Something of an educated guess but I doubt if anything less than a 3kw output would give you a steady enough

supply for easy sawing.

I would have thought you would need a generator that will handle the start up surge which can be 3-10 times FLC depending on load. I think 3/4hp is a bit under powered for a 10" saw but maybe it's ok for your application.

Mike

When running, it will take more power than its rating horsepower dependent on the efficiency of the motor – say around 110%.

Starting it, as Mike states, is an entirely different ball game.

If down on power, check the A/C voltage and the frequency of the supply. It may not be even achieving full speed, if the start windings are not being sufficiently energised at start up, so a check on rotational speed would be good, too.

The rule of thumb I have heard is to size the generator at three to four times the power of the motor. That should give enough reserve to cope with the starting surge. Most of these small generators don't really like to be worked too hard anyway.

Another way to do the job is to fit a suitable petrol motor to drive the saw directly. Not so good if you also want to use the same saw indoors as well as outdoors.

One interesting effect to bear in mind is that if the frequency drops due to a heavy load, the motor will take more current, loading the generator more heavily, and hence depressing the frequency even more. I've heard of a case where every fridge motor in a small hospital burnt out due to this effect. That was a somewhat large standby plant of course, but obviously not large enough for the job. A more modern plant might have had an under frequency trip.

John

I have a 2.5 kw generator, petrol 4stroke, and cheap, rated at3kw max for short time. This runs an electric chainsaw no probs once warmed up. Chainsaw is rated 1.8kw. It is important to keep all the governor connections etc. clean and adjusted. A 500w 2stroke genny runs drills etc. no probs.

NDIT- you are most likely correct, but I thought it was the power, ie. the wattage used by the tool, that was being discussed ?

Does the saw run ok on a mains supply? If the equipment you mentioned runs ok it seems the generator makes power but is the saw is the only induction motor? As others have posted you need correct voltage and frequency for an induction motor to deliver its rated performance. Many manufacturers big up their equipment with big numbers, compressors often give the swept volume rather than free air delivery and stereo systems used to quote peak music power watts to kid you it would fill the Albert Hall.

Mike

It also depends on the type of generator. One cannot really beat a rolled steel magnet framed armature generator for motor starting. Stator wound with rotating field and electronic AVR are the usual order of the present day – both cheap and more likely to need a greater size margin to start any particular load.

I’ve yet to have a problem with my Stamford 4.5kVA genny powered by a Hatz diesel, whether cold or otherwise. It will black smoke at 3.5kW but runs 3kW (resistive) loads all day long.

Several decades ago, my first back-up generator was a 1.5kVA genny, powered by a B&S (supposed) 3HP engine. It would only start the freezer motor if one held the governor wide open. Freezer motor was rated at 160W.

With all the losses within the electrical generation & problems with startup loads what sized petrol/diesel motor would be needed with correctly sized pulley to give correct RPM of the saw blade? Presumably a diesel would be a better power unit.

Seems to me that it would be a far more efficient way of operating the saw. A belt tensioner to disconnect drive could be installed.

If a 3/4HP electric motor will drive it, then any 3/4HP engine will run it. Power is simply a rate of doing work – it matters not a jot from what the rotary power supply used.

Starting the saw blade with a fuelled engine might present the same problem as starting an equivalent induction motor, but less so if there is the possibility of slipping a clutch or drive belt. But even a slow revving engine with a large flywheel could start it satisfactorily.

Fuel type comes down to cost. My diesel genny currently costs less than twice the cost of grid electricity. But my genny is only mobile, not portable!

SB5 could likely get away with his 2kW generator if the saw blade could be decoupled from the motor, as the surge current at start up would be neither as great nor of the same duration.