 40w panel would do it?
Any recommendations on batteries and a panel?


This is going to be setup for extended power outages.
When this happens, I usually run my generator about six hours a day.
I could use a 12/2 amp automotive battery charger during this time.
Or I could charge them from my car.

Looking at this panel
http://www.solar-electric.com/so40wa12vomu.html
Voc 21.8 volts
Vmp 17.3 volts
Isc 2.57 amps
Imp 2.35 amp

I have budgeted about $300-$400 for the batteries and panel.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Simple 12v system

    Welcome to the forum.

    With you right up to the panel.
    A 150 Amp hour battery will want at least 7.5 Amps potential peak charge current (5% minimum) and will be a lot "happier" with 15 Amps, especially if loads are being drawn while charging (like the fans running 24 hours per day). At a "best current" of 2 Amps that 40 Watt panel will provide little more than a trickle charge to that battery.

    Then there's the Watt hour "replacement". 70 Amp hours @ 12 Volts is 840 Watt hours. Even if the panel were to put out its 40 Watt rating (they don't; figure about 77% of that) it would take 21 hours of direct sunlight for it to produce the amount of power you expect to use.

    You're about 240 Watts short on panel. Sorry, but that's the physics of it.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #3
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    Re: Simple 12v system

    To add to Coot's post, the average sun is only about 4hours a day so you would be looking at over five days to recharge the battery.
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  • woowoo2
    woowoo2 Registered Users Posts: 13 ✭✭
    #4
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    Re: Simple 12v system

    Thanks for the reply, I may have to rethink things
    Maybe the panel will just serve as a trickle charger, and I will rely on the generator to charge the batteries during the day?
    I am nine months out on delivery of the shelter, lots of time to think about it.

    I take it a 30-40 watt panel would work to maintain a charge while the shelter is not in use?
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #5
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    Re: Simple 12v system

    5% of the battery amp hour is really the minimum you want on a battery for "storage" use.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #6
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    Re: Simple 12v system

    As far a a battery recommendation, you could start with the golf cart style batteries from costco. They are inexpensive and seem to be decent.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Simple 12v system
    Seven wrote: »
    5% of the battery amp hour is really the minimum you want on a battery for "storage" use.

    Not exactly; that's the minimum max current rate for recharging. Works with no-load recharging, but not if things are drawing from the battery at the same time (net charge rate: controller output minus loads).

    For storage 1-2% is plenty, but still should be regulated. Even a minimal controller like this: http://www.solar-electric.com/sg-4.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Simple 12v system
    Seven wrote: »
    As far a a battery recommendation, you could start with the golf cart style batteries from costco. They are inexpensive and seem to be decent.

    Yes, but they're 220 Amp hours. That means even more panel!
    And if these batteries will be kept within the "living quarters" you'd want AGM's so there's no problem with off-gassing or accidental spills.
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  • woowoo2
    woowoo2 Registered Users Posts: 13 ✭✭
    #9
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    Re: Simple 12v system

    Just a little clarification.
    This is a concrete shed, it will be used only during bad storms.
    http://www.safesheds.com/
    My house does not have a basement.
    When the shelter is not in use there will be no load.

    Here are the specs on the cheap controller I purchased.
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220818814805&ssPageName=STRK:MEWNX:IT
    Rated voltage 12V / 24V
    Voltage of stop power supply *10.8V or 21.6V
    Rated charging current 10A
    Voltage of resume power supply *11.8V or 23.6V
    Rated load current 10A
    Voltage of stop charging *14V or 28V
    Working temperature -20 ~ +60°C
    Temperature coefficient of voltage stop charge -3mV/°C/cell
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Simple 12v system

    You know, during a storm the solar panels aren't going to produce any power anyway. You might be better off planning on a few more Amp hours capacity and a good charger for when the grid is up or the generator is running. Panels are not a very good bargain for emergency power purposes.

    Don't expect much from that Chinese charge controller; several variations on the same theme have crop up here from time to time with less than stellar performance. Ought to be good enough to keep the battery in float, though.
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  • woowoo2
    woowoo2 Registered Users Posts: 13 ✭✭
    #11
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    Re: Simple 12v system

    So maybe two of the costco golf cart batteries and a battery tender?
    I knew the controler was not going to do much, but i figured some discharge protection was in order.

    The shed will sit right next to my garage, where I have 120v, off air tv, and telephone.
    I could put a charger in the garage and run a 12ga 12 volt line out to the shed.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
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    Re: Simple 12v system

    That would be good, providing you can vent the batteries. You'll want a good battery charger too, like one of these Iota units: http://www.solar-electric.com/ioen12vo15am.html

    You'd probably be better off running a 120 VAC line, as there would be less Voltage drop. And you'd be able to keep an eye on it to see if grid power was up or down during the storm.
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  • woowoo2
    woowoo2 Registered Users Posts: 13 ✭✭
    #13
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    Re: Simple 12v system

    This is the charger I currently have, I guess its no good.
    http://www.toolking.com/schumacher-se-520ma-10-2-fully-automatic-and-manual-dual-rate-charger-with-led/
    Boy you guys are full of good news :)

    Venting should not be an issue, the shed has four vents built in.
    I could also run a computer fan 24/7 while the charger is working.

    If I run 120 volts, then it's another $35 for a permit.
    Low voltage does not require one.
    I could keep a 12 volt line under 20 feet and I have the cable (12/2 no ground).

    Thanks for putting up with me.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
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    Re: Simple 12v system

    Schumachers are good chargers. Trouble is automotive chargers aren't designed to recharge deep cycle batteries. There's a difference in the profiles.

    You might want to look over the battery FAQ's here: http://www.windsun.com/Batteries/Battery_FAQ.htm

    12 AWG is a bit light for 20 ft @ 14.4 charge Volts and up to 22 Amps, but it just might work.
    They won't let you run an AC line without a permit? You could always use an extension cord and recharge the batteries and roll it up when done. If you keep the 40 Watt panel the batteries could be kept up without bother. Just check the specific gravity once a month and make sure the water level is up so everything is good to go when you need it.
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  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    #15
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    Re: Simple 12v system

    Schumacher has models that can handle several types. http://www.landmsupply.com/department/automotive/maintenance/batteries-chargers/schumacher-21015a-12v-battery-charger

    I've had one for a few years and used it on all types of cells with good results.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #16
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    Re: Simple 12v system

    I have that one, only problem is if you had the 10 or 15 amp mode selected and the power goes out, it defaults back to 2 amps. Which does make sense, it fails safe to a trickle charge. I don't remember which battery type it defaults to.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • woowoo2
    woowoo2 Registered Users Posts: 13 ✭✭
    #17
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    Re: Simple 12v system

    Thanks for your contributions to the thread, you have given me something to think about.
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