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Discussion Starter #1 (Edited)
I just received my $50 1500W 24VDC to 220VAC inverter, and I modified it to produce 240 VDC for use with a VFD. Here are the pictures:





I removed four screws from each end and took the input and output plates off, then slid out the cover to reveal the innards:



I found that the 240 VDC was on a capacitor and the PCB trace was on the opposite side. It's a pain to remove the entire PCB, so I drilled a hole in the bottom to access the trace:



Here you can see where I soldered an 18 AWG wire to the trace:



The negative is tied to the battery (-), but I soldered a black wire to the diodes instead. There are two sets of four diodes in parallel, and two capacitors of about 47 uF and 400 VDC, so it is probably a doubler circuit.



I reassembled it and connected it to a 24VDC supply. The output is just about exactly 10 times the input, as you can see here. The input current is 300 mA.



Although this unit is clearly labeled 1500W, the instruction sheet only shows units up to 400 or 600 watts. It may be able to put out more DC than AC, since it bypasses the modified sine wave stage. I may use this and another unit like it in series to get 480 VDC to use with a 440 VAC VFD that I have. It will be for a 2 HP motor, so each unit will only need to provide about 750 watts. I will be using 4 12V 12Ah SLA batteries for the proof of concept and they will be pushed pretty hard. About 30A or 3C.

I have a 1000W 12V to 220VAC inverter for my smaller tractor project which will have a 1 HP motor. I have a 100Ah deep cycle battery for that, so it should be able to provide 750W for about 30-40 minutes.
 
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