my air burner build


 
J

Johannes S

TVWBB Member
i really struggle to keep a constant temperature in my 18.5 wsm.
this may have different sources but an air burner can't be wrong to heat it evenly.

i already bought a qmaster senior and have the 10cfm fan with the adapter for the wsm that i can use.

i want the air burner to be detachable just in case, and i want to reuse the qmaster adapter as it has a little flap inside the cuts air supply if the fan is off. this is done purely by gravity. no computer needed for that :)

so this is what i have right now, together with 3m of 15mm copper rod.

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i will update the thread as the build goes on.
 
to explain: the 2nd part from the right, which is the same as the 1st from the right will take the 15mm copper rod soldered into it. that's what the made for. so it's a clean fit. i plan to make two inlets to supply enough air as needed and to not stall the fan too much.
the two inlets will be very close to each other. 2x 21mm holes. the 1st part from the left will be screwed in from the outside to fix the air burner.
the air burner's shape will be like a big U. i have 10x 90° angles to build it. holes will be 3mm to start with.
 
this is to show you what my temperature looks like now. a total mess. and PID tuning is something i just don't understand. :(
can't handle PID tuning of my quadcopter as well.

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your blower is to big. Try the max speed at a very low percentage. You can see that when the blower turns on the temperature continues to drop and when the coals get to a point where they over come the cool air coming into the WSM the temperature starts to go up and then you have the overshoot and repeat.

A 10 CFM would be something that a 55gallon drum would use.
 
Thanks. I heard to limit fan speed. And I had it set to anything between 40% and 70%. But if i set it too low it can't get the temperature high enough. I hope that it will be better if air enters at many locations instead of just the one at the side as it is right now.
Another thing i don't understand is that the fan is still on when the temperature reaches it's setpoint. I would think that it would slow down long before to avoid overshoot while now it's still doing 100%.
Another issue may be that the flap that kills the air supply completely when the fan is off making the coal almost go out if this phase lasts 10-20min+.
 
I agree with John, your blower is too big, and 40-70% is too big as well. Try running the MAX way lower, like 10-20%.
The thing people overlook the most with the HM, because it is counterintuitive after years of grilling without the active stoking of the HM blower... When the blower kicks on it forces cool air into the pit, if your blower is moving too much air it can push your hot air right out of the pit and replace it with cool air. This is what you are seeing when you blower is ramped up to 100% and the temp of the pit keeps going down down down..... TOO MUCH AIR FLOW.
I know PID tuning is PITA, but honestly tuning the blower speed properly FIRST will generally do the trick with even stock PID settings, or at least make it so PID tuning is much easier.
I tend to run the Startup max at 100% and the MAX really low like 10-20% for low and slow. And since I have a roto damper I generally run the blower on at max only and let the servo damper control the pit. This way there is no forced air pushing your heat out of the pit, so you can leave the top vent open wider to let the stale smoke move out and the pit doesn't dip like when the blower is running. (This is on a kamado)
Though I think you would be happy with an air burner if you get one together, they really do a good job of delivering air to and stoking the fire.
 
ok. i'll try with 10-20% when the air burner is done. it seems i don't even need to solder as the parts are a very tight fit. i still will solder to keep it from falling apart over time i think.
i don't have a controllable inlet. i can only let the fan run to move some air into the wsm. and even worse the fan HAS to run, otherwise it will go out.
 
The Heater Meter is very versatile so you can set it up to work with just about any system and combination of hardware/grill etc. Your gravity flap is simple and effective, but as you note, perhaps too effective because you find the fan must blow or the fire will go out. Still, if you get the right balance of conditions, like proper size fire for the pit and setting it up so it breathes well, I'm sure you could make it work awesome.

If/when you do the air burner, you can TUNE the air burner to your pit and should be able to get to the point where you can run without the flap without overshoot. The air burner itself presents a natural resistance to flow, having only small holes to let air through. Start off with fewer small holes to limit the flow, you can add more or enlarge them later if you aren't getting enough flow. With fewer smaller holes when the fan turns on it will blow narrow jets of air up into the fire and stoke it real good, when the fan turns off a trickle of air will continue but not enough to sustain the raging fire like the jets. Running an air burner like that without a damper works real good, but a different setup in which you may want to run the blower Max higher than the 10-20% I suggested with your current setup or a kamado.
 
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RalphTrimble said:
... Your gravity flap is simple and effective, but as you note, perhaps too effective because you find the fan must blow or the fire will go out. Still, if you get the right balance of conditions,...
Click to expand...
how does the rotodamper handle that? if the rotodamper is closed it will be like the flap closed. no air supply (if the grill is more or less air tight).
so if the temperature declines the rotodamper has to open (and/or the fan starts). if you don't have one, only the fan starts. so this is no big difference, correct?
but i guess under normal instances (and if i look at the other's temperature logs) there will be no long phases w/o air supply. so i guess my problem is just existant as there is such massive overshoot. when the overshoot is gone there will be no long "no air" phases anyway. so all should be fine.
 
I would remove the flapper and lower the max the blower uses. It sounds like maybe the flapper is to blame for your problem. Since, you need to have the blowers speed up to over come the flapper and then that air that is blowing in to the WSM is way to much and strokes the coals. Then it closes. The heatermeter is trying to react to the temperature once it starts to drop and turns on your blower but it does not open the flapper until the temperature again is close to the point when the blower again needs to be at 100% and has enough pressure to open the flapper. And then Repeat. Remove the flapper and you will get much better results at a lower max speed. If you want bette control then try a Servo controlled damper, as it opens automantically as soon as the blower turns on
 
The roto damper can be used in "On at Max Only" mode for the blower, letting the valve control the pit for low and slow. The blower wont run at all unless the HM decides it needs 100% flow, so way different than a gravity flap.
 
i tested all % setting with manual fan and the flap moves at 5% already. it though seems that air flow is somehow restricted a bit. but this is hard to measure with the fan blowing in my face only ;). i will try w/o flap as well and see how much it reduces performance in real life.
 
I think you will find the whole situation a bit different without the flap, it should work better though overshoot MAY be a problem, may not...
I ran a gravity valve for a brief while that I developed made from a ping pong ball, it floats up when air flows and down to close the valve when the blower turns off (think Lotto machine). It actually worked great, but there was a whole other set of parameters that needed to be adjusted to compensate for the % it takes to lift the ball. Much like your flap, the flow was either completely cut off or highly restricted until the blower reached a certain %. So I did tests to determine the MIN speed it took to lift the ball and open the valve fully and set that as the MIN. The result of this is the HM will accumulate the time and volume of flow below your MIN setting and then release the flow in bursts of flow at your MIN value. This works, but you will get a puff, choke, puff effect from that setup when the required flow is down below the % it takes to open your valve, which I am not fond of personally.
 
i played around with the hardware i bought for quite some time yesterday. i couldn't find a solution to make me happy. the 18.5 wsm has not too much space to fit the copper rods. i wanted to drill holes to add the fittings there, but the fittings would hit the lower coal grate. finding a place to make 2x 21mm holes and fit the rods is not easy. maybe i'll have to sleep it over as i don't want to mod the grill in a way that the mod can't be reversed.
removing the flap (or just keeping it open all the time) is easy and i considered for sure, and will be tried out.
 
i bit the bullet and drilled a hole in my wsm. it was super easy with the right tool. 3 layers of masking tape on both sides and a subland twist drill did it. a perfect hole. the sharp edges where smoothed with a dremel and the drum sand paper thing.

i bought some 15mm OD copper rod and some 90° knees and the fittings. the mount i already have for the fan had to go (and with it the flap).
i cut the rod to size, fit everything together to see how it would look like:

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all soldered together:

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turned upside down to close all gaps with solder

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it perfectly fits under the grill

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and this is the fan attached from the outside. once it works the copper reduction parts will be glued with epoxy to the fan and a heatshrink will cover it for better optics.

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there are still no holes drilled, but i will start with 3mm holes. the 12mm ID of the tube has an area of 108mm2 and one 3mm hole has an area of 6,75mm2. so 16 holes á 3mm will have the same size as the 12mm rod. we'll see. i can make them bigger anytime i like.
 
John Bostwick said:
I hope you used lead free solder.

Looks good
Click to expand...
hhhmmm. now that you say so. NO. but i guess this should make no difference as the lead will stay in the tubing. i see no way that it could come in touch with the food. lead will no dissolve and turn into any gaseous emissions. will it???
 
Looks good, frankly I don't think you even need to solder, copper pipe will hold together just fine when press fit, specially after its been put together and used a while. I wouldn't bother with gluing the blower on either, it should hold well enough with the press fit, and you want to be able to remove it if need be, both the blower from the air burner and the air burner from the grill..
 
yeah ralph. you're right for sure. it's just me - i tend to over do things :) and i like my projects to last longer than i have interest in it. normally i build stuff and start to improve it immediately after. it's a never ending story. and i hate all those open not finished projects in my workshop.
i hope that this project will be done soon as i need pulled pork on the weekend!
the air burner and blower are both removeable. this was the biggest problem for me to solve as the WSM is outside all weather (with a cover of course).
the blower can be pulled off easily and the airburner can be removed by the "screw" from the outside. i don't know how to explain correctly. it's two parts one inside, on outside, screwed together. very simple if you see it.
 
Johannes S said:
hhhmmm. now that you say so. NO. but i guess this should make no difference as the lead will stay in the tubing. i see no way that it could come in touch with the food. lead will no dissolve and turn into any gaseous emissions. will it???
Click to expand...

I would err on the side of extreme caution when it comes to lead products being anywhere near food. You're going to be heating up this lead and spilling all sorts of fats and acids on it over time. Yes, lead can end up reacting and particles can get suspended in the air.
 
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