I have several exhaust gas pyrometers in my junk box. Trouble is none of them have a working sensor. It seems most pyrometer sensors fail after a while. I have the correct thermocouple wire but so far have not had any luck fabricating a durable sensor. Has anyone done this and succeeded in making one that stood up to more than a few hours of use?
Where on an air cooled engine is the best location to mount a temp sensor?
If no sensor is available as an option what is the best way to fabricate something home brew.
Most water or oil temp sensors look to be too big to be suitable even if the temperature range is suitable.
Have you looked at omega.com ?
The platinum based PT100 style probes are about $70. http://www.omega.com/ppt/pptsc.asp?ref=PR-13&ttID=PR-13&Nav= (http://www.omega.com/ppt/pptsc.asp?ref=PR-13&ttID=PR-13&Nav=) You can use an ohmmeter to read them because the resistance changes from 100 Ohm linearly as the temperature changes.
Alternatively, Type K thermocouples are cheaper http://www.omega.com/ppt/pptsc.asp?ref=GJMQSS&ttID=GJMQSS&Nav= (http://www.omega.com/ppt/pptsc.asp?ref=GJMQSS&ttID=GJMQSS&Nav=), but since they produce just a tiny voltage, you would need a meter designed to read them, which is an additional expense. The good thing is that replacing the element that goes in the exhaust is relatively inexpensive and the fact is that they do wear out (but that takes many hours, not minutes).
Ooops! : :-[Guess I should explain in better detail. I am familiar with the technique described by Jens and have used that in the lab on previous occasions And I have the Omega catalogue.
I also have the old SS thermo wells from failed sensors. Apart from them being too large physically, it seems a shame to just throw out something that could still work. What I have not yet figured out is how to repair the thermo couple and bed the wires in the well so it is sealed in that white ceramic stuff you can see,
The wires used are actual thermocouple wire ( usually #18 ga or maybe #20 ) but welding the wires leaves them with exposed ends that could short out to the grounded shell of the well. and the typical sensors used on Catapillar or Cummings engines are kinda big for the smaller engines I had in mind.
Yes I know I could buy ready made probes from Omega but being temporarily financially embarassed I simply haven't the $$ to go buy something. Hence my attempt to roll my own.
Quote[/Ok, one last possibility .... Sodium silica .... I do not know if this would be effective as an insulator but it's cheap. The problem I have with potting things is that it really throws the response time of the thermocouple for a loop because of all that mass/quote]
REPLY
Seeing as how the original probes have been potted I don't think thermal response time is a major problem. All the pyros I have seen tend to respond within a few seconds to added loading as throttle is opened up.
Probe failure tends to be vibration induced fatigue where the wire breaks from flexing, If a coiled spring is used to support the wire the break is at end of spring if no spring then the break is right where the wires exit the thermowell casing. either way when the meter is mounted remote from engine and probe is on engine there is vibration. I do have barefoot thermal probes for my test meters but then there is mass in the manifold or the clip used to hold probe to exhaust manifold.
Guys
Have always wondered if a thermocouple out of an older furnace might work? They can be bought new for less than 10 $ and are used to hold open older gas valves. Always thought about trying one, they glow red hot when they are in a pilot flame and give off about 10 milliampers give or take when red hot. Usually last for many years to!
Billswan
And they are all jacketed in copper. The copper would work harden from the engine vibration in short order.
Isn't a thermocouple two partners that share the infliction of thermopiles?
That burning sensation's gotta hurt! For the record, I have no experience in such matters which might best be filed under 'occupational hazards of voluntary lifestyle choices'. :D
And now back to to the actual topic. Sorry I thought this was funny and an opportunity to whore my post count.
Thanks guys now I know :o
Learn something every day.
Billswan
On the subject of thermo piles. The question was asked on another forum. Does a 'thermocouple' in a furnace produce current or voltage. I among many others thought it produced voltage. The correct answer is more current than voltage. It was pointed out the solenoid valve had few turns of large diameter wire not many turns of thin wire to create enough flux to open the valve. I didn't quite believe it so I dismantled a gas valve to find out. sure enough the coil had few turns of relatively thick wire. :o :-[
A couple of years back I read that one truck company was offering a electrical generator of 1kW output that consisted of a exhaust stack section surrounded by "thermo couples" whic hI now realize should have read "thermopiles". Hmmm? Maybe a means to make a non rotating start battery charger if a belt driven alternator for a slow diesel is not practical?
Quote from: elnav on May 05, 2010, 10:28:24 AM
Does a 'thermocouple' in a furnace produce current or voltage. I among many others thought it produced voltage.
I think it is called EMF.
http://en.wikipedia.org/wiki/Electro-motive_force
they use 2 disimular metals for wire.
As explained by the wikipedia file a thermopile is more pf a Peltier- Seebeck effect
EMF is also used to denote Electro Motive Force.
The thermopile used in a furnace probe or the truck exhaust pipe generator is direct heat to electricity conversion without any movement of wires in a magnetic field like that used in an alternator.
The thermopile is recovery of waste heat whereas converting rotary motion into electrical energy is not.
In its native form the Lister or Changfa does not include any charging source for an electric start. That was my point. The exhaust heat first passes through the thermopile generator then to the heat exchanger to recover more waste heat.
I suspect a Thermopile is merely a stack or 'battery' of series'd Thermocouples arranged to produce electric current with voltage as a DC generator intended to drive a DC load. I saw a military unit on sale at a hamfest in the US that ran on a bottle of propane and made a half kW or so and produced nominal 12 VDC. They are not particularly efficient. They require one side of the disimilar junctions to be heated and the other side kept cool. The unit I saw used cooling fins ala large finned heatsinks to do the cooling in air with convection currents or possibly blower fan. I forget, that was many miles ago.
Quote from: Jens on May 05, 2010, 08:00:33 PM
Quote from: rcavictim on May 05, 2010, 07:03:20 PM
I suspect a Thermopile is merely a stack or 'battery' of series'd Thermocouples arranged to produce electric current with voltage as a DC generator intended to drive a DC load.
You would be wrong if you suspected that ..... chances are that the item you saw at the ham fest was based on a Peltier effect device.
Jens,
Really? I am aware that Peltier devices work as DC generators when heated on one side and cooled on the other but I also know that any devices I've seen are manufactured using low temperature eutectic solders and they simply cannot handle much heat without simply melting and falling apart. They certainly cannot handle a propane flame. Do you know of Peltier cells that are made to handle higher absolute temperatures for power generating applications? If they exist maybe they would be attractive for concentrated solar power generation instead of Sterling engine technology. Normal Peltier cells are way cheaper per watt than present day solar photovoltaic, so even if the Peltier was way less efficient compared to the ~15% of photovoltaic, it might make economic sense.
Funny, I was looking at Peltier cells yesterday and thinking about this very thing!
Here's how to use a thermo-couple in chp.
Lloyd
http://www.cyclonepower.com/works.html
(http://www.cyclonepower.com/images/cyclone_engine.jpg)
Lloyd
Man you come up with the darnedest stuff ;D ;D
After reading about the cyclone engine I am sold, wounder how much they cost?
Says it can run on WMO, wow.
I will take 2 please.
Billswan
As a side question, does anyone know what sort of exhaust gas temperature one can expect from a single cyl Lister? I'm thinking of fiddling up a thermocouple based temperature sensor circuit which will plug into my fledgling Arduino-based ECU, and since the 1000oC sensors are ~£12.00, I'm wondering if I can get away with a lower temperature probe...
Unless exact temperatures are necessary so as to prevent overlooking the engine the hand held IR thermometers are usually sufficient. I have used mine to detect faulty injectors by noting which exhaust port ran cooler from a misfiring cylinder. Reading a manifold may not be quite exact as reading the actual gas stream but it comes close.
Burning diesel under normal full loading tend to burn at around 750F
Quote from: elnav on May 06, 2010, 10:21:02 AM
Unless exact temperatures are necessary so as to prevent overlooking the engine the hand held IR thermometers are usually sufficient. I have used mine to detect faulty injectors by noting which exhaust port ran cooler from a misfiring cylinder. Reading a manifold may not be quite exact as reading the actual gas stream but it comes close.
Burning diesel under normal full loading tend to burn at around 750F
The purpose behind reading the exhaust temperature is three-fold:
1) It's an interesting data feed for the data logger
2) It will give some indication if there's a problem (overtemp)
3) It's an amusing technical challenge for someone, like me, who is just getting into "proper" electronics design.
I don't anticipate this having any commercial use or value whatsoever, but I'd like to capture (to the nearest 10 degrees C, say) the exhaust temp from my Lister. Who knows, by having 2 sensors, one either side of a heatX, I may be able to tune the heatX to extract exactly the right amount of heat, in real time...
Quote from: billswan on May 06, 2010, 05:33:13 AM
Lloyd
Man you come up with the darnedest stuff ;D ;D
After reading about the cyclone engine I am sold, wounder how much they cost?
Says it can run on WMO, wow.
I will take 2 please.
Billswan
I just find the darnedest stuff...here's their stockholder brief for end of year 09 http://www.cyclonepower.com/PDF/Letter_Shareholders_2009_Annual_Report.pdf (http://www.cyclonepower.com/PDF/Letter_Shareholders_2009_Annual_Report.pdf) It looks like this technology, has spawned some other techs, and is in full swing to becoming reality.
It certainly hold promise for co-gen applications...now if it can hold promise for micro-co-gen...will depend on price...but the tech..sure implies that it could be adapted.
Lloyd
Jens, they use the thermo-couples to control the fuel burn, the elec. developed elsewhere in the system.
http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm (http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm)
circ 1840 ...it's a therompile
(http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/pouillet%20c1840%20cnam%201a.jpg)
Quote from: Lloyd on May 08, 2010, 07:31:29 PM
http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm (http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm)
circ 1840 ...it's a therompile
(http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/pouillet%20c1840%20cnam%201a.jpg)
They sure had a nack for making those tabletop machines pretty with polished brass and artsy hardwood bases. That's a very nice model. Good luck getting an electric spark to jump between those two brass balls though! A Wimshurst machine it ain't. :D The pile cylinders are remotely reminicsent of Leiden Jars though. I've toyed with the idea of scratch building a large Wimshurst machine to dispay in my living room. Just don't have the time to do it all.