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End of burn draft fan shutdown control.

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by ewdudley, Oct 15, 2011.

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  1. ewdudley

    ewdudley Minister of Fire

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    [Edit:

    First consider the 'Garth B' solution. Wiring 120VAC over to a hot flue and back might be a little dodgey but it's nice and simple.

    http://www.hearth.com/econtent/index.php/forums/viewthread/80894/P15/#973718

    [quote author="Garth B" date="1319066537"]I installed an adjustable snapdisc (18$) on the flue and wired it in paralel with a timer which are both in series with a lightswitch and the fan on my econoburn. Have been set up like this for 2 years and has been working great. I start a fire, turn the timer to 15-20min which gives the flue gas time to heat up and close the snapdisc, then when the flue gas drops below 150 it shuts the fan down. The lightswitch shuts the fan down while I load wood so I dont have to shut the boiler and circ pump off with the main switch. I will be posting pics soon[/quote]

    ]

    The topic comes up from time to time and is currently being discussed elsewhere.

    My boiler control includes end of burn draft fan shutdown, but my control also has to control everything else as well since my RK2001U went tango uniform. This is confusing, and so it's not the best example if all a guy wants is just the draft fan shutdown feature.

    What you do is take the hot wire that goes to the fan and insert the components in line to shut the fan off according to temperature.

    So here's what you need to add just the fan shutdown feature:

    -Spring wound timer switch, like for a bathroom fan or whatever. $20

    -Functional Devices RIB RIB1UC SPDT relay. $20

    -TET7100, JLD7100, D1S-2R-200 'PID Temperature Controller'. Be sure to find one that includes a K-Type thermocouple, or order one separately. $50

    If you want to be able to ride out a power failure, then the timer needs to have a long enough range that you can set it to run until plenty of the wood is gone. If the power fails after the timer runs out, and the flue cools off, then the fire stays out until you restart it, oh well.

    Normally the thermocouple should go in the flue neck. If the flue cools off because the boiler idles then burn will be complete at that time, tanks are hot, call it a day. I drilled a hole along the top of a horizontal section and screwed the thermocouple into it, with a little piece of rock wool around the lead to improve accuracy. Shutoff at 285 degF is working for me, temperature setting doesn't seem to be critical as long as it's substantially less than cruising temperature.

    It's nice to prevent blowing cold air through your boiler and up the flue after the fire has burnt out, but what's really nice is that you can shut the burn down while there's plenty of charcoal left to start the next burn. This works great, just rake the charcoal over the nozzle, start it glowing with literally a few seconds of propane flame, place a couple of splits flat on top of the charcoal and walk away.

    [Yes, I know I misspelled 'controler'.]

    Cheers --ewd

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  2. jebatty

    jebatty Minister of Fire

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    Is there a reason not to use a manual reset temperature controller rather than using a spring wound timer switch and a non-reset temperature controller? The same control also can turn "off" the boiler circulator circuit when the draft fan shuts down (if that circulator is not needed to be "on" for another purpose). Will need to pay attention to the contact ratings on the controller, as a switching relay might be needed, depending on the contact ratings. Might also need a DPDT switching relay, depending on contact ratings, if both fan and circulator are to be switched.

    Before I saw your post, I already had put together a sketch of a circuit with components to do the same for a Garn and a Wood Gun.

    Good post, thanks.
  3. ewdudley

    ewdudley Minister of Fire

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    No reason, I'm just using the alarm relay function of the type of controller I'm familiar enough with to come up with something useful for the situation. I've 'standardized' on using these for PID control in my system, which is using four of them, so it's just force of habit.
    Yes indeed! Just wanted to keep it simple, more functionality can be added if something more elaborate is needed.

    The controller relays are typically rated for just a couple amperes, so I never use them for anything but control current.

    Thanks for the feedback.
  4. Sawyer

    Sawyer Minister of Fire

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    I want to install a fan controller on the Garn this winter. Don't want to buy a whole new box. This should work well.
    Thanks for posting!
  5. Gasifier

    Gasifier Minister of Fire

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    EW,

    Thanks for posting that. I need to get this taken care of sooner than later. Because I am electrically challenged I am going to see if my boiler installer can do this for me. Now, I have an Aquastat that shuts the circulation pump off if the boiler gets down to 150. Can he use the same Aquastat and have that turn the fan off at that same temperature? Then how do you turn the fan on to start the boiler up from colder than that temperature? Thanks for your time.
  6. bpirger

    bpirger Minister of Fire

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    George:

    Did you get the new controlelr with your Garn? It should shut off the fan when the temp of the flue is just a few degrees above the temp of the water....should be what you want...

    Bruce
  7. ewdudley

    ewdudley Minister of Fire

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    Just need to review the inrush and runtime amperage of the Garn blower, I was assuming a typical downdraft gasifier, so you probably would need a more substantial relay for a real motor.

    There are bigger RIBs than the RIB1UC, which are handy because of the form factor and the 120VAC coil activation option, or you could find something more industrial with a 120VAC coil.

    --ewd
  8. jebatty

    jebatty Minister of Fire

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    Bruce, do you have the new controller? Where and how do you install the sensor for the flue temperature? Thanks.
  9. rkusek

    rkusek Minister of Fire

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    Ewd, I know you have the ability but isn't your RK20001U covered under warranty? Although I question the default settings on a few things, it does a good job overall and might be worth keeping as a failsafe by designing your enhancements to work on top of it.
  10. ewdudley

    ewdudley Minister of Fire

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    Well I missed my install window the fall of the year I bought the unit, so although it flaked out quite early in its service life it had been delivered eighteen months earlier at that point. So for as little as it mattered to me I didn't feel it was worth hassling the dealer with a warranty claim. There's a thread where someone has identified what is most likely the failed component, so I should just go ahead and fix it as soon as I work up the ambition.

    But although it's a nifty little unit when it is working, the real problem is more fundamental. It's designed to control for minimum idling in a low-mass, non-storage system. I want to burn hot and steady until the fuel runs out, or storage is maxed-out, and then I want to shut down completely until the next burn.

    Therefore the circulator-enable-upon-minimum-supply-temperature function is of no use because for as long as I'm burning the circulator should run and return temperature protection takes care of the rest.

    And the variable-draft-fan-speed-as-a-function-on-supply-temperature function is of no use because when my supply temperature gets hot it's because my return temperature is getting hot because my storage is hot. At that point I don't want to modulate the draft fan, I want to keep running hot and steady until supply is good and hot and then it's time to shut it down.

    And although the shut-down-draft-fan-on-high-supply-temperature function is a capability I could use the RK2001U for, I much prefer to entrust that to an old-school Honeywell mechanical aquastat that I salvaged.

    So although there is certainly a case to be made for keeping the stock control, doing away with it can work out OK as well.

    Cheers --ewd
  11. rkusek

    rkusek Minister of Fire

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    Good points. This will be my first winter with storage so I'm probably stuck in that old idle mindset. I was thinking about the little momentary fan bursts during idle but I guess with storage you should be able to avoid that ideally.
  12. HeatFarmer

    HeatFarmer Member

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    Eliot,

    I like your use of the PID/Thermocouples for boiler control in this situation. I also like having the alarm feature to notify me if there has been an overheat or for that matter and Underheat--like the fire bridged--....as my boiler is in the attached barn. I have been studying the pathetic RK-2001U-D manual and have been wondering if it doesn't fall short of the purpose of our tank storage situations.
    You mentioned that you are using other PID controllers in your setup....care to expand on how?

    I am wondering if they wouldn't be an effective method of controlling the pumps in my Primary/Secondary loops per this new thread I started http://www.hearth.com/econtent/index.php/forums/viewthread/85431/
  13. Medman

    Medman Feeling the Heat

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    Elliot, the repair to the controller is very simple, if your failure is the same as mine was. There is a capacitor on the main board that dries out, causing the display to flicker and the pump/fan control to get flaky. Truly a $5 fix if you can perform a simple desolder/solder job. Even though you have a mechanical system to do the job, you should get the controller working again.

    Here is the fix:
    http://www.hearth.com/econtent/index.php/forums/viewthread/67513/


    Ryan
  14. Singed Eyebrows

    Singed Eyebrows New Member

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    I'm glad my Atmos was factory wired for low flue gas temp fan shutdown & the Laddomat plugged right in with an Atmos supplied wiring harness. While I don't have a fancy controller there are quite a few components that work together & I wish I understood it more in case something fails, Randy
  15. wood thing

    wood thing Member

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    I finally built a control. Its like the "Garth B " deal only I used 24 volt and a dpdt "ice cube" relay. Pulled a loop out of the fan aquastat and bingo. Added a switch & indicator light. I think I will abandon the use of a timer. It has been difficult this fall to quess the length of burns. Today I am going to add a light powered from the relay and hang it in the window. Hope to sit in the lazy boy and keep a close watch on.
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