Fan speed controller

Busysawyer · January 13, 2019, 09:21:57 PM

Could someone reccomend a brand or model of fan speed controller. I am using a large owb to heat my barn, kiln, domestic hot water and house. The boiler is designed to burn green logs and the fan has too much power for burning dry material. If I load it with logs it works great with really long burn times. I have a mountain of edging and slab cuts from the sawmill I want to start burning. If i load it with dry split firewood or mill scraps it burns too hot and fast and most of the heat comes out of the chimney in the form of a 10ft blow torch. I want to be able to dial the fan speed back for the days I'm burning mill scraps and crank it back up when I load whole logs. Thank you

gspren · January 13, 2019, 10:03:28 PM

The blower fan on mine has a plate with holes that you can turn to restrict the air flow.

Busysawyer · January 13, 2019, 10:10:52 PM

The boiler has a blast gate that restricts the opening. Even with blast gate all the way closed I'm still getting way too much air flow. In the fully closed position it is still leaving about 1/4 of the air path open.

E Yoder · January 14, 2019, 05:19:38 AM

Is the fan motor the type that can be slowed without heating it up?
Might need to modify the damper/gate to throttle it more?

thecfarm · January 14, 2019, 07:06:07 AM

I have no idea what you have for a blower. I had a heat exchanger put in my basement. I did not want to hear a loud fan. I had them put a speed control on the fan. I run it about half,that makes it quiet. But slower,as you want. I would think it would work. I can turn it down and the fan will turn slow,quiet or turn it all the way and that will will speed fast,and loud.

Busysawyer · January 14, 2019, 11:09:54 PM

I talked to the boiler manufacturer and he has been running a dart fan speed controller on his personal boiler for years. He said they are considering installing it standard on their boilers. Here is a pic of the controller he reccomended and also a pic of my boiler blowing about a 3-4 foot flame tonight. This is burning some good sized red pine logs I cut down about 6 months ago. Burning dry split hardwoods or mill scraps really gets her blowing a big flame. Burning hardwood logs I get little to no flame out of the chimney and a good consistent burn.

E Yoder · January 15, 2019, 06:41:32 AM

What brand of OWB is it. That's a great flame.

albirk · January 15, 2019, 06:52:57 AM

I use a controller like that on the blower in my garage works great. If we are leaving for a long weekend just turn it off.

Busysawyer · January 15, 2019, 09:38:13 AM

@E Yoder , it is a log boiler tl-400. It's the same thing as a natures comfort Tc 400.

E Yoder · January 15, 2019, 09:43:36 AM

Thanks, just curious. I've been interested in those top loaders for a while.

hedgerow · January 15, 2019, 09:55:43 AM

Busysawyer

You will like that Dart controller. We used a lot of Dart controllers at my retired day job. The ones we used were for controlling speed on equipment like conveyor's, packing lines fill machines and they were using DC motors with Dart controllers. I have used there AC models to control fan speeds on smaller motors. The only thing you won't like is the price of the Dart that controller will probably run $150 to $200. I wouldn't buy the China knock offs they don't last.

Al_Smith · January 16, 2019, 07:06:55 AM

You basically have two options other than a multi speed single phase induction motor .Reduce the voltage or change the frequency .You have to be careful the lowest speed is high enough you don't cook the motor using either .The cheapest is just a fan controller like used on an exhaust fan which uses a "trimmer" type circuitry to lower the effective voltage .A VFD changes AC to DC then back to AC with a higher or Lower frequency.

Al_Smith · January 16, 2019, 07:23:52 AM

You could have other options also depending on the design .One could be mechanically throttling the induced draft blower discharge with a gate which would lower the CFMs .
I have to giggle at that picture with fire flying out of it like a blast furnace at a steel mill in about 1920 .If that stack were closer to the ground you could forge horse shoes in the flame .What a person might do with that horse shoe I have no idea .Make 4 I suppose and toss them at a stake and try to get a ringer ?

ButchC · January 16, 2019, 07:59:06 AM

I throttled the draft fan on mine with a piece of scrap tin over the intake attached with one screw so it is adjustable. Saves a lot of wood when burning dry splits. I also placed a switch in the fan circuit so it can be shut off and run draft only when heat isn't needed but still heating domestic water.

Al_Smith · January 16, 2019, 11:58:19 AM

It might not makes sense to a lot of people but standard practice is to throttle the exhaust discharge rather than the intake .

Jack S · January 16, 2019, 12:35:06 PM

Also throttling the inlet side to much you will overload the motor. same is true with pumps.

ButchC · January 16, 2019, 09:31:34 PM

Initially I intended to throttle the exhaust side of the blower but before that got accomplished I bought a Lannair waste oil furnace for the shop which has a nearly identical combustion blower as my OWB and the throttle is on the intake side. Since it is much easier to do it that way that's the way the OWB got done.
None the less you got me thinking so out came my spare blower motor, amp probe and a piece of tin. No matter which side of the blower I throttled the amps went down and motor speeds up all the way to blocked off. Without instruments I have no way to know which way is more efficient, I would assume the exhaust but restrictions to flow do not increase the motor load, they reduce them, no matter which side they are placed which is as I suspected ;)

Al_Smith · January 17, 2019, 06:59:11 AM

Just to clarify I didn't say throttling the intake wouldn't work just the fact that in most cases on a pump or blower the discharge was throttled .What ever works ,works .

ButchC · January 17, 2019, 07:25:13 AM

Understood, ;) I was responding,to the other comment concerning motor loading. As we say in the shop, it wouldn't work for the lunar lander,, but we ain't worken on it.

gspren · January 17, 2019, 08:33:28 AM

The picture of that flame amazes me, I sometimes, actually usually, don't see a single spark out of mine the whole year. It just looks like a lot of wasted heat.

thecfarm · January 17, 2019, 08:41:07 AM

That is why he is asking,alot of wasted heat.
I know the top loaders are diffeant. On my Heatmor the smokes goes up in the front,into a 4x6 inch piece of rectangle tubing,goes the full lenth of the OWB and than goes out the pipe.

Busysawyer · January 17, 2019, 09:31:31 AM

Thank you for all the suggestions. I think the dart fan controller will probably be the best long term solution. It will allow me to easily run the fan off/on or anywhere in between. This boiler isn't designed for efficiency. It is made for ease of loading with a machine, long burn times and big heat loads. In a perfect world I'd feed it nothing but 5ft long 20in diameter green red oak logs. 20f outside and heating my house , kiln, barn and domestic hot water I can easily get two days between loads. On days where I have more time to mess with it I'd like to start working through my mountain of mill scraps. I'm hoping to get 24 hours of burn time with scraps or better. I really think if I can slow the flow of air by switching the fan off I can achieve that.