Author Topic: Help replacing IGBT's (Read 9929 times)

dawesy · « **on:** February 07, 2014, 03:14:02 AM »

so the replacement VFD turned up ( last one lost its magic smoke

)
got it all mounted up in the new enclosure, tested all the wires from the motor for continuity
, leakage to ground etc all ok. turned on the VFD and put the required settings in pressed go.............DL error code. checked the book and it lists 'output short' as the cause.
confused i once again checked for leakage to ground, nothing. checked my meter was working, it was.
OK we'll try again........BANG..... from the motor (no smoke though) turned off the VFD and put the power back on in the shop.
took the motor apart and found one of the supply wires had moved and been catching on the fan and had shorted (this is what killed the original VFD

)
i then replaced the damaged wire and insulated it all up again, reconnected and very gingerly put the power back on to the VFD

it powered up fine, phew looks like i got away with it.... press go again

lights out again. this time the bang came from the VFD

realising that i wasnt going to get this one replaced FOC i decided to strip it down. one of the tracks to one of the IGBT had gone and one pair of IGBT's have continuity across all pins so im guessing they're toast.
now i looked on line at the part number (KDG20N120H2) and fount the spec sheet for it but not able to find a UK stockist. had a look on RS's site and found two possible replacements, the major specs are the same ,voltage,amps etc but there are a few differences.#
could some one with knowledge of these components have a look at the spec sheets and tell me if the replacements from RS will work?
ive attached the PDF spec sheets below .
many thanks

awemawson · « **Reply #1 on:** February 07, 2014, 05:40:40 AM »

From a brief look they both look suitable. Both have a lower Vce(sat) value than the original, which is 'good' in that they will dissipate less heat when working.

Be aware that with a s/c ibgt the driver circuitry may also have suffered from electrons in the wrong places

dawesy · « **Reply #2 on:** February 07, 2014, 05:51:41 AM »

hi thanks for that andrew much appreciated. would i be best swapping all 6 to keep them all the same or will swapping 2 be ok?
if its toast then thats ok but if it is just these then its a cheaper fix than a new vfd.
really wished id checked the motor befor i put this one on, but with not getting any shorts to ground when i tested it it seemed ok. obviously as the fan rotated it caught the wire and shorted

John Rudd · « **Reply #3 on:** February 07, 2014, 06:51:22 AM »

My advice would be to replace all 6....but if cost is an issue then the decision is easy.....
As Andrew suggested there may be other parts damaged....especially the igbt driver chip (I assume it has one!)....
Do you have a variable bench power supply?....if so that would be a good aid to diagnosing any further issues....(especially if it has current limiting)....Failing that a variac and a 60 watt lamp in series with the supply to the vsd will limit the current.
Make sure all connections at the vsd and the motor are sound before power up else you'll end up with your own firework display....
Good luck and keep us posted

awemawson · « **Reply #4 on:** February 07, 2014, 06:51:37 AM »

You may well get away with just swapping the pair that are short circuit. If they are pricey that'd be my first approach but don't be too disapointed if powering on gives another pop.

I've no doubt that the 6 are arranged as pairs of totem poles across the internally generated DC from the mains, with the three common points being the generated phases. Sadly this means that if they have gone short circuit the driver stage will have had that high voltage on it. A picture of the circuitry may give a few clues.

John Rudd · « **Reply #5 on:** February 07, 2014, 07:37:03 AM »

Like Andrew said,
Can you take a few snaps of the pcb showing the components?
We can then give you some pointers yo check before you power up.....

Ah..... Just read your other thread.... I remember now, it's a Huanyuang vsd.... I'll try and have a peep at my spare unit...

dawesy · « **Reply #6 on:** February 07, 2014, 08:05:15 AM »

Hi guys. Thanks for taking time for me. Here's some pics as requested.

I've removed the dud IGBTs in this one but you should see where they were from ( I'd added a repair bridge for testing but removed with the IGBTs )

board topside

toasted IGBT

Dawai · « **Reply #7 on:** February 07, 2014, 08:54:17 AM »

I've often wanted the load carrying components "on a heat sink" away from the digital driving portions of the unit, fan cooled. I tried making a stepper drive in the mid 2000's that did just that. My skills were not enough to create even a mediocre drive.

THE monitoring and controlling of some industrial VFD (Hitachi) was just wonderful, I had one, the no-Habla employees crushed the conduit going to the motor with a pipe, the drive shut down between phases from the direct short. NO damage, just a reset.

I have been scratching my head since, humbled by others engineering.

awemawson · « **Reply #8 on:** February 07, 2014, 09:06:33 AM »

The three 8 pin DIL's to the right of the IGBT's look suspiciously as though they could be opto-isolators driving the IGBT's with two per package. However there seem to be some components labelled PC1 - PC5 (at least) that could be involved - can't really make out much from the photo.

Dawai, the advantage of these more modern semiconductors is their low forward voltage drop when driven 'on' hence they dissipate far less power than the good old 2N3055 !

PekkaNF · « **Reply #9 on:** February 07, 2014, 09:20:27 AM »

Quote from: awemawson on February 07, 2014, 09:06:33 AM

....
Dawai, the advantage of these more modern semiconductors is their low forward voltage drop when driven 'on' hence they dissipate far less power than the good old 2N3055 !

OT Huh, that brings me way back when I was sent GB and one day one of the linear power supplies (24V, but big amps, even the choke looked like a buzzbox welder) startted getting hot and I rushed into local electronics shop (Chester, I think, with roman walls) and bough a box full of them and some drivers+ resistors. Probably changed least six 2N3055. Poor linear "regulator" = Heatsink full of 3055s was really hot. Electric cabinet was like a sauna.

Just got out of school before thay started to teach about IGBTs. Those fancy ones, that both can be conductive for a little while on totem pole.

Hope you'll get this fixed.

Pekka

dawesy · « **Reply #10 on:** February 07, 2014, 09:47:43 AM »

cheers guys, ill try and get some more detailed pics, any areas in particular?
6 IGBT's ordered (theyre only a few pounds each so no big loss if theres somthing else fried)

awemawson · « **Reply #11 on:** February 07, 2014, 10:42:18 AM »

Try and get some numbers off those 8 legged DILs that I mentioned - and also the PC1 .... PN (n) to the left

dawesy · « **Reply #12 on:** February 07, 2014, 12:32:56 PM »

Hi Andrew. Got the best shot I can. Removed the sealant from all of them and they all have the same p/ number. PC923L which is an optocoupler from what I've googled. Is there likely to be any damage and is there any way to test? ( I have a multimeter and a soldering iron but no lab type power supply. )

awemawson · « **Reply #13 on:** February 07, 2014, 12:48:56 PM »

Yes I thought that they probably were opto-isolators. Hard to say if they have sustained lethal damage without the circuit. Personally, I'd buy a few just in case seeing you have two inverters to fix - also I'd put them in sockets.

dawesy · « **Reply #14 on:** February 07, 2014, 12:57:29 PM »

we'll suck it and see, £3 each so no biggy. good idea about the sockets, didnt fancy trying to solder SMT components on

hopefully should get the new IGBT's tomorrow so we'll soon know.
i only have the one inverter as i got it replaced FOC (just had to send the damage unit back), ive a feeling that one was a little more FUBAR though as after the bang and flash that came from it, when i applied power to it there was a pop and the magic smoke escaped,it didnt even power up after that. this one at least powered up after just blew the fuse when 'go' was pressed

dawesy · « **Reply #15 on:** February 08, 2014, 06:16:04 AM »

So the new components turned up at 8:20 this morning. Impressed the turned up so quickly ( got them from farnell on line), not so impressed at being woken on a sat morning (especially as I have a dose of man flu at the mo). Decided to just replace two IGBTs as I didn't want to fry all 6 if it went pop

Put it all back together, which was fun as the securing screws for the IGBTs don't fit through the holes in the pcb

I've decided to junk the original motor even though now it seems ok I just don't trust it. I connected up to the new motor, pluged in and switched on .............. After a short delay the inverter started up, bonus at least I've not broken it any more, set the parameters to the new motor, closed my eyes, held my breath and at arms length pressed start......................................... IT ONLY BLUMMIN WORKS!!!!!!!
One happy bunny. Just got to fab up a new mount for the motor and it looks like we're away.
Once again I'm indebted to those who helped me on here, I owe you all one. Thanks again.

John Rudd · « **Reply #16 on:** February 08, 2014, 07:16:02 AM »

Good to hear your success story....and with no further tears....

awemawson · « **Reply #17 on:** February 08, 2014, 07:21:10 AM »

Excellent news Lee, glad it worked out ok in the end

dawesy · « **Reply #18 on:** February 09, 2014, 12:11:46 PM »

Celebrations were short lived.
Spent an hour or so last night making chips with no issues.
Came out this morning turned on the inverter, no probs. pressed run and the lathe started up but I remembered that I still had to swap two of the phases as it was running backward ( ran it in reverse last night, so it turned the right way), pressed stop ( I kept it pressed but don't think this had anything to do with it) and the lights went out

confused I went and put the power back on came back and turned the inverter on but was greeted by smoke from it!!! It won't power on at all (fuse is ok)
I've taken it apart and the two IGBTs I replaced yesterday are shorted. I can't see anything else damaged bar the contactor next to the green 330rj resistor has a melt mark from the resistor in it ( top of board pic) so it looks like something else took damage in the original short. Not sure what else to check and think I might be better junking this one and getting a new one ( this one has had random electrons buzzing around wrong bits already). Good news is the lathe runs good though.

News:

Author Topic: Help replacing IGBT's (Read 9929 times)