Quote:
Originally Posted by MPaulHolmes
...We have a 12500btu or something like that window air conditioner that I plugged in, and the stupid inverter shut off due to overcurrent protection. But... Since I'm in charge of every stinking line of code on that thing, I just changed it so the hardware overcurrent protection clears itself automatically if it trips. That's the short term fix...
|
If it's similar to my window air conditioner, there's a single phase induction motor in there that draws a very short peak of 6 times rated current (6X). It's connected to your compressor, so it starts up under load. It will trip generators .. that you would EXPECT to be big enough to handle starting up a 0.75 - 1.0 HP motor ... as well as inverters.
Instead of measuring the very high spike of current (which your power electronics will have to supply without melting) it may be more reasonable to put in a 'pre-charge resistor' or 'soft start' that limits the current on a few AC cycles when a SERIOUS overload is detected. Assume that the load is faulty - like a short circuit - and size the resistor - perhaps 6 ohms and 20W - to take a surge of 20 amps for 6 cycles (0.1 seconds). If you energize power electroincs - SCR, MOSFET - to 'bypass' the resistor at that point and the current is still pinned at 20A at that point, let the hardware over-current take it down. I realize that the resistor should be 120W, but that would be continuous. 20W should be a reasonable size and give you a decent safety factor if you limit the time.
This will cost you some board space and an additional SCR or MOSFET switching loss in efficiency. But it should save you 4 sizes on your MOSFETs for handling the surge start of an induction motor. It shouldn't mess up your hardware over-current ... too much ... I think ...
Just my opinion ..