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No brand/5500W inverter disaster porn
Pete:
I just bought a dead 8000watt 24 volt powerjack.
I have repaired the mosfet board, new mosfets and replaced the very fiddly 47 ohm surface mount resistors. The rest looks fine.
Just wondering if you folk who play with inverters lots can tell me what the waveform from the driver board should look like.
I read somewhere here that folks test the driver board output before connecting the mosfet board just to make sure that the smoke doesn't get out.
The man I bought this inverter from said he replaced the mosfets and it blew up on him again. I am guessing that the dead 47 ohm resistors may have been a big part of the problem.
This model I have does not have the removable mosfet boards, I would have to remove the whole heatsink and main power board to fix it if the smoke got out, so I am hoping to test the driver board output first.
Anyone know the wave shape I am looking for and if it is possible to test without the mosfet board in place.
Pete
lighthunter:
Hi Pete, yes it is and it does save a lot of grief and ruined fets. From memory :P the procedure i used was to unplug the ribbon cable from the fet/heatsink board and then cut wires 9&10 and 1&2. Connect negative 12/24/48 (your flavor) to wire 9 or 10 leading to control board and then connect positive to 1 or 2.
this allows you to power up the control board without energizing or connecting to the power board. If you can do the same thing without cutting the wires, go for it. You just need to get ribbon disconnected from power board and get power and ground to control board. Next put scope probe on each pin 3/4/7/8 (i think these are the 4 H bridge drive wires. Of course ground pin on scope goes to negative on pin 9 or 10. You will also need to plug in the long flat connector so you can switch it on/off. Since it wont be generating a sine wave for feedback it will fault within a few seconds of each power on cycle but immediately after each power on cycle you should see a decent square wave, it wont be a continuous duty cycle so it looks strange but the basic thing to look for is that the voltage goes high enough, the transitions look fairly square and all 4 are very similar. Usually all 4 do not have same problem so just comparing the 4 will get you there. Frequency is gonna be somewhere north of 20khz range i think. Its been a few years now so i'll see if i can post a photo and better info this eve. Good luck. One other cool solution is just to buy a driver daughter board for $25 and replace it. They still have those, i think the new version still uses the same board.
have fun!
(CAUTION pin numbers were edited if you read this earlier today, power and ground pins were reversed)
i had a couple wrong. If you want to get picky, the probe neg is different for the high side drivers, each has its own negative pin 6-and4+ are a pair, 5-and7+ also a pair. 9/10 are - for pins 8 and 3 which are the two bolted to the heatsinks with the AC connections. I dont think i fussed about the correct ground though. If you just use the 9/10 ground for probing all 4, two will be inverted and look a bit wierd but there will still be two symmetrical pairs that look alike if all is well.
LH
noneyabussiness:
Even easier , take the bulk caps off board ( very important) and power it up through a 20 ohm resistor... if any issues there won't be enough juice to blow mosfets.. you can even hook up to a transformer, but you will need to play with resistor value , start with 20ohm, then 10, then 5 etc....
Pete:
Thanks Lighthunter, I do have a spare driver board for the running inverter I have, but unfortunately the dead one has a different driver board. The ones that powerjack sell these days have one row of pins underneath to plug in and the one on my dead 8kw inverter have two rows.
So far the transistors on it look fine, not sure about the optocouplers. Mine has a plug in cable that goes from the driver board to the heatsink/mosfet board so I was thinking of just unplugging it and testing the output of the opto's.
I will read your description through a few more times before I do that.
Thanks again
Pete
Pete:
I just read the second way you suggested. That may be worth a try too. Like you say better than cutting cables etc.
I remember a tech at a place I worked who used to power up TV sets he repaired with an incandescent globe in series with the supply to rob the set of enough power to die if there was a fault.
Thanks will let you know how it goes
Pete
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