DIY Stove Top Fan - Show me yours

[billi]

Thanks Lurk

So there is some hope for my 10 Tegs   i have  ..... will go playing

[Lurk]

10 TEGS - are you made of money ?

I have been trying to work out how to fix a large number onto the upper section of the stove flue pipe so that the heat from it can be put to some use. As it is out of sight under the chimney lintel - The problem is ensuring that the TEGS surfaces are fully covered one side by heated metal the other by the 'cooling' side - which brings its own problem being stuck in an alcove and not wanting to fix another cooling fan and use up the limited power generated. The whole assembly has to be removable for sweeping out the soot etc.

If I had some sheet copper that would be a starting point to make a flanged collar to strap to the flue..... alas, the local scrap man has removed all possible local sources !

[billi]

10 TEGS - are you made of money ?   

      investment  was done in  celtic tiger  times .........          time to buy some heat paste now instead of diesel  for my generator   

[Ivan]

Here's my DIY TEG fan - eventually, the solder connections inside the TEG 'creep' causing open circuit. You need to restrict the maximum temperature with a bimetallic strip or somesuch.




Why stop there? How about some LED lighting. These are by the stove for the photo,but I'd actually run these up to the top of the telly mounted on the wall above the fireplace. When the fire was going well, the lighting was as bright as having a couple of low wattage lamps on ( 3 x 1W LEDs). Note the use of the ecofan for cooling the heatsinks by blowing cooler air over them



My plan was to bank up several TEGs to get enough voltage/power to run the 4Watt wireless internet router that I had back then, but, I never got that far. I did get a low voltage radio to run perfectly happily from TEGs and quite loud too, but not the sort of thing that I can demonstrate well in a picture.

[Lurk]

Thanks for sharing Ivan, if I could ask, where did you source your fan blades ?
Lurk

[Ivan]

The blade is a replacement for an ecofan - very expensive for what it is. You can get just as effective 4-blade fans from China, but I never really developed it any further otherwise I would have ordered some in.

[Lurk]

Ive made a MK 2 version which you can see here http://www.peakdistrictcreations.co.uk/about-us/environmental-policy/recycled-stove-top-fan/ at the bottom of the page. It now starts up quicker and runs very quietly on top of my stove. I have two more TEG units on the way ready to make another couple of fans. I want to make one to strap onto the flue pipe !

[stannn]

Lurk
It looks neater with that round base. Does is shift enough air to be useful?
Stan

[Lurk]

Difficult to say - there is no huge gushing of air - but subjectively the room feels warmer - could be a placebo thingy... I normaly obly run the stove very low heat - where the top plate is just about 80 degrees - the fan needs 85 + so I'm running the vents slightly open to get the fan running - so more heat from the stove anyway.
The Mk2 fan is 85mm diameter - where as the Mk1 was 60mm - you can feel air off the Mk2 on the back of the hand at 12" - I have a 140mm fan unit I am going to have a play with when the next lot of TEGs arrive - but I suspect it will require a bigger drive and multiple tegs to operate....

[murraymint]

Is there any way of adapting this idea for normal central heating radiators, I have used battery powered fans before but using some of the heat from a rad works for me.

[Lurk]

Murymint - I doubt you could get a TEG to operate at such a low temp (40 - 50 degrees at most ?). I think you would want to start with a low temp sterling engine - adapt the fly wheel into a fan some how. - I looked at the £40 units on fleebay but couldn't see an easy way of adding the fan blades without them getting in the way of the drive shafts..... I'm sure someone would be able to work it out.
lurk

[billi]

Is there any way of adapting this idea for normal central heating radiators, I have used battery powered fans before but using some of the heat from a rad works for me.

http://thermalforce.de/engl/product/module/index.php

http://www.thermonamic.com/products.asp?cid=363


I know  prices  for them  ( based on TEG s).....  and  still  am surprised how much they are , for such  a small piece of... what exactly  ?

Guess   the wattage  they can produce is not the problem ,more the heat and cooling  that  we have to supply  is the problem  

Not an Copperfield trick  

But still  ideas exist to change waste heat into electricity   

Billi  the PV-kid

[martin W]

hi, what speed is the motor rated for, as the 3volt ones I have seen are around 13,000rpm which seems a bit fast , anyone got a link for 1.5-3volt low speed / low mAmp motor?

I also bought one of the tegs form that ebay supplier who did not impress me with their responsed when i can hardly get 2.5volts out of they supper fandangled teg which they hinted at was 12v. however i now realise I need the lower voltage dc motor say 2-3volts. I also took a tec module out of a beer can pc cooler I had, and it seems to have similar voltage and mA output as the super teg module

[Lurk]

Hi Martin
yep thats the motor. Yep 12v suggested rate is when the TEG is used as a 'cooler' so you apply that voltage - they are useless at comm's - it was like pulling teeth - I had to write that I had no intention of taking any form of legal action I was just trying to develop a project and wanted advice - I got the impression they were 'rear end covering'.
I get approx 0.2 amps @1.4v at 100 degrees flue pipe temp'
I would love to able to find a low rev high torque low amp 1.5v motor...oh and cheep.... I looked but couldn't.... one other thing - don't try to glue the motor down - I first used a PU foaming adhesive - good and strong but the foam got into the motor and stopped it ! - It took half an hour to strip and rebuild the motor !

If there are more people interested maybe a group purchase of the TEGS - and see if we can get a better price ?

Have fun

Lurk

[Ivan]

The only difference between the coolers and the TEGs is the temperature rating of the solder. Even the 250C units will eventually fail on a woodstove, due to 'creepage' of solder ie at temperatures  below the melting point, solder tends to flow very slowly - like glass does in old windows. It takes about 6months, from my experience on a woodstove fluctuating between 120C and 220C.

Mostly, sellers quote the cooling wattage rather than the generating wattage - which is a bit like quoting the heat flowing through the device for TEGs rather than the power it produces.

The TEGs are actually multi-junction thermocouples, with solder tracks on the surface of two ceramic plates. Actually, the TEGs should not have silicone around the edges (they do this for coolers, so that you don't get condensation inside the unit) - but in practice, we're all buying TECs rather than TEGs. You could pull this silicone off, which would improve the efficiency a little by removing a heat-bridge.

If you buy a 12v module, you'll probably get 1-2V under normal circumstances, but if you get a good temperature difference across it (like 100C) you'll probably get 8V or so from it. You need to keep the hot side hot and the cold side cold. Bear in mind that the cold side is being heated by heat flowing from the hot side and the hot side is being cooled by the heat flowing to the cold side. There are difficulties in getting the heat to the hot side fast enough and getting the heat away fast enough. So in practice, when you place your TEG device on your woodstove, you'll have probably 150C on the hot side and 135C on the 'cold' side of the TEG (I did experiments with a tiny thermocouple temperature sensor to find out). To get a good temperature drop across the TEG, you need four things 1)Good heat supply on the hot side 2)Good cooling on the cold side 3)Good thermal contact on hot side (think tightly clamped) 4)Good thermal contact on the cold side.

Remember it generates electricity in relation to flow of heat through the device, not temperature differences between the two sides

So, in MartinW's case, it might be more to do with the temperature drop ACROSS THE MODULE ITSELF, rather than the TEG output per se.