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Never forget yer flyback diodes on an inductive load. Some guys blew out two access control panels before I went in to check it out for myself. Drops to -15v and then shoots up to 50 when you engage/release the door strike. Panels didn’t like that too much and gave up the ghost. 11
Never forget yer flyback diodes on an inductive load. Some guys blew out two access control panels before I went in to check it out for myself. Drops to -15v and then shoots up to 50 when you engage/release the door strike. Panels didn’t like that too much and gave up the ghost.
deutscher?
But how do you protect the oscilloscope from the inductive spikes?
Some inductors can makes spikes hundreds of volts in amplitude and scopes have a max rating of 300-400v on the input.
Do you put a TVS diode across where you’re going to measure?
[(Here)](https://www.diyaudio.com/community/threads/relay-coils-polarity-why-some-matter-and-others-dont.339981/post-5953442) is a nice experiment on diyAudio.com, showing the flyback voltage that occurs when shutting off a 12 volt relay coil, *with no flyback clamping diode*. It peaks out at six hundred volts.
(100 volts per vertical division) x (6 divisions) = 600 volts. Sonya Vabeetch!
[**image**](https://www.diyaudio.com/community/attachments/scope-jpg.789781/)
What got damaged on the panels? I take it was a relay to drive the solenoid or are they using high side switches now?
Sounds like a shitty access control panel. How could it not have protection on its outputs?
We are oscilloscope brothers 🙂
And today of all days, someone on my school came te me with his story: his system was shorted and couldnt find the error two hours laters he found it! He forgot the flyback diode on a buck converter. So he was like never forgot that piece of **** ,… hahaha
Amazing how many engineers forget this.
I recently had to control solenoid valves using relays and forgot about the flyback diodes for the valves. Everything was behaving weird and I thought it must be some odd software issue. Turns out that there was so much interference and noise that the microcontroller crashed, despite double galvanic isolation and a separate power supply. Added the flyback diodes and everything worked fine again.
I had an old Tektronics that would cut off and display “ouch” if it got overranged.
However, I never hit it that hard
What is happening here? Can someone explain please.