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Topic: Arduino hangs on switching AC 24V with opto-isolated relay board! why? (Read 1 time) previous topic - next topic


Is there a question ? ( I know what you have. You didn't need to draw the schematic. It changes nothing)

See Reply #8

Didn't you say that you were going to run a test of the Mega running off a 9Vdc PP3 battery to see if the unstable behavior goes away ?

Interesting thing to test it. From a clean 9V battery. I don't know how long can last such a battery, since the mega with eth shield draws a lot of current ( I guess around 300mA)...But it's worth testing it.


I had exactly same problem for same application.
I added a snubber consisting of 100nf 400v cap + 100ohm res (in series) parallel to each solenoid valve.
Works magic.
Not sure optoisolators serve any useful purpose. Who would have a bunch of isolated power supplies?


So, so what ? Do you actually think that 24V noise generated on one wall socket outlet WILL NOT affect something plugged into the OTHER socket on the SAME WALL PLATE ?
I have noticed it is an old thread but I wonder: do you really think a spike from a solenoid will get through the 24V transformer to the nearby socket, through switching power supply input filter, transformer, output filter, possibly long wires and Arduino onboard decoupling caps and still stay strong enough to consistently cause soft processor fault? There is so much inductance and capacitance on the way. I think there must be some other explanation. Such as a SW bug or interference with some other part of the system (i.e. unhandled I2C bus error).



I was aware of the use of snubbers to eliminate relay contact arcing but don't see how they apply to a solenoid that has no contacts.

Can you provide any math to support that ?
Doesn't matter very much if the snubber is across the relay or across the switch contacts _if_
the supply is stiff...  The snubber's job is to divert current flow _somewhere_ to limit the voltage
increase due to the inductor - in other words it limits the peak value of dI/dt to something

Having it across the switch allows AC to leak through at low power when the contacts are open,
having it across the load doesn't.

If you have an isolator switch having the snubber across the inductor means you only need one
snubber, rather than two.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

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