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Motor Control for Woodgun

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by emesine, Jan 5, 2013.

  1. emesine

    emesine Member

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    Hello all, I haven't posted for several years.

    My woodgun E200 is doing a great job keeping my 5000 sqft house warm. It's the right unit for me; I can pack it with wood twice daily and basically forget about it otherwise. What I don't like is this:

    The E200 turns on at 140F. It then heats up to ~170F. At this point it turns itself off and closes the air intake. Then, as my house continues to call for heat, the unit slowly drops back down to 140F, at which time it turns itself back on.

    Usually this works great. However, if the unit was burning particularly hot, and if my house is calling for a lot of heat, and the wood is seriously pyrolized, and the moon and tides are just right, the firebox reaches flashpoint while there is an optimal balance of flamable gas and air. This results in a gas explosion in the firebox, which vents out the air intake (or the user's eyebrows- see my previous post on that.)

    I'd like to fix the problem by puting a speed control on the draft inducer fan. This control would do the following:

    140 to 150F...........Full power
    150 to 160F...........50% speed
    160 to 170F.............30% speed
    170 or above.........Turned off by existing controls on E200

    I think that this will cure the problem. It allows the E200 to match the heating load required by the house. So, instead of turning competely off then back on with a bang 5 minutes later, it will turn the fan DOWN, and run a bit cooler to match the needs of the house.

    1. Do you think this is a particularly bad idea? Any other solutions?

    2. Does anyone out there know how to get an AC motor to run at 50% power?

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  2. jebatty

    jebatty Minister of Fire

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    The first time I experienced this type of gas explosion was with an E500 -- thought that I was blown out of the kingdom. Besides the fact that the E500 is set to shut down at 185F, back on at about 175F, the problem was solved by adding 4000 gal of storage. With that the E500 always operates full bore until it burns out its load of wood. And storage meets the heat load between firings. No more cycling, no more explosions, sweet nirvana enjoyed now.

    As to your questions, perhaps not with the WG but with other gasifiers, others including me have made numerous efforts to "modulate" the draft fans to "modulate" output. None that I am aware of have been particularly successful. I think that draft fan cfm is engineered to the size of firebox and engineering of the boiler to produce an optimal burn rate which results in high efficiency and low emissions. Reducing the air input likely will result in over-production of wood gas that cannot be fully combusted, which also likely results in "puffing" for smaller boilers or uber-explosions for the WG.

    Do your own experiments and report the results. There is much yet to learn.
    Fred61 likes this.
  3. Fred61

    Fred61 Minister of Fire

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    AGREE! The Wood Gun needs the high air flow in order to get a complete burn. It's design does not provide secondary air, therefore lowering the fan speed will not burn all, the gasses and will produce a dark acrid smoke. I would suggest raising the maximum temperature and leaving the minimum where it is now to prevent "short cycling".
  4. mustash29

    mustash29 Feeling the Heat

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    What are the electrical specs on your draft fan?

    The only reliable way to slow an A/C fan is with a VFD or variable frequency drive. Essentially what they do is rapidly turn the power on and off. In the simplest form, an SCR (silicon controlled rectifier) may work. An SCR has a positive leg, a negative leg and a "gate". When the gate is triggered, the SCR conducts. When the gate is not triggered, the SCR will not conduct. In theory, if you pulse the gate 50% of the time then you will have 50% power going to the fan, effectively feeding it a 30 Hz signal instead of full time 60 Hz.

    What you would need is a temperature input to feed a PLC (program logic control) which would feed the trigger signal to the VFD.

    I know the basics of this stuff because I work around it all day and have a background as an electronics technician but when it comes to building a PLC to do something like this I am lost.

    The (desired) operation of the boiler you are describing is pretty much what a Froling does. It can run full bore or throttle down as low as 40%.
  5. avc8130

    avc8130 Minister of Fire

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    A few opinions after operating a 180 for ~2 months:

    1. There is no secondary air injection on the wood gun. Because of this, I think slowing the fan will result in loss of gassification and a significant hit to efficiency.
    2. Your set points are VERY far apart and way off what wood gun suggests. Dropping all the way down to 140F is nowhere in the manual. Are you SURE this is how it is setup?

    What type of heat are you using? Baseboard/radiators/radiant/etc.

    I run mine with 185F control setting with a 10F differential with baseboards. This means the unit fires to 185F and shuts off. It then resumes fire when the water drops 10F (175F).

    ac
  6. maple1

    maple1 Minister of Fire

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    170 seems a bit low to go into idle to me - but I'm not a Woodgunner.

    I would think more like 185-190?

    I ran my old unit at something like 170/190. It was a smoke dragon though.
  7. Fred61

    Fred61 Minister of Fire

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    About how long after shutdown (idle) does the boiler re-start and explode? I found on mine that if I waited 15 minutes after shutdown that it was safe to activate the purge switch. By then the gasses had been dispersed. If you could replace your aquastat with a Johnson Controls A-419 aquastat you would be able to use the "anti short cycling" feature built into the unit.
  8. emesine

    emesine Member

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    Thank you all so much for your help.

    Fred61- I'm not sure, but it seems like explosions happen within 15 minutes. It's a really odd phenomenon. I'm not sure if I could make it happen if I wanted to. I had considered putting a delay timer. Not sure exactly how, but I bet I could do it. All I need is the right time-delay relay. I can work out the circuit board, box, etc. and incorporate it into the woodgun wiring harness. I'll look into the A-419. And I bet I could find a well that would work somewhere on the unit.

    AC and jebatty- Your concern is that the woodgun needs a high air intake to burn right. However, the woodgun is equiped with a damper. The purpose of a damper is to limit air intake. If it has a damper, it stands to reason that it is OK to limit air intake (turing the fan down is just like closing the damper.)

    D
  9. Fred61

    Fred61 Minister of Fire

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    Actually not that odd. A) Combustion fan stops, damper closes, fire dies down due to lack of oxygen with embers still glowing, box full of wood gas, start combustion fan and open damper :ZZZ BOOM. B) Wait 15 minutes or so, gas disperses, open damper ;) no boom.
    You would be replacing yout present aquastat with it so you would use the existing well. Check the anti short cycle range to see if it exceeds 15 minutes.
  10. avc8130

    avc8130 Minister of Fire

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    I have considered a time delay relay to replace the cycle timer for the same reasons. If I could find a setup that would trigger when the WG's call for heat ends, then delay 1 hour and run for ~2 mins it would be perfect.

    I have looked at the damper. I'm not sure what it is for. I have never had results playing with the damper. Full open/full closed, always seems the same.

    ac
  11. muncybob

    muncybob Minister of Fire

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    From what I have read, the A-419 has a max delay of 12 minutes...it may be enough time?
    ac, the damper has made noticable changes for me. I cannot run with it wide open for very long without the WG start to "rumble". Limiting the air intake minimizes this happening for us and I also notice a reduction in wood used.

    BTW, if you want to induce the rumble(not sure why you would) let it run with the air flap door open....don't ask me how I know!
    Gasifier likes this.
  12. Fred61

    Fred61 Minister of Fire

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    This may be a little "off topic" but this thread got me thinking of the past when I was using ovens to process materials. I thought I would throw it out here so Wood Gunners would see it. I used "percentage timers" in controlling the heat applied to the product. I Googled "percentage timers" and found a myriad of timer configurations. I just thought that anyone with more incentive than myself or someone with more electronic knowledge who can see the possible advantages at a glance or flexibility that these may offer, could study them. Some could have an advantage over the present "cycle timers" that are being used presently on Wood Guns. Perhaps even inserting a "time delay" in the circuit.
  13. emesine

    emesine Member

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    AVC9130: My E200 is in a main boiler loop 120 feet in length of 1.5 inch pipe. I have a TACO 4 way mixing valve that pulls hot water out of this loop and delivers it to 4 in-floor zones in my house. The mixing valve is set at 130F.

    From the discussion above, it sounds like a speed control on the inducer fan is going to be difficult, and may or may not help. A time delay circuit is more likely to fix the problem and likely easier to engineer. the time delay needs to:

    1. Keep the main aquastat from turning the unit on within 15 minutes of it having turned off.

    2. Even if it's been less than 15 minutes, I need to be able to open the door and load wood. This means the cycle timer still needs to be able to turn the fan on, or the time-delay circuit needs to have a button that allows me to override the delay and turn the fan on.

    It sounds like my next step is to get out the woodgun manual and take a very close look at the wiring diagram and see what would work best- see if the A-419 would even work in the Woodgun wiring diagram.

    Andrew
  14. Gasifier

    Gasifier Minister of Fire

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    What I have found is similar to Jebatty's findings. Although I do not have 4000 gallons of storage. :( I do, however, have 400 gallons of buffer tank. ==c I have had a few of these explosions in the 15 months I have had my Wood Gun. <> However I have found that was just operator error on my part. I run it all year round. In the shoulder seasons and summer I burn one short fire a day, or two, depending on heat load. But generally one short fire a day for DHW and a small heat load. My 400 gallons makes the time between having to fire again a much longer time, therefor greatly reducing the chance of an explosion from gases. My Wood Gun is set to turn on at 170 and off at 190. Works great!
  15. Gasifier

    Gasifier Minister of Fire

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    Emisine. I am surprised that with in floor radiant heat and that much delta between on and off that your boiler would turn back on after it had just shut down with it's temp up to 170. Why do you think it turns back on that fast? Could you just increase the high temp shut down to 195 and see how that works? I would think that is something to try first. Just a suggestion.
  16. emesine

    emesine Member

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    GASIFIER- adding 4K gallons of storage would certainly fix the problem!! However, I like the simplicity of NOT having any storage. It's what I really like about the wood gun- the heat is stored in wood in the firebox, not hot water in a storage tank. On the other hand, a modest 400 gallons might make a big difference. Sigh...... another project!

    I only get a fast restart if the house is REALLY pulling heat. I have 2400 sqfeet of in-floor radiant heat, 1800 sqfeet of basement slab, and ~600 sq feet of garage slab. If all those zones turn on at the same time, my house is capable of sucking a lot of heat out of a boiler. I have found that the cement loops especially can really pull the BTUs.

    On changing my boiler settings- Well, why not give it a try? I can change that in just a few minutes. I'll broaden the delta and see if that helps some.
  17. Gasifier

    Gasifier Minister of Fire

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    I hear you on the cement loops. I have a 900 sq.ft. garage with in floor heat in the concrete floor. I love it, but boy can it make some heat demand. I found that out on two occasions now when someone left the garage door open. <> Luckily it was not for too long.

    The buffer tank helps, but I wish I had 1200-1500 gallons of storage all in one tank for my Wood Gun. But the price of it means it is not going to happen. As it is right now my payback should happen in about five years or less for the entire system. Time flies when your having fun! Let us know how you make out.
  18. emesine

    emesine Member

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    I changed my settings last night- I was running at 160F for the high temp. My differential was set at 15F. I changed this to 170F and 25F. I'll run it for a few months and see how that goes before doing any serious changes to the woodgun!

    D
  19. Fred61

    Fred61 Minister of Fire

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    Cranking up the high temp does two things for you. It widens the differential and allows you to store more BTUs in the boiler. The higher temperature should slow the flow to your mixing valves.
    Is that two or three advancements?
  20. mark123

    mark123 Member

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    I had these explosion at first and after talking to Jeff at AHS he told me to raise my high limit to 210 (top of boiler) and my operating limit (back) to 190 and the little dial behind to 25 I assume that is the differential. I have not had any explosion in a couple of years now. I have an E-180 stainless.
  21. Nofossil

    Nofossil Moderator Emeritus

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    I'm experimenting with controlling combustion temperature by modulating blower speed. I get totally satisfactory secondary combustion early in the burn cycle with fan speeds around 40%. As soon as you go down this path, you discover the explosion problem.

    I've poked around this phenomenon for a while. My conclusion is that you can't cut off the blower suddenly. For any fuel mix and level of primary combustion, there's a minimum amount of air that you need to prevent explosions. Best I've come up with is to do periodic 'purge' cycles as the original EKO controller does.

    I don't know the magic number yet, but I'm currently running a 20 second purge (more like 10 given fan spool-up time) every couple of minutes whenever I need to keep fan speed below 50%. Pretty much perfect operation so far.

    In the first half of the chart below, it's modulating fan speed to try and maintain 1100 degree combustion. In the last half, it's modulating to keep outlet temp below 190. You can see the periodic purge cycles. Combustion and flue temp are divided by 10 to fit on the chart.

    [​IMG]
  22. 711mhw

    711mhw Feeling the Heat

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    I turn off at 210, on at 185. I like your thinking, "heat stored in wood in the firebox"

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