2023/24 VC Temperature discussion thread

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Clarify the stalling. The cat stalling is one of the biggest problems along with the cat going to overheat. The firebox doesn't stall unless it's green wood.

The firebox DEFINITELY stalls in these stoves.. Its not here say., because its happened to me as well as others. Its not a complete stall as if the entire rest of the load completely stopped burning. Is a lot slower burn due to the lack of draft and because the draft and burn is slowed your getting more incomplete combustion both in the firebox and in the secondary burn chamber. Stalling the stove.. and im not suggesting your purposely doing this.. creates alot more creosote..

If our stoves are the same size .. saying for arguments sake.. My firebox is 2.3 CUFT... loaded half way is 1.15 cuft or roughly 20 lbs of wood.. oak.. thats roughly 1.33 lbs of wood burned per hour

Thats better then blaze king numbers. Our stoves burn good.. but not that good.. your box is stalling.. but not completely going out..
 
Conversly, if the cat was not installed in my case, at the same primary air setting the fire would go out sooner leaving more unburned wood in the box. I believe this is because that cat is buring the unspent gases created from low primary air settings.
Now, keep in mind this is with my Dauntless stove.
Lots of thoughts and discussions going on at once. This is the stalling I was referring to.
I never have unburned wood in the box and the fire go out.
Is this happening with the secondary engaged but no cat in the stove?
 
Correct but only with lower air settings.
When the cat is installed and operational I don't have this issue at low air settings.
 

You all may have talked me into it jumping on the data logging bandwagon…

Also I call this my cat high temperature air quench override! I also tuned on my thermostat, door was basically shut before I ever started working on it.
IMG_0192.jpeg
 

You all may have talked me into it jumping on the data logging bandwagon…

Also I call this my cat high temperature air quench override! I also tuned on my thermostat, door was basically shut before I ever started working on it.
View attachment 319994
Couple thoughts:

DAQ Module:
  • This DAQ module is +/- 10V analog inputs..... FAQ's says not very accurate for thermocouple inputs. How are you planning to measure temps?
  • It has no storage capability. So you need to connect it to a PC which does the data logging. No PC no data.....
  • The unit I use has storage capability (can collect data on its own for download later) and it can stream live data to a PC for real time plotting.
    • I use the real time plotting when I am diagnosing a problem or trying something new. Other than that the PC next to my stove is just annoying....
Secondary air control:
  • In that picture is the cat hot?
  • Trying to figure out how it works....
 
@ Rusty18
What stove is that? What have you observed as far as the secondary air control with the thermostatically controlled spring? What are you trying to accomplish with the chain?
 
I have several laptops that I can set up for storage and no WiFi at the house other than hot spot on the phone. The daq is a set up for 10vdc inputs (4-20 ma with 250 ohm resistor) and I have a pile of watlows I saved from the dumpster at work so thermocouple to 4-20 isn’t an issue. The daq can also do double duty for Monitoring energy usage with the addition of a current transformer.

In my picture the stove is cold.

The spring is supposed to close the secondary air supply as the flue gas through the cat heats up. I’m pretty sure they expect the cat to operate on the fuel rich side of the curve but it doesn’t, at least not the way I run it.

I rigged up the chain as a way to manually open the secondary and hold it open when my stove try’s to go nuclear. I haven’t tried it with the chain yet but opening the secondary does quench my cat.
 
Sweet.... sounds like you got it worked out. I got my Watlows from the same source.... dumpster! They have served me very well over the years, I use them for readouts and I wired in a piezo for an audible alarm (which is a mixed blessing)

In that picture (with the stove cold) it looks like the secondary is full closed (do I have that right?)

As the stove heats up the bimetal moves CCW (viewed from the back) and lifts the flapper? Seems like that would be increasing the secondary air as the stove heats up? Or do I have it wrong?
 
I've been running my stove hotter than I typically have in the past and it's amazing how differently it runs overall. By hotter I mean higher stove top temps, air more open. Running higher stove temps has equated to lower flue temps and lower cat temps overall. It's been more difficult keeping the cat above 1000 running things hotter upfront. I was always worried about letting the cat get higher than 1000 with the air fully open on a fresh load. I've been leaving the air fully open and monitoring the cat temps to see what they really do. It's been difficult to get the cat to 1200. Once I start lowering the air the cat doesn't stay high for too long.
 
In my picture the stove is cold.

The spring is supposed to close the secondary air supply as the flue gas through the cat heats up. I’m pretty sure they expect the cat to operate on the fuel rich side of the curve but it doesn’t, at least not the way I run it.

I rigged up the chain as a way to manually open the secondary and hold it open when my stove try’s to go nuclear. I haven’t tried it with the chain yet but opening the secondary does quench my cat.
What stove model?
On my stove I have the same setup. Tried all last year to get a definitive answer from VC or anyone about the actual purpose and function of the secondary air control. On my stove the flap is open slightly like yours when cold. As the temps heat up the flap closes. Then as the temps rise at the cat the spring unwinds and the flap opens. Does your do that automatically with the thermostatic spring. I replaced my thermostat as the sensor itself had burned quite a bit. If you search secondary air control you'll find a lot of posts where people kept the flap closed instead of opening it.


There are other threads about this flap. I called VC multiple times and no one could ever answer how this flap is supposed to function.
 
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Sweet.... sounds like you got it worked out. I got my Watlows from the same source.... dumpster! They have served me very well over the years, I use them for readouts and I wired in a piezo for an audible alarm (which is a mixed blessing)

In that picture (with the stove cold) it looks like the secondary is full closed (do I have that right?)

As the stove heats up the bimetal moves CCW (viewed from the back) and lifts the flapper? Seems like that would be increasing the secondary air as the stove heats up? Or do I have it wrong?
It’s the pic angle. Flapper is open and as the stove heats up bi metal moves CW and closes the door. It currently has a stop on it to keep the bi metal from opening it up letting the door go beyond full closed.
I have a manual for it somewhere I need to pull out and verify because if the bimetal worked the other way and opened the air as temp came up to quench the cat it would make a lot more sense.

At no point in the process does the bimetal ever try to lift the flap as the stove gets hotter. The only logical purpose I can think of for having the flap open then closed would be to limit the amount of flue gas the cat sees on a cold start. With flap open stove would draft fresh air through the cat vs pulling it out of the firebox (assuming bypass is open like it’s supposed to be).

And yes, I’m one of the ones that tried blocking it off completely, it did make cat more controllable but I wasn’t happy with what little smoke I had coming out the stack. With door full open/air quench method i get my cat cooled and still have a clear stack (no smoke).

Model is an encore 2550.
 
1st pic
Cold stove primary air lever full closed, note secondary air damper is full open. The little spring you see is just out of my junk drawer to keep my over ride chain from slipping off.
IMG_0206.jpeg


2nd pic
Stt 500f- primary air lever at about 60-65% open

IMG_0211.png


3rd pic
Stt 500- primary air damper at 40%. Primary flapper is closed.
IMG_0209.png
 
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This is my run last night. I wanted to do a little experiment and keep the air mostly open on a 3/4 load to see how everything reacted. I've never done this because I didn't want the stove to run away on me but I also wanted to see if I could control it with my new found knowledge of my primary air lever.
12-4-23.jpeg

The 3/4 load burned pretty fast, which would be expected with the air open all the way, but the interesting thing is when my cat got to 1600 I lowered the air down to about 10% open. The cat temp dropped about 20 degrees and pretty much hovered there while it burned down. I have not been able to do that yet. Usually by this point my air is already pretty low and lowering it more doesn't have much of any effect. Then about 10:15 I added two splits to keep the temps up for awhile.

I have my high alarm set at 1550, which is what all those H's are.

P.S. - I don't plan to run like this. I just wanted to see what kind of control I could have when the cat gets high.
 
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You all may have talked me into it jumping on the data logging bandwagon…

Also I call this my cat high temperature air quench override! I also tuned on my thermostat, door was basically shut before I ever started working on it.
View attachment 319994
This what I use for tracking and logging. It allows me to check the temps whenever I want, where ever I am. Two things that could make it better would be the ability to connect more than two thermocouples (I sent them emails so I'm working on them) and more control over the graphs that are automatically created from the data. But it was very simple, basically plug and play.

 
So I found the interesting from another VC thread going on.. and its about the heat we get from our stoves as well as some efficiency.. cat VS non cat Im tagging @Ashful and @sargeott

The question more being how much heat do we actually get from our catalyst being in.. As I said in the other thread.. We definitely get some advantage of the smoke burning and creating additional heat. I did do a minor rebuild to my stove this past summer and have a better understanding of have the stove
operates. This is excluding inserts BTW..

Here is my stove running this morning

My cat temperature is 1423
STT is 445
on my double wall pipe is 300
on the back of the stoveis 657

Now granted Im not taking off the heat shield to measure alot of the back area but it is significantly higher at the back.. if the actual griddle temperature was 657 the stove would be considered hot.. the back half of the stove is actually putting out a good amount of heat in relation to the actual firebox temperature.

Im not saying that this should be marked as a plus for this stove.. We are definitely gaining heat from the smoke that is being burned in the cat chamber

I thought this was kinda neat..

All thoughts/opinions are welcome..

20231209_071434.jpg 20231209_071503.jpg 20231209_071517.jpg 20231209_071536.jpg
 
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What I've gleaned from that other thread, as well as my own personal experience, having burned five examples of cat stoves of two very different designs on two very different chimneys:

1. On most modern cat stoves, where the cat is above the firebox and the bypass is literally in the ceiling of the firebox right under the flue, burning the bypass open creates a scenario of catastrophically high heat loss. If you do this in my stoves, you will quickly overheat the chimney, as flame basically shoots directly up the chimney from the firebox.

2. If you remove the combustor from one of these stoves and close the bypass, the path becomes slightly more circuitous, eliminating direct flame-impingement, but still likely sending quite a lot of heat up the flue. Moreover, you'll be forced to burn at a sufficiently high rate to keep flue temps above 250F all the way to the top of the pipe (so maybe 500F+ at bottom of pipe), limiting your available burn range.by

3. Many older cat stoves are of the downdraft variety, in which the bypass is usually located in the rear wall, rather than the ceiling of the stove. These may suffer less direct flame impingement into the chimney, while operating in bypass.

4. Many of these older downdraft cat stoves provide an extremely circuitous path for the exhaust, once the bypass is closed, making the penalty of running with bypass closed and no cat installed far less than a good/modern cat stove.

5. Owing to 4 above, a BK might see a drop in flue temp from 800F (and still climbing) down to 300F, after closing the bypass, with the cat installed. This is a direct reflection of the efficiency of this stove, with the cat installed. Other users report they don't see nearly the same difference in temperature in the VC Defiant in question, indicating that they probably have much lower efficiency.

Personal note: Since the primary reason most buy a cat stove is to achieve lower burn rates than is possible with a non-cat, it seems kind of silly to spend money on a cat stove, to then defeat its ability to do the one thing that caused you to spend the extra coin on one in the first place. If you're burning a cat stove without cat installed, you will want to run it hard enough to keep flue temp over 250F at top of the pipe, accounting for the cooling that will take place between stove collar and top of flue.
 
So I found the interesting from another VC thread going on.. and its about the heat we get from our stoves as well as some efficiency.. cat VS non cat Im tagging @Ashful and @sargeott

The question more being how much heat do we actually get from our catalyst being in.. As I said in the other thread.. We definitely get some advantage of the smoke burning and creating additional heat. I did do a minor rebuild to my stove this past summer and have a better understanding of have the stove
operates. This is excluding inserts BTW..

Here is my stove running this morning

My cat temperature is 1423
STT is 445
on my double wall pipe is 300
on the back of the stoveis 657

Now granted Im not taking off the heat shield to measure alot of the back area but it is significantly higher at the back.. if the actual griddle temperature was 657 the stove would be considered hot.. the back half of the stove is actually putting out a good amount of heat in relation to the actual firebox temperature.

Im not saying that this should be marked as a plus for this stove.. We are definitely gaining heat from the smoke that is being burned in the cat chamber

I thought this was kinda neat..

All thoughts/opinions are welcome..

View attachment 320392 View attachment 320393 View attachment 320394 View attachment 320395
In that other thread I'll take pictures and post over there.
The orientation and placement of the catalyst in the duantless is drastically different than the other VC stoves. I made a rough diagram and Dont want to muddy the waters here.
But I believe this is why the dauntless doesn't care if the cat is inside or not.
 
In that other thread I'll take pictures and post over there.
The orientation and placement of the catalyst in the duantless is drastically different than the other VC stoves. I made a rough diagram and Dont want to muddy the waters here.
But I believe this is why the dauntless doesn't care if the cat is inside or not.


ok let me know when you post
 
The Intrepid flexburn is different yet from any of its sisters as far has placement of the cat but flue gas is generally pulled upward through it instead of down through it ax in its bigger sisters save for maybe the Dauntless. The older Intrepid 2 was an updraft design stove. Never heard about any problems with them on here. Maybe that's saying something? Or just not much of a learning curve?
 
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What I've gleaned from that other thread, as well as my own personal experience, having burned five examples of cat stoves of two very different designs on two very different chimneys:

1. On most modern cat stoves, where the cat is above the firebox and the bypass is literally in the ceiling of the firebox right under the flue, burning the bypass open creates a scenario of catastrophically high heat loss. If you do this in my stoves, you will quickly overheat the chimney, as flame basically shoots directly up the chimney from the firebox.

2. If you remove the combustor from one of these stoves and close the bypass, the path becomes slightly more circuitous, eliminating direct flame-impingement, but still likely sending quite a lot of heat up the flue. Moreover, you'll be forced to burn at a sufficiently high rate to keep flue temps above 250F all the way to the top of the pipe (so maybe 500F+ at bottom of pipe), limiting your available burn range.by

3. Many older cat stoves are of the downdraft variety, in which the bypass is usually located in the rear wall, rather than the ceiling of the stove. These may suffer less direct flame impingement into the chimney, while operating in bypass.

4. Many of these older downdraft cat stoves provide an extremely circuitous path for the exhaust, once the bypass is closed, making the penalty of running with bypass closed and no cat installed far less than a good/modern cat stove.

5. Owing to 4 above, a BK might see a drop in flue temp from 800F (and still climbing) down to 300F, after closing the bypass, with the cat installed. This is a direct reflection of the efficiency of this stove, with the cat installed. Other users report they don't see nearly the same difference in temperature in the VC Defiant in question, indicating that they probably have much lower efficiency.

Personal note: Since the primary reason most buy a cat stove is to achieve lower burn rates than is possible with a non-cat, it seems kind of silly to spend money on a cat stove, to then defeat its ability to do the one thing that caused you to spend the extra coin on one in the first place. If you're burning a cat stove without cat installed, you will want to run it hard enough to keep flue temp over 250F at top of the pipe, accounting for the cooling that will take place between stove collar and top of flue.
I can confirm in my Defiant, model 1975, I get flames ripping up the stack with an active fire and bypass open.

I would also caution that measuring the surface temp of the back of the stove is not really good way to assess how much heat is coming off it. For the the Encore and Defiants (not sure about other models) the back is finned and it is vertical. That adds a lot of surface area and improves the heat transfer coefficient due to natural convection. For the same surface temp a finned vertical surface will pump out a lot more heat (btu/hr) than a flat horizontal surface at reduced surface temps. So I suspect the back is pumping out a lot more heat than a surface temp comparison might suggest.

Also, the heat that comes out the back is not all from the cat, certainly some of it is but if we remove the cat the back still gets hot due to the circuitous path @Ashful mentioned in #4 above. Would be interesting to compare the back of the stove with and without a cat. I expect it will be hotter with the cat.

I have often wondered (but never tried) would we get more heat out of the stove if we remove the rear heat shield? I suppose the risk is the stack runs too cold?
 
Burn from last night..... annoying.
  • Stove was stone cold
  • Built a small fire to get things warmed up, engaged cat (had to double clutch it) and got the cat lit off, let it burn down to a very hot bed of coals.
  • Did a full load, not packed real tight due to some oddball pieces.....
  • Immediately engaged cat, cut air to 75%, 50%, 30% over about 30 minutes.
  • Burn looked good, went to bed.
  • Woke up to find a lot of coals still burning, STT=400, Cat=500
  • Overnight the cat went over 1600 a couple times.... very frustrating.
  • Other than that the burn went very nicely and lots of coals in the morning, this burn will easily go 12 hours before reload.
1702383044114.png
 
Burn from last night..... annoying.
  • Stove was stone cold
  • Built a small fire to get things warmed up, engaged cat (had to double clutch it) and got the cat lit off, let it burn down to a very hot bed of coals.
  • Did a full load, not packed real tight due to some oddball pieces.....
  • Immediately engaged cat, cut air to 75%, 50%, 30% over about 30 minutes.
  • Burn looked good, went to bed.
  • Woke up to find a lot of coals still burning, STT=400, Cat=500
  • Overnight the cat went over 1600 a couple times.... very frustrating.
  • Other than that the burn went very nicely and lots of coals in the morning, this burn will easily go 12 hours before reload.
View attachment 320581
Where do you measure you're STT?
 
Burn from last night..... annoying.
  • Stove was stone cold
  • Built a small fire to get things warmed up, engaged cat (had to double clutch it) and got the cat lit off, let it burn down to a very hot bed of coals.
  • Did a full load, not packed real tight due to some oddball pieces.....
  • Immediately engaged cat, cut air to 75%, 50%, 30% over about 30 minutes.
  • Burn looked good, went to bed.
  • Woke up to find a lot of coals still burning, STT=400, Cat=500
  • Overnight the cat went over 1600 a couple times.... very frustrating.
  • Other than that the burn went very nicely and lots of coals in the morning, this burn will easily go 12 hours before reload.
View attachment 320581
Loving that graph, @arnermd. If you have a thread describing your data collection rig, I'd love to see it.

But more relevant to this thread, is this a thermostatically-controlled stove? If not, do you believe the midnight and 1:40am spikes in cat temp, separated by lulls before and in-between, are simply due to wood mechanically rearranging itself as the load burns down? Most interesting is the more rapid cycling 1500 - 1600F, from 1:40 - 2:40am. Looks like classic snap-action thermostat behavior, assuming that it's not just dithering to either side of an ADC resolution threshold, which does not appear to be the case.
 
Loving that graph, @arnermd. If you have a thread describing your data collection rig, I'd love to see it.

But more relevant to this thread, is this a thermostatically-controlled stove? If not, do you believe the midnight and 1:40am spikes in cat temp, separated by lulls before and in-between, are simply due to wood mechanically rearranging itself as the load burns down? Most interesting is the more rapid cycling 1500 - 1600F, from 1:40 - 2:40am. Looks like classic snap-action thermostat behavior, assuming that it's not just dithering to either side of an ADC resolution threshold, which does not appear to be the case.
DAQ:
  • Perfect Prime TC0520: Amazon Link
    • Data is exported as a .csv file and I do plots and archiving in excel.
  • Flue gas temp: 1/8" type K insertion probe, ~14" above the stove top
  • Cat Temps: 1/16" type K insertion probe. Inserted in the factory provided hole. Tip is 1" below the cat in the center.
  • Griddle: Magnetic type K, center of griddle 2" in front of griddle hinge line. Link here
is this a thermostatically-controlled stove?
Yes, VC Defiant model 1975. However the thermostat is controlled by the temp of the incoming primary air (preheated), not the cat. The newer VC stoves (2n1) do not have secondary air control so the cat can go to infinity, until the heat from the cat bleeds its way into the primary air preheating, the thermostat (bimetal spring) will not sense the cat temp. I really do not like this design choice by VC....

That spike at the very end of the secondary burn (@01:40) is very typical of my burns. It is very normal to see that to varying degrees. I believe it has something to do with the state of the coals / fuel. I am not and expert in wood combustion phases....

Maybe the last of the wood chunks are coming apart and that exposes more surface area for combustion just before the coaling stage? That might explain the oscillations, multiple chunks broke apart at different times?