Design Battery Cart+Charging system for portable A/C

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This discussion was created from comments split from: Batts / inverter / window AC unit..
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset

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  • ashaseashase Registered Users Posts: 4
    Photowhit, I apologize if I am posting this in the wrong place but you seem to be doing the closest thing I need to do.  I need to run a portable a/c around 10,000 BTU's.  Since I haven't bought it yet, thats all the info I have.  I need it to be somewhat portable.  I run a nonprofit and will be on a traveling music festival all summer. We will have heavy duty carts to wheel out battery banks.  I have been told I can use an inverter with a 4-6 12v batteries (no solar, but I can plug in the charger at night).  Do you know of anyone who has done this successfully or have any ideas on a better way to do it? I can't use a gas generator and solar seems impossible given the chance that the panels will get destroyed the first day 10,000 teens start milling about...Any help would be so appreciated!
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited May 2016 #3
    ashase said:
    Photowhit, I apologize if I am posting this in the wrong place but you seem to be doing the closest thing I need to do.  I need to run a portable a/c around 10,000 BTU's.  Since I haven't bought it yet, thats all the info I have.
    Welcome to the forum,  Don't worry, if your comment is in the wrong place, the moderators will move it.  It could be its own thread in the off-grid section.

    Because you will be recharging with the grid, what you want to do is very straight forward.   You need a battery and charger similar to what a golf cart or forklift truck uses.  You also need an inverter to turn battery voltage into AC for the air conditioner. 

    Designing a system is engineering. and engineers use formulas.  Formulas require numbers.  I need two numbers from you... peak load (watts) and energy use between charges (kilowatthours).  Then we can discuss the options.

    The MOST important thing for you to do now is research air conditioners.  Efficiency is critical, not just of the air conditioner, but of the whole room that is to be cooled.  Better insulation and efficiency can shave hundreds of pounds and thousands of dollars off the battery bank.  Can you find an air conditioner with a variable speed compressor?  They are more efficient and have virtually no startup surges.  No startup surges means a much smaller inverter is needed because the peak load is smaller.  Smaller inverters have lower tare losses (self consumption losses).  

    Your battery is the heart of the system and must be chosen carefully.  How much weight can you handle?  Perhaps LiFePO4 batteries (more energy, less weight, more money) should be considered.

    Industrial lead acid batteries (forklifts, etc) are used and charged differently than RE (renewable energy) batteries.  It is cost effective to do much deeper discharges than with RE batteries.  But that assumes that you immediately recharge them with unlimited power and time (in other words: the grid).  If you can do that, you will need only half as much battery as we usually recommend.  It will require 220 volt service to power an industrial battery charger.

    To be any more specific to your needs, I need those numbers for peak load and energy use between charges.

    --vtMaps

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PhotowhitPhotowhit Solar Expert Posts: 4,996 ✭✭✭✭

    That is a huge load! You can't get by with a minimal window unit?

    What type of duty load will it have? Will this be an insulted structure you are trying to air condition?

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • 706jim706jim Solar Expert Posts: 251 ✭✭✭

    Consider some sort of fan and forget the A/C. If you are outside or in a large hall playing music or whatever, the A/C is giving off more heat than cool.


    So the venu will just get hotter.


    Speaking from experience as a longtime professional musician.

    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 27th year.
  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    Buy an electric forklift and mount the AC to it.  It's now a huge portable power pack
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • ashaseashase Registered Users Posts: 4
    mike95490 said:
    Buy an electric forklift and mount the AC to it.  It's now a huge portable power pack
    Are you joking or is that something that I can really do? Electric forklifts are surprisingly low priced.
  • ashaseashase Registered Users Posts: 4
    edited May 2016 #8
    I am looking at one of these to A/C units.  Thank you so much for all of your help.  We leave 6/24 and I am in a complete panic!

    http://www.climax-air.com/documents/Climax-VS12-SpecSheet.pdf

    http://www.climaterightair.com/climateright-cr12000sach-ductless-mini-split-12-000-btu-air-conditioner-with-heat-pump.html
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited May 2016 #9
    ashase said:
    I am looking at one of these to A/C units.  Thank you so much for your help.  We leave 6/24 and I am in a panic.
    I looked at the first unit... it draws 1100 watts.  If you use it for 10 hours, it draws 11000 watthours = 11 kwh.  You will need to draw more than that (about 12 kwh) from the battery because some power is lost in the inverter.

    The storage capacity of a battery bank is measured in kwh, and you need to decide how deep to discharge your battery in those 10 hours.  That will depend, in part, on the battery technology that you choose.  If, for example, you intend to draw your battery down to 50% SOC (state of charge), you will need a 24 kwh battery. 

    Batteries are rated in volts and ah (amphours).   Volts X amphours = watthours.   If you have a 48 volt battery bank, you need a 500 ah battery bank. ( 48 volts X 500 ah = 24000 wh = 24 kwh).

    A deep cycle, flooded lead acid battery bank of that size will weigh about 2000 pounds. 

    Does this help?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ashaseashase Registered Users Posts: 4
    edited May 2016 #10
    That helps very much and really puts things in perspective. I am not going to carry around 2000 lbs of batteries.  I suppose a generator like the Honda 2000eu or the Yamaha 2400is truly is my only option.  I was very much hoping to have a more environmentally friendly option. If anyone can come up with a better way, I am open to anything! Thank you all for your help, it is greatly appreciated.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    edited May 2016 #11
    ashase said:
    I am not going to carry around 2000 lbs of batteries.
    My example was based on many assumptions... for example I assumed flooded lead acid and 50% discharge.  Forklift batteries can be discharged down to 20% SOC on a daily basis... as long as they are fully charged before the next day.  That means your battery can be smaller. 

    You might consider LiFePO4 type of lithium batteries.  Much less size and weight than lead acid.

    One more thing... I assumed that it drew 1100 watts all the time.  That may or may not be true... depends on inside temp, outside temp, humidity, insulation, how many times a minute the door opens, etc.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490mike95490 Solar Expert Posts: 8,377 ✭✭✭✭✭
    ashase said:
    mike95490 said:
    Buy an electric forklift and mount the AC to it.  It's now a huge portable power pack
    Are you joking or is that something that I can really do? Electric forklifts are surprisingly low priced.
    If you have a good floor surface, and the wheels don't sink in, sure, I'd do it in a heartbeat.   Portable power pack. Buy a junker with dead hydrualics or something.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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