12V > AC inverter question

Discussion in 'General Electronics Chat' started by Mike33, Apr 6, 2015.

  1. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005

    All things being kept equal, does anyone have a quick and dirty answer for "what is the better unit" when looking at 12V inverters? My buddy is putting together a solar project - wants to run his camp off 12V batteries. Some LED lighting, maybe a radio, very small-scale. Perhaps the occasional power tool, but it's not a house.

    His options are a 12V > 110VAC 8000W or 12V > 220VAC 8000W unit. I'm not sure what to tell him about 'better'...I know that mains are generally wired up with 110 on each side, neutral in the middle, so it appears he could get more 'bang for the buck' with 220. That said, 110 may be more convenient....as he's not running anything on 220, it seems like that might just complicate things for the same (similar) outcome...he has to run about 75' from where the inverter will be TO the camp, and he's thinking about transmission losses, which may be a real concern.

    Any thoughts?
  2. MrChips


    Oct 2, 2009
    Do the math.

    8kW @ 110VAC is 73A.
    8kW @ 12V is 666A

    How are you going to draw 700A from a 12V battery and for how long?

    If you want to power LED lights and a radio, connect it directly to the 12V battery with proper voltage/current limiting.
  3. crutschow


    Mar 14, 2008
    8000W seems like a huge over-kill. 8000W requires at least 700A from the 12V source.
    And such a large inverter will likely be rather inefficient at the low power levels he will normally operate at. Better to buy an inverter with a rating closer to the maximum power he intends to use (say 1000-1500W).

    Losses from the inverter output at 110V going 75' to the camp should not be a problem if he uses a reasonably sized extension cord (12-14 gauge).
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    Why not use 12V devices and skip the inverter? LED lights, radios, power tools can be found in 12VDC versions.
  5. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
    Thanks for the input - I know nothing about inverting applications, just basic principles. And I'm somewhat lacking in the area of transformers, too, lol... One thing is for sure - power doesn't come from nothing, and your source is the limiting factor! I agree - tried to tell him he won't gain much by going back to AC - and there are lots of fixtures, LED lighting etc. made specifically for this purpose! He was concerned with losses, and probably read about AC vs. DC transmission. Since the run isn't 200 miles long, I^2 R losses don't seem to be a huge issue!

    Wanted to get the opinion of a few more knowledgeable in this area than I am - appreciated!! 12V is the suggestion I'm giving. One could keep a smaller inverter around to plug in for the use of say, a skil saw...
  6. Reloadron

    Active Member

    Jan 15, 2015
    As a matter of some perspective, I have run my entire home, all lights on, TV, radios, the furnace blower on 4KW. 8KW is one huge inverter which for a camp is likely well over the top of overkill. Under a full load you would likely need a battery half the size of my truck. :)
    If for some reason 120 volt AC power is needed or wanted I would look at the max loads, add them up, and then get an inverter that meets the demand. Also as to inverters there are MSW (Modified Sine Wave) and TSW (True Sine Wave) with the latter costing more. Certain motors (depending on the motor) will not run or will burn up on a MSW inverter so all things need considered.

  7. crutschow


    Mar 14, 2008
    The loses in the inverter inefficiency will likely be larger than any DC I^2 R losses in the leads, especially if he uses large gauge wires.
  8. Mike33

    Thread Starter AAC Fanatic!

    Feb 4, 2005
    Once I took a look at how the inverter would drain those batteries, it all came back to me ;) I should've had the answer for this one right off, but choked on the 'inverter' process. Same as figuring out how much your primary will draw when you're working with tube circuits!

    He's going with 12VDC, RV lights etc. and will pick up a small inverter for occasional use. I told him to just run the generator when he needs a saw ... ;) I bet his total needs won't exceed 1A with everything turned on at once, which would never be the case. Thanks!
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
    An 8 Kw solar panel array would be what, hundreds of square feet? Check with your buddy and see if he has an extra zero or two in there.