I purchased 2 "Mechanical Relay Board, 8 gang, 10A 220VAC, 24VAC 30ma coil" relay banks that I am trying to control from a raspberry Pi. To do this I've built out 2 595 shift registers and I'm using an external power source, not the power from the pi.
Testing on LED's everything is ok but for the life of me I cannot get the relays to activate. I figured that maybe the input was too small, not enough mA to activate it.
I'm supplying 12v DV from a 12v 1A transformer to power the relay bank and I tried to activate the relays using 5v from USB, 5v from 9v battery running through a 5v regulator, 9v directly from battery and also 12v directly (from the transformer used to power it).
Nothing. I notice that when I test the voltage across the input power terminals, it reads very low (0.10v) but when I unplug the adapter from the relay bank, it reads 12v. So when the power is plugged in to the relay bank, I'm imagining that the bank is causing a fault in the transformer? I noticed that when I had the 9v battery plugged in to the bank as the power source it got really hot.
What am I doing wrong? I changed the jumpers to both positions and tried the same tests on both setups.
Best Answer
The relay board doesn't have 'power input terminals'. If you mean the two common terminals, they are both connected to the relays' common connection. So if you connect a supply across them, then you're shorting it out and measuring the drop along a pcb trace.
The datasheet says you can run at 12V DC by setting the jumper (presumably removes a half wave rectifier from the circuit), connecting +12V to the common, then connecting the terminal for the relay you wish to switch to 0V. You don't seem to have tried this.
If you want to run it from arduino level, use a FET which turns below 5V and connect the FET between the relay terminal and ground while supplying 12V DC to the common terminal.