Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1173
Posted: 10:15am 31 Jul 2018
Copy link to clipboard
Print this post
Wouldn't you know it, here we are in the middle of winter (NZ) and the bloody wood burner has stopped working, its full of electronics, potted blue modules and lots of odd colored mains voltage wires running every where. When I purchased the thing second hand about 8 years ago, I thought it had better not crap out, getting parts would be a nightmare.
This model is no longer current, newer ones have a big cpu board, this one has what looks like off the shelf potted modules that are Timers, Pulses, Fan speed controls, mechanical heat switches, which probably are easier to replicate than the later versions. Well there is a module that connects to a front panel 470K variable pot and pulses the motor that drives the auger that sends pellets into the burn chamber, and its very intermittent; almost dead, the pot is fine. These modules are available on order at near $200 which is a ripoff, and obviously they can blow up, so why would I buy one.
Having used the fire a lot, I know pretty much how long the motor runs for and its on/off cycle duration's as the front panel knob is turned, so figured I would build a replacement, using an 8 pin Picaxe and a few components costing about $20. Here is a circuit, pretty basic but should work. U2 value not shown is a 74HC14 Schmidt trigger to sense mains zero crossings, the op-amp buffers the high value pot input to low impedance source voltage for the cpu's adc input. Motor has a 1 second on period with variable off between fully off then stepped to 8 and 2 seconds duration as the pot is turned to set the heat output. Could have almost done this with 555 timers....
Cheers Mike
Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667
Posted: 10:24am 31 Jul 2018
Copy link to clipboard
Print this post
Cool,
One of my works in (slow) progress is a wood heater controller to adjust the fire's damper according to temp, both room & flue.
And also alert the light sleepers to get up and add wood at 3:00am.
A pellet feeder; that could be controlled with feedback too, unlike my large chunks of iron-bark....
Cheers
Phil.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1173
Posted: 09:20pm 31 Jul 2018
Copy link to clipboard
Print this post
I don't think I would want to control this one too much, its only rated for 10KW heat output, the variable rate control for turning the auger seems very effective, once the room or house is warmed, we turn it down to 1/3rd and the temperature is maintained; there is manual adjustment of the heated air flow output and the damper setting. Would be difficult to automate the damper as some sort of sensor would be required to detect incomplete combustion ie no smoke being produced from the flue.
I wouldn't buy another one of these, the cost of pellets has doubled in the past 8 years, with most of that being freight from the factory that makes them. A standard wood burner that takes logs would be cheaper to run especially so if you grow your own trees or have access to free wood, these also have the advantage of not requiring power to run and you can cook on them if required. Now I would get a heat pump as the least expensive heating device if you are on grid.
Cheers Mike
Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769
Posted: 09:13am 01 Aug 2018
Copy link to clipboard
Print this post
Pellet stoves are finally rapidly losing favor over here. The complicated feeders and blowers tend to get fouled by ash deposits. It turns out that the stuff they use to bind the pellets together doesn't burn very cleanly.
We grow a lot of trees over here and out in rural areas a lot of people burn wood. The cheapest and most efficient way seems to be to burn chips or sawdust in a very heavy masonry or tile stove with a lot of flue passages and a lot of room air passages designed in. You can build a very hot fire and let it burn out in a few hours and the massive stove will continue to supply even heat for many hours. These tile stoves were developed in the Scandinavian countries over the centuries and they still seem to be the best solution.
If you have a natural gas pipeline the choice becomes very simple. Forget the wood, oil and electricity and burn natural gas. It's a lot cheaper and the burners are very simple.
Paul in NY
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1173
Posted: 11:24am 02 Aug 2018
Copy link to clipboard
Print this post
PCB, quick diy job here, not worth it to send it off to Fab house, have to get this built before the next cold snap.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
