Forum Index » Editor's Roundtable » The Evolution of a Winter Stove - Part 3


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Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Cliff Notes on 10/22/2013 00:08:06 MDT Print View

> > and still expect to receive a stove before the New Year
> Barring death and disaster, I would certainly think so.
The X axis power driver on my CNC has suffered a slight misfunction and is away being repaired. This will create a delay of a few days in manufacturing.

No, 'slight misfunction' does not mean a catastrophic bang with smoke everywhere! It just means that the safety circuit started to trigger becasue of excess current draw at high speed. We know what the problem is likely to be - a damaged FET in the H-bridge.

Do not adjust your set, we will soon be back to your scheduled program.

Cheers

Edited by rcaffin on 10/22/2013 00:08:41 MDT.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
stove arrived on 10/22/2013 09:33:12 MDT Print View

Yup, mine arrived yesterday. I did some preliminary tests and was getting about 10-12g/L, with no tweaking. Weight was 86g.

Jan Rezac
(zkoumal) - MLife

Locale: Prague, CZ
Stove arrived + safety issue report on 10/31/2013 08:57:57 MDT Print View

Roger, thanks for perfect timing. The stove arrived last week just on the day I was leaving for a four-day trip. It was an opportunity to test it a bit, although we cooked mostly on fires.

The stove is very nice and light and the attention paid to some construction details is really amazing. I like it a lot.


However, I've encountered one quite serious issue: I was screwing the valve onto the canister and although the safety valve lever was in the "off" position, the gas started to leak. At first, I wanted to tighten it quickly to get a seal, but the leaking only increased so I disconnected the canister. It turned out that the brass pin was stuck in the "on" position, regardless of the position of the lever (which I previously turned to "on" for storage and switched to "off" just before use). I found that this can happen because the white body of the safety valve moves horizontally a couple of millimetres and when it is pushed into the valve assembly, the eccentric region is not aligned completely with the pin (see photo). As a result, the pin is caught on the edge of the full-diameter region of the white part, being engaged regardless of the position of the lever. Pulling the white part out a bit fixes the issue for the moment.

valve_problem

Since then, I was checking the pin before every use, and this problem occurred again once or twice. The design should be updated, most easily by making the eccentric region a bit wider to accommodate the possible shift, or by preventing the shifting movement by some other means. I will fix that myself on my stove; I will probably insert a spacer into the valve assembly so that the white part can not be pushed inwards any more.

Additionally, I would prefer to have the on and off positions of the lever to be left and right (with labels on the sides of the black block) rather than up and down. As it is now, the lever in the off position points outwards, and because its quite thin and sharp rod, I'm turning it down when I pack the stove. Being able to pack the stove as is would be nicer, because the stove will be ready (in off position) for next use.

Edited by zkoumal on 10/31/2013 13:53:04 MDT.

Jan Rezac
(zkoumal) - MLife

Locale: Prague, CZ
Stove problem fix on 10/31/2013 14:34:11 MDT Print View

I have just fixed the problem described in my post above. To prevent the safety valve (white part) from being pushed inside, I inserted a spacer that fills the small empty space between this part and the aluminium hose connector on the other end.

I cut a thin (1.4 mm) ring from a plastic tube of approximately right diameter. A piece of this thickness perfectly fills the empty space. To allow free flow of the gas from the outside into the ring, I cut several tiny notches into one face of it.

It works well, now the valve can not be moved into the position where the pin would be blocked.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Stove arrived + safety issue report on 10/31/2013 15:00:34 MDT Print View

Roger, is there any necessity for a world wide product recall?

--B.G.--

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Stove arrived + safety issue report on 10/31/2013 19:33:12 MDT Print View

Hi Jan

If that photo was taken with the pin removed and the cam valve in place with the retainer plate screwed in properly, I am a totally puzzled by the position of it. It just looks wrong. It should NEVER get there.

Actually, I am really puzzled by the whole photo. Could you send me the original photo without cropping please.

If you wish to post the stove back I will check it out and fix whatever the problem is, no charge. It really is not meant to do that.

Cheers
roger@backpackinglight.com

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Stove arrived + safety issue report on 10/31/2013 19:47:18 MDT Print View

That couldn't have been the result of a customs inspection, could it?

--B.G.--

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Stove arrived + safety issue report on 11/01/2013 02:51:48 MDT Print View

Hi Jan

> I would prefer to have the on and off positions of the lever to be left and
> right (with labels on the sides of the black block) rather than up and down.
Yes, I thought of this, but it failed one test.

7 pm, bad weather & snow & wind, very cold & tired, dim light, incipient hypothermia from pitching the tent. Goes to set up stove. Which way is OFF? Left or right? Can't even read the writing.

Solution: handle out of canister, pin out; handle in towards canister: pin into canister.

Gas is dangerous. I never ever assemble the stove without checking: safety valve off, needle valve gently closed.

Cheers

Jan Rezac
(zkoumal) - MLife

Locale: Prague, CZ
Stove problem on 11/01/2013 03:49:54 MDT Print View

Roger, I sent the larger photo via e-mail.

I'm curious whether somebody else can reproduce it. Here are the steps that would lead to this problem if it affects your stove (do not attach the cannister):

1) Set the cam valve to the "off" position (lever points away from the threaded connector)

2) Position the whole thing so that the canister connector end points downward. Gravity pulls the brass pin down, out of the cam. Press the cam valve (the white knob with the lever) inwards. In my stove, it is possible to move it in and out a bit, a little force is needed to overcome the friction of the o-ring inside.

3) Turn the assembly upside down and look into the connector. Turn the cam valve lever - if the brass pin in the connector moves up and down, everything is ok. If it does not (it is stuck in the "on" position), congratulations, you have reproduced the problem. Let us know.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Jan's problem on 11/01/2013 04:20:07 MDT Print View

The photo jan sent me was excellent. I was confused by the small photo shown above.

I may have accidentally included in the pile of white valves for assembly one early unit which was not to spec. Such a unit would cause this problem. I await reports from anyone else who has this problem. In the meantime, the dimensions in the master drawings and CNC programs have been tweaked slightly to prevent this from happening again. It's a beta test after all!

Jan's solution used a bit of tubing, but not everyone will have something suitable. If your stove shows signs of this problem, there is a much simpler cure (which has been tested). Take a short bit of 1 to 1.2 mm copper wire and form the letter C. Round the two ends so they are not scratchy. The OD should be about 7 mm, and must be < 8 mm. It has to fit easily into the 8 mm bore in the block. The two ends of the wire should not touch: it's a C, not an O. Remove the connector (do NOT lose the screws!!!), drop the loop down the hole, jiggle it flat, replace the connector, replace the screws. Caution: do not use hard wire, and do **NOT** scratch the inside of the 8 mm bore! The loop should fall in easily.

Cheers
Roger

Jan Rezac
(zkoumal) - MLife

Locale: Prague, CZ
Stove modification for lightweight butane canisters on 11/01/2013 15:55:11 MDT Print View

After fixing the problem with the valve, I moved to hacking the stove so that it can be used with lightweight butane canisters (for refilling lighters). The stove with a full canister (50 g of gas) weights less than 160 g!

I created a separate thread for this topic in the MYOG section:

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=83643

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Stove modification for lightweight butane canisters on 11/02/2013 04:31:52 MDT Print View

> I moved to hacking the stove so that it can be used with lightweight butane canisters
> (for refilling lighters).
Oh My Gawd. My stove has been hacked already!
I suppose I have to see this as a compliment ... :-)

(Jan and I have been discussing this by email. Interesting ideas kicked around.)

Cheers

Anthony Britner
(ant89) - F - M

Locale: North Wales, UK
my comments on 11/02/2013 15:13:31 MDT Print View

I'd certainly be interested, mostly in the 116T version without the burner as I already have one. It seems to make sense to use the burner I already have available.

Edited by ant89 on 11/02/2013 15:16:05 MDT.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: my comments on 11/02/2013 16:55:52 MDT Print View

email me.

Cheers
roger@backpackinglight.com

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Update on beta test feedback on 11/11/2013 00:52:38 MST Print View

Hi all

Yes, I have received some feedback from beta-testers. The resolved issues are:

* Tab at bottom of leg used for opening them could be bigger, for gloves.
Good idea, and I have updated the drawings and the programs. I will be making some more legs soon, with the bigger tabs.

* Brass pin in canister connector not retracting.
This was probably partly due to a bad clash of tolerances, but also to the white cam valve being pushed a long way into the canister connector while the brass pin was fully out. The user solved that problem by pulling the white valve back out by a millimetre or two using the Ti wire handle. Should any other user have this problem, please contact me. The cure in the field is to pull the valve back out a millimetre or two - it won't come right out as the retainer plate holds it in. But I do have an extremely simple 'fix' for the problem as well.

* Tiny flame
User cleaned out the needle valve, removing two little bits of aluminium swarf. My fault, apologies, more care with cleaning needed.

* Filler cord jammed and broke when user tried to extract it from hose
This required a detailed examination of the hose, which was returned to me. It turned out that the clearances I had been using were a shade small for comfort. I had to buy some special drill bits to deal with this: 1.25 mm and 1.35 mm. They exist, they just are not common. However, with those drill bits the problem was eliminated. All future stoves will have the improved clearances. Anyone with an existing stove who want the upgrade should contact me. You will need to remove the hose and post it back to me.

There is one more bug which has yet to be fixed: I am waiting on the parts being returned.

Meanwhile, I have repaired my CNC machine and started machining again. Happy days!

Cheers

Jeff McWilliams
(jjmcwill) - M
Temperature limits? on 11/20/2013 21:15:13 MST Print View

On about 10/09, jerry adams stated he felt the stove would be good down to about 12F.

Is that widely regarded as an accurate estimate of its lower range of usability?

I'm planning a trip to the Adirondacks at the end of the year. Last year's temps in the area averaged 15F. Accounting for elevation change of 2000', that's about 11F in the proposed camp area. However, several days saw lows of 0F to -3F, which could be almost -9F at elevation. If an inverted canister is useless at that altitude, I guess I need to take a white gas stove regardless of the "cool factor" of Roger's stove.

I have the 116T burner version, and was sort of hoping to take it with me, but not at risk of being unable to melt snow and boil water.

Douglas Frick
(Otter) - MLife

Locale: Wyoming
re: temperature limits? on 11/20/2013 21:55:57 MST Print View

> On about 10/09, jerry adams stated he felt the stove would be good down to about 12F.
> Is that widely regarded as an accurate estimate of its lower range of usability?


It's possible Jerry was referring to the Winter Stove running from a pure-butane canister, or perhaps the original Fire Maple canister-top stove, without any form of warmth being transferred to the canister. (+12F is the approximate boiling point of iso-butane.) The context of his post wasn't quite clear.

However, +12F is NOT a lower limit for an inverted-canister iso-butane/propane stove, such as this Winter Stove. That, in fact, is exactly why and how Roger's design differs from the original Fire Maple stove. As long as the propane in the canister can vaporize (the approximate boiling point of propane is -40F), then the pressure from the propane gas at the 'top' of the canister will force the iso-butane/propane liquid out of the (inverted) canister valve and down the fuel line.

I wouldn't expect the stove to run quite as low as -40F without some help, however. My Coleman Exponent stove gets a bit balky below -30F under worst-case conditions: canister sitting out all night, exposed to the air and sky and insulated from the ground, then allowed to cool even more as the stove runs. However, simply putting the canister in a shallow pan of cold water (or even packed in relatively-warm ice or snow) should allow the Winter Stove to run when the air temperature is below -40F.

Edited by Otter on 11/20/2013 21:57:21 MST.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Temperature limits? on 11/20/2013 23:25:31 MST Print View

According to wikipedia, the boiling point of isobutane is 8 to 16 F.

If you have propane and isobutane, and operate at the boiling point of isobutane, the propane will evaporate more than the isobutane so after a while, you will be left with mostly isobutane. What do they have, 15% propane? You should be able to use that much.

Then, with an inverted stove, it will only work above the boiling point of isobutane, which I said might be 12 F. Maybe you could go down as low as 8 F.

This is theortical, I haven't used an inverted stove. Maybe the actual boiling point of your canister is different. It also depends on altitude I believe.

You can always use one of the techniques to warm canister, like with body heat. An inverted stove would work much better because it has very little evaporative cooling as happens with upright.

Edited by retiredjerry on 11/20/2013 23:27:04 MST.

Douglas Frick
(Otter) - MLife

Locale: Wyoming
Re: Temperature limits? on 11/20/2013 23:46:41 MST Print View

Jerry, the problem you describe applies to canister-top stoves (canister sits upright, with burner on top) operating in the +12F range, where the propane alone boils and burns off, leaving 3/4 canister of (useless) liquid iso-butane. However, the key to the liquid-fed Winter Stove working at well below the boiling point of iso-butane is that the canister is physically _inverted_ after the stove warms up: the "top" of the canister (with the valve) is pointing down, and the "bottom" (concave) part of the canister is facing up.

As long as the temperature of the canister is above -40F (boiling point of propane), then as the pressure in the canister drops, some of the propane will boil out of the liquid iso-butane/propane mix. The propane gas floats upwards, and so occupies the space between the liquid mix and the uppermost part of the canister (its concave bottom). There's no way out for the propane gas, so the pressure forces the liquid iso-butane/propane _mix_ out of the valve (which is the lowest point), along the fuel line to the stove, where heat from the lit stove (transferred through the heat shunt or a vaporizer loop) converts the liquid mix into vapor, which burns.

So, the stove should work down to the boiling point of propane. Once all the liquid iso-butane/propane mix has been pushed out of the canister's valve, its last gasp will be mostly pure propane gas, leaving an empty canister.

Edited by Otter on 11/21/2013 00:02:46 MST.

Stuart R
(Scunnered) - F

Locale: Scotland
Re: Re: Temperature limits? on 11/21/2013 02:11:56 MST Print View

Douglas, you need to read about the effect of cold on gas canisters

The gas above the liquid mix does contain propane, but it also contains butane (and/or iso-butane, depending on the contants of the canister). As a rough analogy, think about air - it contains water vapour at temperatures well below the boiling point of water. The proportion of propane depends on the constituents of the liquid mix, but is typically 60-70% propane. It does not depend much on temperature - the percent propane gas will be almost the same at -40F as at +40F. This is not the same as the air/water vapour analogy, but then the boiling point of water is vastly different from oxygen and nitrogen.

"So, the stove should work down to the boiling point of propane."

Definitely not.
The minimum operating temperature will depend on the pressure generated by the aforementioned propane/(iso-)butane gas mixture. For canisters such as MRS IsoPro Red (20/80% propane/iso-butane), Coleman (30/70% propane/n-butane) and Primus Power Gas (25/25/50% propane/iso-butane/n-butane) you can expect the stove to work with an inverted canister down to 0F (-18C).

Edited by Scunnered on 11/21/2013 02:27:31 MST.