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[SOLVED] Adjacent Relays Interference

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sharikbaig

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Hi,
I have this PCB on which there are 7 relays adjacent to each other. They may be on all at a time or may be some of them on others off or maybe all of them on. The problem is, when i turn on 3 relays, the 4th one doesn't turn on. but as i turn off the 3rd relay, 4th one turns on. Also sometimes, as one relay operates, all the relays turn off.
In short, these relays are somehow interfering with each other & hence the circuit is misbehaving. Switching of one relay affects the other. Is this because they are placed adjacent to each other (only 3mm gap in between)? or is there some other issue?
To my knowledge, is it due to EMI?
How to overcome this problem?
Relay Coil - 12VDC / Relay O/P - 5A@240VAC
Relay datasheet attached. View attachment datasheet.pdf
Thanks.
 

In general relays affect much more analog/digital busses than causing cross interference themselves, particularly when being 3mm apart ( ~120 mili inches ) that is not a critical clearance. What you depicted above is likely to be related to the insufficient current capacity of the power supply. You could try turn around by increasing the capacitor supposedly placed at the 12V bus.
 
Did you ensure sufficient power for the coil drive? How the coils are being driven? Via transistors? It appears that when multiple coils are on,there is insufficient power to drive another coil...
 
Wow! I didn't thought of that, currently i am using a 500mA transformer-->Diode Bridge-->Vtg Regulator for 2 ATMEGA's, a ULN, 12 LED's & a few other components. Now i too think there isn't sufficient power. Will upgrade the transformer & update you soon.
Thanks andre_teprom & c_mitra :)
 

Also make sure that the relay coils are protected with diode capacitor snubbers- even a small capacitor and a garden type diode will do...
 

Yes. That was the problem. I increased the power rating of transformer & everything is fine. Thanks for your help. I appreciate it.

c_mitra, Yes the relay coils are protected.
 

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