gabennet:
I have a 110 volt 18 watt air pump i am trying to run from a sainsmart 5v relay board but i think the EMI is surging. Would you recommend a metal oxide varistor or something else?Thanks again.
the only thing that is important here is that you have a mains powered device and your power dips when it is powered.
since it is only 18 watts, that is very odd. a normal AC motor can easily spike 5 times the current on a locked rotor on start. but 5 times 18 watts should not bring down the voltage on a 120v circuit.
since the motor and relay are really totally separate circuits, you can power your pump from a separate source entirely. different wall outlet. by doing this, you have removed the huge draw. now, if you experience the same voltage drop, then the problem lies within your circuit.
best thing to do is to make that sketch.
we are looking for :
110v power separate from everything else for the pump. only one wire goes through the relay.
separate power to the relay board, directly to the relay board. list capacity of power supply.
separate power to the UNO.
you might be able to power the motor separately
use a wall wart to power the relay
use the USB to power the UNO
when this thread started, it said 40 solenoids. your power supply needs to be able to handle that and still have something left.
you could use multiple wall warts and use one to power half of the relays or some such.