Ive had a rough start with my 24/ 48v pj inverter conversion. Does anyone else ever have frustrating moments with H-bridges?
I wanna say i blew it up at least 4 times. The very first run after the conversion ran 1/2 a day before vaporizing the bottom row of fets. Each time i fixed it the inverter would run great for a while and then start to get noisy and then poof. Eventually watching the board powered on in the dark i could see fire flashing around the board in front of the fet bridges. I cleaned board very well replaced fets again and it ran for a few more minutes, poof.
After blowing up one more time i had the "thats it, i've had enough moment!! I dug out an old dataq instruments computer scope "148u" I cut the ribbon cable leads for pin 1 and 2, connected 48v supply negative where it belongs and the +48v fused at 1 amp to the cut wires leading to control board. Then, i rigged a "110v actual voltage" to simulate the feedback.
Powered up board and repaired issues until i got identical pictures of all gate drives with no FETs in the main board. Then because i was totally out of 4110s and needed 7 more to finish the set, I took a pile of used ones and put each on a 4 amp load with 8v on gate and measured voltage drain to source in this "on" state. Some measured as low as 24mv while some as high as 36mv. I choose those in the middle at 29 mv. I then finished out the complete set of fets with "tested" components. Again i looked at all 4 drive outputs with fets in circuit. When all looked perfect i started with a 24v control board and 24v supply. It seems like the 48v circuit is more picky. One thing i want to point out, the idle current on 24v was 2.8A with no choke, i noticed the band around the toroid was warm in one spot after only a minute of on time. I took the metal band off toroid and watched idle current drop and again when i removed bolt from middle. Something someone here may want to consider. After switching to 48v setup i then installed a choke
Thank You Oztules,
The idle current went from 1.4A at 48v no choke all the way down to .4A for 19.6w
By the way the pics of top and bottom H drive reveals bipolar modulation on even the 2013/08 control board. The first pic is the bottom gate drives and the second is the top pair, 3rd pic is of a different time base and one top / one bottom; this scope is very speed limited at 7000 samples/sec with 2 channels at same time.
One thing to note, since the 3rd pic is a top and bottom the timing should reveal a 180 degree offset. I was extremely puzzled about this, so much so that i thought the gate drive leads were switched around, i proved the timing was in fact correct by swapping in the 24v control board and it showed the same timing error and i knew it worked. Then i unplugged the feedback which causes the modulation to go 100% to 60hz square wave, then it shows the 180 offset. I think the problem is created because im only using 1 ground reference for scope and top/bottom drives do not have the same ground, in fact since i have the power supply disconnected on main board, the charge pump for upper drive cannot even function. Surprised it worked as well as it did.
This inverter has now run about 14 hours and ran only about 2.5kwh before it tripped on overvolt with dead battery. I did the R14 voltage mod, Today may go better.