Haha! Welcome Friends! I’ve made another stove top fan from junk. This time it’s improved though, it’s got overheat protection! If you’re curious to see how that’s going to work, stick around and I’ll show you how.
We are going to want about a 13mm hole for that plunger. While I get on with that, let me explain what is going on here. So we are drilling the hot side riser block.
It’s job is to transmit heat from the top of the stove to the TEG unit. If none of that made any sense to you go check out my previous article all about stove fans, or follow the link in the description that goes to an Instructable that explains right form the ground up all about them. But honestly, if you are patient and you read along I think you will get it anyway.
So, the problem we’ve got is these little dudes, the TEGs, they fry really easily, even on the proper modules, the expensive Caframo ones that you can buy, that are like £20 each. They just don’t last very long, the solder inside melts.
These ones here are rated for 150 degrees C and although I try and make the riser block reduce the temperature enough so that by the time it gets to the peltier, it’s down to below or at 150 degrees C, there is always these occasions where it rises above, when the fire is going a bit crazy, and going a bit nuts, and then: Boom! There goes your peltiers. So, the solution is going to want to be somehow reducing the temperature, when the stove is too hot.
One way of doing that would be just to make a bigger riser which would dissipate more heat. But then you loose the workability (of the fan) at low temperatures then. So another possibility is to change this so that as it warms up, if it gets too hot, somehow a gap appears between this and the bottom, and that’s the one we are working towards, so that we can save our annoyingly fragile peltiers. How did we do? Not perfect.
So I have got my old surface plate here. It’s still flat in some places! This was actually scraped very flat at one point. But anyway… 600 grit wet and dry.
This scrap of copper is very un-flat. to start with. It’s just a bit of old bus bar, so it has no reason to be flat, but we want it to make as close as mating contact with the TEGs as possible, so it’s getting flattened – slowly. The trick here is to start with a nice low [course] grit and work you way up.
I started at 600 and I was way over optimistic about how flat it was to start with. We’re getting there. So it is definitely a tad tedious but is probably worth it to get a really good connection. Now after doing one side of that I was loosing the will to live so we are ploughing on and we can do the other side later.
Yeah, left handed! It can be done! I forgot to mention one other solution, which is to increase airflow through this, so it dissipates. As the power increases. So as the temperature rises, ideally the power thats coming out of the peltier will increase, therefore speed will increase, cooling this better, which will kinda provide a little check and balance.
So if we increase the power of the peltier, by say, doubling them, and having two peltiers, that should also hopefully provide a bit of extra cooling, and therefore reduce the risk to the peltier. And the hotter it goes the more it will tend to cool it down, and bla bla bla. Back to the hot side riser and the hole we are making in it…
This bolt is going to fit quite nicely. It’s a bit rough and will need some rounding off. I was really struggling to scribe down through the cylinder to accurately mark out these four holes, and then I remembered that I had this gasket, so I can use that to mark out. Otherwise it would just be a question of measuring and marking out the old fashioned way with a calipers.
So we are all marked up and ready to go. We are going to be drilling a 4.2mm hole and that’s, of course, for an M5 thread. So I will probably have to stand it up on something.
Perhaps this… Lets drill!
So I am using one of those machine taps that’s got a helical thread. For aluminium it should be just fine. I need more hands for this operation… It’s not the safest, but it works.
So I think it’s definitely time that we clean up this surface a bit, that the peltier is going to sit on.
This old CPU heat sink had a ground flat surface anyway, which is very useful. I just have to clean away any traces of old thermal grease and make it respectable. Lets chuck it up…
We can make the sliding pin that will push the hot side riser block away from the stove top, out of just a regular bolt, and here I am just rounding that off so the treads and the head are nicely smoothed over and wont catch on the spring or hole they sit in. Once that sliding pin is nicely rounded off, lets mark up the copper plate. we have got these little divots we need to make.
Now I am using the mill for this, it would have been much easier to drill the holes, but because they are right on the edge I have got to make these divots. You could easily do this with a file or an angle grinder. Two hands or one hand?
That’s the question. Next time I’m using the power hacksaw. So we want a little scrap of pipe like this to support the wax thermostat inside the cylinder bore.
And it wants to be as square as possible to do this, so careful hacksawing is recommended. In my case I needed to square them up a bit on the disc sander. What is this pipe actually supporting? I hear you ask.
Well, it’s this automotive style wax thermostat which is, kinda the prime mover of this whole operation. It’s whats going to push that sliding pin, which will eventually lift the whole thing away from surface of the stove. These things are simple, reliable, and robust so they should serve this purpose quite well. I’ll leave a link to the one I’m using, along with all the bits, in the description. Lets recap.
This piece, I remade, because it wasn’t seating on the top very well. So now what we have is, this little bit of tubing that I found. This sits in there really nicely because i made a little ridge for it to sit into, and that goes in there… So now the thermostat – the wax thermostat – is sitting in there really quite nicely. So we just need another bit of pipe on here, to fit on top of that.
Just to hold it all firmly in place. I’m just marking off where that’s going to go. And you certainly don’t need a lathe to do this, a hacksaw would do just fine.
But any excuse to get the camera phone lathe crocodile going. After that this is what we’ve got: these two pipes are sandwiching the wax thermostat nicely and holding it nice and sturdily inside the cylinder bore. The problem we’ve got is that the wires are going to struggle to get through, down through all these pipes.
So we can make a hole in the pipe that lines up with the port on the side of the cylinder bore, so the cables can run through that. Guys we are so nearly ready for assembly I can taste it, Final assembly that is! I just need to clean this copper pad up really nicely, sand it down a bit, because that’s making important contact with the cold side and the peltier, so it really needs to transmit the heat well. And then we are set to go, for this thing!!
So with those through, now we can put that in. Its in quite nicely. Then this – also seats in quite nicely. Awww. Spot the mistake! They are coming out, sort off the wrong side! So peltier wise I am going to be soldering these up in series. So black’s going to red, just joining, and then we’ve got these two. And in series rather than in parallel should hopefully give us a bit more OOOMPH. Lets get soldering! It makes assembly a whole bit more messy, but dont forget the thermal compound.
Round the cold side especially, and that’b between the cylinder and the copper and the copper and the TEG. They are the most important bits to really minimise resistance. OOPS! Forgot to put the rounded over bolt in there, so some disassembly and re-assembly…
So before I go any further I just want to test the direction it is going, on the iron there. I am loading up the fire really well… So we should get absolute roaring. These are really dry bits.
OOOOO This is exciting, it’s getting going.
It’s just started, we’re just under 100 degreed C on the stove top, well more like 75 really, but it is going really well. No sign of the wax thermostat doing anything. This very exciting, I wonder when it is going to pop up, if it pops up!
Look at this guys, it’s still running, which is great, but look at the temperature – it’s WAY HOT. It’s like, 250 down there, you can see that there is a gap there, which means that the thermostat has worked! Look at that, it’s worked.
Wooohoo, it’s hot too! The white of the TEG seems to be about 150 which is of course the limit. OK guys, this is working great, you can see how its tipped up there.
And everything is just on the corner down the bottom, which is basically stopping the heat transfer up to the peltiers here. The stove top here is about 300 degrees C. Which is a lot hotter than you would normally want to run it, but I was over burning it just for this test. So it’s working great!It’s lifted up, how great is that!? I’m pleased in general. Time will tell how long these peltier elements last.
You seem to get different quality ones but at the moment this is top notch. So the fire surly can’t be going too much longer and the temperature should start dropping and hopefully when that happens this is going to lower down. I kinda feel like I have seen it lower down already, but it’s hard to say because I think that might be placebo.
So we are going to leave it recording and see how long it lowers down and see what temperature it is when it lowers down… So It has lowered enough to be… seem in contact, it’s not quite in contact. You can tell be rocking it. Another way of doing ti, if I wasn’t using a chainsaw cylinder, an old one, as the cold side heat sink, would be to extend out here and just have a little thermostat.
Something like that, round there a little mechanism there, and it would just tilt everything up that way, That would be fine too. To either side, something like that could work just fine. You could even add it on to existing stove top fans, and that would be quite a big improvement I think, especially if you have already replaced the peltier TEG elements once or twice already, next time you come to replace them, I definitely would recommend creating some kind of safety system like this, that prevents it from overheating and they should last a lot longer that way. Now it has cooled down a bit I can actually pick it up.
And we can have a look underneath and, ooo, look at that,that bolt has retracted all the way back which is really good – that’s ideal.
So it’s working just as I’d hoped really. You can see the bolt just through that little gap in the middle there. OOO its hot on the bottom still. So yeah, it’s all go.
If you want to know where I got any of the parts from I’ll leave a full list of places you can get them from in the description. Mainly scavenging though! I recommend you get fully into the scavenging spirit. It might be hard to scavenge one of the wax thermostats though you could probably pull one from a scrap yard, it’s going to be a very oily coolanty joy. So it’s probably worth paying the five pounds or few bucks or whatever it is to get one.
Friends, thanks for joining me for that. It’s been a blast! I hope you find this useful if you do make one of these chainsaw cylinder stove top fan things. As you’ve obviously enjoyed this and sicked with it through to the end, you’re going to love some of my other articles, so I really recommend you hit the subscribe button, possibly even the alerts thing so you get told when my new articles come out. aaahhh