Opto isolated relays + bistable electrovalve resets arduino

Hello,

I’m trying to drive a bistable 9V electrovalve (which needs opposed polarity at the coil to open/close) by using 2 relays. I already did this in the past and it works perfectly.
The problem is that now I need 4 electrovalves, so 8 relays + 4 more relays for other things, and I can’t anymore power them only from the arduino +5 V.
I used a different power supply for the three 4-relay boards but when I close an electrovalve arduino resets.
Schematics and board details attached.
Last time I did this (a single 4-relay board powered directly from arduino) arduino and the relay were half a meter far apart in two different boxes and it worked ok.
I guess it’s a back EMF problem, but shouldn’t it be opto isolated?

What can I do?

I saw that some people use a diode after the relay, but in this case the polarity is inverted every time I change state of the electrovalve, I don’t know how implement it eventually.

Many thanks

Update: (I updated also the title)
I tried disconnecting the 9V power supply and everything works!
So the problem aren’t the relays but the electrovalves!
Could be back EMF from them?
What sould I do?

OptoRelay4X_Wiring.png

your power supply gives in. try powering the relays from another source or use a better powersupply.

Already did (please read carefully).

Update: (I updated also the title)
I tried disconnecting the 9V power supply and everything works!
So the problem aren't the relays but the electrovalves!
Could be back EMF from them?
What sould I do?

Hi,

Link to specs/data of the electrovalves?

Can you post a picture of your project so we can see your component layout.

Thanks… Tom… :slight_smile:

Kind of a H-bridge is required for a bistable valve. See how the freewheel diodes are connected there and try to mimic the same back EMF protection with the relays. I'd think that 4 diodes are sufficient, 2 at either side of the valve, to + and - supply.

Inductive loads need back-EMF diodes.

Use a bridge rectifier.
Connect the two AC pins to the valve.
Connect the +/- pins to the +/- of the 9volt power supply.
Leo..

A bridge rectifier for 50-60Hz may be too slow for proper EMF suppression.

DrDiettrich:
A bridge rectifier for 50-60Hz may be too slow for proper EMF suppression.

Common misunderstanding that 'slow' diodes have a slow turn-on time.
'Slow' diodes have slow turn-off time, which is irrelevant for solenoid kick-back protection.
Leo..