inverter size vs battery

mountainmanmountainman Registered Users Posts: 353 ✭✭
With a 1000 watt array and a 210 ah 24 volt battery. Whats the largest inverter I could safely use?
 I plan on running 2 inverters  a 300 watt 24-7 for TV Led lights etc. And a  larger one part time for washer and Microwave.
Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.

Comments

  • wellbuiltwellbuilt Solar Expert Posts: 469 ✭✭✭
    For a 300 watt load I would use a morning star suresine 300 watt 12 volt inverter . 
      I run my 2800 sf house on less then 300 Watt with a frig . 
         I used the 300 watt unit with 2 golf cart battery’s and 500wats of solar on a old travel trailer . 
         The morning star will  Surge to 600 watts  and is Very reliable 
       
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • wellbuiltwellbuilt Solar Expert Posts: 469 ✭✭✭
    I think you would need a 1500 watt inverter for the microwave 
      My microwave was small and would only run on low on a magnum 1000watt inverter . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    For a 210 AH @ 24 volt battery... Use C/5 as the maximum inverter and C/10 as the "comfortable" inverter (for flooded cell lead acid battery capabilities):
    • 210 AH * 24 volts * 0.85 AC inverter eff * 1/5 hour discharge = 856 Watt inverter max suggested
    • 210 AH * 24 volts * 0.85 AC inverter eff * 1/10 hour discharge = 428 Watt inverter "nice" size
    The other rule of thumb, for a 24 volt battery bank, ~500 Watt inverter (and suggested maximum array wattage) per 100 AH @ 24 volts:
    • 210 AH battery bank * 500 Watts * 1/100 AH = 1,050 Watts
    AGM, GEL (and Li Ion) can surge more current and support a larger AC inverter... But you sort of want to avoid taking a battery bank "dead" in ~5 hours (or less), or to 50% state of charge in 2.5 hours or less for a home/cabin.

    When you compare to, for example, 5 hours at night for 2 nights, with 50% maximum discharge, the average load would be:
    • 210 AH * 24 volts * 0.85 AC inverter eff * 1/2 days * 0.50 max discharge = 1,071 WH per day average battery load
    • 1,071 WH average battery load / 5 hours per day (evening) usage = 214 Watt average loads for 120 VAC
    And why a 300 Watt inverter with 600 Watt surge is not a bad fit for a small system.

    Of course, these are really rough rules of thumbs (C/5 and C/10 discharge rates)--But do get you a pretty reliable system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mountainmanmountainman Registered Users Posts: 353 ✭✭
    So to run a  microwave would 6 Gc Batteries at 630 ah configured for 12 volts.
    With a1500 watt array
    Be a better fit for a 1500 watt inverter?
    Or should I go to 420ah at 24 volts and a 2000 watt array?
    @wellbuilt are you saying you ran a refrigerator on a 300 watt inverter?
    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • BB.BB. Super Moderators, Administrators Posts: 30,502 admin
    Around 1,200 to 1,800 Watts is about the maximum I would suggest for a 12 volt battery bank:
    • 1,800 Watts * 1/0.85 AC inverter eff * 1/10.5 volts battery cutoff = 202 Amps
    • 202 Amps * 1.25 NEC derating (to lessen the chance of blowing fuses/breakers) = ~252.5 Amp rated branch wiring+breaker/fuse
    And if you look at voltage drop, trying to keep below ~0.5 volts (12 volt bus). Using the NEC cable and ~250 Amps would be a 4/0 cable.
    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
    Using a voltage drop calculator, the one way run for 202 amps @ 0.5 volt drop @ 4/0 cable would be:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.1608&voltage=12&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=202&x=0&y=0

    In this example, you could go out to ~25 feet (0.5 volt drop)--Although, you probably would generally be much shorter cables...

    Same thing at 24 volts:
    • 1,800 Watts * 1/0.85 AC inverter eff * 1/21.0 volts battery cutoff = 101 Amps
    • 101 Amps * 1.25 NEC derating (to lessen the chance of blowing fuses/breakers) = 126 amp minimum rated wiring+breaker/fuse
    That would be ~2 AWG cable... And the voltage drop at maximum one way run @ 1.0 volt drop is ~30 feet (again, keep inverter wiring short).

    If you go with a 420 AH @ 24 volt battery bank (~2,200 Watt inverter suggested maximum), the array size based on battery usage would be:
    • 420 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 791 Watt array minimum
    • 420 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,582 Watt array nominal (full time off grid min)
    • 420 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,056 Watt array "typical" cost effective maximum
    Your 2,000 Watt array looks good with this bank. A 12 volt bank would be 840 AH @ 12 volts... That is about the largest AH battery bank I would suggest (heavy wiring, need >80 Amp charge controller for 10% rate of charge, etc.).

    So, yes, a 24 volt battery bank looks better--And unless you really need 12 volts (HAM radio, other "12 volt devices")...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wellbuiltwellbuilt Solar Expert Posts: 469 ✭✭✭
    No I do not run the frig on a 300 watt inverter .
     My house really Dosent go over 300 watts at any time but I have a 3600 watt out back system now. 
      The inverter system uses 50watt a hour just being turned on. ,  
        
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • mountainmanmountainman Registered Users Posts: 353 ✭✭
    Ok with a 2000 watt inverter @24 volts and 
    420 ah bank.
    A 1500 watt array puts me  @~10℅ charge rate.
    Panels are cheap but good quality mppt controllers are not.
    What amp controller for a 2000 24 array.
    80 amps? or 2 40s for redundancy.
    With a 1500 array would a 60 or or 2 30 amps be about right?
    This is a 10k battery~ 2150 watts per day after inverter efficiency.
    A 1250 kwh daily usage  fridge would leave me about 900whs. With 50℅ on 2 days without sun.
     I think i Icould  get buy by being conservative  on ~1kwh
    Use genny  for A/C. my 2000 runs a 10000 btu window unit 8 hrs on 2 gals $1.50 a gal
    $240 a month.
    Wow grid is so much cheaper @11.6 per kw
    I'll still trying to wrap my head around what wellbuilt  means about  the 300 watt inverter on a refrigerator 

    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • mountainmanmountainman Registered Users Posts: 353 ✭✭
    Ok so your average peak is 300 watts.
    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • PhotowhitPhotowhit Solar Expert Posts: 5,173 ✭✭✭✭
    Sorry, I should have jumped in earlier...

    We still don't know what your total loads are, so we're running blind, seriously! now your talking fridge, your a moving target, this just frustrates people. Why don't you calculate your daily energy needs, and then build a system to meet your needs.

    I've happily run a microwave on a 1800 watt inverter on a 24 volt system using 4 golf cart batteries... I did this for 4 years... no issues, I didn't use it every day, but often popped popcorn at night... Starting with a 1000 watt array, I also charged those 4 Sam's Club batteries, and discharged them running a window airconditioner to provide sleeping temperatures here in Missouri. the cabin was built to air condition. 6" walls, built in shade, we also cool off most nights during the summer.


    I later increased the size of the array to provide some day time running of the air conditioner and reduce the night time/cool down running. I got up to 1650 roughly watts. I charged with a PWM charge controller. I added a fridge (tiny 2 door) the 2nd and 3rd year with the larger array, though I shut down the fridge the final year during the summer as the batteries had some reduced capacity. They were a year old when I started so lasted 5 years, being drawn down to or below 50% most days during the summer.

    Even after I was forced to move, I used the same inverter for many years running a full size fridge, window air, microwave (not with air conditioner unless the fridge had just kicked off. I also used it to run a washing machine, a table saw

    So to figure out what you need, we need, what your energy use is per day, location of your system(to figure out how much sun per day you get on average), availability of sun exposure (southern sky) with no shading...
    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
  • softdownsoftdown Solar Expert Posts: 3,137 ✭✭✭✭
    Microwaves vary in consumption from 900 watts to 1500 watts. The bigger and better ones draw 1300 to 1500 watts. Giving the microwave it's own dedicated circuit is a nice touch. Otherwise it is easy to trip kitchen. circuit breakers when cooking for groups. 

    1500 watt inverters are nice size for most general purposes. Larger inverters are energy hogs. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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