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Forum Index : Other Stuff : Reed switch, tank float switch
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| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, Need to stop over filling of rainwater tank using a 24VAC 1" solenoid and a float switch. They seem to work by lifting a magnet close to a reed switch, which then opens up once the float has lifted the magnet close enough to the reed switch with the float arm in a horizontal position. Problem is those sub-$10 float switches on Fleabay do not tell me the wattage they are happy to switch and if they do, then it might be DC, not 24VAC. Or they come without a nut on the thread for mounting inside the tank. Any guess here what I must do? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
The DC & AC rating are very similar. Issues generally only arise at higher DC voltages where arcing across contacts is more likely to happen as the voltage does not swing through zero. Do you have any other characteristics of the solenoid, like the current it draws? Either Amps (A) or milliamps (mA)? Or maybe the wattage. Something like this will handle 0.5 amps, which would be 12 Watts @ 24 VAC. I'd think solenoids would use under 10 watts. Cheers. |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi Phil, Thanks for that. Dr Google tells me such a solenoid uses about 0.3A (holding) and a bit more for the inrush. Do you think the reed switch can handle something like that? dom Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Have a look at the Altronics catalogue (page 302) or their web site. They sell 2 types of float switch item numbers S 1160A & S 1163A. The specifications are given in detail. e.g. the switching current is 1A DC. If you're using DC, you will need a diode in parallel with the coil in order to reduce the back EMF when the solenoid is released. If AC, you need a capacitor & resistor in series across the coil. EDIT: If you wish, I can calculate the R & C values for you - but I need to know the inductance of the solenoid coil.. |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks for the help with this problem. I have ordered a floatless level switch, which has a contact rating of 5A at 250VAC, which can easily drive a timer at 240VAC and an attached transformer to 24VAC for the solenoid. My son as a chemical engineer does not like those switches, which use the resistances in the rising and falling water column to switch something on or off, hope, hope. They use three electrodes in the water column of the tank. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
You're welcome. I've never heard of a floatless level switch. Could you give me more info please. I don't fully understand your second para. Are you talking about the floatless level switch? If so, I agree with your son. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
even with plastic tanks and rainwater corrosion seems to get the better of them, they work fine while they are new and shiny, but not long term. I'm confused, no wait... maybe I'm not... |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Larny: One electrode is at the top, where I would like to switch the solenoid off. A second electrode is at the level where I want the solenoid to open to fill the tank. The lowest electrode measures the resistance of the 2.7 m os so of the total water column and is at the bottom. I believe some clever comparison of resistances of the column is used to switch on/off. A clever system, but as yahoo says, perhaps not the best. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
Dom have you considered a pressure gauge with high and low adjustable alarm settings. Clearly more costly but should be more reliable also, you may have to scratch around a bit to find one but IMHO worth the effort. Cheers Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi Allan, Have seen tricks like that once before and remember links to pressure switches. Is this my friend Allan of Wokalup fame?? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| larny Guru Joined: 31/10/2011 Location: AustraliaPosts: 346 |
Silicon Chip have published several water level articles in the past. One of the 2007 ones used a pressure gauge & the 2011 did it by ultrasonic measurement. See:- Water level indicator 2002-04 Water Tank Level - PIC based 2007-11 Water Tank level gauge - Ultrasonic 2011-09 Water Tank Level Indicator 2007-07 I have all of these mags & can scan any article if you wish. |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
Hi Dom yes. A pressure gauge with alarm contacts is a convenient option as it can be remote from the water source (here it could be argued that at times flow may affect the operation but.....). However when the gauge is placed at the height of the bottom of the tank it also tells us the level of water in the tank. In your case if you had a 0-50 kpa gauge then 37 kpa would = full tank. Consideration of pressure surges from your pump must be considered if it pumps into the outlet pipe as opposed over the top. allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks for the help and offer of scanning. Will see how well or badly the floatless level switch is working first. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Pete Locke Senior Member  Joined: 26/06/2013 Location: New ZealandPosts: 181 |
There are many and varied monitors for level control out in the big wide world. At the dairy plant here in Hokitika we use these for sump level indication (same as a tank, only below ground) http://www.multitrode.com/products/multismart-and-probes/liquid-level-sensing-probe/ It will give you a 4-20mA output, as well as dry relay contacts. Not saying you should buy one, but just another idea maybe for considering as a concept. And yes, they do work in clear water. Cheers Pete. |
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| isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689 |
often washing machines (ie clothes washer) use an air pressure switch to detect water level. It is arranged simply enough, the sensor inlet is a pipe extended downwards to meet the rising water level, and as the water level rises at some point it starts raising the air pressure in the pipe. The one I saw was a a basic membrane and switch contacts in a robust housing from a un-electronic model, probably switched a relay to control the valves. Must be very obdurate and reliable you would think. |
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