I have an Ampinvt 6000W 24V split phase low frequency inverter.
It was operating properly for several weeks. Now it seems to function OK, but the DC current is oscillating from 0V to 2X of the required current for the output. For example, if I have a 1400W AC 120V load, the DC current will swing from 0 or negative to 130A. My home made BMS samples the current and updates the display every 2s, and it plots this gyration.
I then put a Reidon SSD digital shunt inline and took recordings every 4.87ms. I put those samples into a discreet Fourier thing and it had a strong signal at 34, which means 6Hz. I was expecting to see 60Hz, but maybe the sampling is a bit too slow. It seems logical that the DC current would oscillate, but only if all batteries were capable of delivering the power at that frequency. I expect that there should be capacitance that would smooth out the DC current. Am I right?
Ampinvt customer support is absolutely dreadful. They say it is normal, but I think the expert behind the scenes did not look at my full email thread and simply answered that the DC current can vary. Can someone tell me if this is indeed a failed inverter?
I've reviewed the reference designs in this that was referenced in this thread but it seems to me that the +24/+36V goes straight to the mosfets and I see no capacitors.
I plan on opening it up and inspecting the components to see if there are any fried/fat capacitors. Am I on the right track to expect to find some large caps on the DC side of things?