opus:
everyone here is trying to give you the best advice they can give you
it is very difficult to help one who is set on not helping himself however.
the welder is constant current, but the voltage will swing significantly depending on load
and you have no way of stabilizing the voltage that i can see.
then there is the issue of voltage spikes when the load varies, new alternators that provide power
to sensitive electronics/computers use avalanche diodes to clamp these damaging spikes.
the welder does not use avalanche diodes.
not having any means of clamping these spikes means that under the right circumstances you can have
a spike of many times the design voltage of 28volts, perhaps upwards of 100 or maybe even twice that
on a short term basis.
batteries can clamp a certain amount of these spikes but nowhere near all of them, and especially those that
are likely to be generated by the welder/generator you reference
it also appears from the pdf schematic that while the welder has dual stator windings, the recepticals are provided
with DC power at something like 120volts, and not AC,, this is very typical of a small portable welder/generator
where brush type drills and grinders are generally used and don't care whether the power supplied is AC or DC.
also it is very typical for the duty cycle to be well under 50% at near full output on many welder/generators of such small
size, although there are examples of others such as ones made by miller that are capable of 100% duty cycle at full range output.
it is not my belief that this welder is a miller or one that likely has much more than perhaps 30% duty cycle at 100amps.
you have to remember a welder generally is not a 100% duty cycle proposition, one usually has a lot of down time, setting up, chipping
slag, grinding, and just changing rods.
you have been asked what you plan to power with this setup, but so far i haven't heard what that might be, so
i for one would never counsel you to use such a setup under any circumstance, especially when the word aviation is mentioned.
its one thing to burn up a set of cheap golf cart batteries for a small power shed, as something to dabble in, but
quite another if you plan on using this setup on anything that might get airborne with folks aboard.
i want no part of getting someone hurt or killed either from falling out of the sky, or being hurt or killed by something falling out of the sky
which can be traced back to some crazy idea of using a welder/generator to power up anything related to it.
in short and not so sweet terms
don't do it! its crazy, its nuts! and you will likely either damage a bunch of equipment or get someone hurt!! or worse!!!
bob g