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I would need to power a AC voltage compressor with 12v car batterys.
There are some large inverters for changing 12v to AC, would that kind of thing work ?

Biggest question i have is how long would the batterys last ? Well of course thats a little stupid question with out any more info, but i dont have the compressor yet or the batterys either.. So lets say a decent size air compressor with a 20l chamber and maybe four car batterys. Weight is not problem here.

One way would be to use DC compressor but those large ones cost very much !

Any ideas if there is better way to make battery powered large compressor or a ready one from some manufacturer ?

There are little ones that plug into cars or come with battery clips. Should be fine for 20l chamber.

You can also get a pulley drive compressor and rig whatever 12 v motor to it but then you are into time and $

AC compressors (like most ac tools) may draw 5 times (or more) the running current at start-up, so a 400 watt compressor may require a 2000 watt inverter and there you are into $ again.

I lived off the grid for 6 years

Sounds like fun project though.

Anatine Duo wrote:I lived off the grid for 6 years

Spoken like a true Canadian

There are plenty of decent DC air compressors made for on-board air systems on vehicles that are not too expensive. Look up "Viair", an example of a reputable brand : http://www.ebay.com/sch/i.html?_trksid= ... &_from=R40

Hi,

Lets say that your compressor is draving 2A @ 230v so it is 500w copmressor.
That means you need 700w AC converter to be on safeside.
If you have four 100Ah 12v batterys each of them holds 1200w so with 4 batterys you have 4800w
So if you run your 500w compressor for one hour it takes 500w/h and you have 4800w usable 4800:500=9.6
So with four 100Ah batterys you can run your 500w compressor for 9.6 hours (i think so) correct me if I'm wrong.
But your compressor probably aint 500w and your batterys capacity can vary. That just was an example.

Anatine duo
If you did live of the grid for 6 years where did you load all the batteries

BTW
Matti are you from Finland?

JSR, I know Viair compressors, I have been looking them for some time, they would be ok, but I'm wondering if they are too small (well i could use two, but not four or five ). I haven't done any calculations yet, but I would need to fill 6.5 litres chamber to 3bars in a..few seconds.. or less. I don't know hoe to calculate fill time for compressors, they give data for example "at 3bar = 36.5 litres per minute" and at 1bar it's= 42 LPM. How could I calculate filling time from those ?

finland66, thanks for the informative example, and yes I'm from Finland, and a long time member of spudfiles, there have been about four users here from Finland that I remember.

I can vouch for this compressors performance.
http://www.harborfreight.com/12Volt-150 ... 69285.html

It filled one of my old pneubmatic's with about a 1-2 gallon of air volume chamber to 120 PSI in under a minute.

Found this: http://www.atlascopco.us/usus/products/ ... id=1520968

Lol - I can't imagine that's anywhere near cheap - correct me if I'm wrong though!

mobile chernobyl wrote:Lol - I can't imagine that's anywhere near cheap - correct me if I'm wrong though!

It's propably over 1000.. but it would be a good compressor

4 by 100 amp hour by 12 v = 4800 watt hours, these are what I used (they are commonly sold for electric wheelchairs)

If deep cycle batteries (not car batteries) then you can draw down to 50%

so that's 2400 watt hours

so running a 400 watt compressor for 6 hours, assuming 100% efficiency

Assume 50% efficiency, 3 hours run-time

With car batteries you should never draw them past 80% charge.

Filling in seconds complicates things, you may need higher wattage compressor, so higher surge capacity for your inverter.

I mostly used vehicular electrical systems during my off grid time... and an ac generator. China has been sending us those things dirt cheap.

If you want a lot of air at pressure a gas powered compressor might be the way to go. That battery bank has other uses though, like 4000 amp welding out in the bush!!!

If those batterys arent requirement buy this
http://www.finnkone.fi/index.php?section=9