Cat stove not working for me

[Marko Botsaris]

I had a quick question about the cat stoves I have made, though I have a good idea what the problem might be. I made the standard one out of a fancy feast can, 1/4 inch holes in two rings, about 16 or 17 per ring. Not getting much heat transfer to my SP 700 ti cup sitting directly on top. 2 cups of water don't get very close to a boil with 1 oz of denatured alcohol. Used a proper winds screen. Zero external wind either.

My guess is that perhaps a wider pot would be better for heat transfer. I suspect if I lifted up the pot somehow (e.g. with stakes) this might help, but then the stupid-simple part kinda goes part way out the window. My question does this seem right for the SP 700, or am I doing something wrong?

Edit: Ah brilliant. Of course there is an answer for everything here somewhere. I had assumed this was just my weird problem, but you guys/gals are VERY thorough. Sorry for duplication – I will double check for old posts next time.

[Hikin’ Jim]

Mark,

You've probably already figured it out (sounds like it), but yes a skinny pot doesn't work well with a side burner like a cat can stove. The flames go out around the pot and up the sides, and the heat is wasted.

A wider more shallow pot works a lot better. The Evernew 900ml UL titanium pot is well regarded with a cat can stove.

HJ
Adventures in Stoving

[Harald Hope]

Mark, you got it, while easy and tempting to make as your first stove, the cat can stove from jim wood is not good for narrow pots. Those were my first too, and I gave up on them, though I will bring one as a spare if I feel like it because it doesn't weigh anything.

I will be at some point posting a link to a how to make a penny stove for narrow pots, that gives roughly a similar efficiency as the better models out there, it takes some 20 minutes to make it, easy.

Short version: 2 7.5 oz pepsi type mini cans, cut properly, drill holes, 1/16 inch, 4, pointing IN, instead of out, center 1/8" hole for filling, pre 1982 copper penny to seal that hole. With proper wind screen/heat shield, yields a consistent 17.5 ml boil of 2 cups, 500ml, if you get it all right, 15ml will do it at normal temps/elevation, which is close to as good as it gets, I believe 12, 13ml is the best reported. Very easy to light with the priming tray.

Requires a small priming tray to really work right. With simmer ring, lets you simmer after a boil on 10 ml, maybe 12, fuel, for about 18, 20 minutes, which means you could roughly cook a non dehydrated meal on about 1 oz of fuel, give or take.

I believe though I'm not certain that the most efficient stoves are almost all focusing their flames in the center of the pot, whether those be a starlight type or this type.

I was actually unable to see much difference with this design on a wide pot and a narrow one, at least not one that mattered in the real world, though in theory, the wide pot should be a bit more efficient.

[Hikin’ Jim]

Hi, Harald, sounds very interesting. Do you have some photos, particularly flame shots?

HJ
Adventures In Stoving

[Harald Hope]

I have a few flame shots, I think I posted them here, but that's an earlier draft.

Here's the pictures on another thread, a few postings down. Of course the flame pattern is different because the screen is open, but it's close enough to give the idea. The pot stand was crooked in those pics, which is why the pot is crooked. The pot is a snowpeak 900 ml, but I'm also testing on an 11 cm wide 750ml pot.

However, note, that one was still using a pinhole outward pointing hole, along with 4 inner pointing ones, so it's burning a touch hotter than the new one.

It took me a while to realize that the outward pointing jets have to be removed to get consistently good efficiency, and it was only once I got the priming tray tested and done, and the amount of priming fuel, which is VERY important, you cannot just randomly squirt some fuel into the tray, too much and the fuel in the stove will overheat and flare out, that I was able to get a consistent ignition, easy, without an outward pointing heating jet.

I may do as well a quick how to on making this penny stove using only a swiss army knife classic and a tack/needle, to demonstrate that you can build it anywhere, any time, using only materials from any normal store.

[James Cahill]

I just recently started using a fancee feest style stove, but before that used a super cat with my stoic 700 ti kettle and didn't have any problems bringing 2 cups of water to a boil with ~3/4 oz denatured alcohol in around 6 minutes. It sounds like we have similar setups.

But i agree, the flames sneaking up the sides of my pot seemed like a waste, and the fancee feest stove is just so much cooler.

[John Donewar]

+1 for the Fancee Feest

The cook pot diameter is no larger than a Fosters can.

Party On,

Newton

[Harald Hope]

To be clear, apparently it's necessary to translate units: first, the units I'm measuring are calibrated using an irrigation syringe, ie, they are accurate, not approximated by eying out a measuring spoon or something.

When I used the term 'efficient', I' referring to 15ml = 1/2 oz, ie, 50% less than what the fancy feast is giving you at ~ 3/4 oz. There's an even more efficient design that yields about a 15% further improvement, if my math is right. 3/4 oz is 15 ml p+ 7.5 ml, ie, 22.5 ml. Hopefully this makes it more clear, but I will use ml in my statements because ounces are too confusing, being both weight and volume measurements. to be very precise: using a standard slx 50/50 ethanol/methanol fuel, somewhere between 11 and 12 grams of fuel boils 500 ml, or 2 cups. Not almost two cups, or 400 ml, which I see some people posting about, 2 full cups. 'Boil' means very close to 212 degrees F, not some bubbles coming up.

For what it's worth, jim wood noted that apparently the very thin big beer can pots seem to absorb heat well as it goes up the sides, which makes the fancy feast stoves work ok.

I should give the fancy cat stoves another try and see how they do, in fact I will, will only take 10 or 15 minutes to check them.

[Bob Gross]

Harald, to be precise, 500 ml is more than 2 cups U.S.

–B.G.–

[Harald Hope]

The fancy feast doesn't do too bad at all, but there some caveats:

Continued use of it with my tight wind screen is going to roast it to a crisp.

Pot is a snowpeak 900ml titanium.

Screen is .8 inches larger diameter than pot diameter, which focuses the flames along the side, but at the cost of I would say fairly quickly turning that flashing into crisped aluminum from my experience.

Screen is 5" tall, which focuses heat along the sides, flames are shooting up visibly above the screen top and along the edges, the penny has almost no visible flame at all.

Significant yellowing of flames suggesting not enough air is reaching it.

Time to max temp is quite fast on fancy feast, if I was dying of cold and needed hot water fast, the fancy feast would be the winner.

I used the jim wood suggested base for the fancy feast, which gives you more ground insulation, it's a larger cat food can thing, kind of unwieldy re size since you have to attach part of a fancy feast can to it to hold the other fancy feast can.

Here's the results for fancy feast:

15ml: water starts at around 70F, ends at about 195F. Penny stove reaches a full boil, 211 or so degrees, and stays there a bit, maybe 15 seconds or more, I didnt' really time it in my last tests.

17.5 ml, fancy feast very close to a full boil, ends at 209F, close enough to boiling among friends, fuel exhausted almost immediately after hitting max temp.

At 17.5 ml, the penny stove boils it first to 211 or so, then keeps boiling it for 30 to 60 seconds more.

That's not bad at all for the fancy feast though given how simple it is, but I believe these results should be checked with a wider wind screen, this narrow width only works with smaller efficient flames in my opinion, and these results may actually burn out the screen over repeated testing, I'd test it with 1.5" or so extra diameter on the screen..

In terms of the burn quality, basically the fancy feast is a flame thrower, and burns out very quickly, the penny stove delivers a slow, steady flame, and is more efficient, but that's not a surprise, but what is surprising is that the fancy feast is not too bad. Not sure how it will do with a screen large enough to not get roasted on the sides, I'll check that.

[Harald Hope]

Yes, a bit bigger, Bob, but relatively to the two cups, it's pretty close. I think I'll just stop using US measurements except in parentheses because mixing units gets too confusing. But I do generally measure 500 ml to keep it accurate.

Now to avoid some more real work and test a wider screen, heh. Again, I believe the above results were the result of sacrificing a screen that will otherwise last for months of trips, maybe even years, so I'm not going to do that anymore with it, I've crisped enough flashing wind screens by now.

[Harald Hope]

Ok, as I suspected, and this is why I stopped using the fancy feast stove very quickly during my initial foray into stove making:

With a wider wind screen, about 4" tall, didn't have a wider 5" one, performance was not just bad, but truly dismal.

At 17.5 ml, 500 ml water with fancy feast reached only 168F.

The reason was totally obvious, because the flame is totally uncontrolled, it shoots up the sides of the pot, in a sort of interesting circular way, ie, the flame shooting up the side circles around the pot outside slowly, kind of groovy to watch unless you actually want an efficient stove, then, not so much. It was precisely this thing of flames shooting up the sides that made me decide to find a better way to do penny stoves, but the fancy feast stove is what it is, it can't really be changed, whereas penny stoves can be highly modified and tuned, the only limit is your patience and willingness to inhale too much alcohol toxic fumes during testing. Any time you see flames shooting up the side, you know that you are looking at an inefficient stove, because those flames are almost all lost heat energy, though it might be a fast boiling stove because of that in some cases where you trap that heat energy with a wall tall enough to funnel it in a bit, but at the cost of roasting the wall over time.

Even with the wider screen, and increased air flow to the stove, I still saw significant yellowing of the flames, which fits with the discussion of the two flame types these stoves use, the turbulence created by the tight jets of a penny type stove I guess mix in oxygen well. This compares to the almost pure blue of the penny stove jets, suggesting the penny is getting a much better combustion of the vaporized fuel, which I knew already, that's why I spent so much time fine tuning the design in first place, to achieve that end.

So that's that, either roast my wind screens and begin to approach the efficiency of a well made center flame focused stove with a fancy feast stove, or get truly dismal performance using a wider screen. With more testing I'm sure I can get a steady 22.5 ml 500 ml boil without roasting my wind screen with a narrow pot, but really, why?

My testing by the way is NOT done on a work bench inside out of the moving air, it's done outside in a space where the air moves a bit, so the tests are reasonably close to real life.

It was good to go back and retest, thanks for the excuse to avoid working on a tedious real job project, but the tests show me why I stopped using fancy feast cat stoves on narrow pots, honestly I wouldn't use them on anything if I want efficient burns, maybe quick ones, on a wide pot, yes, but not efficient. I should have videoed the wide screen burn, and then shown a video of a well controlled penny stove burn, there's literally no comparison at all, one is just a basically out of control flame, one is tightly focused jets that don't get too hot or large, and basically focus all of the heat right in the center of the pot. I have been carrying a spare stove just for the heck of it, a fancy feast, but I think I'll swap that to a penny stove, that would make more sense I think in terms of a spare, maybe with a slightly different burner hole configuration for difficult environments.

[Bob Gross]

"I think I'll just stop using US measurements except in parentheses"

If you want to be consistent, then use the Celsius temperature scale.

–B.G.–

[M B]

Cat stoves suck.

There. I said it.

[Harald Hope]

but nobody knows the C stuff, and for some reason, it never stuck in my head.

The real area where this matters is fuel measurements, volume vs weight. But you are right, I should convert it.

Normally I don't measure my water temps since a rolling boil is going to be around 210 or more if the bubbles are big, but for this I did so I could be very clear.

What struck me, by the way, before I used a irrigation syringe to calibrate my measuring device for fuel, was that my attempt to use measuring spoons was way off, about 10, 15%, those can't be used if you want to actually make statements comparing your results to others, the surface tension rounding alone is a significant weight. Weighing the fuel is a better way of course, but that's too tedious to do, so it's easier to just calibrate a measuring thing with lines.

Anyway, as my long since passed initial narrow pot tests showed, fancy feast isn't very good, it's ok, if you use a certain type of screen, and a certain height, but it's not very good, and its not remotely close to the efficiency of a well designed stove. Convenient, easy to make, yes, no doubt.

MB, to Jim Woods credit, he never claimed to be an engineer, he said he's just a guy who came up with this idea after sharing ideas with others. The guy who designed the penny stove is an industrial designer, and it shows, every part of it is makes total sense in a functional way, and the design itself, like all good programming and designs, is very flexible and easy to modify.

For those counting, the weight of the thing that acts as the penny needs to be about 3.5 grams, ie, an old pre 1982 copper penny, the new ones weigh about 3 grams, which I guess is not quite enough to hold the pressure in.

[Bob Gross]

"but nobody knows the C stuff, and for some reason, it never stuck in my head."

You will never make it as an engineer. Where is David Thomas when we need him?

Just remember that when you align the Celsius and Fahrenheit scales, -40 = -40, and the boiling point of water is +212 F or +100 C, but that is only for standard conditions.

–B.G.–

[Harald Hope]

yes, I know, c = 5/9(f – 32), f = 9/5c + 32 ( I think that's right), 212f = 100c, 1 km = 5/8 mile, I know the formulas etc, every time I go to europe I do the conversions in my head so they stick, but the c just doesn't stick intuitively, I don't have a sense of what it means, I know that 40 c is pretty hot but I don't know how hot, for example, whereas I know exactly how hot 108F is, or whatever, I always have to convert c to f, whereas I know what grams, kg, meters, cm, mm, km, ml, liter, dl, etc, are roughly.

Luckily in my area of engineering this doesn't matter, with the exception of that pesky , , decimial point difference between euro and us numbers.

Maybe if I had spent just a year or two more in europe it would have finally gotten to mean something to me, don't know.

For stove stuff however, I think actually using 2 cups is more meaningful because that's what most people measure, but ml makes more sense because ounces are too small already, it's easier to count ml than ounce fractions, same for grams of weight, I never weigh stuff to see what it weighs in ounces, always grams. And since most americans use F, that's also fine, because there is no actual ground for confusion.

But you're right, I'd never make it in mechanical type engineering.

[James Cahill]

"But you're right, I'd never make it in mechanical type engineering"

That's because they use silly scales like Rankine.

[Daniel Fish]

…

[Paul Ashton]

This thread has quite a wealth of information
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=42874&startat=20

[Harald Hope]

That thread kind of repeats the standard error of not comparing apples to apples, ie, standard amount of water boiled, correctly measured amount of fuel used to boil, tests indoors without a windscreen, which given the fact you just cannot use alcohol stoves in the real world without some type of real wind screen, are essentially a total waste of testing fuel, but the main error is that people were very focused on boiling times, and it's worth noting that they were getting very fast boil times, because they were shooting uncontrolled flames up the sides of pots.

The truly horrendous performance of the cat stoves as well was obvious in that thread, some people required 2 oz (60ml!!) to boil 500 ml of water, others 30, but almost nobody actually measured, and many who did didn't test it outside, with moving air.

All in the name of science, heh. I'll write some of this up as soon as I have time, given that this is basically just physics and chemistry, there's not a lot of subjectivity involved.

Its also worth taking a very close look at stoves like the starlight and ion that are getting very good results, but I'm also curious about altitude. I may in the near future give a set to someone who goes to higher altitudes routinely and who is willing to actually measure and be a bit scientific in their testing, there's some higher altitude performance questions I can't answer non-empirically, I can nail down the real world lower altitude stuff pretty easily.

By the way, my motivating thing for this was having bought a used snowpeak 900 pot, narrow, reading that wider pots were 'more efficient', but realizing that I really really like the size and diameter of the snowpeak, it holds heat in food super well as you eat, with cozy, it packs perfectly, it's perfect size to store the entire kitchen, it fits perfectly into the backpack, just like any other 6" rolled type item, and, huge plus, a 5" tall windscreen fits snugly inside it, sticking out just a touch, and the lid holds that in perfectly as well, making for a very snug package, so I wanted to see if the 'wider pots are more efficient' was true or false. Basically my initial conclusion is that it is false, but that the easy to make, thus popular, stoves are very inefficient, and because of that, you have to squeeze out the most efficiency with a wide pot. sgt rock has done good actual engineering analysis of this stuff, particularly with his ion stove, so the actual science is out there to be empirically tested, my tests so far agree with his, the best by far stove is center flame pointing up, there are several variants of this, but they all shoot the flame to the same place, just in different ways. For UL focused forums, saving 50%, or more, per meal, of fuel should be of some interest, it is to me, it's far easier trimming weight off total fuel carried at this point for me than anything else, I already, for example, knocked off 3, 4 ounces (with improved consistency of burn, easier lighting as well) on a 7, 8 day trip just by playing around a bit while avoiding real work, and that was starting at an already reasonably efficient point, just not consistent or easy to control. And that's 8 volume ounces, about 6 ounces by weight. ie, an 8 ounce container, but I believe that's pushing it because once you get to altitude you are going to need more fuel per boil, so you'd have no extra there, even with a smaller 2oz bottle for daily fuel pouring in the pot itself, it's still close if you hit bad weather or need more because of altitude.

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