KVA rating conversion

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raytaylor

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# 251251 14-Jun-2019 23:26

Hi Guys

I have a 2kVA generator (1.6kVA continuous, 2.0kVA 30 mins) and an 1800 watt chainsaw. Do you think they will work if i stay under the 30 minute time limit?

I normally assume the kVA should be much higher than the consumption wattage but i cant seem to find a chainsaw to purchase that uses less than 1800 watts. Am trying to avoid going out tomorrow and buying a cheap petrol one.

This is where i get confused with kVA, resistive loads and motor loads.

What do you reckon?

Ray Taylor
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sqishy

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# 2258575 14-Jun-2019 23:56

1800W chainsaw is likely max wattage under max load, if the generator has auto cut out then it will just turn off so probably safe.

Aredwood

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# 2258579 15-Jun-2019 00:19

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Generators are rated in KVA, due to power factors.

Assuming that the generator is not an inverter type generator. You should be fine with that chainsaw. Although if you jam the chain while cutting a big log, you will probably trip the generators overload protection system. The 2KW for 30min rating will be based on how long it will take for the stator windings to get too hot due to the extra load. But since a chainsaw will get used in lots of short bursts. There will be enough no load time for the generator to cool down.

With resistive loads KVA = KW. Non resistive loads KVA * power factor = KW.

Aredwood

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# 2258580 15-Jun-2019 00:53

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The motor in an electric chainsaw will probably be a universal motor (ac brush type). Their power factor isn't too bad. As they behave like a DC motor in relation to load changes. (same type of motor as most power tools and vacuum cleaners)

Induction motors - power factor varies with load. Low load = bad power factor. Take the full load amps rating as specified by the motor manufacturer and multiply by the voltage to get the KVA of the motor. You still have to allow extra capacity for starting currents as well. Allow 3X full load amps for non inverter generators. And 10X full load amps for inverter generators.

Inverter drive motors, if the inverter has Active power factor Correction (inverter heatpumps normally do have active PFC) then they behave like a resistive load. But only connect them to a pure sine wave output generator.

Non Power factor Corrected inverter drives. PF is typically 0.5

raytaylor

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# 2258618 15-Jun-2019 08:59

Thanks Aredwood. I shall give it a go :-)

Ray Taylor
Taylor Broadband (rural hawkes bay)
www.ruralkiwi.com

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