CobyRupert
Super Member
So I should be looking at larger than the 7000 watts area?
Scenario 1: 7000 Watt genny can handle (I1Eff) 3600 Watts all day. Any voltage/rpm dips while genny reacts to 6800Watt surge has no impact on welder performance.
Scenario 2: 7000 Watt genny can handle welders I1Eff 15A (3600 Watts) effective load all day but the initial 6800W surge, and voltage/rpm dip may take the genny an unacceptable amount of time to recover.
Is the surge 3 seconds or .05 seconds?
IMHO, we just don’t know enough about the time duration of the surge, the recovery characteristics of the genny/motor, or how the welder performs during this “recovery”, to know how the two will dance together.
So going bigger is like buying insurance. Will you really need it? Yes. No. Maybe. Sometimes. Just once. How’s wallet vs risk tolerance?
That being said, in all likelihood, IMHO, a 7000W (continuously rated) genny can handle a 15A (3600W) welder that has a 6800W inrush.
…that is, comparing the “continuous” 7000W rating of the generator to the “instantaneous” 6800W inrush of the welder is apples to oranges.
Another scenario:
Let’s say you ONLY knew the welder’s I1Eff current rating was 15Amps (3600Watts) and was asking how to size genny. We might say, “4000Watt genny might run it, but bump it to 5500Watts to cover the inrush surges.”
…but now that we have a “inrush number” (but no duration time) we’re talking about bumping 7000Watts to something even higher? It won’t hurt, good insurance, but… to upsize again is what I’d call “double dipping” on the safety factor. It’s not comparing peak to peak, or looking at the time durations at those peaks. Having a 10kw generator for a 15A circuit seems ridiculous.
Another scenario:
Imagine a (say) 5000 Watt generator for the 15A (3600W) welder. It might have a 500 pound flywheel, or maybe it has a 10 pound fly wheel (not real numbers). Then there’s the 6800W pulse demand. We don’t know how long the pulse is. We don’t know anything about the torque curve or response time characteristics of the motor. We don’t know how much voltage dip for how long the welder can tolerate until it becomes unacceptable. In this scenario, it’s easy to see there’s no way to tell if this “generic” 5000Watt genny wins or loses the battle. That’s why people upsize.
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