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Forum Index : Solar : simple flame detection in HWS
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| rgormley Senior Member  Joined: 22/02/2006 Location: AustraliaPosts: 245 |
looking to have a LED light when the ring burner comes on my solar panel hot water setup something that will have simple open/close a contacts (i will do the led part) when it detect flame /heat from the gas burner. ideas?? jaycar electronics resettable 50Deg thermal switch pop riveted somewhere near the burner on part of the metal work jaycar electronics resettable 50Deg thermal switch mounted on a bit of right angled brackedt mouted close to the flame source. http://jaycar.com.au/productView.asp?ID=ST3831&keywords=ther mal&form=KEYWORD http://www.ebay.com.au/itm/DFRobot-Flame-sensor-FREE-CABLE-/ 160626199603?pt=LH_DefaultDomain_0&hash=item2566114c33 i think the wave length of natural gas will not trigger this???? i have a capillary tube thermostat but it has a huge copper/bras? bulb and the tine hysteresis is to long after it heats and and closed the contacts the flame goes out and the bulb take 2-3 minutes to cool and open the contacts. actual flame detector from a Gas hot water service (outputting Milli volts??) when heated? will need transistors to drive a LED (to much stuffing around) help!! 
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| aargee Senior Member Joined: 21/08/2008 Location: AustraliaPosts: 255 |
What about detecting the resistance of the flame, flame ionization detection. Flames are conductive, all you would need are two wires sitting in the flame and measure the resistance? Never done it myself, but look here , might be worth an experiment. For crying out loud, all I wanted to do was flash this blasted LED. |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
hhhmm sounds a little to finite... small changes in resistance (meg ohms i presume?) will need electronics to see that kind of change in resistance.....to complex i`m shooting down to a local parts place in the morning to see what they have off the shelf... |
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| Georgen Guru  Joined: 13/09/2011 Location: AustraliaPosts: 462 |
Not sure how it can be done, but sensor for lights that come on at dusk would turn off when flame lights up. Bit in reverse what you want to achieve, but some kind of signal anyway. George |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
the faster acting flame sensors are oxygen depletion sensors, ionisation detectors and UV photoelectric sensors they are sometimes part of the auto igniter on heaters, stoves, furnaces etc. the first two go in the flames, the photoelectric sensor looks at the flame through a slot or down a tube. If you are after something simple and cheap how about a frying pan thermostat DIY temp switch yahoo I'm confused, no wait... maybe I'm not... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The bimetallic temperature sensor method is by far the simplest method, where speed of response is not an issue. Flame ionization detectors work well. A flame is electrically conductive, and that is very easy to detect with a polarising voltage, a very high value resistor and a very high impedance voltage threshold detector such as a CMOS logic gate or MOSFET. Many gas water heaters use a thermocouple probe in the pilot flame. This only generates a few millivolts, but it can source a few tens of milliamps. Certainly enough to pull in, and hold in the main gas solenoid valve, which releases if the pilot flame goes out. Cheers, Tony. |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
thanks for the feed back and ideas. The DIY temp switch site gave me an idea that i will look into. The fry pan has a stainless probe with the bi metallic switch contacts inbuilt. If i have a dig in our local "op shops" i`m sure i will pick up a frypan for a couple of bucks. The rest is easy from then on...... So yes the back shed has fullfilled me ideas once again.... (oh funnily enough as for detecting the gas burner, we had 38 and 34 deg days here so the burner wont come on anyway, as my 270 ltr`s is up around 56 deg!!) but come the cooler days, and a little extra hot water usage, yes i will be burning some gas.... just like to see it with a indicator LED. |
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| AndyL Newbie  Joined: 27/02/2012 Location: CanadaPosts: 3 |
http://www.ladyada.net/learn/sensors/thermocouple.html Maybe not so simple, but arduino, thermocouple, still cheap - and way more expandable, if perhaps you want to know the bigger picture later... |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I started reading this thread and the idea of a frying pan thermostat jumped into my head, but I see Yahoo got there before I did. Those fry pan bi-metal sensors are pretty reliable, and you can fiddle with the spring tension to get a wider range of temperature sensing. A simple once use only flame detector is a length of solder between two fixed posts. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I found an old general electric one (mid 1970's ?) that triggers in under 2 seconds so there are some goodies out there. I'm confused, no wait... maybe I'm not... |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
picked one up locally for $10 http://melbourne.gumtree.com.au/c-ViewAdLargeImage?AdId=3358 42953 will have to run a relay as contacts are closed when cold and they open as it heats up (makes sense in a fry pan.... 
just need to run 12vols to the bimetalic contacts to a coil of another relay then use the contacts and run up to a LED with a limiting Resistor. i played with the probe/bimetalic switch near our stove top, works fine! 20 second hysteresis but i can live with that. the inbuilt handle thingy is some form of Bakelite so should take a fair amount of ambient heat from around the gas burner ring. OR i`ll just scrap the handle and mount the thermal probe+bi-strip contacts on a bit of metal bracket. and mount near the flame. we have fire rated cable at work i can use for the connections, bonus! |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
A bimetallic "Clixon" sensor from Jaycar part number ST3831 closes at 50C and costs only $5.75 brand new. The ST3821 opens at 60C and costs the same. If either crap out in service, you can very easily get a replacement. These are very common industry standard parts, available with both normally open, and normally closed contacts in a wide range of temperatures. Readily available on "flea-bay", and many domestic appliances you can find down the rubbish tip for free. For example, tumble dryers, and microwave ovens always have these as over temperature cut outs. 
Cheers, Tony. |
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| rgormley Senior Member Joined: 22/02/2006 Location: AustraliaPosts: 245 |
yes i do have this unit (added to my artillery of thermo devices) it has a fair temperature hysteresis though.... will play with the optical flame detection unit i got of flea bay. (when it arrives) that should give me a flame on/flame off outcome... most bimetallic or thermo driven devices have a fair hysteresis swing |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
They sure do, and they can be pretty slow to operate/release too. For many applications the simplicity, high current carrying capacity, and low cost make them a very good solution, but not always. Cheers, Tony. |
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