Variable Speed Blower fan control

[Smoky Stoker]

Hello!
Has anyone seen a temperature controlled, variable-speed wood stove blower? I've seen the thermal switches that turn the blower ON once the stove is warming up and OFF when it is cooling down.

I'm curious if any stove manufacturers have made fan controls that can automatically increase the blower speed as the stove gets hotter and decrease the blower speed as it cools.

Thanks!

 

[Highbeam]

The wood furnace world does this with their blowers. At least the good ones.

 

[snaple4]

We have controls like that in the HVAC industry for different things. You would be looking for a condenser/HP head pressure control or similar; as temperature goes up it will adjust the speed but the ones I am familiar with work off of around 70*-100* temp. Would have to find one that would be in the 200+ range? Maybe if you could find some of the wood furnace parts and adapt them to the stove?

 

[Smoky Stoker]

Thanks, that's helpful. I have an old Regency with a thermal switch, which turns the blower off and on. It's a nice feature, but hoping to add some automatic speed control to its operation.

 

[DBoon]

I've searched for something like this for several years - it just seems unavailable as an off-the-shelf item (not sure why, except for cost, perhaps). My primary reasons for doing this would be to save some energy, reduce noise and avoid having to turn up the blower when the stovetop gets hot (or when I am not there).

I've thought about building my own - the control part of it shouldn't be too hard. I'd have to buy my own variable frequency drive (there are not many low-power off-the-shelf options for this) and then pair it with an inverter drive designed blower motor (which seem mostly unavailable). Without the right kind of motor, I'd need to install some inductors to filter the drive output PWM signals, and these are not generally available in low power ratings - or I could make my own. Regardless, they consume power too...so the setup wouldn't really be any more energy efficient.

Overally, not available and/or too much work to make. So, I still have the same not ideal blower that came with my stove all those years ago.

 

[Mike M.]

I've searched for something like this for several years - it just seems unavailable as an off-the-shelf item (not sure why, except for cost, perhaps). My primary reasons for doing this would be to save some energy, reduce noise and avoid having to turn up the blower when the stovetop gets hot (or when I am not there).

I've thought about building my own - the control part of it shouldn't be too hard. I'd have to buy my own variable frequency drive (there are not many low-power off-the-shelf options for this) and then pair it with an inverter drive designed blower motor (which seem mostly unavailable). Without the right kind of motor, I'd need to install some inductors to filter the drive output PWM signals, and these are not generally available in low power ratings - or I could make my own. Regardless, they consume power too...so the setup wouldn't really be any more energy efficient.

Overally, not available and/or too much work to make. So, I still have the same not ideal blower that came with my stove all those years ago.

I would go DC drive if you plan to do this. DC drives scale down much lower that AC drives. You can get a board style DC drive real cheap then just find a small DC motor. Could use 2 or 3 of the on/off disks with different temp ratings as inputs to the drive, basically setting up different speeds for different temps. Seems like a fun project.

 

[brenndatomu]

We have controls like that in the HVAC industry for different things. You would be looking for a condenser/HP head pressure control or similar; as temperature goes up it will adjust the speed but the ones I am familiar with work off of around 70*-100* temp. Would have to find one that would be in the 200+ range? Maybe if you could find some of the wood furnace parts and adapt them to the stove?

There are a bunch of us here that have been using head pressure controls to automatically vary the distribution blower speed on wood furnaces for a few years already now...works darn well! FIY, a 5k pot wired in series with the temp sensor will allow you to add resistance to tweak the controller into a usable temp range...or might take a 10k pot (more?) for a stove...with its higher operational temps.
The only down side for doing this on a wood stove would be how to hide the extra equipment, and sometimes the motor will hum at lower speeds...so that could be annoying on a stove that's right in your living room.

 

[snaple4]

There are a bunch of us here that have been using head pressure controls to automatically vary the distribution blower speed on wood furnaces for a few years already now...works darn well! FIY, a 5k pot wired in series with the temp sensor will allow you to add resistance to tweak the controller into a usable temp range...or might take a 10k pot (more?) for a stove...with its higher operational temps.
The only down side for doing this on a wood stove would be how to hide the extra equipment, and sometimes the motor will hum at lower speeds...so that could be annoying on a stove that's right in your living room.

Know of anyone who has done a write up of how to do it or what parts they used? I am curious how they went about it. You are correct about the Hum with motors turned down. Ball bearing works better than shaft but they will still make noise. Not sure what most wood stove blowers use.

 

[EbS-P]

I’ve been thinking about this too. My approach, if I ever do it, will be to use an arduino board to read the thermocouple and then have it control the fan rheostat via stepper motor. This way I could use any variable speed ac blower. Like I said I haven’t done but all parts can be found on amazon for less than 200$ Ordepending on the blower.

You could even get an lcd and display temperature and set alarms with it too. Run a loop that reads the temp every t seconds and sets a motor postistion and displayed temp.

Heck you could add a second temp probe and monitor stt and flue temp or even add a second stepper to control primary air or a shutdown damper on your air intake to prevent over fires.

Keep us posted. And if in the off chance I build something like this I will write it up.

Evan