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

netratenetrate Posts: 2Registered Users
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

Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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
  • netratenetrate Posts: 2Registered Users
    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.

    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
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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:
  • PhotowhitPhotowhit Posts: 4,473Solar Expert ✭✭✭✭
    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, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • waynefromnscanadawaynefromnscanada Posts: 3,009Solar Expert ✭✭✭✭
    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.
  • BB.BB. Posts: 27,335Super Moderators admin
    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
Sign In or Register to comment.