Relay shield Isolation Problem

Hi I got an Seeedstudio relay shield on my arduino ONO controlling 4 valves (24V, 1,2W). These valves all use the same power and have a common ground and the positive pass in parallel in all the relays.

Just to mention that I did put some duct tape (2 layers) on top the USB port to shield it from the relay contacts.

The system works but if I switch the relay on and off too fast it hangs the Arduino board (and sometimes it hangs just out of the blue during normal switching). This only happens when I got the 24 V plugged in.

The Arduino is powered by its USB port (it is also used to communicate with the computer for my application);

The Relay shield is powered by it’s 9V transfo. (Is that grounded to Arduino? or is it completely isolated? since it can use Arduino 9V I feel they might be some communication, that could be my problem right now…)

And finally my Outside circuit is powered by a 24 transfo. This is not grounded to the Arduino at all.

It looks like I’m getting 24V interference in the USB port that in turn mess up the Arduino board.

Any Ideas? I tried to increase the spacing between the boards but that didn’t help.

Right now I’m thinking the problem comes from the relay circuitry, that is somehow linked to the arduino…

Thanks in advance!

EDIT: As there is no real blueprints of the board I just looked at it… seems the design is flawed as the ground of the optoisolator is the same as the one of the relay. So that goes straight to my Arduino. The pin circuit should be completely isolated and only go the ground of the arduino, not the one of the module. Any idea on how to salvage this? I guess Ill just unsolder the component and throw the board out.

Very disappointed customer here

EDIT: Well I grinded off the optoisolator input circuit off the board and soldered wires directly in it… Now should work, of course it wont go on top of my arduino anymore as I would need to cut off all ground pins to it. I’ll verify its isolation monday at work.

You should really consider changing the design of the board: add a jumper to allow or not the Arduino power and ground connection and completely isolate the optoisolator other wise it is useless as a high power switch. As it is now the EMP feedback is definitely not compensated for 24V.


After reinstallation the problem still persist, any ideas on the protect pins and Arduino ground?

I’m having this exact same problem. I’m using the same voltages and everything. Any solutions?