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Scoping a mains powered switched inductive load

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techman-001:

--- Quote from: Truglodite on June 06, 2019, 12:05:27 am ---@techman-001

--- Quote ---I haven't given much thought about spikes on the mains causing an issue like this, but I suppose it wouldn't hurt to add an MOV in case. I do have a few extras laying around so it wouldn't be difficult to do. Do you think that would be adequate?
--- End quote ---

Personally I'd run some tests such as removing the problem switch cct and shorting the GPIO pins to eliminate the switch circuit, then I'd replace the wall wart with a battery and short power leads to eliminate the PSU..


--- Quote ---I did do some testing, and found the hardest part was triggering the relay off at the right time... not that my cheap oscope's poor response helped much. Using slope triggers was not working well given the somewhat random waveforms involved. I ended up doing most of the testing with a pass/fail mask at 10ms/div. That seemed to capture more than other configurations, but even then only 1 out of 4 events showed usable data; the other 3 would be useless flat line waveforms.  |O  I figure the rigol 1104z just can't keep up with the task at hand (too much 'time off screen' if you will). It got the job done, but I'm definitely not looking forward to researching AC transients with it in the future.  :palm:
--- End quote ---

AC transients can be incredibly fast and hard to pin down, but your device shouldn't respond to them. If your device is repeatedly triggered by the relay, use your device to trigger the scope ?


--- Quote ---When I did get a strong transient to display near zero cross without a snubber, it was impressive/scary to see the slew rates and peak voltages involved as the contacts were arcing. The first 3 images show no-snubber at various zooms. Compare that to the last image from one of the better snubbers I tested (Kemet 0.22uF/220ohm X2). So far so good in limited real world testing.  :popcorn:
--- End quote ---

But did the snubber addition cure the relay arc triggering problem ?

A old fashioned heavy duty arc welder operating nearby will create all kinds of transients as well, and it probably won't have a snubber ;-)

--- End quote ---

T3sl4co1l:
Hi,

Can you edit your quote markup to be readable?

If in doubt, hit preview :)

Tim

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