Looking to solar charge a 12 volt battery - any suggestions?

netrate
netrate Registered Users Posts: 2
in General Solar Power Topics #1
Looking to solar charge a 12 volt battery - any suggestions?

What I am trying to do is this :

Run this portable air conditioner with a 12 volt battery/charger. And when the battery runs out, trickly charge it back with solar. Any suggestions?

http://www.homedepot.com/p/LG-Electronics-7-000-BTU-Portable-Air-Conditioner-with-Dehumidifier-Function-67-Pint-Day-and-Remote-Control-LP0711WNR/202562960?N=c4m4Z12l5#.Uaucvtjm840http://forum.solar-electric.com/register.php?do=addmember
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Looking to solar charge a 12 volt battery - any suggestions?

    Welcome to the forum.

    Any suggestions? Yes: forget it.

    That unit is rated for 7.6 Amps @ 120 VAC: 912 Watts. The start-up surge will be even higher than that. We've tested a few A/C units here; they have pretty high power demands and even higher start demands. That one's rating (which may not be entirely accurate) is even more Watts than the 11,000 BTU unit I tested.

    Trying to run such a beast from a 12 Volt inverter system will not be easy. You'd need a 2kW inverter, really good battery cables, and a substantial battery bank (900 Watts on 12 Volts is 10X the current it is on 120 Volts, plus powering the inverter). In one hour's cycling it would consume about 1 kW hour of power, which is roughly 100 Amp hours @ 12 VDC.

    This is really not a practical thing to try and do. Read through this thread on the Fedders test: http://forum.solar-electric.com/showthread.php?16201-Fedders-5000-BTU-A-C-test
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  • netrate
    netrate Registered Users Posts: 2
    #3
    Re: Looking to solar charge a 12 volt battery - any suggestions?

    Ok, I am teaching an adult class over the summer and I wanted to make it tolerable for the students is all. The school will not let me use their hydro unless it is a fan, so I was trying to come up with an alternative. I do have a 2KW inverter already.

    Cariboocoot wrote: »
    Welcome to the forum.

    Any suggestions? Yes: forget it.

    That unit is rated for 7.6 Amps @ 120 VAC: 912 Watts. The start-up surge will be even higher than that. We've tested a few A/C units here; they have pretty high power demands and even higher start demands. That one's rating (which may not be entirely accurate) is even more Watts than the 11,000 BTU unit I tested.

    Trying to run such a beast from a 12 Volt inverter system will not be easy. You'd need a 2kW inverter, really good battery cables, and a substantial battery bank (900 Watts on 12 Volts is 10X the current it is on 120 Volts, plus powering the inverter). In one hour's cycling it would consume about 1 kW hour of power, which is roughly 100 Amp hours @ 12 VDC.

    This is really not a practical thing to try and do. Read through this thread on the Fedders test: http://forum.solar-electric.com/showthread.php?16201-Fedders-5000-BTU-A-C-test
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Looking to solar charge a 12 volt battery - any suggestions?

    Think of it like this: trying to supply 900+ Watts while running would basically mean you'd need a 1kW PV array just to break even during daylight hours while the thing runs. Compressors are big power users and there's just no way around it. :cry:
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    Re: Looking to solar charge a 12 volt battery - any suggestions?
    netrate wrote: »
    Ok, I am teaching an adult class over the summer and I wanted to make it tolerable for the students is all. The school will not let me use their hydro unless it is a fan, so I was trying to come up with an alternative. I do have a 2KW inverter already.

    Where are you teaching the class? if it's in a dry desert area, a swamp cooler might work, the may components are a fan, some sort of wicking fabric and something that holds water.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #6
    Re: Looking to solar charge a 12 volt battery - any suggestions?

    You would be FAR, FAR, FAR ahead to make a deal with the school to give the them some extra $ to pay for running the AC off their power supply.
    To install a PV and battery system to do what you're asking, will cost you thousands of dollars, perhaps even reaching into the tens of thousands of dollars. Not kidding.
    AC is a relatively HUGE load for any solar system, many many times the consumption of running a fridge, freezer etc.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: Looking to solar charge a 12 volt battery - any suggestions?

    How many people in the room? Roughly each person is good for ~100 watts (314 BTU per Hour). Plus any other appliances/lighting in the room (over head lights, any computers/protectors).

    Does the school have A/C already installed, or do you have to bring your own? A mini-split could be a very efficient when compared with a typical window mount unit (about 2x as efficient or 1/2 the power usage).

    Anyway say you are using ~1.5 kW to keep the room cool (you could get a Kill-a-Watt type meter and measure the kWH per day/class usage). If you are in Canada, you may be paying down down towards $0.10 to $0.15 per kWH:

    1.5 kW * 1 hour * 1/$0.15 per kWH = $0.225 per hour of cooling

    If you can arrange to pay for the power usage, you will probably come out way ahead unless there are other things afoot (such as you want to build out a portable solar power system for demonstration, eventually move to home for emergency power, use as part of the call teaching aids, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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