Starting an old window unit AC with an inverter.
Thos information was posted on https://diysolarforum.com/.
What happens when my inverter can't start my window AC unit with my solar generator
Many inverters can not supply enough current to get cheap air conditioner units to start up successfully. This is clear enough from a top level viewpoint, but I was curious about what it meant on a detailed level. I used an oscilloscope and a clamp-on current probe to look at what happens when I try to start my 20 year old GE window AC unit (runs about 500W) with my Bluetti AC70 Portable Power Station (1000W rating).
First, I captured a startup with grid power. The startup was successful, and the AC draws about 25Arms for about a tenth of a second. That is all pretty reasonable. It is important to note that if you unplug this unit and plug it back in, it draws a longer surge of about the same magnitude. Apparently the compressor has not started (air not really cold). It then just runs the fan for a few minutes before drawing another startup surge (0.1 sec) and successful starting the compressor (air nice and cold). If you leave the AC off for several minutes, it starts the compressor properly the first time.
Grid startup
I then plugged the AC into the Bluetti AC70. It did not succeed in starting the AC, both with a wait period and without. The waveforms are shown.
startup from Bluetti AC70 startup from Bluetti AC70 closeup of startup from Bluetti AC70
The Bluetti is running with "power lift off". It is not capable of starting my AC with "power lift" on, either. It appears that if the load tries to draw more than a certain current, the Bluetti distorts the sinewave that it is outputting to limit the current. It looks like it effectively clips the current sinewave at a level of about +/- 20A instantaneous current. If this continues for more than about a second, the Bluetti shuts off the output.
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