Hall Effect sensor

Richard Burns · Aug 4, 2012

I am having problems with a home built magnetic water level sensor using a reed switch, whereby the reed keeps sticking or failing to operate and I was thinking of using a hall effect sensor and a power transistor but I am unsure of the characteristics of hall effect sensors.

Are they susceptible to failure on exposure to high magnetic fields and are they sensitive to the angle of incidence of the magnetic field.

For clarification this is for a solar powered rain water recycling system running a 24W 12V water pump, I am trying to keep the circuit as simple as possible: magnet floating in water as water falls it activates the reed switch and switches on pump until water level lifts the magnet away from the switch. let me know if you need more information.

Cheers

ruston · Aug 4, 2012

Would a float switch do the job ? or something like a totally enclosed roller shutter type reed switch ( alarm system) with relay.
12v Float Switch: Amazon.co.uk: DIY & Tools

telectrix · Aug 4, 2012

i'd use a float switch. simple mechanical, nothing to go wrong.

johnboy6083 · Aug 4, 2012

A liquid level relay would do what you need. You will have to use level probes, but these can be made from all sorts. For fixed levels I've used bolts drilled through a tank.
I don't like float switches, as in a pervious job I've had a lot suffer from mechanical failure.

Darkwood · Aug 4, 2012

http://docs-europe.electrocomponents.com/webdocs/01f5/0900766b801f5ac3.pdfetter

Have a look at this its a floatless level controller but ive used them for various things including 'wire break' relays to shut machine down.
Buy Level Controllers Floatless level controller w/alarm o/p Broyce Control EFLC3 230VAC 50/60HZ online from RS for next day delivery.
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Richard Burns · Aug 4, 2012

darkwood said:
http://docs-europe.electrocomponents.com/webdocs/01f5/0900766b801f5ac3.pdfetter

Have a look at this its a floatless level controller but ive used them for various things including 'wire break' relays to shut machine down.
Buy Level Controllers Floatless level controller w/alarm o/p Broyce Control EFLC3 230VAC 50/60HZ online from RS for next day delivery.
.

Hmm.. looks good but slightly over specced for what I want to do and may be difficult to connect to a 12v system. I will admit it will work, but it would take my total budget to buy that!

I will have a think about level sensors and see if I can't make something up, but tending toward the float senors so far as they can't have more mechanical failures than I have had so far!
I really ought to be designing a full system with appropriate controls for alarms, overflow, supply voltage, etc. but I am too lazy!

ruston · Aug 4, 2012

Here's another link that may help with some of the suggestions you have been given.

Level – Applications Engineering

Darkwood · Aug 5, 2012

Richard Burns said:
Hmm.. looks good but slightly over specced for what I want to do and may be difficult to connect to a 12v system. I will admit it will work, but it would take my total budget to buy that!

I will have a think about level sensors and see if I can't make something up, but tending toward the float senors so far as they can't have more mechanical failures than I have had so far!
I really ought to be designing a full system with appropriate controls for alarms, overflow, supply voltage, etc. but I am too lazy!

rich its an example but their are different float level relays out their that have 230 input so saving a 12v DC supply unit and dont rely on sensors as such but voltage.. so no wear and tear on moving parts etc

jumpin jax · Aug 5, 2012

You could try a pressure switch style as you have in a washing machine working on pressure up the tube to activate contact, never really known a washing machine one to go wrong but am no doubt going to be corrected.

plugsandsparks · Aug 5, 2012

I sometimes work on water treatment plants and we use level switches. You may be having problems with the reed if you are trying to pass too much current through it.
You really need a relay between the sensor and the pump.

johnboy6083 · Aug 5, 2012

i agree. ive always done this out of habit, as the cost of a relay is nothing compared to a pressure switch, liquid level relay ect.

Richard Burns · Aug 6, 2012

plugsandsparks said:
I sometimes work on water treatment plants and we use level switches. You may be having problems with the reed if you are trying to pass too much current through it.
You really need a relay between the sensor and the pump.

That was one I had tried to avoid thinking about, the reed switch is from my local independent electronics shop and does not go in for technical specs so could well be overloading it. I have not got any relays that will take 2A, may have to splash out £3, hmm!
I have realised this is easier to set up than I had thought as the switching can be at the tank and the relay at the pump and I can use the existing wiring, probably works out cheaper than a float switch, I still have about three reed switches left so could be a good alternative.
I could also easily add in control switching to the coil circuit as and when required.
I can't think of an easy and cheap way to manage a level sensor with bits I have here or without spending too much money and having to set up a control circuit.
A pressure switch would not be applicable here as it is a non pressure system, and solenoid switches would consume too much power for the solar, especially as I am using second hand batteries. Now I think about it I should try harder here!

Thank you for all your help, certainly got me thinking about it better and given me some good alternatives, and made me think I should set this up properly.

plugsandsparks · Aug 6, 2012

Just pulled a 12V 30A relay off a car (well a spare really) and it will pull 144mA on the coil, so i think your reed should be able to pull that in and they are ten a penny at the breakers. Perfect i would have thought.

Richard Burns · Sep 2, 2012

As I said in post 6 I am far too lazy however I have managed to modify the set up, I am still waiting for the float switch to arrive so I have wired in my last but one reed switch, but I am now taking it through a relay.
I have also tidied up the mess it was in before (to some extent). Thinking as an electrician rather than a home built mess did help and posting did get me to think about it and solve some of the problems.
I would like to thank you all for your suggestions and (with some trepidation) show you the improvements made.
It is working at the moment, but should be more reliable with a specific float switch, rather than my home built job.
I have gone for maximum cost saving using any parts I could find around the place and think the total outlay for the mods was about £5! (quarter of my monthly food budget!).
Thank you

DPG · Sep 6, 2012

I think you've probably got it all sorted now, but just to confirm, reed relay contacts will stick at fairly low currents, especially with an inductive load like you've got there. Daz