thermoelectric lamp tutorial

What you see above is a generator that converts heat to electricity. [Reukpower's] thermoelectric lamp is one of those hacks that makes you scratch your head even though you understand why it should work. The heart of the system uses a Peltier cool, just like the thermoelectric solar generator. When there is a temperature differential from one side of the Peltier to the other a small current is generated.
In this case a candle heats one side and a heat sink cools the other. The tiny voltage picked up from the Peltier’s contacts is then boosted using a joule thief. We’ve seen LEDs powered with a joule thief before, benefiting from their own low power consumption. In this case, the boost circuit is scavenged from an emergency phone charger and probably achieves higher efficiency than if he had built it himself.

LET's MAKE IT THEN:

introHow to build a thermoelectric lamp

The thermoelectric lamp generates electricity off the temperature difference between the hot candle and the cool heat sink. This we can use to power small devices, like a radio or very bright LEDs.  You may be able to charge an mp3 player off of it too!

Here's what we'll need:

A thermoelectric peltier chip, the bigger the better. I used a 100W version.
A large heat sink, I used a dell one with heat pipes. The success depends on this heatsink, get the best you can!
An emergency phone charger (we are going to steal the joule thief out of it)
A Small amount of Rock wool insulation, small amounts available from garden centers.
A small tin can with a lip around the top. (Heinz beans will do)
A coke can.
Thermal heat compound
Some heavy duty foil, about 30x30cm
A foot of thick copper or steel wire, for the handle.
2 25mm long M6 Bolts
4 40mm long M5 Bolts
1 50mm long M5 Bolt.

The bolts don't need to be any exact size, just use whatever is available, almost any will work.

Tools you'll need:

Tin snips
Soldering iron
Pliers (with cutters)
Drill bits
Sandpaper
M6 Tap for cutting the threads. The not essential as you could just use an ordinary nut, but it's neater.
Drill (Drill press makes life easier...)
Glue or Glue gun

step 1Drill the holes in the can and fit the feet and central adjustment

You can see that I have drilled 5 holes in the bottom of the can. These are for the feet and candle height adjustment. I fitted little rubber feet to them, this is not essential.

step 2Tighten them all up and glue the central nut in place.

Once you've tightened all of the feet up, you need to glue the central nut in place.
You can see I've added a cardboard shim inside of the can. This because the coke can is slightly too small for the tin can. This prevents it from tipping slightly when the candle height is adjusted. The cardboard only needs to be about 25mm high.

step 3Cut the candle door

Next you need to cut the hole for the candle in the side of the can this should be around 30 - 35mm by about 50mm long. I started by drilling a small hole and worked from there using the tin snips. After this you can drill the ventilation holes all the way around the top of the can. I used a 3mm drill bit for this.
Make sure you sand all the edges so you can't cut yourself on the metal!

step 4Cut the coke can to size

Now cut the coke can to about half off the height of the tin can, you can see in the photo I am testing the height of the flame, we want it to be around 6mm away from the ruler with a new candle. You'll probably have to make a few adjustments to get this right.

step 5Fit some Rock wool to the coke can

Next turn the coke can over and fill it with Rock Wool insulation. Poke a space in the middle with a pen or something similar for the bolt to go into.

step 6Test the coke can fit in the tin can.

Now you can fit the coke can in place. You can see a little dimple in the middle, this is because the coke can was forced down to give the bolt something to rest on. The coke can might not fit perfectly on the bolt because of the insulation, you might need to wiggle it about a bit! Test the movement to make sure you can adjust the height smoothly.

step 7Fit the handle

Next, you can form the handle for carrying the device. I used some thick copper wire as a handle because it matches the heat sink pipes. You need to bend the handle back through the holes to prevent it from turning, see the photo. This stops the device rotating upside down when you are carrying it (the heat sink is the heaviest part).

step 8Drill the heatsink for the peltier holder

Now we can work on the heat sink. Here I have drilled two holes to mount the peltier. You can either tap the holes, or use a locknut on the other side. The two holes need to be set so that the bolts fit inside of the tin can, this keeps the peltier in the right position. I have also cleaned the heat sink ready for the thermal compound.

step 9Cut the peltier holder to size.

Next you can make the cover for the peltier. It's easier to cut the square out with this part still attached to the can - cut the square and then use a can opener to remove the bottom. Mark around the peltier with a marker or a scribe and drill a hole in the centre, work out from this using the tin snips to make the square. The square needs to be slightly smaller than the peltier chip so that it grips it. Mark the two holes the same as on the heatsink and drill them for the correct size. I made the cut out slightly round so I didn't cut through the strengthening ribs on the tin lid

step 10Apply thermal compound

Now you can apply the thermal compound to the heat sink. Make sure it is clean and spread the compound over the contact area. Note: as some people have commented the thermal compound only needs to be a very fine layer, not a thick paste like I have done here. There is a little too much thermal compound in the photo.

step 11Fit the peltier

Now you can fit the peltier to the heat sink. Press it down into the thermal compound and wiggle to smooth out the compound. You can see that the peltier is very dirty from soot, this is from my testing.  The side that is in contact with the heatsink must be clean though. When you use the device dry and avoid getting soot on the peltier as it blocks the heat transfer. Use the candle height adjustment to get this right.

step 12Insulate the peltier

Now you need to make a thermal insulator for between the heat sink and the fire tin.  Cut a square out of the foil the same size as the peltier chip and fit this over the peltier. Fill around the sides with 5mm thick strips of rockwool. Fold the foil over and you should end up with something like this. Don't worry if it is too thick as the bolts will compress it when tightened.

step 13Cut an aluminium patch for the peltier

Now cut a square of aluminium the same size as the peltier chip. Sand the patch with fine paper to remove the paint. Apply thermal compound (the same as in step 10) and gently place it over the peltier ready for step 14.

step 14Bolt the peltier down

Now you can bolt the peltier down. You'll need to punch some holes in the Rock Wool insulator for the bolts

step 15Solder and fit the joule thief

You can remove the battery pack from the emergency charger and just use the plastic end cap with the circuit in it.

First check the polarity of the wires to make sure that you know which way to solder them on. You can do this by just trying them both ways to see which way works, do this with the peltier heated by the candle. You'll need to solder the wires on to the joule thief and attach the joule thief to the tin can. I just used hot melt glue to fix it in place. You should have a nice 2.5mm output jack where you can plug things in

step 16

It should be finished now! You try various loads in the output to see what kind of power you get. Different peltiers will put out different amounts of power,  it also depends on the temperature difference you manage to achieve. I managed to charge  my small MP3 player, but it didn't have enough power to charge my phone. You can see it powering an LED torch here.