Help figuring out what's wrong - won't burn all the fuel


 
R

RKHanso

TVWBB Fan
I made a homemade smoker and have tried a couple test runs with it. It doesn't seem to burn all the fuel before the temperature drops off. This has happened each of the 3 test runs.

I'm using a Micro-Damper and a BGE top vent with just the little slots open. Do I need a larger damper? Bigger motor?

Here's a link of what's happening right now

http://heat-makarios.ddns.net/

There's plenty of fuel left to burn (Kingsford Charcoal) - currently left while the temp won't hold at 250.
IMG_20160821_111118.jpg


I have PID set to 7, .01, 4

IMG_20160821_111152.jpg
 
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If your blower is at full and the temps are dropping, you've got too much air going into the coals and its effectively cooling them down. Combustion needs fuel, oxygen and heat. You're removing the heat by blowing on the coals too hard.
 
It would seem to me that your fire is not getting enough air if it is snuffing itself out. Since fans aren't very good at pushing air against restriction the first thing I would try is opening the top vent a good bit to see if you can get enough flow with less restriction. If that doesn't get you where you need to be then I would suggest you change over to a blower rig instead of a fan, a blower is much more capable of forcing air through restrictions than a fan.
 
Steve_M said:
If your blower is at full and the temps are dropping, you've got too much air going into the coals and its effectively cooling them down. Combustion needs fuel, oxygen and heat. You're removing the heat by blowing on the coals too hard.
Click to expand...

Steve, he said the coals are going out before they burn up, that seems to indicate the fire is starved for air, not getting too much? If there were too much flow you would think the coals would burn completely and burn out fast, right? That, coupled with the info that he has the top vent just cracked open and is using a fan rather than blower makes me think he has too little flow.

One way to find out for sure, click the HM into Lid Mode and see if the temp blooms way high... If the the temp shoots way up then you have too much flow, if the pit still flounders then you have too little.

I can't really see how the air is getting into the pit, but you want to make sure it enters in a way that it will flow over the coals rather than around them.
 
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Ralph, I think you're correct. I didn't notice the he wasn't using the standard HM blower. CFMs are useless without pressure!
 
I do have the air going more what I would say is 'around' the coals instead of directly through them. I built a little castle-top pipe and welded a plate on top so the ashes wouldn't go into the air inlet.

I'm thinking I just don't have enough air flow also. I'll run the test that Ralph suggested and run it with the exhaust vent removed. From the testing I've done so far, I believe that the temps will still keep dropping though. I'll reply back after trying that.

Here's how my air-flow comes into the smoker. MD on the left side is the Micro-Damper.
smoker%20001.jpg
 
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That air flow setup should work really nice. I think with the top vent open you may get the flow you need to achieve temp, however, a long-ish tube like that will restrict flow and reduce the effectiveness of a fan quite a lot so you might end up having to move to a blower.

I would be interested to see where the pit settles with an open input tube without any damper on it? Since this is a DIY pit it's hard to tell how it will burn, the open tube experiment will give you a bit of an idea how the pit will perform on it's own, which is always a good way to start when tuning up a HM rig...
 
I did take the Micro-Damper off and the top exhaust vent off. It's just sitting wide open now on the input and output, and the temp has dropped to 165 and going lower.
I guess the thing is sealed off pretty good....

There is about 10-12" of 1" pipe, an elbow and about 2" above that into the smoker...so about 14-15" total of airway before it gets to the fuel.

I'll look into switching to a different blower.
 
The standard HM blower should work fine for you I think. Keep in mind I mean BLOWER, not fan. As Steve pointed out, blowers apply more pressure behind their air movement ratings so they are able overcome restrictions without losing flow, while the flow from a fan will drop greatly when you restrict it.

Since your temp seems to drop without a damper on the input tube I'm thinking the pit will probably be stable without any damper at all. Hard to tell for sure because you're not hitting the target temp right now, but if you have the pit heated up to 250F and the temp drops if you do not force air through your input tube then you shouldn't need a damper. In that case you could probably just put the stock HM blower on your input tube and get good results.
 
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I fueled it up again and it looks like it holds a pretty good 255-260F when there is no restrictions on the input or exhaust. Both the Micro-Damper and the exhaust vent are removed.

260.PNG
 
OK, now that you've achieved 250F I see that it is trailing off... I would be interested to see where it settles, this will give you a good idea where the grill wants to settle on it's own with that size vent. If it settles at or below your lowest desired cook temp then you shouldn't need a damper, just put a blower on your intake tube and have it stoke the fire gently until it achieves your setpoint.
 
Here's a longer graph. The spike is when I opened the smoker to take out the grate. Then I closed it right away.

I'd say it 'settled' at about 222F. I doubt I'd cook any lower than that. It's only about 70-75F outside today.

Ralph, was the link I posted the blower you were talking about? And, do you know if anyone makes a housing for it that will connect to a 1" NPT? Or is that a do-it-yourself type thing?

no%20damper.PNG
 
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Yah, that's the standard 50mm HM blower, it should do the trick. For connecting you could DIY something, shouldn't be too hard to do. An RD3 is essentially a housing for this blower that could mate to you 1" NPT input tube if you wanted something fancier. Shoot me an email if you are interested.
 
This is not a blower vs fan problem. This is simply a problem with the exhaust - it's too small. Your rig is darn near the size of a UDS. You cannot run a pit that size with your exhaust closed up so much. I run a Weber lid on my UDS and keep the vent open full. That'll give you a ball park of how large your exhaust needs to be. With that said, you might be able to get a blower to run on your pit, but if you do you will fly through fuel because of the small exhaust, and your food may not taste so great.

Also for reference, I run my UDS with a 30" black iron running up the side for the intake. I have the ball valve up there so I don't have to bend over to adjust intake when running manually. With my MicroDamper hooked up to that I have no problems, the fan that I have spec'd out for the MicroDamper has enough static pressure to run it properly. I'm not at home so here is a quick sketch in case you can't envision what I'm saying.
jnQqMR7.png
 
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My exhaust vent is a 5" pipe. The BGE daisy-wheel type vent is on top of that. My input is a 1" black pipe with the Micro Damper.
SteveCK - you got me thinking..I've not tried just removing the exhaust vent and running it that way. I just tried it.

Now, the smoker will run about 225-250F naturally, with no fan or exhaust vent on it at all. I fired it up today, without the BGE Exhaust vent on it. Only the wide open 5" pipe. The HM would regulate about 225F, 250F and 265F, but that was in the range of the natural action of the smoker. I bumped it up to 300F and it kept that temp fairly well. Went up to 325F and it couldn't keep up. 350F was not possible. I do belive this is a problem with not enough air being pumped into the smoker.

I don't believe with a blower capable of more airflow that the fuel will be burned up overly fast. The amount of air should depend entirely on the temperature maintained and the design of the smoker. Whether it's a smaller fan struggling to keep the temp up or a larger fan having an easy time, the amount of air to keep a smoker at 350F should be the same. A larger fan/blower should just be capable of higher temps (and thus, faster fuel burn). I have to expect it will take more fuel to keep the smoker at 500F vs 250F.

I did order the standard HM blower from Arrow Electronics for less than $9. I'll try the same test with that blower.

The Micro Damper works perfect with my Weber Grill. It might be a bit ambitious for a 64gal pressure tank smoker.

Here's a snapshot of my test today, with no exhaust vent....just a wide open 5" hole.

MD%20but%20no%20BGE%20vent.PNG


IMG_20160708_155414.jpg
 
Yeah, that's a big pit to get the MicroDamper with the standard fan to run your pit at 350. The good news is that the MicroDamper accepts a wide variety of fans. The standard fan (EFB0412VHD) will control 95% (made up percentage, but prolly close) of all the pits that people come to this forum with - yours is a bit bigger. Shoot me an email at microdamper@gmail.com. I'll point you in the right direction for a different fan for that big pit you've got. Oh, but keep in mind, you've got to ditch the BGE exhaust. It just doesn't have the cross sectional surface area of flow to be able to run a big pit like that.
 
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My guess is if you rig the standard HM blower to your input tube you will be able to achieve the range of temps you are looking for with your top vent in place. You can rig it up in any fashion you like, some tape would work for a test I guess... If you find it works I'd be glad to print the body of the RD3 for you with an output cap that will fit your input tube for free if you pay the shipping...
 
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