0n/off switch

[dfurlano]

I know what I would like but I don't know what it is called.

I would like a switch that will turn a 120v motor on and off when hit. But I need a switch with a sensitive touch mechanism. Basically I want to create an automatic fluid return system and the pump needs to turn on when the level is high and then turn off when the fluid level is low. I have a pump and I just need a switch then I can mechanically create a float to actuate the switch and turn the motor on and off.

I have limit switches but they are NO or NC. I need something like a limit switch but like I stated - will turn on when hit and then when hit again will turn off.

I looked for detection switches and snap action switches but they seem to only work momentary while pressed.

Any insight on what type of switch I should look for would be greatly appreciated.

TIA

Dan

[Al_The_Man]

There are several way to do it, depending on the mechanics etc.
What has been done in the case of a VAT say, is to have a N.O. switch at the top and a N.O. switch at the bottom they are wired in series and operate a small relay with two N.O. contact on, one contact is wired across the top N.O. limit.
The other switches on the motor.
A vertical rod runs the height of the VAT, the rod has a float actuator that will trip the limits at the top and bottom.
If the VAT is empty the bottom switch is open, and closes as the VAT fills, the motor does not turn at this point, once the upper sw is operated by the full VAT the motor picks up until the VAT empties and the level reaches the bottom limit.
It can also be done with two dedicated float switches if you wish.
This is the basic logic, it could also be done with two limits and a Smart Relay
EZ Series Intelligent Relays : Intelligent Relays, the programmable smart logic relay they can be had cheaper than this for 4 output 6 input, especially off ebay.
Al.

[doorknob]

You can buy ready-made float switches (try eBay, for example).

You might also be able to make a float switch using a sealed "reed switch" affixed to the tank at the proper level (inside or outside of the tank, as long as the tank walls are made from a non-magnetic material), and a magnet attached to the float (and constrained to move within the proper proximity of the reed switch).

If I were designing such a setup, I would probably keep high voltages (including 120 vac line voltage) removed some distance from the tank and liquids, and instead use a lower voltage through the float switch, which in turn could actuate a relay for controlling the higher voltage.

As far as momentary vs. sustained switch operation, I would use some electronic logic circuitry, which could be fairly simple, to handle that.

[vger]

A single reed switch with a biasing (holding) magnet would work for you. The reed switch has a small (weak) biasing magnet attached to it. The biasing magnet is not strong enough to cause the reed switch to close, but once closed it will hold it closed. A pair of magnets on a float assembly would be oriented so that when the level is high, one of the magnets oriented the same direction as the biasing magnet, the reed switch is closed. The other magnet on the float is oriented opposite the direction of the biasing magnet and when it gets close to the reed switch, it opens. Use fairly weak magnets on the float, especially the one that causes it to open to avoid it's strength from totally over powering the biasing magnet and closing the switch.

Steve

[jalessi]

Dan,

Stak Enterprises might have a simple solution.

Electronic Float Switches for Sump Pumps

Jeff...

[dfurlano]

This is what I ended up with. I wanted a gravity feed coolant system with an automatic return. I used a 5 gallon bucket and a sump pump switch ($12 Lowes)and a transfer pump ($30 off ebay). Needed some tubing and fittings my guess is less than $20. I also bought a filter for about $15.

Here it is on the test table.



Here is a close up of the bucket and pump.



Here it is in place.



Close up.



Mill with the coolant.