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-   -   Looking for info on combustion blower behavior (http://www.bbq-brethren.com/forum/showthread.php?t=89385)

mschrock 07-28-2010 06:24 PM

Looking for info on combustion blower behavior
 
Hi all,

I've never seen a stoker or guru in person. I've rigged up a scats circuit that I found on the internets. It's basically a cruise control, set it when the pit temp is where you want it and it toggles a fan on and off to keep it there.

I dug through a box of old cpu fans and tried them each to see what sort of air volume it was capable of. I settled on a 1.5" square fan from and old pentium cpu that wasn't overly powerful and adapted it to my smoker intake. I'm confident that it wouldn't move too much air.

I got the pit up to temp, and flipped the switch. When the temp started to settle and the fan kicked on I was puzzled that the pit temp dipped from 224F to 210F then 200F. After 10 minutes or so it was still hovering around 200F. I cut off the intake so the fan stopped blowing into the smoker and the temp climbed up to 230F with all intakes shut.

Next time I'm considering to let the fire get going with the blower on and see if it reacts more as I would have expected.

Does this indicate too large of fan? Or did it just take a while for the fire to transition from naturally aspirated burning to forced air burning? Or is this how a forced air system behaves in an UDS?

I know that many here feel that an UDS works perfectly fine without gadgetry, however, I feel more comfortable leaving the cooker unattended with some sort of adaptive control in place.

Thanks,

Marlin

Chef Jim 07-28-2010 07:27 PM

Not knowing a thing about a UDS or a Guru, this sounds backward to what one would expect. More air, more fire, more temp. Do you have any idea of the volume of air your fan is providing.

And did you take the fan assembly completely off when you shut it down?

barbefunkoramaque 07-28-2010 10:40 PM

forced air and uds = drier air constantly being rushed in = circumventing hands down the greatest smoker ever designed... if done correctly.

I own a stoker and once I got past the internet capabilities.... I realized that my old popcorn air popper fan and a standard stove thermostat was just as good.

antoant 07-28-2010 11:37 PM

Did you try the fan in reverse? In other words are you sure the fan was blowing air in instead of sucking air out?

Norcoredneck 07-29-2010 04:20 AM

Too much air. It is actually venelating the UDS much like a attic fan. make a cover for fan intake and poke holes limiting flow. I had the same thing on a PID controller that I rigged to stoke a UDS with a heat gun blower and ended up putting a valve on it.

Norcoredneck 07-29-2010 04:22 AM

http://i91.photobucket.com/albums/k2...k/IMG_2611.jpg

mschrock 07-29-2010 07:26 AM

antoant, yup I'm sure the fan was blowing the correct way.

Norcoredneck, we have one of those heatguns at work, and my tiny little fan doesn't blow anywhere as much air as the heatgun can. I do agree that there was more air going into the drum than the fire needed.

I guess that you really don't need more air blown into the smoker than what would naturally suck in through the intakes. If you can manage that, I don't see how it would be any different than no fan.

I imagine that blowers work much better on cookers that have the intakes separated from the cooking area, in a way that all the air has to go through the charcoal, instead of blowing air into the cooking chamber, where it is just as likely to go nowhere near the fire and cool the chamber.

I'm surprised just how little air is apparently necessary. It's nice to get feedback from those more experienced than I am on the matter!

Thanks

Norcoredneck 07-29-2010 07:37 AM

Got to remember that fan is blowing through a 1/2" tube, which is cut back again by valve. Is the circuit proportional or "Learning" or a simple sense off then on ?" Refresh ot "hystyresis" affects how well it works also.


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