Pure sine wave inverter repair help - Page 1
Forum section: electronics / repair

author: Stockers
author_rank: Newbie
timestamp: May 30, 2019, 03:34:57 pm
content: Hi allFirst post for meI recently purchased a 3000w inverter as untestedIt was in fact faulty. Switch on, fault light and now powerThe pop. 1 mosfet exploded and 2 IGBT’s shorted.I replaced these components, fired it up and it worked. Was working brilliantly for 3 weeks. Came to shut it off to mount it properly. When I came to turn it back on, no output. Then the supply leads twitched and a small click could be heard. Opened it up and it had blown the same 2 IGBT’s. I replaced these “again”. Fired it up. Had power for about 2 seconds and pop. Gone again.What I would like to know is, why would this be happening? Could it be that they are being switched on at the same time? Is the spwm driver board to blame?I don’t have a scope to test the spwm driver. Only a dmmHelp would be much appreciated as I had reduced my electric bill to 1/3 with the inverter and I’m now back to being over budget every day without it

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: May 30, 2019, 06:05:45 pm
content: Try the "3000 watt inverter" Homepage. Everything you need to know is probably there.

author: Stockers
author_rank: Newbie
timestamp: May 30, 2019, 06:16:39 pm
content: Where do I find this home page?

author: capt bullshot
author_rank: Super Contributor
timestamp: May 30, 2019, 07:27:47 pm
content: Maybe it's this one:https://ludens.cl/Electron/chinverter/chinverter.html

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: May 30, 2019, 07:39:27 pm
content: No, because that one has a model #... PSW3500

author: Stockers
author_rank: Newbie
timestamp: May 30, 2019, 08:24:41 pm
content: That page had no helpful information for me.What I think I am getting is called cross conduction. But why I am, I do not know.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 31, 2019, 10:14:12 pm
content: Hi!What make and model of P.S.W.I. is it?The most likely problem is you've either got a fault in the gate–drivers that is either holding one MOSFET/IGBT partially on with a d.c. bias or there's some overload causing the drive waveforms to distort, either fault in this type of circuit will cause instant destruction of MOSFETs the moment power is applied.You need to remove all the damaged MOSFETs/IGBTs (there will be several of them in parallel for each half of the output stage) and check individually all the small components associated with each gate circuit. As well as the gate circuits, there'll probably be fractional–ohm current sharing resistors in each MOSFET's source lead (right–hand lead) – any of these could have blown open–circuit.Don't forget that catastrophic MOSFET/IGBT failure at power–on will almost certainly cause damage farther back in the drive circuits, so you may have to trace the gate–circuits back to the driver transistors or ICs.Where IGBT output devices are in use, the driver–stages need to switch on and off in timed sequence such that a NEGATIVE gate–to–emitter voltage is provided during the turn–off phase, (this is not always provided with an auxiliary negative supply as multiple cross–connected driver transistors can do this – component – level circuit diagrams of IGBT inverters are virtually non–exsistent so I can't offer an example) – partial failure of drivers can delete the negative turn–off bias, which will also cause instant destruction of o/p devices!The only way you'll trace this is by meticulous component–comparison checks on the smaller stages associated with all the IGBTs.Nearly all PWM bridge–controller devices of reputable manufacture have reliable "dead–time" arrangements built into their o/p drivers to prevent cross–conduction of upper/lower sections of MOSFET output stages, so castrophic failure at switch–on is nearly always to an external fault degrading the drives to the gates in some way, or an overload.If you can post as many clear pictures of your failed unit as you can, we can offer some more tips!Chris Williams

author: Stockers
author_rank: Newbie
timestamp: June 01, 2019, 10:27:09 pm
content: annoyingly i cant upload any images.the make is a "reliable 3000"it is a Chinese make but have had good reviews.i have been through every component, testing everything. all the input stage fets and resistors are good.i only found one fault (other than the igbts) and thats a diode (t4) that is parallel to the resistor feeding the igbt gate. i suspect this died on the first killing of the igbt's after the 3 weeks of flawless operation.i cant find any shorts after the igbts.my money is still on the driver board. this consists of an eg8010 and 4x ltp250 opto isolators.there is no current feedback (and i have heard that this is a good thing. its said that the eg8010 causes shoot through when sutting down due to over current) the last 2 times the igbt's popped, there was no load connected.i have a replacement driver board on its way. along with yet another set of igbts just need to fine a replacement diode. and im hoping this will solve the problem. if this doesnt fix the issue, i dont know where to start looking next as this is as far as my knowledge goes.