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| > At any rate, I've seen 5000W gensets burned up very successfully by a 1.75 HP, 230V motor on a table saw
Yup, just the right load to make the engine grunt but not give up.
Often the key to motor starting is the surge rating of the genset. Its often only 15 or 20% over the full load rating. Getting a bigger surge rating means a bigger engine that then runs inefficiently at most genset loads. The generator itself ought to have a similar thermal overload capability as the motor being started, but its exciter may not hold the voltage well and a motor started on low voltage takes extra current and lots of extra time, which could fry both pieces of rotating machinery.
One solution that has been forgotten is the repulsion-induction motor. Takes 1X running current for starting even under load. Its draw back is it has brushes and a switch that shorts all the commutator bars for running as an induction motor. The good ones also lift the brushes off the starting commutator. They also tended to be twice the size of a conventional single phase motor of the same load rating. But when you don't have the prime power to start the 5 or 6x starting current motor they might still be a solution.
Some electronic variable speed drives also have gentle current starts, at a significant price. Unfortunately many have a very poor power factor (taking current only at the voltage peaks) that will put a genset regulator into orbit. I've found a significant capacitor (20 to 60 uf) across their single phase input can help. At least that did with ham gear on a home wound genset 50 years ago feeding tube radios with that input characteristic.
Gerald J. | |
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What is the smallest generator that will start 1 HP motor?
