Speed Control of Combustion Fan???

 
RFK
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Post by RFK » Sun. Feb. 08, 2015 2:30 pm

After searching the archives on this subject, it's evident that many other members are doing this. I've never read of anyone having any detrimental effects on their fan motors using a ceiling fan rheostat for this purpose. However, I was recently looking over specifications found on the Electric Motor Warehouse site for both the OEM (Fasco), and the replacement (Dayton) blowers for my Harman Mag stoker, and in each case the manufacturers stated that their blowers are "not recommended for" or "not suitable for" speed control. Can any of you electrically savvy folks elaborate on why the manufactures make this claim? I would like to experiment with continuous operation and speed control of the combustion blower to achieve a more complete burn of coal, but figured that the manufacturers had their reasons for not recommending speed control. Am I being overly concerned here or what? Thanks for your help.
Rick


 
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coalkirk
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Post by coalkirk » Sun. Feb. 08, 2015 2:58 pm

Rick, I'm not terribly electrically savvy but I've been using a fan speed control on my Harman combustion fan for about 3 years. I know the specs say not to use speed controllers but it works. What you would not want to do is run the fan speed so slow that it could stop. When my boiler is not calling for heat, my fan runs about half speed just to keep the fire more active. I use a model
KBWC-13 from KB electronics. There is a guy that sells them on ebay for about $15.00.

 
RFK
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Post by RFK » Mon. Feb. 09, 2015 1:54 pm

coalkirk wrote:Rick, I'm not terribly electrically savvy but I've been using a fan speed control on my Harman combustion fan for about 3 years. I know the specs say not to use speed controllers but it works. What you would not want to do is run the fan speed so slow that it could stop. When my boiler is not calling for heat, my fan runs about half speed just to keep the fire more active. I use a model
KBWC-13 from KB electronics. There is a guy that sells them on ebay for about $15.00.
ck, with the comb. fan running through your rheostat do you have the restrictor plate completely open so that the fan output is totally dependent on the speed control? At this point I am just running everything on the OEM control box with the restrictor plate set at 1/2 open, 4 minutes on, 10 min, off, with a 5 min. extend time on the distribution fan. When the thermostat is calling for heat, the flames are reaching the top of the stove which seems maybe too much for continuous operation of the comb. fan. I am guessing that your 1/2 speed setting probably doesn't equal a 1/2 open restrictor plate output. Any thoughts? Thanks.
Rick

 
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coalkirk
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Post by coalkirk » Mon. Feb. 09, 2015 10:53 pm

While we use the same stoker for our coal burners, I'm heating a boiler with it as opposed to a stove. For me running the combustion fan on half speed only when there is no demand for heat was all about keeping the boiler temperature up. I'm taxing this boiler hard when it gets really cold and windy. If I run the combustion fan wide open without the restrictor plate, it over pressurizes the combustion chamber and I'll get s light odor out of the hopper. My restrictor plate is about half closed. I run my chimney draft at .03. If I ran it higher I might be able to completely remove the restrictor plate.

 
RFK
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Post by RFK » Wed. Feb. 11, 2015 2:04 pm

I'm going out today to buy the hardware that I need to try this. What I really would like to do is to be able to control the combustion fan to blow full volume when the stove is calling for heat and the stoker is running , then slow it down in idle mode thus letting it run 24/7. I can't see how to do that using the Harman controller though. I'll just have to experiment with the speed control and watch the Magnehelic until I get the draft dialed in.
Rick

 
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McGiever
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Post by McGiever » Wed. Feb. 11, 2015 5:20 pm

RFK wrote:I'm going out today to buy the hardware that I need to try this. What I really would like to do is to be able to control the combustion fan to blow full volume when the stove is calling for heat and the stoker is running , then slow it down in idle mode thus letting it run 24/7. I can't see how to do that using the Harman controller though. I'll just have to experiment with the speed control and watch the Magnehelic until I get the draft dialed in.
Rick
Using a added relay you can run at 100% fan speed...then when dropping out the relay (after a hold fire or a heat call) the speed controller runs fan at reduced speed.

 
RFK
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Other Heating: Baseboard Electric

Post by RFK » Wed. Feb. 11, 2015 5:45 pm

McG., that sounds exactly what I want to do. Can you explain further please? What relay, where can I buy such an item, and how is it wired in? Today I purchased a single gang box and a switch which will be wired to turn on/off the entire system, a double gang box which will hold the variable speed control rheostat (Lutron FS-5F, 5 amp), and a duplex outlet. One half of the outlet will remain hot at all times (plug from the Harman controller goes here), and the second half of the outlet will be controlled by the rheostat and will accept the combustion fan plug. I can handle the wiring of this set-up, but anything beyond this is probably outside my electrical ability without further guidance. Any help is much appreciated. Thanks.
Rick


 
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oliver power
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Post by oliver power » Thu. Feb. 12, 2015 4:29 am

Personally, I can see wanting to slow down the circulation fan, due to noise. On my KEYSTOKER boiler, the combustion fan is wired together with stoker motor. I surely wouldn't want to reduce power to the stoker motor. So, for those who think they want to reduce power to the combustion fan, make sure you separate the stoker motor. Straining the stoker motor on every push is not good for it. In my case, the boiler doesn't have a circulation fan. My combustion fan is quiet. So I can't see reducing power at all. I use the restrictor plate as designed. For those with stoves /furnaces, and all three (stoker, combustion fan, & circulation fan) are tied together, I would separate, and slow down circulation fan due to noise. The same thing can be accomplished by wiring in re-a-stat just before circulation fan, which does the same thing. It reduces power only to circulation fan. Leave full power to combustion fan, and stoker motor. Adjust combustion air restrictor plate as designed. My whole purpose for this reply is to inform those who don't quite fully understand, and think plugging into a re-a-stat, then into the wall, is all that needs to be done. That's fine with a hand fired, natural draft stove, where all your slowing down is the circulation fan. When it comes to stokers, a little more thinking is required.

 
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Post by Staylo » Wed. Feb. 18, 2015 10:44 am

Greetings all! First time poster, as well as a new coal user. We just purchased a house in November that has a Harman Magnum Stoker and it's been a steep learning curve for me coming off of wood burning. Fortunately this forum has been a wealth of information.

I too was wondering about adding a speed control to my combustion blower. I just recently made two modifications to the stove which necessitates looking at this. First off, I replaced the old noisy Fasco blower with the Dayton which runs at 89CFM instead of 75CFM. Secondly, I rigged up a fresh air intake for the combustion blower because we had very high radon readings in the house and it was suggested that the combustion blower was exacerbating the problem, but in doing so I had to remove the restrictor plate to allow me to mount a flange to the fan housing. So now with the higher volume fan and no restrictor plate I have no way to adjust the draft. Obviously, a speed control would be perfect for this, but I had also read that this fan was not recommended for a speed control. I'm not looking to do anything quite as fancy as RFK, and just want to be able to dial the speed back just enough to set the draft properly and leave it there. Basically, I would just feel much better hearing that people have been running speed controls on this fan with no issues. I added a couple quick pics of the fresh air intake system I rigged up in case anyone is interested.

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titleist1
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Post by titleist1 » Wed. Feb. 18, 2015 1:02 pm

Nice job with the combustion air flange. Looks a lot better than mine!

You could block off the intake screen on the combustion fan with something other than the restrictor plate that you had to remove. A small piece of flashing trapped between the screen & housing would do the same thing as the plate and not get in the way of your flange.

You must have a tremendous draft on your chimney. No way I could run with my plate open more than 1/2 (let alone off entirely) without pressurizing the firebox and leaking CO into the house. You do have CO monitors, correct? Do you have a manometer, it would be helpful setting the fan speed or the restrictor plate whichever you choose to use.

 
Staylo
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Post by Staylo » Wed. Feb. 18, 2015 1:28 pm

titleist1 wrote:Nice job with the combustion air flange. Looks a lot better than mine!

You could block off the intake screen on the combustion fan with something other than the restrictor plate that you had to remove. A small piece of flashing trapped between the screen & housing would do the same thing as the plate and not get in the way of your flange.

You must have a tremendous draft on your chimney. No way I could run with my plate open more than 1/2 (let alone off entirely) without pressurizing the firebox and leaking CO into the house. You do have CO monitors, correct? Do you have a manometer, it would be helpful setting the fan speed or the restrictor plate whichever you choose to use.
Thanks for the compliment! At this point I have been running the fresh air intake for about two months and have not gotten any readings of carbon monoxide on the detectors. I agree the draft is pretty good because according to my hillbilly draft detector if I crack the ash door open just slightly and drop a little fly ash at the opening it sucks it right in. The CO detectors have a digital history function that displays the peak level detected and both have continued to show zero so so far so good. Seeing as how I just installed the new Dayton fan today though, I have a local stove guy scheduled next week to come take some actual draft readings for me. That's why I was thinking about having the speed control installed by the time he gets here so we can dial it in. I had also thought about blocking off some of the intake screen of my fresh air intake. That would act as a restrictor plate I suppose, although it wouldn't be as slick to adjust as a speed control. Plus, with the fan now having to suck on a big straw for its air I don't know if I'm keen to restrict the intake anymore than it already is, although I suppose the original restrictor plate did the same thing and I don't know whether dialing the motor back with the speed control would be all that much different.

 
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coalkirk
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Post by coalkirk » Wed. Feb. 18, 2015 3:10 pm

Do you have a radon mitigation system installed? It's a pretty simple thing to do.

 
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Horace
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Post by Horace » Wed. Feb. 18, 2015 3:13 pm

I've run a speed control on my combustion blower for a few years - maybe six, now that I think about it - without incident. The motor is a lot cooler, it's slightly quieter, and I have pretty much infinite control over it. It's the original blower for the stove that was manufactured in 1986, according to the sticker on the stove.

 
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Post by Staylo » Wed. Feb. 18, 2015 4:14 pm

coalkirk wrote:Do you have a radon mitigation system installed? It's a pretty simple thing to do.
Yes, we had a system put in at the same time I rigged up the fresh air intake for the Stoker. Our original test levels were over 90, and the action level recommended by the government is 4. After the system was put in and the fresh air intake was installed the subsequent retest gave a reading of less than 1. So I can't say for certain how much of that result is due to the fresh air intake as opposed to the mitigation system, but between the two of them they took care of the problem. And it is kind of nice not to be sucking my warm air I just heated out of the house and blowing it up the chimney just to heat more cold air I just sucked in from outside. :)

 
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Post by Staylo » Wed. Feb. 18, 2015 4:15 pm

Horace wrote:I've run a speed control on my combustion blower for a few years - maybe six, now that I think about it - without incident. The motor is a lot cooler, it's slightly quieter, and I have pretty much infinite control over it. It's the original blower for the stove that was manufactured in 1986, according to the sticker on the stove.
Thanks! That was exactly what I wanted to hear. I assumed that since I am only going to be throttling the blower down a small bit that it would not have been a problem, but it's reassuring to hear from someone who's had one in place that they haven't had any issues.


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