Portable generator

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.

If the saw blade hit a hard spot momentarily the diesel may have the weight & torque of the flywheel behind it. It may run a little slower.That is why I thought diesel may be better. A small diesel would start from about 1.5hp - Do they make them smaller? mine is quite compact ( & does power a generator). But there are loads of petrol lawn mower engines about rated at higher capacity complete with clutch that might do the job

I appreciate that the OP may want to power a number of units from the one source, but if he has to have a big generator just for the saw then eliminating that from the equation may have allowed him to have a much smaller generator. Easier to move about etc. It depends what get used & moved the most.

Edited By Sam Longley 1 on 17/02/2018 07:54:26

Slight change of tack. My generator does not have a provision for an earth connection. Should I run an earth to the frame/engine chassis, Should I install an RCD ? As an earth would be as best as I could provide on-site, would an RCD have a chance of working ?
BobH

My home brew portable gen set uses a 3hp Kawasaki motor to a car alternator, and I can get about 500Watts out of it, I have an inverter for it, but I'm yet to try it on the fridge. The base that the unit is sitting on doubles as a sack barrow, and is rigged as a trailer to be towed by my bicycle. I can boil enough water for a cupper in about 20 minutes

Ian S C

Edited By Ian S C on 18/02/2018 09:28:19

Be very wary of trying to start the fridge - unless your inverter is very well protected for overloads! And don’t try it too soon after the compressor has turned off - they can take some minutes before the motor is on minimum load and ready for starting.

All too easy to let the smoke out!

You must either have a much smaller heater (than 500W) or a very large cup, if it takes 20 minutes to boil one cup of water!

ndiy, you neatly outlined the reason why I have not tried it on the fridge, the fridge looks as though it may be about to die without my help anyway.

The heater is just men't to keep a cup of coffee warm but I use a tea pot with about a litre of water.

The little gen set cost very little, I'v got 3 or 4 alternators, the motor came from a garage sale $NZ10, the wheels on the sack barrow $NZ13 each, every thing else out of the junk box. Automotive alternators are inefficient, and a better genny could be built with little difficulty, with that I would expect to get about 1.5k Watt with the 3 hp motor.

Ian S C

Ian,

Apart from the 3kW diesel genny, which cost me £160 almost 40 years ago (Stamford generators are far better than modern ones, but heavy), I picked up a couple of cheap 2-stroke Chinese c.650W gennys for much less than a tenner apiece - they usually only need a new plug and the carburettor setting properly.

We are picky as to which ones we bid on. The ones later in the auction are usually better value than the earlier ones!