is there a design for a simple IGBT brick high current tester? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: October 08, 2021, 04:15:53 am
content: I have a miller welder I am working on but I keep getting two transistors doing something that keep blowing despite a few other bad parts replacements, it works but anyway its making me fucking pissed off, I am starting to get problems that occur under HV or High Current conditions that are not diagnosable with desoldering parts and doing multimeter testing.I see the IGBT is expensive and its just a brick with some connectionsIs is possible to do some kind of test setup to beat up one a little bit within its current specs using the most simple technology, perferably lab equipment, I have some audio amplifiers ETC that might be caapable of driving it, I want to use what I have if its possible, possibly using a AWG and audio PA, or switches, or even steady state to start withIf I got a 200A igbt.. what would I need?Can this be done with a high voltage battery bank with current limiting ? this thing has some PFC shit going on and I don't know what the fuck is going on as a resultHow about all those fat shotkey diodes too? I thought about using my resistance welding transformer with a big ass current limiting resistor to try to do a power test on them, I have a big aluminum brick I can clamp it to hard (6x4x3 inches)The transistors that keep burning are in a patch of around 20 4-lead dip MOS transistors, i think it might be some kind of fucked up multi stage cascode or something, they looked nested and interconnected alot. I did full parts replacement within like 3 inches of the burned component, but it seems the damage is localized to heavy damage/short on 2 transistors and possibly light damage to 3 more transistors in the patch. I hope I don't need to reverse negineer that.I kinda wanna know if I can play dr frankenstein with this IGBT and trigger it with a giant knife switch or something lolEdit:Actually, maybe those transitors are OK now. I had to clean up the PCB because it was really burned under one of the transistors, so I have been looking at it with a thermal camera. It makes a really bad whine, and the transistors quickly shot up to 100C so it looked real bad on the thermal camera.. but they are driving a 0.4 ohm transformer load, and the package is rated for 175C! I figured 125C maximum....I desoldered them and actually tested them instead of tossing them like the burned out ones.. it looks like they might be alright and miller just thought 121C operating temp on a 175C part is 40% derating when its operating in antarctica.. I checked the manual and its rated operating temp range is 40C so that would put that chip running at 140C+ when its used in the hot desert... maybe this is OK for designers.. seems a little hot but I guess I see hot stuff all the time working normally..I will replace them again and run the machine and see if the transistors actually get close to the 175C limit... and if they don't, I will assume that part might be alright, and try to figure out whats squeeling so loud and making me think its broke lol.. the front panel is responsive anyway, I just turn it off quick because I was thinking something is gonna pop (I had to replace the rectifier/inverter front end thing, which exploded after I got it.. but I replaced that part and checked the periferal on that mainboard.. anyway maybe this is not for this thread and lets keep to IGBT testing because I would need to write a shit load more to explain myself).Hmm, it looks like the chip at the temperature I renember is doing its front page advertizement rating, of 1W, with 1.3W being maximum. If that part is doing something to control the signal in a way unrelated to weld current, which I imagine it is, perhaps thats just how they speced it out, then when they started aging so close to the power limit it burned the trace underneath, and my flux is just smoking because thats what it does.. they should have put fatty traces under the part to make use of the heat sink through its linked heavy leads but whatever

author: coppercone2
author_rank: Super Contributor
timestamp: October 08, 2021, 09:44:29 pm
content: I changed those transistors a few times while maintaining a overload, I think I got a distant diode to smoke, maybe it pointed me in the right direction. The noise got more intense too so maybe the thing that was causing the problem is finally causing too big a problem but I located it.the four resistors controlling the driver bank were all severely out of spec, I changed one of them in the begining weeks ago but I had 4.0 there instead of 2.7.. now you guessed it when I changed it out for the same color code, I think I got alot more energy into the culptrit too. might be a shdiode hidden on the mainboard.mmm i will map out 4 square inches of the PCB to see whats going on, this is a problem patch, I need to reference it to the nearby connector,to see what other things those are going to.. I might try to locally power it too.. this is preposterous