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Forum Index : Microcontroller and PC projects : How Log When Gas HWS Runs?
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| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Thermocouples do not change in resistance, they generate a quite small dc voltage due to the "Seebeck effect". That is probably why your ohm meter went negative. Try it again on the dc millivolts range. The voltage generated is only going to be a very few millivolts at most, and much less convenient to use than a direct simple flame sensor using a stainless steel electrode which can much more usefully swing by several volts. Thermocouples are used as flame sensors in some gas appliances that have no electronics or electrical power supply. Although a thermocouple can only generate millivolts, it can source a few tens of milliams of current as the source impedance very low. So the method used to initially light up the pilot flame is to manually hold down a lightly spring loaded button that opens the main gas valve. You then light the pilot flame either with a match or a high voltage piezoelectric igniter. You wait a few seconds and release the button and the pilot light stays lit. If the pilot is not lit or goes out, the main gas valve closes when you release the button. The magic ingredient that controls all this is a thermocouple in the pilot flame, and a weak electromagnet that holds the main gas valve open. This electromagnet is energised by only the few tens of millamps coming from the thermocouple. If the pilot light blows out (in a wind storm) the electromagnet releases and shuts off the gas supply. Without that, the gas supplying the extinguished pilot light could build up inside the gas appliance and cause an explosion when someone tries to relight the pilot light. The thermocouple involved is perfect for that application, but if you want to use it as just a flame sensor, you would need a very sensitive voltage detector that would detect the presence or absence of only a very few dc millivolts. Possible, but why do this the hard way ? For gas appliances that do have a 230v electrical power supply, the flame sensor is much more likely to be a simple stainless steel spike in the pilot flame that often runs quite visibly red hot. Edited 2019-09-22 09:29 by Warpspeed Cheers, Tony. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 840 |
Hi Tony, Thanks for that explanation - it also helps make sense of my Googling of DMM -ve values etc. I'll go back and revisit the suggestions of CaptainBoing et al. Many thanks to you all, Andrew |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
 Cheers, Tony. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2287 |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
A K type thrmocouple will certainly measure temperature, but it will quickly die in a direct flame above about 1250 Celsius. Getting back to the thermocouple and relay idea, you can try it, but its a rather special and complicated problem. The voltage is EXTREMELY low, so even measuring the current with a multimeter will be problematic because the current shunt and multimeter leads will probably have enough resistance to themselves reduce the current. A relay needs far more grunt to operate than to keep it operated. You might find that a 12v relay requires 10v to pull in, but will stay operated until the voltage falls to perhaps only two or three volts. These gas solenoids have few turns of amazingly thick wire (to keep the resistance down). And there is very little spring pressure of a hair thin spring in the solenoid to work against. The valve is opened manually and the magnetic path closed with a push button. The thermocouple only has to create minimal holding in power. Here is a video: https://www.youtube.com/watch?v=7m5ZDvOoVwU I don't think any normal reed relay would be up to the job. The thermocouple for it is pretty special too, usually uses platinum family metals that will not burn up or oxidise at continuous glowing red hot temperatures. They can be fairly expensive as well. Its pretty simple yet also in a way exotic technology that has been around for a very long time. Modern gas appliances usually now with a microcontroller just use a simple stainless steel electrode which is vastly cheaper and far less troublesome. Edited 2019-09-22 12:17 by Warpspeed Cheers, Tony. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 840 |
G'day to you all, An update - MM to the rescue! Recognising that the HWS was sick I set about replacing the most likely, and coincidentally cheapest, parts first - all the way to the AU$170 main gas control unit. A lot of lying on the ground in all weather. The pilot still wouldn't stay lit! But then, thanks to my MM-based plot of temperatures, I noticed that the pilot only went out when the gas hydronic heating was running. There appeared to be a gas supply problem? A call to the gas supply company and 30 minutes later (on a pubic holiday too) a guy came out and said "you've got water in your gas pipes", arranged for it to be pumped out by another team, and replaced the ancient meter - all free of charge. He even suggested a refund of my expenditure on parts from my gas supplier. So, while my simple temperature probe in the flue isn't precise, it did do the trick! I now have a probably working set of parts that I may be able to fashion into a precise sensor. AND, subject to any refund, free of charge . . . Many thanks to you all, Andrew Edited 2019-09-28 08:53 by Andrew_G |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Great news Andrew, I was about to suggest using one of those current sensing coils over the power lead to the solenoid.. But you have the result you wanted.. As an aside when our HWS tank decided it was time to leave this mortal coil we opted for an on-demand gas HWS which is much cheaper to run as you only use gas when the hot water is needed and do not have to store hot water in a tank as a reservoir.. incidentally this water should be above 60c (I think) to avoid legionella and other bugs from forming.. We have a panel where we can dial up the desired temperature up to 50c on one panel (in the kitchen) and 60c (in the en-suite) hence I can have my 45c shower with no cold needed to adjust and the missus can set 42c for hers (woe betide me if I forget to adjust it back for her).. If your setup ever dies I can fully recommend going down this tack, you never run out of hot water providing you have gas and electricity to power the controller. The one down side is if you have a power blackout or the gas supply stops (as happened in Victoria about 15 years ago when an explosion at the gas plant took out our gas supply for a week) you have NO hot water (not even tepid) because no water is stored.. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Did you find your gas bill went down with the instant system? I have read a number of conflicting reports on this. Some say the instant systems are Cheap and inefficient and others say they are more efficient. I remember a c0ouple of my aunts houses having the old instant heaters on the kitchen wall. Scared the crap out of my brother once getting him to look carefully inside the observation hole and cracking on the hot tap which caused the thing to light up with a Mighty whoosh! nearly sat the poor kid on his Butt. None of this safety sissy temp regulation with these things either, They would supply the full water flow at pretty much boiling temperature. I remember one aunt never boiled a kettle, didn't even have one. just waited for the hot water to come out the tap and made the tea with that. No one ever complained about a cold Cuppa! The instant makes more sense to me efficiency wise but I have read that storage is better. No experience either way to know and don't have gas but interested in your thoughts. I have seen these and would love to have one. Half of my showers are fiddling with the water to get the right temp and then if someone turns on a tap or flushes the thunderbox.... I was going to get LPG put in a few weeks ago for the new stove we bought for the full kitchen Reno. So many rules and regs and stuffing about where the tank could be, I went and bought an all electric stove. Anyone in the market for a Brand new unused 900 MM Westinghouse stove going cheap in sydney? :0) I wonder it there is a regular/ mixer that will allow dial up temps from electric heating? I'd renovate the bathroom just to have one of those! The one down side is if you have a power blackout or the gas supply stops (as happened in Victoria about 15 years ago when an explosion at the gas plant took out our gas supply for a week) you have NO hot water (not even tepid) because no water is stored.. I remember hearing 1000 Times as a kid my grandmother saying she would NEVER have an electric stove. Blackouts were frequent then and she always said that in a blackout, she could still cook my grandfather a hot meal when he got home from ( shift) work which seemed very important to her. She thought it quite essential for a man that had been at work all day to have a hot meal when he got home... even in summer ! :0) I'd still say you are probably at better odds with gas than electric for you hot water storage or not. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1985 |
really doubt it. The Wiki Article suggests the voltage will be in the order of micro-volts, maybe 1 or 2 millivots when really hot. Even with a few milli-amps avalable, I doubt you find a relay with a coil voltage of 2mV  On the subkect of the MAX6675, I found them to be quite unreliable. a big difference in measured temperature and wanders around a lot when compared to a lab mercury thermometer. Used one in my re-flow oven where it didn't really matter if it was 5C out but it often was. Really disappointing coz I was expecting superior measurement. That was with a number of different couples too. Maybe I had something awry but I worked on it over a few days and in the end had to settle to a very "ball-park" measurement. Maybe someone else had better experiences. |
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| Andrew_G Guru Joined: 18/10/2016 Location: AustraliaPosts: 840 |
Hi Mick, Good to hear from you. Yes I remember the Longford gas incident (20! years ago). We had a combined gas hydronic heating and HWS unit - I was living/working interstate at the time. Jackie was showering with family etc with a few oil filled electric heaters around the house. The combined unit died so we now have separate heating and HWS units. (You may recall our house is due for demolition so I have been trying to keep everything alive for "another" month or two (town planning has been dragging on - nearly there). The new McMansion will have separate heat pumps for the HWS (with storage) and heating. There will be solar panels (& batteries in due course). We may not even have gas connected.) It's interesting to watch the HWS temperature graph, it gives short bursts with only a 5deg rise in flue temperature approximately hourly, even overnight, but kicks in more when we shower etc. It only took an hour to heat up from a dead cold empty tank. I think it has a 150 litre tank but a hefty instantaneous heating capability. This has been a useful exercise and we'll certainly have to watch when we shower etc with the new house. (It will be mains connected and the heat pump is supposed to be more efficient than gas anyway). Cheers, Andrew |
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| BrianP Senior Member  Joined: 30/03/2017 Location: AustraliaPosts: 292 |
My 2c worth... We have what was an all-electric household from back in the day when using lots of electricity was officially encouraged - circa 1970.s - how times have changed. 3-phase supply from the pole (you wouldn't want or get that now), 24kW of floor heating, & 3-phase instantaneous water heaters for the kitchen & ensuite. A 315L storage HWS for the back section of the house - laundry & bathroom. Today: We can't use the floor heating because of the cost. We have 3 split-system aircons in the main living areas - lounge, study & kitchen - very efficient). 2 x on-demand gas water heaters - kitchen & ensuite. The existing storage HWS for the laundry etc. (uses 3-4 kW per day mainly to maintain the storage temp.) My plan for the future: More solar panels & batteries so that I can generate & store enough energy to last over 24 hours. I don't know what to do about the gas water heating - the kitchen is sink only so lasts a really long time - the ensuite, well if you like a really long hot shower... (I don't think we have enough solar at latitude 38 south to have a viable solar HWS system). So, the upshot of all this - what? Help! B Edited 2019-09-29 13:18 by BrianP |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I have a LOT of solar and for winter heating where I am (34o) I have given up on it. It's not even the fall off in output at any given time seeing I have all the inverters on about double panels, it's the halving of generation hours that's the killer. I was still pushing 3KW + on a 3.6 inverter but instead of it running that for around 6 hours, in winter it's doing it for 2. Maybe. 24Kw is a completely impractical amount of power to be trying to generate in winter from solar even if you have a spare acre close to the house to set up panels in. I have read the split Vs ducted AC many times. I asked a mate about it that does High end AC ( Hospital's and operating theatres, Labs, heat pumps etc) about it. He said the efficiency of the units is no different, it's more of a throw back from the old days people still hold onto. He said the modern inverter units will throttle and if you only want one room cooled, that's all the will do. He said if you want multiple parts of a house cooled then one would be better off with a PROPERLY installed modern ducted. He said a lot of the old inefficiency was from the single layer ducting which hasn't been used in decades. with the new insulated ducting the efficiency loss is negligible and you are going to loose loads more efficiency by opening a door or even boiling a kettle in the same room. He also said there is going to be more efficency losses in running Multiple splits than one Big Ducted unit Gas, bottled or town has a supply/ rental charge attached which also has to be figured into the cost. That said, I was planning to build a frame and just Use 9Kg BBQ gas bottles for the LPG stove we were going to have put in a few weeks ago. $30 to buy, no rental costs. Was told by everyone stove 45 Bottles last forever so 9's should have been fine. May not last so well with water heating but if they lasted a fortnight or a month, may not be too much of a hassle to have refilled. Agrees with my calculations. From a cost POV, eveything I have looked at says the second you go to batteries, you are COSTING yourself money. High as it might be, -I- have not found anything to be cheaper than the grid or near it. I would STRONGLY encourage you to do very careful costings on going batteries before going down that road. There are lots of convoluted and twisted calculations I have seen for batteries but for me there is one very simple one: If you calculate 100% Cycling of the battery every day ( which is a practical impossibility) will the amount of power stored/ recovered be worth more than the cost of the batteries and associated equipment ( inverters etc) over their useful life? I have not found ANY battery that have a positive ROI against the cost of grid power. Yes, I have read endless " My bill was xxx and now it's only half/ third of that then the next thing you read is the person spent $20K+ to lower the bill. Often they will say it has a 5 or whatever year payback but if you look at the numbers, they NEVER add up. The best home battery I can see certainly cost wise is used forklift packs. They have the capacity well and truly, they are 3-4K for something suitably sized, they can be bought guaranteed and are minimal maintence -IF- they are set up right with an auto watering system. They also have the advantage of being worth good money when they are dead as scrap unlike Lipo etc atm. That said, if you amortise the cost of the batteries and other equipment which WILL wear out, then they STILL work out considerably more exy than grid power whether you charge them from solar for free or not. From what I have seen, Solar only is the best way to go. If you are not too worried about all the rules and regulations that are largely designed by the power industry to keep their $2.7 BILLION a year NET PROFITS rolling in, then put up all the damn ( used) panels you can. Again, cruch the numbers though as to what the ROI is going to be. I could get my Bills down more than I have now BUT, the reality is I'm saving the MOST money pretty much where I am and paying the power companies something rather than getting caught up in sticking it to them and going off grid. They provide a real beneficial and useful service I am prepared to pay something for even if I do try and Minimise it. I'll bet if you said to a lot of people off grid, you can have endless 24/7 Power as much as you need such as with certain high demand short term things you want to run for $25 a week, most would jump to it. That's pretty much what I have and looking at the alternatives, I appreciate it. Not to say circumstances won't change, I'm EXPECTING they will, but for right now, I'm on the best wicket I ever can be. Again, looking at the cost of 9 Kg bottles you own may be worth while. Depends what the 9 KG refills go for in your area. I have seen those swap bottles go for over $40. The local Servo charges $18 atm. It's real easy and cheap to try and see how you go with the 9 Kg's.. They fit the same as the 45's so all you need is something to sit them on at the right height and get one filled, screw it in, see how long it lasts and do your sums. DEPENDING on how much solar you have, what the rest of the house uses, how much hot water you go through and the price of haddock in Gdansk, I think solar HW -may- be viable although probably needs to be looked at over a year rather than a quarter. Winter will be a writeoff but there is every chance your summer costings could be zero and Autumn/ spring well if not full covered as well. Again, it's just crunching the numbers that relate to YOU and your circumstance. With hot water, there is nothing stopping you taking that off grid and throwing as many used panels as you want at it and not interfering or putting more load on your grid connected system the house runs off. Must go down see my friendly scrappy bloke and get some heaters to play with this week. I want one for a solar pre heater for the HWS, I want one to make a smoker BBQ out of and one to weld bolts all over and make a lawn aerator with. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
"24Kw is a completely impractical amount of power to be trying to generate in winter from solar even if you have a spare acre close to the house to set up panels in." Yes, but that figure is for the whole house - back end 3 bedrooms, laundry, bathroom. Hardly ever used these days (Darby & Joan)... We are only really interested in the main living area (lounge room) which is well served by the split system aircon anyway. So the floor heating is basically fully redundant (unless I can put a nuclear molten salt reactor in the back yard). Down here in southern Vic the aircon is mainly used for heating. "Gas, bottled or town has a supply/ rental charge attached" Our local gas supplier does not charge a rental on the bottles! A refill currently costs $125. "From a cost POV, everything I have looked at says the second you go to batteries, you are COSTING yourself money." I have just purchased 6 x 120AH NEW (liquidation auction) batteries for $1/AH. This will help the storage side of the equation a little. "I have not found ANY battery that have a positive ROI against the cost of grid power." I agree, but I'm not looking to replace the whole grid usage - just how much I can reduce the grid bill on an on-going basis. The other issue on my mind is the ever-looming threat of blackout/brownouts because of the lack of base load grid. I know I will never recover the cost of the solar/battery/inverter installation, but at least I can have that warm fuzzy feeling.  "From what I have seen, Solar only is the best way to go." Yup! Everything else has a higher ongoing maintenance cost attached, e.g. wind. I'll have to take a trip up north one day so we can cry on each others shoulders...  B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
Davo99 said: "I think for the most part, wind is now dead. There aren't a lot of places Solar won't produce more power for a lot less money. Some of course but the bang for the buck equation with solar is hard for wind to beat. Not much to have a 5KW setup with solar, that's a pretty substantial turbine however and it has to be in the right spot." The only advantage I can see for wind is that unlike solar it "can" run 24/7. Not here at the moment though - it's currently 0/0... Edited 2019-10-02 09:36 by BrianP |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Yes the 24/7 potential of turdbines does mean you can have a smaller alternator that adds up to good power over the course of a day. If you are in the right spot you have the advantage of power at night too. I think the amount of places that can happen is fairly Limited though. I think Scotland, Wales, parts of the UK and Ireland as well as a few other places have good wind but here in Oz I think for a domestic setup, the locations are far and few between. Personally I hate wind with a passion. I find it highly destructive and annoying and easily makes even a sunny day pretty useless and Miserable. But I'm just a cheery sort of bloke that always looks on the bright side so others may not be as optimistic and positive about it as I am of Course! :0) |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
The hardware logistics for a turbine are far greater than that for solar. Mast mountings, guying etc. etc. Also, what happens if a blade shears off in a big wind & injures or worse a neighbor? Then again, I guess a solar panel could break loose & do damage... Having said all that, I have a 500w turbine kit currently un-assembled lying on the deck waiting install. It's been there for nearly 2 years. What do you suggest I do with it? (be nice...) B |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
What I suggest is you do some decent research for your area and do something factual to work out the viability of the thing. It may be near useless where you are or in might make you 20 KWh a day. every situation is different and you have to weight up ALL the factors. If you don't have the wind then it's easy, sell it. If you do have the wind then work out what it's going to cost you to erect it properly and play the cost of that off against the calculated returns. May be you'll be better off selling the turbine and putting the money into more panels. May be your better off getting rig of your panels and putting up more Turbines! :0) My Dads neighbour went off half cocked and bought a turbine. Then realised the logistics of correctly mounting one. He had some BIG gum trees Cut down which the first topped at where the branches started in earnest. I said to him, go get your turbine and get the guy to put it on one of those trunks while the cherry picker is here and you'll have the strongest mast one of those has ever been put on! I have often thought of a turbine just for the hell of it but then I think of the mast I'd need and you can't play with this sort of thing, has to be done right and the winds we get here. I look and see that I'd be REAL lucky to get wind 1 day out of 10 and when we do get it, it's likely to blow the thing to pieces. I think solar is the best option for me but I'm also keen to get my Veg oil fuelled Diesel generator up and running. |
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| BrianP Senior Member Joined: 30/03/2017 Location: AustraliaPosts: 292 |
not in this millennium!!! |
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