Electronics > Projects, Designs, and Technical Stuff
EMC testing, problems with MeanWell power supply
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honeybadger:
Dear EEVblog forum,
I am really desperate  |O

I designed, build prototypes of a new product for my colleagues. It is rather simple, Arduino Nano (will probably be replaced for just Mega328 in the future), 4x20 LCD, linear voltage regulators, some relays, OPAMPs and bunch of passives. It has a pack of 8x2,2mF  capacitors. And it is powered with 12V/1A DC power supply - MEAN WELL GS12E12-P1I.

Now it is being tested for EMC.

I was not present for the test but it failed to survive the 2kV pulses injection to the 230V AC. (we will sell it as a complete unit with the power supply so we were told it needs to be tested with the power supply)
My colleague (not an electrical engineer) was there and the only info I have is - it was dead and it was not able to recover by itself - unplugging of power supply was necessary.

I added the watchdog (I know it should be there from the beginning) and added a massive ferite of shame to the 12V power cable.
Again I was not present but it failed again - this time at least I have a video of that. It indicates that Arduino is working but the LCD is dead and the rest is almost dead - the circuitry (mainly relays) which is powered directly with 12V is not working.

Now I have two questions:
Is it possible for the hd44780 LCD to freeze without self recovery with such pulses?

Is it possible that MEAN WELL GS12E12-P1I power supply enters some kind of half dead state in which it does not provide 12V but maybe only 5V (5V-1,2V drop = 3,8V...  enough for Arduino to be alive, probably not enough for the LCD, not enough for 12V relays)? I mean it already has all the certifications. Or is it some kind of undocumented safety feature?

From what I saw it looks the power supply is the problem.
Next time I will try different power supply and will measure voltage after the test but I need to be prepared.
nctnico:
Post a picture of your contraption. Likely the wiring is picking up the pulse and distributing it where you don't want to have it. Did you create your own board or slammed several boards together?
honeybadger:
I would not say it is a contraption  ;D . It is a product ready to be sold when we get the required papers. There is a proper PCB. From symptoms I am 90% sure it is the power supply (I will be 100% sure next week).

I am not allowed to post pictures of the product. But there are no long power traces - no it is definitely not picking anything. It either goes through input power circuitry (polyfuse, TVS diode - I guess TVS diode is too slow for such pulses, 2x2,2mF caps dedicated for 5V rail, LM1117-5.0 and few other caps according to LM1117 datasheet). Or it messes up the power supply. That's why I am asking if someone know if this is some kind of undocumented safety feature.

Is it possible that MEAN WELL GS12E12-P1I power supply enters some kind of half dead state in which it does not provide 12V but maybe only 5V ?
IconicPCB:
Ahhhh...
Yes, the Lazarus state readily broken by unplugging the corpse from power and breathing new current of life into it.
You have the hardware,,, be there the next time it fails and make the measurements.
Tomorokoshi:
2kV pulses onto AC... Specifically, is this the EFT test? Which test standards and methods? It should be on the data report you got from the lab.

Who knows about the Mean Well supply itself. It's possible it could be running at perhaps half voltage after being hit. The switcher could be going into some kind of protective mode.

As for the LCD, they can absolutely get blanked out. If the LCD controller is only initialized once, then after the interference it won't process the commands and data properly. LCD interfaces for those types of displays are a marvel of cost reduction. No redundancy anywhere. Interference could be through power glitches, corrupted data packets, etc. A couple options are to attempt to read back status registers to see if the controller is still running properly, and to have either an occasional re-initialization or some kind of user-initiated initialization without dropping power. However, that won't help if your supply drops out.

A small plug-in supply may very well pass a fair amount of transient through when hit with 2kV. A ferrite won't do much; these really aren't high-frequency RF transients getting through. You would need some good filtering at the input of your board, and ideally the Mean Well would be able to filter it out.

4uF on 5V could get jolted by one of these tests.

Take apart one of the Mean Well supplies. See if you can identify the switcher, any protective components, etc.

Note that for some EMC tests, you get to somewhat declare what the symptoms of failure are.
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