SmartStove Integration with Regency Hampton HI300 Insert

[SmartStove_Dan]

This thread will go through the integration process for a Hampton HI300 insert.

The biggest challenge with this insert is the draft control.  Buried deep inside the stove is a heavy sliding steel plate that passes over the draft intake port.  This plate slides about 3".  Dragging this heavy plate over 3" is too much for the servo used with SmartStove, so an alternative needed to be developed.  This required surgery. 

Gaining access:  With the stove flipped over, a rectangular opening was cut through .1" steel into the bottom, directly under the intake port.  This created access to the airway that the blower pushes air through.  There was still another layer of .1" steel that needed to be cut through in order to get to the port itself.  The attached photo shows the openings cut through both layers, with the draft port finally exposed.  The sliding plate is on the opposite side of the port and it's not visible since the draft control is set wide open.  The draft port is a laser-cut opening in the 3/16" steel plate that forms the bottom of the firebox.  There's a channel welded onto the top side of this plate that feeds the fire at the bottom and also runs up the sides to feed the airwash.

[SmartStove_Dan]

The next step was to fabricate a rotating vane to replace the original heavy draft slider.  A pie-shaped piece of aluminum was cut, and set to rotate about a pivot.  A flat-head 4-40 screw was attached to the vane and protruded enough to thread a brass fitting that the pushrod grabs onto.  This fitting is threaded loosely onto the 4-40 screw and rotates as the vane rotates.  A brass guide was machined to limit that vane travel, and to ensure that the plate would stay in place when the stove was flipped upright.  Remember that this rotating vane would be hanging from the underside of the stove.  The brass guide was attached using two 8-32 machine screws that are threaded into the 3/16" steel bottom of the stove.  These two screws protrude through the bottom of the stove and into the original heavy draft slider, securing it permanently open. 

This mechanism worked beautifully when the stove was upside down.  However, once the stove was set upright, it tended to hang down when it was near the travel limits, and would bind up.  Two additional guides were machined to secure the vane at the limits.  This worked OK, but after the first couple firings, it started to bind up.  The attached photo shows the final state of this initial failed design. 

[SmartStove_Dan]

Final draft vane mechanism.

The initial attempt to make this draft vane failed because it was imbalanced, needed guides to keep it in place and had problems with binding up.  A new aluminum vane was made that was more symmetric and balanced, eliminating any issues with it hanging down when the stove was flipped upright.  The original brass guide was also found to bind up against the soft aluminum, so a new part was made out of teflon.  The two additional brass guides were removed and the residual holes filled with high temperature silicone.

Teflon melts at 621 degrees F, and is usable up to 500.  This part of the stove is on the bottom, which is a good thing, and additionally it is part of the fresh air channel that feeds the fire.  This part of the stove won't be getting much above 200 degrees and surely will not get close to 500, so teflon will be fine here.  

After this new larger vane was completed and in place with the teflon guide, it was still experiencing a bit of binding with the bottom of the stove.  Aluminum is not a good wearing part.  The solution to this issue was to pick up a teflon-coated oven liner and cut it to shape to use as a lubricating layer between the aluminum vane and the steel stove bottom.  The teflon oven liner material is secured in place using the flat-head screw that the pushrod attaches to.  This solution works beautifully.  The final vane operates perfectly smoothly with almost no friction at all.  The teflon oven liner material can be seen extending out around the aluminum vane.  The attached photos show the bottom of the vane with the teflon oven liner attached and final design.

[SmartStove_Dan]

With the draft control replaced with a new mechanism that operates smoothly and with little friction, the servo was mounted on the side of the stove where the original draft control rod exits.  The original draft control rod is cut off leaving a short stub.  A bracket was built that attaches to the sheet metal shroud on the side of the stove.  This attachment point was chosen because there's a bit of separation from the hot firebox side and little heat will be conducted to this point.  The pushrod extends into the stove through the fresh air opening to reach the vane.  In this location, the servo is perfectly cool even if the blower is not running.  

The second photo taken a bit further back, shows the thermocouple wire extending down from the top of the firebox.  The thermocouple and servo wires have enough length to be able to pull the fan housing out for servicing.

[SmartStove_Dan]

Location of the thermocouple.  This is easy.  A hole is drilled and tapped into the 3/16" steel on the top of the firebox, behind the air channel that feeds the airwash.  The thermocouple is screwed to the top with an 8-32 stainless steel machine screw.  

UPDATE: Upon initial testing with the thermocouple attached in the center like this, temperature readings were peaking out at about 950 degrees.  Although SmartStove can measure up to about 975 degrees F, it would be better to select a different attachment point with lower temperatures.  In all of my testing, I have found that the temperature profile measured on the typical stove with burn tubes is just about the same regardless of where you put the probe, it's just that you'll measure differing amplitudes.  So, I have moved the thermocouple over to the left side, about 4" from the corner.  Now the peak temperature should peak out at about 600 degrees.  This is much better for a number of reasons.  I will be posting some test data using the thermocouple at this location.

[SmartStove_Dan]

Locating the electronics.  The fan housing with this stove provides an abundant amount of space to add everything needed.  On the left side where the power cord comes in is where the CPU module, backup battery, beeper and the power supply are all located.  Holes are drilled and tapped to screw the CPU module to the plate that covers the fresh air intake.  Velcro is used to attach the backup battery to the plate, right next to the CPU.  The wall adapter power supply was opened up and the prongs that normally plug into the wall were removed, and a power cord was added to it.  The power cord to the power supply, another power cord that runs over the fan control board are connected to the incoming power cord using orange wire nuts.  The power supply is then mounted using velcro.  The beeper is attached next to the backup battery using velcro.

All the original wiring going to the switches and the snap disk has been removed along with the snap disk thermal switch. 

[SmartStove_Dan]

The final part to hook up is the fan driver module.  This board is connected to the intake baffle plate using nylon standoffs.  The black power cord coming over from the other side connects to the power terminal block.   The black and white fan wires also connect in to the terminal block.  The gray control cable coming over from the CPU module is plugged into the fan driver module.  The red wire goes to the low speed winding of the two-speed motor, and is not connected.

This completes the installation on the stove itself.

[SmartStove_Dan]

I forgot to mention -- After finishing up with the draft control vane, plates were made to cover the openings cut though each layer of steel in the stove bottom.  The plate covering the inner opening is visible through the two ports in the front that the blower pushes air through.  The plates are screwed in place.  

[SmartStove_Dan]

The stove is now installed into the fireplace opening.  At this point it has gone through a number of loads of wood.  Control thresholds have been set with the User Interface panel and it operates very nicely.  The temperatures are surprisingly high, so a second thermocouple was attached and a meter used to confirm the readings measured by SmartStove.  The temperature readings are good.  The thresholds are set to start closing the draft at 500 degrees F and reach full closure by 750 degrees F.  The fan is set to start up at 300 degrees and reach full speed at 500 degrees. 

This is one beautiful insert, and it's a dream to use now with SmartStove installed and running things.

[SmartStove_Dan]

Here's a plot showing the first firing with the thermocouple located on the top of the firebox, about 4" from the left side.  The data shows the initial start up with kindling, then when there was a decent coal bed, it was loaded with a small load of large splits.  Each data point represents 5 minutes.

The blue trace shows the draft position.  The scale for this trace is 100 fully open, 200 fully closed.  Similarly, the fan (yellow trace) is off at 0 and full speed at about 245.

It can be seen how after the initial start up, loading the stove with about 5 splits pulls a great deal of heat out of the stove and cools things down quite a bit.  Once the fire came up to temperature at around 400 degrees, it stabilized for about one hour, then started to taper off.  This is the common signature seen with most stoves.  A full load should show a higher peak temperature and it should have a stable peak for up to 3 hours, then taper off.  When I first started doing this testing with a Napoleon 1401, back in about 2005, I thought there was something wrong with the measurement because when you look at the fire, you just don't see such a dramatic-looking drop-off.  This just is the way these stoves operate.  

[Brian]

I'm curious what your using for your feedback control algorithm.  Is it a PID controller or something similar?  Does it need to be tuned for different stoves or do you just change set points from one stove to another?

[SmartStove_Dan]

Hi Brian,
It's a proportional only control.  Settings need to be selected for each stove, and are fully user-configurable. 

Tuning amounts to setting a temperature at which the draft control will begin to close and another temperature (target temp) at which the draft control will be fully closed.  Between the two temperatures, the draft control will close linearly from open to close.  I've experimented with other control methods and this simple approach has proven to be simple, yet works very nicely.  Of course, the fan speed also factors in there too.  In a manner similar to the draft control, start and target temps are also specified for the fan, with a linear relationship between the two.  So as the stove heats, once it reaches the fan start temp, the fan will start, and the speed will increase as the stove heats.  The fan speed and draft control both have an affect on the temperature of the stove, so the system establishes an equilibrium in the stove between draft control, fan speed and the fire itself.
--Dan

[Brian]

It looks like it works really nicely.  Do you notice a difference in the dynamics of cast vs steel stoves?

[SmartStove_Dan]

Hi Brian,
I don't have any data relative to steel vs cast stoves, but it comes down to a difference in thermal mass.  A cast stove, being a bit heavier, will heat up slightly slower than a steel stove.  I don't see that this is going to create any noticeable difference in control given that the fire takes so much longer to get going than the stove does to heat up.
Dan