I know it’s early on the calendar but my focus is starting to shift back to my heating hobby. After two years of experimenting I have a proven performer with both the mechanical unit and the software I used last winter. I could change nothing and go through the winter fairly smoothly but there is always room for more improvement. So this is my plan: 1) Build a new unit very similar to the proven unit I have been using but with greater feed range capability to allow the unit to feed wood chips as well as pellets. By building a complete new unit I can always roll up the proven unit after the experiment is over and the data collected and resume heating without a hiccup. 2) Make slight modifications to the boiler to allow a larger interface plate between the feed unit and the boiler. This will allow a greater range of experimentation with burner designs. 3) Continue making small experimental changes to the working pellet unit such as a vibrator for ash removal, different burner designs, different draft designs. 4) Continue to make changes and improvements to the software. To start I would like three modes of operation. Continuous, run for some amount of time, and run until a set time. I changed the software to run to a set time by calendar date last spring but it was built into the software by date not menu or button choice. I would like to have the option of running for a few hours for both experimentation and also to occasionally heat hot water and be able to choose these options by menu. This fall I am sure I would like the unit to be able to take the chill off and then shut down. 5) Build a chip dryer. This is going to get to be a priority , I know the days are getting a little shorter and it is amazing how much less solar there is in the fall. Time to giddy up on that one.
I know I have to prioritize the work, and work as time and cash flow allows. But I think the first step will be to make a new interface plate and boiler opening. This will allow standardization for the next design and this work can be done while there is no particular need for heat. I went dumpster diving the other day and got a great new electrical box, so I guess I can get going on the that part of the new burner feed. I like free stuff. I may hit that dumpster again soon.
In the mean time it is still summer and there is still sailing weather.
It took me longer than I would like, but the hopper/auger assembly is now painted and the electrical box is mounted and the wiring is functional. I have mounted the Arduino and LCD display. That box also contains the board that accommodates the thermistor electronics, which are the sensors that read various temperatures.
The main electrical box is a stainless steel box I picked up used from a scrap yard, putting the frugal in frugaltinker.com. That’s the reason that there are so many holes in the box, however it was such a good deal I thought it was worth it, despite the cosmetics. The cover was just too ugly to leave be, so I attempted to skin the cover with a plate which I plasma cut in “Frugaltinker.com”. This doesn’t show up too well, I probably should paint a background behind it to make it stand out better. Painting a background seems low on the to do list right now, so I think I will skip that task and focus on the burner.
The CNC was invaluable in the production of the electrical mounting plate, mounted inside the electrical box. It was great to not have to drill any holes to mount anything. All the holes were cut with the CNC and fit just fine.
So the final task is complete before the burner is welded up and tested.
I built a homemade brake to bend sheet metal and it works OK, not great. The corners are really radius’s and fairly large ones at that. The second and main issue I have with it, is the inconsistency that comes from the bends. I find that even though I try to align things perfectly it does not work that way. Some of the parts I have made lately I have cut some slits with the CNC to weaken the folded edge making it more consistent and I wish I had done this for this part of the project….Anyway, a quick reminder of last years effort.
As you can see the hopper is quite small and I ended up adding an extension later. The burner is integral to the hopper and auger, making it very difficult to make any changes to the burner. Lastly the legs are welded on and have no adjustment and seriously two wheels what was I thinking? So while the principal is the same there are some major differences.
It’s pretty challenging to align four pieces of steel of such odd shapes and weights, so in this iteration I cut some gussets with tabs to fit into a slot in the end pieces of the hopper. This keeps the end pieces fixed from side to side because of the slot and plumb as it is butted up to the square the gusset forms. All from welding a gusset plumb. So that was an aid to success, of course as soon as I finished I tossed some ideas around with a friend and we thought up a perhaps better way by making two peices instead of four and doing a different bending technique. Next time. In the meantime this is straight, level and functional. Almost done with the hopper/auger assembly, The last task is to mount the electrical box and paint the entire assembly while it is still apart and then assemble it into a working machine and test the auger drive.
I often have to cut multiple parts, so when I do, I take the opportunity to experiment a bit. In this series of cuts I changed the amperage of the Plasma cutter, a Hypertherm 45. Hypertherm plasma cutters are American made, designed and built, only about a 45 minute drive away from me. I still haven’t gotten my free T shirt for buying and registering the machine but I guess that’s another story… anyway, amazingly enough there really is not a lot of difference in the dross or slag between the three different amp settings I tried. I’ll keep experimenting to try to optimize the cut quality and speed of the CNC machine, plasma cutter combination.
The auger pipe connects the burn plate which attaches to the boiler and forms the interface between the auger feed and the boiler/burner units. I took a piece of 6″ pipe and welded it to the boiler plate and this attaches the plate to the auger feed via screws that tighten. With this assembly I can detach the auger and hopper and test a different burner simply by loosening 6 screws. Modular design for ease of design changes and maintenance.
I attached the hopper plate first because this determines the wheel height required. I slotted the holes in the saddle plates so that there is about 3/8″, or about a centimeter of adjustment up or down adjustment. Then after careful alignment I assembled the entire assembly with clamps and threaded rods. I did cut and weld in some cross pieces with gussets
This will make maintenance of the boiler, ash removal, scraping of the burner holes, boiler tube cleaning very easy by simply rolling the auger/hopper assembly out of the way.
In this step I mount the auger drive motor, it has a built in right angle drive and speed reducer which adds torque. The motor comes complete ready for wiring and mounting using four screws. Again I drew up the parts in SketchUp and then cut them out on the CNC plasma cutter, it was almost too easy. The further I get down this path the more I take advantage of the CNC’s capabilities. Note the rounded corners, I also added an extra hole on top of the motor mount plate to make adding a wire routing clip easier in the future. I remade the worm drive plate to improve some of the adjustment capabilities and added at the same time some decoration, rounded corners and used less material.
I used a Lovejoy type shaft connector to connect the motor to the worm shaft with a Buna-N spider in between to minimize any vibration or backlash to the motor, although with the worm and worm gear combination there should be none.
This step was made simple by the use of the CNC plasma cutter to make a part which I then bent up on both ends using my homemade brake. But first let’s revisit the old configuration for comparison.
I had to rob the motor and some parts from this transmission so it is in disarray but you get the idea of the complexity. It requires four sprockets, two chains, a motor and two chain tensioners. Here is a picture of the newly implemented and untested solution for mounting the worm and worm gear.
The CNC made it easy to slot the holes for adjustment, so the vertical adjustment comes from the plate to plate mounting screws, and the bearing mounting holes are slotted to get correct in and out adjustment to the keyed worm. After cutting the part and mounting it I decided what to change in the next iteration. I modified the part to round all the corners so that there are no sharp edges and extended the plate to pick up a second set of holes so the plates are attached with four screws instead of two. I think this part is perfectly functional so I won’t implement the changes but at least the SketchUp drawing has been updated.
It may seem like a small bite but step two actually requires some machining and tweaking to get correct. In this step I am going to add the auger to the pipe assembly I have already built. To do this I need to support the auger with bearings so the shaft will be cantilevered in the pipe. The auger should not touch the pipe and needs to be centered in the pipe, at least within a reasonable distance. To do this I cut some 1 x 2 square tubing and then drilled holes on the Bridgeport using the Digital Readout to measure the distance so that the bearings would fit perfectly. These particular bearings are an oil impregnated bronze bushing in a pillow block configuration. The pillow block configuration is aluminum which makes machining the pillow block easy. Here’s a picture of the key way which I machined into a piece of 1″ cold rolled. If you have the choice cold rolled is much easier to work with then hot rolled for shafts. Of course this is really not shaft stock it is round stock but it works just fine and is inexpensive.
After welding the auger onto the shaft I do the calculations to center the shaft in the pipe. To make the shaft centered I have to mill some of the pillow block bearing, as you can see in the picture I had to use a circular shim to get the auger centered in the pipe.
Finally after some adjustment you can see the end result of the auger centered in the feed pipe.
After last winter’s experience, I decided to start from scratch on the auger/hopper assembly. I varied the height several times through different burner designs. Now it looks like it was modified once too many times. The other main reason to rebuild the hopper assembly is the difficulty removing the burner from the boiler because it must stay balanced. I don’t remember exactly my thoughts at that point, I probably just had two wheels around the shop and was in a hurry.
So this fall I am rebuilding the hopper with a different auger drive system, and additional wheels and supports to make it much more robust and simple. The foundation of improvement in the new assembly is the ability to draw the parts in SketchUp as well as cut the parts with the CNC. Here’s a view of the cut out parts.
The parts laid out I call the saddle, angle iron, and side alignment plate.
The parts below are the angle iron plate with the side alignment plate. The angle iron plate is tabbed to fit into the slots of the side alignment plate, this way the parts are self aligning and jigging. Adding strength and ease of assembly. This makes the welding so much easier.
Finally here is the assembly on the welding table ready to weld, note the threaded rod, which also aids in the rigidity and ease of adjustment to make sure all the pieces are square and parallel prior to welding.
And finally the partially finished welded assembly, this assembly will be the foundation to cantilever the auger in the feed pipe as well as support the auger drive motor and gears.
The CAD designed parts combined with the CNC, combined with self jigging design for success make a nice finished assembly with light material for cost savings combined with good strength.
Minor changes in the software that force the boiler to maintain a tighter range from the set point has cut the fuel consumption from 3 (40 pound) bags of pellets to 2 daily. These software improvements and a extension to the pellet hopper mean the boiler will now run 24 hours without needing additional fuel. The hopper extension adds at least another 40 lb bag of pellets capacity bringing the total capacity to approx. 2 1/2-3 bags. I haven’t measured only estimated.
The boiler set point is currently set at 135°F which seems to work just fine for the temperatures we have been having and the software is consistently running within4 degrees of set point. This range may seem excessive but seems to run just fine. The program is becoming more modular in that there is only one number to change, the set point. The set point currently is a variable declared in the setup section of the program but eventually the set point will be self adjusted by the program based on the outside temperature. Economy and efficiency by software optimization is the goal for this next week.
We have had a very mild winter in my opinion. The Heating Degree Day total for the month of Dec 2011 was 1091 as measured by the local weather station. The normal is 1209 HDD a difference of 118 HDD, not as much as I would have thought. The total for the month of January 2012 so far is 1140 with four days to go, with a normal of 1419. We’ll see how the month ends but if it continues as the average day it will be short approx the same number of HDD as last month,December. My interest in HDD is to see if there is a correlation to HDD and fuel consumption. There should be and if there is than the fuel economy is starting to improve. As I told a friend of mine, at this point the boiler is like a truck I used to own, 10 mpg going uphill loaded, 10 mpg empty going downhill….so seeing fuel consumption changing to track the weather will be the first step to seeing some optimization.
Software work on fuel economy and the extrapolation of costs for the upcoming remainder of the season is of great interest. The next step in fuel economy may be better insulation of the boiler and piping and will not be as simple as software improvements. But if I can get a correlation between the outside temperature and fuel consumption that is measurable then the software will be nearly optimized and further improvements will have to come from physical changes. This week sees a 40 pound bag and $4.00 improvement per day, $28/week, $112 per month. Next week’s goal: another $60/month. I am hoping for a total seasonal heating cost of $500 or less using $200/ton pellets. I will consider that a huge victory for heating a 2300 sq ft house with 3 garage doors.
The sprockets have been replaced and improved with key ways cut into the jack shaft and auger. This allows positive feeding without slippage. The jack shaft placement was constrained so adjustment of the chains is limited to what linkages can be removed or replaced with half links and adding a slack tension device on the slack side of the roller chain. With this complete the LCD problems appear to be fixed. Without proper tension the chain did not ride on the sprockets smoothly and the tension could take up suddenly adding a jerk to the system. Without this mechanical jerk in the system the motor can work more smoothly allowing the LCD to not get the power fluctuations that garble the display. The feed problems appear to be fixed but in the last test the unit ran for four days without fail and at this point although there is a marked improvement that time has not been surpassed. Next on the list is the hopper extension to allow feeding of two bags of pellets. This will allow 16 hours of run time without any software improvements.