Arduino-dht freeze, help make/select rc snuber, mov, caps to protect from 220v

[dlloyd]

Btw is it ok if I use lower watts resistor? 220 ohm 1/4w 5%? or ceramic one with 5w? what is a better/safe option?

The 1/4w 220 ohm resistor wouldn't have a high enough voltage rating, but the 5W 220 ohm resistor should be OK.

[sone0121]

Ok, I just don't know the difference between small ones and these and why are they so big, that's why I asked

[dlloyd]

If your supplier can get the RR02 or similar, it would have about the same size as shown on those snubber modules. The main thing is the voltage ... the RR02 has a limiting voltage rating of 500V. I wouldn't go with anything less than 500V.

[sone0121]

Ok, while you mention voltage, I can't find anything about the one in the pic

[dlloyd]

With low ohms resistors, can't test continuous max voltage as this would exceed the power rating. They do state this in the datasheet:
Dielectric withstanding voltage: No evidence of flashover, mechanical damage, arcing or insulation break down

[sone0121]

The reason I ask is I already got them, before you posted about RR series, I was in town and picked them up.
So I wonder can I still use them? I don't care about size, latter on I can change them if I decide to go smaller.

[dlloyd]

Yes, you can still use them.

[sone0121]

If I would add one more relay module to control 12v (about 6-7A) power only, how should I power it?
From arduino alone or I need another new power source or same old that is powering 220V module?
Would I need also some protection across the switch? I saw ppl go with simple RC only

[dlloyd]

Controlling 12V loads is much simpler. If its an inductive load, then only a flyback diode is needed and connected across the coil (solenoids). Yes, sometimes simple RC or a capacitor only is used across motor loads. Many have had success without Opto-isolation and use the same external power source as the Arduino. I would recommend that the supply be separate from the 220VAC relay power supply.

[sone0121]

I want to try something with Peltier module, I suppose it is a resistive load, but as I understand, it can produce "Seeback voltage".
What would you recommend, if anything at all is needed for protection?

[sone0121]

I connected snubber across the switch and my devices started working although relay was closed, which I was afraid it might happen as they pass through some current, and they are to be used with much higher consumers which don't mind little current flowing through. Live and learn I guess...

So far everything works fine with MOVs and ferrite rings, I moved AC lines further away from the board and PSU and lined them better.

So far my only trouble is when the relay is closed (working) and if I manually switch off one of the devices I get an instant error and arduino freezes.

MOVs are all placed across the switches and one more on the main L&N terminal.

I have also checked PSU and it got a few MOVs, resistors and capacitors where the main lines come in, so it is protected too.

So is there any other solution on how to sort this out or I'll have to live with this and continue without touching manual switches?

[dlloyd]

So far my only trouble is when the relay is closed (working) and if I manually switch off one of the devices I get an instant error and arduino freezes.

Ahh, while any relay is energized, it essentially shorts out the snubber and MOV. When the relay contacts open, the snubber and MOV do their job and protect the relay and reduce arcing/EMI. However, if there's a manual switch connected in series and its opened while the relay is energized, there's no filtering or protection.

If you could connect the manual switch like this, then all contacts would be protected:

[sone0121]

Hmm, I will try that in the next couple of days. Now when I look at it, it's logical and I feel sort of dumb now. . .

I just noticed I did a typo here:

I connected snubber across the switch and my devices started working although relay was closed, which I was afraid it might happen as they pass through some current, and they are to be used with much higher consumers which don't mind little current flowing through. Live and learn I guess...

Which I actually meant open (not working)!
I just want to confirm if this is as I described or I did something wrong?
So I dumped snubbers and left it with MOVs only.

[dlloyd]

Maybe you had the switch connected in parallel to the relay contacts. In that case, the switch would only work if the relay contacts were open. Anyways, connected in series is what you would need. The switch could also be connected in series but be located on the load side of the relay.

[sone0121]

Urgh, another typo or we misunderstand, sorry it's getting late over here.

Across the relay is what I mean, so NO and COM was where I placed snubber and while relay was OPEN (not working) my device turned on.
That made me take off snubbers and left it with MOVs only.