I'm working on making a switch that can be turned on with a microcontroller.
I have it mostly wired on a protoboard, and it kind of works, except that even when the relay coil isn't energized and the relay is open, there is a little bit of current still flowing.
The relay I'm using is a PCJ-112D3M.
I hooked the black multimeter wire to the neutral AC wire, and the red multimeter wire to the hot AC wire after it goes through the relay. When the coil is energized the meter reads 120VAC as expected.
But when the coil power is turned off, the meter reads 40VAC.
I'm not sure if it's just a bad relay, or if this is somehow expected behavior, but it doesn't seem right.
I just wanted to double check before I desolder the relay and replace it with a different one.
Best Answer
Are you driving load? Even a simple load such as a lamp will do for testing.
I expect then that you will find the voltage drops to zero when the relay is off.
The voltage you are seeing is probably caused by capacitance either in the relay and wiring or in the cabling to the relay. (or a snubber as suggested by @Transistor).
Your meter is sensitive enough on the AC voltage ranges to detect even the few microamps of current that flows through the capacitance. It is negligible compared to the current required by normal AC loads.
I often see this in house wiring, especially where the live and switched circuit run together in the same cable.
Solid State Relays (SSRs) require a load to operate correctly and can pass a few milliamps when in the off condition. Conventional mechanical relays only pass a a few microamps due to the proximity of the contacts and wiring.