Newbie relay question

Community PCB Design
1

Okay I’ve worked with 12v car electronics for a while and am used to the standard BOSCH relay but I’m working on a DIY project for my fish tank and ran into this question.

Do they make something like this?

Let’s say I have pins: 1,2,3, and 4. If I join pins 1 + 2, 3 and 4 will be connected. Ideally I want to run 120vAC to pin 3 and a water pump to pin 4.

I’m trying to make a auto top off system where when the water evaporates below a certain level (float switch) my setup will turn on a water pump to fill my tank back up until the float switch isn’t closed.

At first my design had a 5v DC power going through the float switch until it closed triggering a solid state relay for AC power to a external pump. But the more I thought about it I didn’t want to expose 5v DC to my fish tank setup and came to this question.

Thanks guys!

2

Any type of relay will need power to flow through pins “1 and 2” in order to make “3 and 4” connect. Float switches are sealed so you should have any issues running a 5V one in your tank. If you prefer electrical isolation, why not use a float switch that has a linkage between the float and the switch? Better yet, if your tank is large enough, you could use the float valve assembly found in toilet tanks that don’t require any power at all!

-Bill

3

5V is perfectly safe. Its much better than running 120VAC switching an inductive load through a float switch - they don’t have stunning reliability due to contact arcing.

And relays are electromechanical switches - they require current to build a magnetic field which closes the switch.