My answer,No power(mains),No welding,simple as that
I faced this exact problem.
My solution the lorch Micor tig, and its portable battery pack, you can buy for it and a pure sine wave 1500w inverter and two deepcycle batteries to recharge the battery pack if needed.
You can get them from wasp supplies. Mind you its an extremely expensive solution circa £3000 worth of welder and special charger and battery and another £500 of deep cycle batteries and inverter.
There is an offering from foronius too they have an intergrated battery so the whole welder is £3000, but it has the ablity to run continuously off of a small suitcase 2.2kva generator.
I would point out that the lorch will run 29 2.5mm stick rods, thats actually a hell of a lot of welding time. Take into concideration that fabrication is 90% cutting shaping, prep work, cleaning etc etc. So conceivably your battery will last about half a day worth of "welding" stick it on charge over lunch and you be ready to go at some point in the afternoon ounce you have done all the rest of you panel forming and prep work.
£500 worth of batteries is a lot of weight and a large bank of cells. (Presuming standard types)
For that sort of weight I would rather be loading up a diesel generator. Might cost twice the price to start with and need a bit more mantainance but it will have a better resale value, much better power output and run time and could probably male you a few quid back hiring it out if you wanted more return on it.
It was only 2 deep cycle batteries from halfords, the bulk of the money was spent on a decent inverter.
Can it be done? Yes
Can it be done on the cheap? No
When the fronius/lorch get to about half that price I would have another look at them. If they turn out to be popular I expect the cheaper manafactures will be releasing them as well.
I was talking to a mate about them as he works mantainance in a quarry where money is no object for kit but he has not got one as he would rather the stuff was brought to him in the workshop!
I would have one myself as I get asked to drive accross farm fields to fix a gate or something and half a dozen rods would be plenty but I am never going to see a return on it at that price. Farmers always seem to have plenty of staff with enough time to hitch up a pto generator or put on the front loader to put my pallet of stuff onto a trailer and drag it out to site
For me it worked out cheapest, i didnt have a generator to start with, dont have space to store one or transport one, was wanting a seriously good dc tig machine any way. And the welder generators didnt have the amperage control i was after can only do scratch start tig and the ones that were roughly the same price as all my kit like the mosa magic weld dont seem to be that reliable or last that long, i havent heard of one up my way that has survived more than 3 years of light use, and they are still £3000. I figured if after 3 years the lorches battery went pop i was only half the investment of a small engine drive again to get back up and going and i suspect the micor tig will last much longer. Plus if they catch on and become more popular the batteries even from the big reputable manufacturers will get cheaper.
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