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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 Co. 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

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