I need to run a battery spot welder from my solar system, which is based on a Multiplus 2 3kW inverter. However, the strength of the spot weld is limited due to the limited transient current performance of the inverter. Rotating generators have much higher transient currents - i.e. the current & energy you can get if you instantaneously short the output. The spot welder is a transformer based design - a capacitative discharge design would not have this problem- that turns on the transformer for a few mS to do the weld.
One solution I have tried is to run a small motor in parallel with the welder - with a capacitor to correct the power factor. The motor is a 1.5kW old compressor motor, with a quadrature winding. the power factor was 0.75 with no load on the motor. With a 20uF capacitor, this is corrected to 0.97 (still inductive). This has significantly improved the weld quality - the motor instantaneously acts as a generator when the welder 'fires'.
At the moment, I don't have any method of measuring the transient currents, and am relying on a strength test of the weld - however that is a destructive test.
Any one got any better ideas? I might try a larger motor if I can find one....