Introduction: Stirling Engine Hot Plate, Pushing the Envelope on a Cheap LTD Stirling Engine

Picture of Stirling Engine Hot Plate, Pushing the Envelope on a Cheap LTD Stirling Engine
Here are a few photos and videos of a hot plate i built to display a cheap LTD Stirling engine I bought on eBay.

I was browsing eBay on my phone one sleepless night and spotted a cheap LTD Stirling engine being sold out of Singapore and purchased, 9 days later it arrived in the post.   eBay mobile makes you feel like Wylie Coyote as you order and then just wait for the postman.

Out of the box the little engine would run on a cup of boiling water but would barely tick over on the router and just about ran on the PSU of my laptop.



 I decided to tweak the engine here and there to see how fast i could get it to go. I bodged together a simple stand and used a small stub of candle from about 3-4 inches under the base plate.  The engine  ran much faster but would quickly over heat after only a few minutes.

I picked up a stainless steel spirit burner on eBay for £8 and decided to make a wooden display stand/hotplate that could also be used with other engines or for keeping a pot warm.

The base was turned out of mahogany and is recessed to take the spirit burner. the uprights re turned from seriously hard boom handles, I have no idea what the wood is but its so hard even the sharpest of tools seem blunt.  The hot plate was made from a disc of aluminium i had planed to use for a sterling engine i was gathering parts for. the hot plate was drilled and countersunk so the screws would be flush with the plate.

The following tweaks to the engine have greatly improved its performance, and after a few hours flat out at approx 300 rpm it seems to be running in well and will run on low temperature object much better and even ran on a friends hand heat but he has better circulation than I do.

The linkage joints all where very loose fitting and had serious lateral play so i used needle nose pliers to squeeze them in for a more snug fit. this was a good improvement as the power piston would twist about 10-15* during each rotation and this is now almost unnoticeable.

I removed the power piston from the tube and used the graphite core from a builders pencil to colour in the piston so it had a uniform coating of graphite to lubricate the piston.

On examining the top of the glass power piston tube i noticed that it had sharp edges and there was a audible catch, so i used a round 600 grit wet diamond file to bevel the inner edge and remove and sharp edges.  I made sure to wash away any traces of the powdered glass from the inside of the tube so they would not bind up the power piston.

The instructions said not to use oil on the model but to use pencil graphite, i tried this and it made no noticeable difference, so the inner engineer rebelled and decided to use a very light weight oil in a lubricating pen to lube the joints and the tips of the axles and the cups they spin in, this was a noticeable improvement over graphite, the oil was sparingly applied on the end of a piece of fine.

The displacer was fixed to the displacer rod with CA glue, it was also adjusted so there was about .5-1mm of a gap between the bottom of the displacer and the base plate at the bottom of the stroke.

Because the base of the engine was designed to sit on a mug of hot water it will not sit flat on the hot plate and needs a riser, i used copper 2p coins to make a riser, this required a stack of 2 coins to clear the base so i reversed the clamping bolts so the nut was on top and this allows for a single coin and gives better thermal transfer but coins are not perfect and still heat the base plate in hot spots rather than a uniform heat over the full plate, i will need to cut a 3mm disc of aluminium to use as a riser to improve the thermal transfer.

To stop the top plate overheating due to thermal transfer up the clamping bolts i folded up some TP into pads that fit the pot plate then wet them so the keep the top plate cool. they require regular wetting as they heat up and dry out if the model is left running for a long time.  To reduce the thermal flow through the blots i plan to make either wood or plastic pillars with counter sunk screws to clamp the plates together, this should cut down the thermal transfer from the hot to cold plates.

I have a few more ideas as how to improve the performance of this little engine, this is a fun little toy to tinker at on the wet and rainy day like today when my pains play up and I tend to stay indoors so i plan to keep tinkering at this.

The engine will now run at approx 300 rpm and is happy to do so for hours at a time a long as few drops of water are added to the pads every now and then. the more it runs in at high speed the better it seems to be at running at low temperatures.

Thanks for looking and i hope the Stirling enthusiasts enjoyed this,i will leave you with a video of the engine running at approx 300rpm, I will post any future additions or improvements as they happen.

PS the hot plate cooked the crap out of the displacer tube and I had to redesign things check this Ible for the details

Comments

Bill WW (author)2012-12-24

Here is the link to the Stirling engine I made.

http://www.youtube.com/watch?v=WsKVp6RvV

I have not yet posted construction details, but likely you can deduce what I did.
Mainly used all copper materials for heat conductivity, and included cooling fins on bottom. Extra large heat collection plate on top.

Cheers.
Bill

Bill WW (author)2012-12-24

Very nice, Dr. Qui.

You might be interested in seeing my Stirling engine on YouTube. It is totally solar powered. no Fresnel lens or other magnification.

I will post the link in a bit.

My agenda is much similar to yours.

rickharris (author)2012-06-16

LTD Stirling magic is all about reducing friction and getting good seals. If you have those they can run from the heat of your hand.

Dr Qui (author)rickharris2012-11-06

Yo are right about the friction, all these tweaks and mods and run it fast for 13 hours to see how long a tank of fuel lasted have caused so much wear to the displacer tube that it barely runs now at all. Might try and fix it when i get the lathe back which is soon. It was fun pushing it to destruction though. lol

Dr Qui (author)rickharris2012-06-17

I have since found that a hard disc platter is a perfect riser and the hole in the center stops the center getting to hot. I replaced the TP with a piece of cooker hood filter as it don't fall to bits once wet, its going even faster now.

rickharris (author)Dr Qui2012-06-17

Ice cube help.

Dr Qui (author)rickharris2012-06-17

These ones are mass produced and there are not precision engineered, when i posted the you-tube videos i saw a few other vids of these and people was mentioning what they had done to them to improve things, one guy had to solder the flywheel o the axle lol.

The better quality ones seem to be in a pricing war at the moment and when they decide what the rock bottom price is I will pick up a better quality LTD and still deciding which of the high temp ones I like best.

I could replace the stainless steel base with aluminium but i decided again as i must draw the line between tweaking and rebuilding.

This was running on my friends hand but he has super strong arms and great circulation, I have have pains and aches and I cant hold it steady long enough to warm up.

I need a proper riser or to counter sink the clamping bolts, the coins do not give decent thermal conduction and the base plate is not heating evenly but in small hotspots, i could have used thermal grease but you know what a mess that stuff is.

it seems to be well enough sealed and running smooth enough the problem seems to be thermal transfer to the top plate along the bolts but that can be remedied.

This is only a toy for me to tinker and play with as I gather the parts to build a monster Stirling, this one is by no means finished, I just want it to be a surprise what I add to this next.

rickharris (author)Dr Qui2012-06-17

Bohm are the rolls royce of the model Stirling world.

Dr Qui (author)rickharris2012-06-17

Yeah I have been aware of Bohm but have you seen the price of them they are to rich for my blood, lucky these days they are coming in from the asia at the right price they price sellers are trying to establish the benchmark price.

rimar2000 (author)rickharris2012-06-17

WOW, their designs are beautiful!

dreamberry (author)2012-06-19

Love the engine! Don't stop posting! Write your 'ibles in your computer, (I use Notepad) save often, then you can just copy and paste. I've also had bad luck trying to type them in "live" as it were.

Dr Qui (author)dreamberry2012-06-23

Well i tried the type it in kwrite as im a linux user and i posted 2 Ibles, the first one worked great although the formatting seems a bit odd but its there and visible. the second seems only to be visible by me and there is no sign of it on the site.

Dr Qui (author)dreamberry2012-06-20

These little engines are great, at first i thought it was going to be junk but with a few tweaks they work great, its almost like an AK47, roughly made and not to pretty but it don't half work well.

rimar2000 (author)2012-06-17

Very nice support base, Dr Qui.

Dr Qui (author)rimar20002012-06-17

Thanks Rimar, its a fun toy to play with, the hot plate will also be useful for other things too.

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Bio: Learning to live with Fibromyalgia brought on be numerous injuries some old some quite recent. Currently under no fixed agenda, just going with the flow ... More »
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