Hi
Reading through some of the postings on fridges and freezers tripping inverters into overload, and having a few hours to kill, I decided to have a look at the output waveforms and voltages on the two inverters I have. One is a 1000W Nikkai, the other one is an IBM badged UPS.
The Nikkai produces 255V at 50 Hz with no load, connect it to a 1000W ceramic fan heater it drops to 250 V at 50 Hz. I wondered if the high readings were due to transients, or harmonics. I then put the scope on the waveform, Tektronix 465 with a X10 probe. The output was a very good square wave, rise time 2uS no overshoot, no apparent harmonics, zero volt dwell 1 mS between positive and negative half cycles. I then connected a 370 W induction motor, the inverter tripped. Next my Pillar Drill 500 W induction motor, that ran perfectly, but all the time the output remained a square wave, and the motor was noisy AC/DC motors ran perfectly including several that pull more than 1KW on load..
The IBM UPS, the output looked as if it was from an ADSR filter, rapid rise time, a long reducing voltage and a rapid drop off. Add an inductive load and the waveform becomes almost a sine wave, but with transients and overshoot to over 300 V. They both run a standard flourecent lamp with no problems, albeit with a lot of noise from the choke.
Its been a long time since I did the maths on induction motors and I am not going to attempt to remember the electronics or look for my books, but I am sure there are others on here that can.
If anyone can use this infomation I would be interested in reading their reply.
Brian.