| Electronics > Projects, Designs, and Technical Stuff |
| Power supply topology - will it work? (Control theory, stability) |
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| Neomys Sapiens:
--- Quote from: Yansi on February 11, 2019, 03:08:19 pm ---Hello, unfortunately not many news - what exactly do you have on mind? I could make some pretty interesting series of episodes of the design failures in those two EA power supplies I have repaired. --- End quote --- OOOh, yes please! Black cloud of shame over Viersen! |
| Yansi:
Well... just as a sneak-peek: Our team bought a 10kW up to 1000V 30A power supply from Electro Automatik Gmbh (EA-PS 81000), to charge our prototype EV traction accumulators with it. The damn thing exploded like at least! four times (and at least three times was sent for warranty repair), and under the most bizarre circumstances. It has even exploded once, sitting turned on on a table, with no load. BANG! Something blew inside. Most of the time, the power supply had like 10-20 hours of run time before the big bang happened. You know, these blow ups were one hell scary, if it did that, while the traction accumulator was connected to it. Fortunately, we have had it always connected through fuses and safety disconnect relays and the damage never occurred on the secondary side of the PSU. One time we desperately needed to power supply (but it was again kaputt gemacht), so we have requested a temporary replacement. We were given a different type (1U rack-mount 3kW 500V one, don't know the type off-hand). And guess what! Once upon a time at the place wee needed it the most, it blew like hell too, just after I have plugged it in the wall and flipped the switch. It has just shown the obligatory "Device is starting up" and then all hell broke loose inside. So, ended up with two exploded very expensive power supplies which one of them was not even ours, the company finally stopped communicating with us (as far as I was told so - I was not the one in charge of "communication"). We ended up voiding the warranty on both PSUs deciding to see where the issue was (the manufacturer never told us, they have just swapped the modules inside and sent it back with a paper attached to it how within specification the unit was after repair). Later we have learned, that the temporary 3kW power supply exploded due to short circuit on the DCbus after the PFC circuit - due to them (Elektro Automatik) using a fucking damn stupid thin kapton foil as an insulation for the components on heatsinks, and that further due to cheaping out on a €3000 or €4000 power supply, to omit the obligatory Y2 caps to couple the heatsink to ground (to reduce RFI, it was rather directly sitting on the hard DCbus+ potential, increasing the potential (no pun intended) of the big bang. The kapton foil failed, due to probably a burr being present on a TO247 shunt resistor (stamped aluminium back side of it) in the PFC circuit that have over time pierced the kapton, or the resistor failed itself, resulting in the damage of the insulative kapton tape. Not really sure which one first, that would require further writing, which I currently do not have time to do. The other PSU, the big 10kW guy is a completely different matter. Although still kapton tape insulation on the heatsinks, the failure mode was completely different - probably arc-over on badly designed PCB. Combined with the fact, we used the PSUs on mobile basis in all kinds of different environments (but never damp, mind you!) coupled with absolutely NO particle or dust filters on the fans and lack of conformal coating, was a disaster waiting to happen. The 665V DCbus jumped across to the control circuitry and blew the shit out of it. I have once tried repairing it with my friend (after spending numerous tens of hours reverse engineering the schematics of that over-complicated thing), but it blew again in the same spot just as we were slowly bringing the PFC section back to life, which was just pita and a show stopper. The smaller 3kW PSU was successfully repaired. Fortunately just the DCbus was shorted, no damage in any of the electronics occurred. I have replaced the fucking kapton with kerafol. It is working flawlessly ever since (and hopefully will still be). We still posses the 3kW PSU, they never wanted it back. If they will, we will likely charge them the repair costs. So the lesson learnt here: 1) Elektro Automatik PSUs are not really worth the money they are sold for. Although nice and shiny on the outside, the PCB designs inside are just pure hell. It is I'd say obvious, the designer haven't had much of a clue* how to do layout of switchmode power stuff, the power components are all over the place with in my opinion just extreme lengths of parasitics within the current loops and the control circuitry aint any better: Looks like someone dropped a bucket of SMDs on a PCB and let the auto-router software loose. (It was absolutely evil to trace the control circuitry). Also some shape features on the PCB were found very funny looking. *or he wasn't let to do it better in the first place. 2) do not use kapton tape/foil as (the only) thermally conductive insulation material, between heatsink and components. Can be easily nicked and punched through. (And also I think it even doesn't have that good thermal properties, does it?) As I have said, this would make a few very interesting episodes by itself, now I will just end with a couple of photos of the aftermath. Inside of the 10kW PSU Where the arcover occured (There is straight DCbus right on the pinheader) Mess after the PSU was raided by us reverse engineering almost every single PCB of it. Inside of the 3kW PSU You could probably tell where the sharp burr was |
| Yansi:
--- Quote from: marcopolo on February 11, 2019, 04:13:34 pm ---Hello, Something like the final schematic :) --- End quote --- The original idea of building the 400V 300mA PSU is not completed yet, see above. The circuit is a huge spaghetti ball across a couple of veroboards, including the tracking pre-regulator (nothing special there either, just an inverted buck topology with 500V at the input side with an UC3843 in control of it). The schematic partials I think are still available in this thread. I do not see much value of posting a schematic of an unfinished circuit/product, I see more value in the thread being as a guide how to design such PSU and verify its performance. Also, currently I am toying with a completely switchmode based 200W regulated PSU of 0-350V - so I have something to employ my brain cell with, as a medicament for my otherwise very bad mood (due to other things in my life) :-/ |
| 001:
--- Quote from: Yansi on February 11, 2019, 11:29:33 pm --- --- Quote from: marcopolo on February 11, 2019, 04:13:34 pm ---Hello, Something like the final schematic :) --- End quote --- The original idea of building the 400V 300mA PSU is not completed yet, see above. The circuit is a huge spaghetti ball across a couple of veroboards, including the tracking pre-regulator (nothing special there either, just an inverted buck topology with 500V at the input side with an UC3843 in control of it). --- End quote --- Thank You for Your work! It is amasing project But can You help me with schematic of analog variant since I`m no need any microcontrollers? |
| Yansi:
Switchmode power supplies do not typically require any microcontrollers in them. (By analog I meant linear, sorry for the possible confusion). Also attaching photo of the switchmode supply I am working on to have some stress relieved. PS: Please fix the quotes in your answer :) |
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