I made my first penny stove today. when i preheat it the fuel starts to boil. Is this ment to happen? I can also hear it boiling when i put the stove out.

Jay

Hi Jay,

>I made my first penny stove today. when i preheat it the fuel starts to boil. Is this ment to happen? I can also hear it boiling when i put the stove out.

Yes the alcohol is supposed to boil, it is an important part of the operation and the alcohol will for a while after putting it out which is a waste of fuel.

The best way is to learn how much alcohol you need for a given quantity of water and only use that much in the stove.

Tony

ok i just thought i might be doing something wrong. I was just putting it out because i didnt want the dogs around it.
What should i use to make a pot stand?
Here's a couple of pictures before i sanded the paint and crap off of it.

Edited by jay590 on 11/27/2008 21:40:22 MST.

Hi Jay,

Nice effort for first stove.

A lot alcohol stove makers use bird wire, this can be obtained from most hardware stores, it is easily cut and joined, I got my supply from Bunnings. I will post some pictures of my alcohol stove pot stands later when I get home.

I am sure others will some pics of their stands too.

Tony

Ok thanks. What size drill bit do you recomend for the jets? as the flames are to big at the moment so onmy next stove i want to make my holes smaller.

Hi Jay,
I generally use 1mm jet holes, 3/64" is ok too. You will find that this isn't the issue though. What will happen is that the flames just get longer, because the factor which determines the rate the stove burns at is less to do with jet hole size, and more to do with the amount of heat getting back down the stove body to the fuel, i.e. the vapourisation rate.

There are several ways to slow it down a bit. You can try making another with a taller stove body, this will create more cooling area on the stove sides, and move the top a bit further away from the fuel, so less heat gets radiated back onto it.

Another thing to try is moving the row of jet holes higher up so the flames heat less of the stove top on the way upwards. You need to drill at an angle into the upper ridge so you don't pierce the opposite side or snap the drill when it breaks through.

Lastly, you can make fewer jet holes. Getting the right number for the ambient temperature is tricky, so experiment by covering a few of your existing stoves jet holes until it seems about right. Sticky backed aluminium flue tape is handy for this job. You will need to make a stand and get the pan at the optimum height above the stove (about 1/2" - 3/4") so you allow for the reflected heat feedback to the stove off the pan base too.

Another trick is to stand the stove on a light foil dish, and pour in a few drops of water once it gets going strongly. If you do that, be sure to press a few ridges into the dish round the stove base to prevent it floating off to one side once the fuel level gets low. Also, you can put a piece of wick around the stove on the dish and soak that with alcohol to prime the stove. This is much quicker than trying to prime it from the top. Be sure to start with a stove less than half full of fuel, or you may cause liquid fuel to boil out of the jet holes and cause a flare up. Again, experiment will teach you the right amount to use.

Have fun!

Edited by tallbloke on 11/28/2008 02:35:40 MST.

Hi Jay,

Roger has given you some good advice, he knows a lot more than me about alcohol stoves, my speciality is making canister stoves not alcohol although I have done some playing around with them.

I use 1.3mm holes, a few other alcohol stove makers use 1.3 mm also.

Here is a picture of a bird wire pot stand that I made for my little volcano stove

Tony

Tony may well be right about optimum jet hole size, 3/64" is 1.19mm. Anyway, as I said, size is less crucial than number and placement of jet holes.

Tony: thanks again for the drawings you sent me, they've given me much food for thought concerning light gas burners.

Edited by tallbloke on 11/28/2008 09:35:46 MST.

Try using a pin (like the ones that come in a dress shirt) to drill the holes. I know it's not a drill bit, but it works and makes a small hole. Just chuck it in your drill and let her rip. I've had good results using a pin to drill 24 evenly spaced holes. See photo.


By the way, an open can stuffed with fiberglass insulation appears to have the same power output as a penny stove and is a lot easier to make. Not as sexy though.

Edited by herman666 on 11/29/2008 20:17:49 MST.

my drill chuck wont go small enough to hold pins. i think the smallest it will hold is a 2mm drill bit which i used for my stove. Also how high do u cut the cans to make the stove in the photo?

EDIT: I'm going to make another tomorrow and was wondering how i stop the flames from being 6 inches high.

Jay

Edited by jay590 on 11/30/2008 00:58:42 MST.

Another tip apart from the three ways I already mentioned for slowing down the vaporisation rate of the stove is to add around 10-15% water to the fuel.

Try wrapping the pin with foil or tape. It takes very little force to spin a steel pin through the 4 mil aluminum. With care, you should be able to get enough gripping force to do it.

I marked the can by rotating it against a nail resting on a block of wood. I cut the can with a pair of scissors. I removed the paint with fine steel wool. 0000 I think. It imparts a nice polish without abrading the aluminum the way sandpaper will. If you want the polish to last, you have to clearcoat it.

As you can see from the photo, my stove, fueled with denatured alcohol, does not produce 6 inch flames. No need to add water. It puts out a fairly constant 325 Watts.

Hi Roger T.

>Another tip apart from the three ways I already mentioned for slowing down the vaporisation rate of the stove is to add around 10-15% water to the fuel.

What does adding the 10-15% water to alcohol do to the efficiency of the fuel.

Tony

Nice job Herman, looks very smart. Fuels do vary a bit. From what I've read here, the brake line cooler is higher calorific value, but I don't know for sure. In the UK the fuel is around 90% ethyl and 5% methyl.

The pin sized holes certainly look right for your stove design. I use 1mm on small stoves, and 3/64 (1.19mm) on larger models. Clearly, jet size does make a difference, because the circumference of the hole affects the amount of heat transmitted back to the stove too.

> What does adding the 10-15% water to alcohol do to the efficiency of the fuel.

Hi Tony, It does strange things which I haven't experimented enough to quantify. If you are in a warmer than normal environment and the stove is working too hard, adding a bit of water can help pevent heat being wasted up the side of pans. On the other hand, it generates more condensation on the pan underside, which can drip onto the stove, slowing it down further. Doesn't seem to affect heat transfer to the pan too badly though.

In Spain last month, I added a lot of water to an already running stove to see what happened. It kept going for a looong time with as much flame height as before, but boiled the pasta less vigorously, which was a good way of getting a strong simmer in a hotter climate than the one at home I optimised the stove for.

So much to learn... :-)

thanks everyone for your help. I made another today. It turned out perfect. I'll post pictures tonight when i can get a picture of the flames at night. I used a pin to make 24 holes, and it worked beautifully.
So thanks everyone really.

Jay

Hi Roger,

>So much to learn... :-)

Thanks for your observations, I was very interested in reading them.

I recently did some testing with alcohol/water mixes, these where not easy to analyze and understand and the results that I have are interesting and not what I expected.

Tony

Tony: Tell us more.

Jay: Result!

Hi Roger,

>Tony: Tell us more.


Soon.

Tony