Help making a switch work the opposite way with a relay

[SluggerB]

I have a very small float switch, I'm using in a very small tank. It only fits in one way. Link https://www.amazon.com/uxcell-Switch.../dp/B07DZ1J2GB

I want the switch to be open when the water is high, and closed when the water is low. Unfortunately it works the opposite. And since this switch is designed to be underwater, it's all sealed up, there is no taking it apart or hacking it up.

It will be driving a water pump, basic idea, when the water is low, switch closes, which turns on water pump, when enough water is in the tank, float switch floats, switch goes open, pump turns off.

Would I use some sort of external relay or something? The wires will be outside the water of course. This is all just a few volts DC. If someone could link me to an appropriate relay and how to wire it up it would be appreciated

[sam_sam_sam]

Why not use something like this float switch

https://www.amazon.com/dp/B07DZ11BWB...f8c74978&psc=1

Then you would have a set of contacts for the low level and a set of contacts for high level and use the appropriate contacts for what you want to do of course you will still need a control relay for your pump

If you have to use the float switch that have linked to there is going be an issue and that is if you do not have a maximum limit switch you could have an overflow condition

Or

You could use a timer with your float switch if you know how long it takes to reach the maximum level limit and do it this way

How you would use this is setup is you use the float switch to activate the timer and once the timer times out it should be at the maximum level that you are after

What I do not like about this company is that they do not tell you if the switch contacts are normally open or normally closed so it is very difficult to know which type you are getting

[SluggerB]

Why not use something like this float switch

https://www.amazon.com/dp/B07DZ11BWB...f8c74978&psc=1

Then you would have a set of contacts for the low level and a set of contacts for high level and use the appropriate contacts for what you want to do of course you will still need a control relay for your pump

If you have to use the float switch that have linked to there is going be an issue and that is if you do not have a maximum limit switch you could have an overflow condition

Or

You could use a timer with your float switch if you know how long it takes to reach the maximum level limit and do it this way

How you would use this is setup is you use the float switch to activate the timer and once the timer times out it should be at the maximum level that you are after

What I do not like about this company is that they do not tell you if the switch contacts are normally open or normally closed so it is very difficult to know which type you are getting

The problem with those is they are to big. This is for a CPAP machine so I am working in a very small area. Finding a tiny, reliable float switch is really a challenge. It's distilled water to so I can't use any conductive sensor

I actually managed to get the right angle float in upside down, so it works as I want it to. I had it all rigged up, and it worked fine, until about 10 minutes in, the float switch failed closed. So if this was in use, it would have ran the pump until the water bottle feeding the tank was dry and dumped a gallon of water all over my carpet. So I need to figure something out someway to prevent overflows.

The timer idea sounds interesting, do you have any links to the type of timer I would use? I would like to run all of this off the pumps DC power supply so I'm not having to plug in more than one thing.

[mscottdoran@gmail.com]

An external relay would easily do what you need it to do. You have to find a relay with a coil voltage equal or nearly equal to the voltage going through the switch currently. Take one wire from the switch and land it on the relay coil base, the other side of the coil would be wired to ground if it is a ground referenced DC, or to whatever common the DC is referenced to. Then parallel the power DC wire to one of the relay’s common terminals and take a wire from a normally open relay contact to the power input of the pump. You have now inverted the logic of the float switch. Omron sells some 6 vdc coil relays. Probably can buy them from Mouser, Jameco etc., you will need the relay base also, they most often can be mounted onto din rail.

[mscottdoran@gmail.com]

Correction it would be the normally closed contact, not the normally open to reverse the logic, sorry for the confusion. I’ll make a drawing of what I’m saying and post it here soon.

[mscottdoran@gmail.com]

Here you go:


As I mentioned above the relay coil voltage needs to match the voltage of the pump power, and the contact rating for the relay you select should be able to carry more current than the pump will draw. Relay contacts will also give a horse power rating which should be more than the horse power of the pump.