Powere sources for a stirling

[Bogstandard]

Nick,

It is frustrating, but just another trial on the journey thru life. A shrug of the shoulders and carry on doing what you enjoy.

This is way off topic, but this post is going nowhere until my metal stuff turns up. So I may as well show something of interest.

I don't know if you have seen it before Nick, but this is the one I dropped.

When eventually the storage box gets opened again, I will finish off all three that are all made except for assembly, and of course, make a new crank for this one.

I am wondering if they will run off the heat of the heater pads they put under vivariums, rather than an eggcupful of water being heated by a candle. They would be a lot safer for me, if they work.

I can't be trusted with matches any more.

John

[BillTodd]

I am wondering if they will run off the heat of the heater pads they put under vivariums, rather than an eggcupful of water being heated by a candle. They would be a lot safer for me, if they work

John,

What about putting  cheap 50/100w  soldering iron element into a block of aluminium? You could control the heat/temperature with a simple  light dimmer

e.g.

http://cpc.farnell.com/duratool/d00757/heater-element-for-zd-415/dp/SD01389



Bill

[Bogstandard]

A good idea Bill, unfortunately I think I will need a few to cover the area I want. I would like a small table top, say 18" square, where maybe a dozen low temp stirlings could sit, all running.

Vivarium heaters are ready made heating pads, and you can get them in fairly large areas for not too much money. I think they only generate heat on the area that is covered.

http://www.discountleisureproducts.co.uk/Heat_Mats

I just don't know if they will provide enough heat. I will have to buy a small one and try it.

I think I still have some 1/4" diam heating elements from when I was working on cellulose ribbon cutting. The only problem is, they glow red hot when working, and the electric meter would spin itself off the wall.


John

[slowcoach]

Hi Bogs, What about using a few peltier pumps. http://www.greenweld.co.uk/acatalog/Shop_Peltier_76.html

Rob 

[Bogstandard]

Rob,

Getting rather expensive for the size I want to do. A quickie calc comes out around 3,200 squid, plus maybe a bit of overkill.

I am looking for a KISS solution.

I was hoping someone would have a vivarium AND a low temp Sterling and maybe they could try it out for me.


John

[slowcoach]

Yeah, it is a little steep that 

Rob

[Bogstandard]

Everyone, please don't stop coming up with suggestions just because I have shot a few down in flames.

Your ideas might spark of something in someone else's projects.

Those peltier jobbies, I think, would be ideal for running just one, sitting on a nice ali or marble base. I know the experts at Harrogate use small tungsten bulbs for theirs.


John

 

[andyf]

Maybe a hairdrier, heating an ally plate from below?

Andy

[mklotz]

Although it deeply offends my model engineering sensibilities to run Stirling engines on electricity, the Peltier device does offer an interesting possibility.  Clamp two identical Stirlings to each side of the Peltier plate and run them both simultaneously.  Sit back and have a good laugh as technically clueless onlookers try to explain what's happening.

[Jasonb]

What about a hot plate or plate warmer, these usually have an element set into a glass/ceramic and have a thermostat, would also keep your coco warm

Jason

[DMIOM]

Have never been into (making) homebrew but they sometimes use low-level heating mats like these to aid fermentation.

Dave

[Bogstandard]

Jason,

Now that looks a good idea, just need to find a reasonably priced one than heats continuously.


Marv,

I know exactly how you feel. Unfortunately, nowhere in the UK any more allows you to display with naked flame, or are very reluctant to let you do so, so I am actually making some tiny bunsens for the ones that normally have a meths or candle, hoping that will satisfy them. I used to display a fair amount at one time, but there are just a couple of local ones I would like to try to attend in the future.

About the Peltier devices, good idea, will Stirlings work with cold on the bottom plate, and do low temp stirlings run when on their side or upside down, or would the friction be too much?

Dave,

I think they are the same as the vivarium heaters, just more expensive.


John

[mklotz]

John,

Stirlings require only a temperature differential to run.  They don't care which end is hot and which cold.

At shows, I run my LTDs by sitting them on one of those freezer packs one can buy for use in picnic coolers.  With the sun warming the top plate and the freezer pack cooling the lower plate they run quite nicely, albeit in the opposite direction of rotation from the heated lower plate configuration.

My LTDs will run upside down but that may be a fluke.  I suppose one could "pipe" the bottom side of the Peltier device to the (right side up) engine somehow.  A thin aluminum or copper plate could act as a pipe.

[NickG]

John, that's brilliant, really good. As Marv said, it would just run the other way if you cooled the bottom. Mine doesn't run (not that surprised, didn't have time to troubleshoot and there were a number of things I knew were iffy) but I've had to package it up for my dad's present tomorrow - pretty rubbish present though, just hope he can see that I've put quite a bit of effort into it  . I guess I'll try to make another one for myself, maybe but got a stack of other projects to do too.

Nick

[Bogstandard]

Thanks very much for the info Marv, it gives me something else to think about now.

Nick,

I still haven't forgotten. When I get them finished, one of the burners, and a gas regulator, will be on it's way to you, for either your flame gulper or a hot cap Sterling, if you build one.

Thank you everyone for your ideas on the heating solution.



John

[madjackghengis]

Hi John, didn't want to push you on the issue, but I've dropped my share of carefully machined bits and pieces, and don't much care for having to redo what I've just finished.  I've just gone through the whole of your log, and got a better understanding of the many issues which have come out in it.  I try to salvage everything which once worked doing anything, and have several old coffee makers, disassembled, and their "hot plate" for keeping the pot warm would probably work fairly well, they have a thermostat in them, to keep it below boiling, if you put a diode that will carry ten amps, such as a 4004, you cut the heat in half, and would probably make it better for the LTD types, and even for the not so LTD, but close types.  The same mod with the diode can be used in any electrical circuit of a/c, and cut your wattage in half, I've used it with an old coffee pot to keep wax melted, but not burning, for dipping sharpened tools to protect the edges, before.  I've also got several "potential boilers" which have come from expresso machines, as I truly enjoy my expresso in the winter, when I can drink it, and while they don't meet esthetic standards as boilers, they probably would meet safety standards of the "safety police" who seem to poke noses into everything these days.  By the way, what are you using for your displacer, if you don't mind my asking? mad jack

[Bogstandard]

They are a little small in surface area Jack, I want to make a heated table to accommodate about eight to ten smallish Ltd engines. You can in fact buy small coffee mug warmers that plug into an USB port that could be used if you wanted a Ltd Sterling on your desktop.

For my eggcup Stirlings, I used thin slivers of building foam (about 3mm or 1/8" thick) for the displacement pistons, but now I have some thin acrylic (2mm), which I will use when they are rebuilt. I have noticed that the foam is 'sagging' slightly and is going slightly mis-shapened after being in there a couple of years. Even very light materials succumb to gravity after a while, especially when supported at just one point.


John

[madjackghengis]

Hi John, while I've not yet built an LTD stirling, from the way most are made, it would seem pretty natural for them to run upside down just as well, since all the movement is verical except the rotation of the flywheel.  That double engine Peltier device idea ought to work out pretty well as long as everything is pretty well balanced.    mad jack

[Bogstandard]

Jack, I just might try that out on the eggcup ones I have yet to assemble.


John

[John Stevenson]

Anyway, the bearings turned up today for me to carry on with this Division Master topic.


So the postings about heat sources and Sterling engines is now closed. Many thanks to all those who contributed, it has given me a lot to think about.


John

Thank Christ for that.........................

[j45on]

Sorry to resurrect an old thread but I thought these may be of use to somebody.
They are tiny ceramic heaters carefully cut out of car O2 sensors
(potentially free from scrappies as they are pocket size )


They run on 12v and the one on the left reaches 230 c quite quickly
The one on the right I have not tested for temperature yet
Maybe they could be fitted to in to a base plate with a thermostatic switch ?

[cuog]

I guess since we're pulling this thread back from the dead, any reason an electric griddle wouldn't work? 

One of these: http://www.amazon.com/Presto-07030-20-Inch-Electric-Griddle/dp/B001078UCC/ref=sr_1_4?ie=UTF8&qid=1297349186&sr=8-4

I can't see why such a device wouldn't be for sale in the UK, but it is a strange world out there so who knows. 

[cidrontmg]

About the vivarium mats. I don't think they will be warm enough for your purposes, Bogs. They all seem to be 28 cm wide, the length varies with wattage. The smallest, 15x28 cm, puts out 7 watts to that area. It's not much. Many years ago I was working with IC chips that dissipated some 5 watts to a device of 17 mm x 52 mm x 4 mm. The IC was warm to touch (finger), I figure about 40 C^o. The surface area (17 x 52 mm) = 8.84 cm². The surface area of the 7 watt mat is 420 cm², or 47 times bigger. I can't imagine that power to be able to warm the mat more than a few degrees above ambient, even well isolated from excessive cooling. Which well may be what the reptilians prefer, but hardly enough to power a LTD Stirling.
There are also electric blankets, and similar electric bed warmers to be used above the mattress. We have a number of those, in their intended use, and they are very nice! Their power/heat can be (usually) adjusted in steps, and they might offer an alternative. Except they are maybe too large (=size of a bed). But you could maybe build some more LTD Stirlings... 

[picclock]

Hi Bogs

The surface are that you are heating is quite large, and I'm guessing that you will need a temperature of 50-60C for the stirlings to work well. So you probably need a reasonable power output to warm it up quickly and temperature control to make sure it doesn't get too hot.

If you can live with the depth, how about an electric iron with the sole plate attached to your aluminium sheet (upside down). The handle can be removed, but the temperature controller is built in and attached to the iron sole plate. 

If that's too deep, a scrap slow cooker should contain the heating elements and controller you need although you would have to preserve the wiring and remotely mount the thermostat control, which may be a good thing if you want a external controller.

I think you will need a lot of watts for this to work well, so covering the top with an insulator, using cutouts for the engines will help to maintain an even temperature and increase the temperature differential (If you have an exposed hot plate the cold ends are going to warm up pretty quickly).

Just a few ideas, hope they are useful.

Best Regards

picclock

[Bogstandard]

Some of these engines work as low as 35degs C (body heat), even a lot lower if you cool the top plate with say an ice cube or a small pot containing cold water, or even ambient if you stand the engine on a cool pak, they work on differential temperatures.

So I am not looking at anything where a kiddy could put it's hand on and be burned.

I will be buying and experimenting with a cheap vivarium mat for the time being, and take it from there.


Bogs

[John Hill]

Bogs, there are a number of chemical reactions you might consider for your heat source. 

For example, it was my dubious pleasure some years ago to exist for a couple of weeks in Baghdad on American "MRE"s, military field rations that include food packs that self heat when water is added.  Maybe not those exact chemicals as the reaction appeared to give of hydrogen.  Maybe slaked lime and vinegar?

[Bogstandard]

John,

These items would need to be run continuously for say six hours, non stop for say three consecutive days. Methinks chemical reactions would a little off putting to be running for that length of time, plus maybe rather costly in the long run, and of course, I would have to supply reams of documentation as to what is actually happening in that chemical reaction.

That is why I am looking for the safest, cheapest and easiest methods possible, where they have to be safe for everyone, as they would be being displayed in public places. That is why I am trying to get low pressure gas accepted as a safe medium to use at certain venues, in a totally rigid setup using mini bunsens, in a contained cage, rather than methylated spirits in a moveable tank, for running engines like flame lickers and other types of Stirlings.

I want to get back onto the display circuit, but now things have all changed regarding safety and public display. As long as I can get my modelling insurance to cover it, then there should be no problems from the display organisers, and for the insurance to accept it, it has to be proved that no one should get hurt by having the safest means possible to achieve the goal.


John

[arnoldb]

Bogs, another idea that might be worth looking at if the mat does not work...

With Heat Sink Mountable resistors - here's a sample - (I didn't search for the cheapest though)

If you get some of these heat sink mountable resistors, you could make up a base from wood or plastic with smallish aluminium pads in it, and mount these resistors from below on the pads and wire them up to a variable power supply to control the amount of heat generated.

While you would lose random placement, a layout like this will allow you to maximise efficiency, as well as control how fast the LTDs run - even in different ambient temperatures.
I didn't do any calculations on best values to use or anything; If you'd like that I'll be happy to work it out for you.

Unfortunately I have not yet built any LTDs to test such a scheme, but I do think it will work.  I do have a USB coffee cup warmer for when I build that first LTD though, seeing as these new flat screens don't have space on top to pit it on like old CRTs had :-)

Kind regards, Arnold

[John Hill]

John,

These items would need to be run continuously for say six hours, non stop for say three consecutive days. Methinks chemical reactions would a little off putting to be running for that length of time, plus maybe rather costly in the long run, and of course, I would have to supply reams of documentation as to what is actually happening in that chemical reaction.

That is why I am looking for the safest, cheapest and easiest methods possible, where they have to be safe for everyone, as they would be being displayed in public places. That is why I am trying to get low pressure gas accepted as a safe medium to use at certain venues, in a totally rigid setup using mini bunsens, in a contained cage, rather than methylated spirits in a moveable tank, for running engines like flame lickers and other types of Stirlings.


John

Hmmmmm....... I see what you mean John, those organisers might not believe your engines are running on just the plain water that you pour into those plastic bags. Just a wild idea but how about taking the heat in with you as hot water in thermos flasks?  I know you live in England so obviously a cup of tea must be permitted!

[Bogstandard]

John,

That is the way a lot of the low temp ones are run, sitting on top of thermos flasks, but always behind screens where kiddies can't scald themselves with hot water.
The stirling society are starting to get the right idea, they have small incandescent bulbs hidden in what looks like blocks of wood and in the wooden bases as the heat sources.

This is a very bad vid of them I took a couple of years ago at the Harrogate show

John

[NickG]

I wish more engines could be seen running at the shows too. I think we were allowed meths at the last Harrowgate show, obviously it needs 100% supervision though.

I guess putting a light underneath it demonstrates the principals but there's something about doing that that just doesn't please me in the same way, for instance, even a tea light under it would, or a flame licker with a burner, an i.c. engine or steam engine would. Suppose the majority of steam engines are run from a compressor so it's the same sort of thing.

Nick