Backyard Aquaponics
A place to discuss aquaponics

Its a pressure switch. Very simple and adjustable too! Thats a good idea! They are durable and I have adjusted those down to stop at only a foot of water in a washing machine. (I once worked on appliances for a living). I have one rated to pass 15 amps. Thats not bad.

I tend to think that pulling apart a washing machine, locating and removing the differential pressure switch, modifying the switch and/or putting together the necessary electronic circuitry (simple though it may be) is fine IF one is into that sort of thing. And, no doubt a large number of people here are into exactly that sort of thing!!

But, for those of us who would scarcely know the difference between a resistor and a capacitor, let alone finding and modifying a differential pressure sensor and soldering up a circuit to accommodate it (simple though it may be), I still think my mechanical float switch has potential.

Sorry, just trying to steer the conversation back to discussing my original idea

Its just a switch activated by a 3 inch diaphragm. Many are single pole double throw, so you can have it turn something of or on when the level is reached.

But if you're using a diaphragm-switch purely as a pressure-activated switch (i.e. because you don't know the first thing about electronics), then how do you build hysteresis into the system?

That is, how do you get it to turn the pump on at the low-water point and then stay on until water reaches the high-water point? Surely this would require (a) more than one pressure-activated switch, and (b) a circuit, albeit a simple one.

Jimmy the diaphram will have a spring constant like any microswitch. It will have built in hysterisis. You will not be able to change this easily.
Nor will you (based on your admitted inclination to tinker) probably be able to alter the pressure at which it turns on.
If you could alter the pressure, and wanted large hysterisis, you'd need 2 switches and a contactor (or relay).
I'm sure you can buy adjustable pressure switches from industrial stores. It's just a matter of shortening hte stroke of the diaphram.

jimmy, just use a reed switch. The floating part has a magnet on it. When they make contact voila. You could make this thing tiny.

Agreed Tim, but can you run decent current through a reed switch without it failing closed after a few sparks?
Genuine question, I've never tried to buy reed switches, all the ones I have seen have been low voltage.

Jimmy, if Tim says Low voltage only, it's very little effort to buy a motor contactor (like a relay but designed for high current and wont wear out as fast). So all you need is a 24VDC Power supply, $30, a contactor $10 a reed switch?? and a big powerful magnet, $2 - $30 depending on where you find them.
The magnet then gets inserting into a float. Reed switch goes outside your GB where there's no water to upset it, and contactor goes somewhere clean and dry for 240VAC connection to pump.
This is possibly the best idea. Hard to do with an IBC (where I want to use my float) because of all the steel caging around it.

KP

Here's an interesting one you might want to play with http://www.farnell.com/datasheets/65437.pdf

Yes, low voltage. No problem at all just use it to drive a opto-isolator, then to a triac to switch 240V simple.

So with the reed switch idea, the float drops as the GB empties, the magnet comes into "contact" (magnetically speaking) with the reed, switching the pump on via a relay or equivalent. Then the float moves up as the GB fills, and the magnet moves away from the reed. Now, I have two questions:
(1) how do you ensure the pump stays on, and
(2) how do you get it to switch off when the GB is full?

use two reed switches and a contactor. Tim, surely a reed switch could handle the switching current of a contactor?

please see this postfor more information.

Cheers Sleepe.
It would seem this is a reed switch and magnet in one.
You slide a non ferrous piece of metal between it, and the magnetic flux is distorted enough for the switch to turn off.
So the switch is always on, interfere, and it turns off.
It would be possible to mount these like we mentioned. It is IP65 rated which is submersible if I remember correctly, so that's great.
Now we just need a float with neat little flags on it to hit the switch.

I think I'd prefer prox with a metal float ball, but that's increasing the price somewhat.

IP65 isnt submersible.....IP67 onwards is

Damnit, thanks for clearing that up bk... off by two

BK KP

Did you look at the diagram by Jimmy at the beginning of this thread?