Nigel wrote:

Of welders

At max output the power is 6200 VA (6.2Kva) power factor 0.75 therefore
output power in watts is 8267 watts
At 75 amps output the power is 2900 VA so an estimate of power in watts
(pf approx 0.6) is 4833 watts

You have that backwards!
6.2KVA @ 0.75PF is 4.65KW, but is still 27A@230V.
2.9KVA @ 0.6PF is 1.74KW, but is still 12.6A@230V.

Use the VA number to calculate the load current, and multiply VA by power
factor to get real power.

Note that the PF will probably be lagging in this case and you will need to
be careful about the inverter ratings....

Note also, that the VA rating determines the minimum current that the supply
must be able to source, but the real power determines engine size. It is
quite possible to have a very large alternator driven by a small engine
which will give a spuriously high current rating for most loads.

You could always just hook the electrodes up to some of that battery bank
(reconfigure it to give 24V or so), and weld that way (BTDT), it does work
to get you out of a tight spot!

Regards, Dan.