30nc auto draft

This is the part that fits over the 3" inlet behind the stove that regulates the draft. Now all I need is linkage. It's just exhaust tubing with a butterfly.

mellow said:

So are you doing something similar to Dans smartstove?

http://inveninc.com/SmartStoveForum/index.php?topic=75.0

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Yes, it's similar but not smart. There are no electronics with my design. Just a simple bi-metallic coil on top of the stove. I've already posted the pics in another thread. I'll try to get them here.

Here's the bi-metallic control pics.
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Here is the finished project excluding paint. I haven't decided whether to go with chain or solid linkage. It's been trial and error so far and hard to get it dialed in. I need to locate a spring handle if I decide to go with this.

It's very smooth. If you look closely towards the rear of the lever there is a counter weight.

I thought I would give an update on the operation and settings. It hasn't really been too cold here to really test this thing out. Here's the way it works. From a cold start the lever needs to be at the 12 o'clock position. The draft fully open at this position. Start the fire as normal. Temps slowly climbs and ends about 400-450°. Draft is mostly closed at this point. This is kind of the sacrificial load since everything is just warming up. Once the temp is up it time to load stove with larger splits so the lever is pulled forward to about the 10 o'clock position. The draft will slowly close once temps approach 500-520°. I kind of weird to watch it go from primary to secondary burn automatically. Once the stove temp drops to around 300-350° it's time for a reload, draft is about half way open and the cycle repeats. It's not fully automatic, but is less time messing with the draft control. It seems to be very smooth as to the way it throttles back the primary air.

Made a spring handle for it also.

Yes, it's directly related to the stove top temps. The hotter the stove top, the more the coil expands. The more the coil expands, the more the draft closes.

JA600L said:

So, if the system were to malfunction could the stove run away? I saw the counterweight on the butterfly. I'm just curious if you leave the primary on the stove wide open.

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I suppose it could. There is still forward weight on the draft arm even with the counter weight so if the linkage or spring would happen to break the damper would fall to a closed position. I designed it that way. The draft rod is left wide open in front. Remember there is no modification to the stove that can't be reversed.

blades said:

When you get a little more run time on this , please report on your coal build up level. Great build by the way.

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I do have some run time on it now and the coal build up seems to be no different than when using manual draft control. I do like the fact that as the stove cools, the draft opens to burn help down the coal bed. I am having a problem with air leakage somewhere because when the valve is closed there is still air leaking in somehow. I think maybe the in rushing air through the tubing is slightly opening the butterfly valve when the draft is high. This may be solved by going back to solid linkage. Other than that, it is working very well.

Here's a new cover for the coil and lever.

mol1jb said:

That is for manual operation of the damper?

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No, this adjusts the bi-metalic coil that is connected to the primary air. The further forward the lever is pulled the longer it takes to close.

It's for primary air only.