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Solar powered solar kiln

Started by Jason_WI, April 06, 2005, 02:47:46 PM

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Jason_WI

I am looking to build a solar kiln this spring. My plan is to build it on a running gear so that it can be transported and also not to worry about building permits and taxes. It is going to be 16' long and 8' wide. I want to be able to dry 14' stuff for molding. I am on the 45 parallel and to get better winter performance a 55 deg collector angle is going to be used. Collector will be corrugated fiberglass sheets on the outside and uv resistant plactic on the inside.

Another plan was to make it totally solar powered. I looked at the solar powered attic vents but at $300 a pop and would probably need 2 that is $600 right there. Looking at other options I found some 24 volt radiator fans at Surplus center that take 2.1 amps each and cost $25. I will probably need two of these fans in the kiln for proper airflow. Calculating the amount of power that I need to run two fans 24 volts * 4.2 amps = 100 watts of power. With solar I will probably need 50% over that so 150 watt panel should supply enough juice to maintain a 24 volt system with 2 fans running plus some other controls.  Currently the problem is finding solar panels that don't cost $5 per watt.

Another plan was to use proportional vents. Surplus center has 18" x 7" shutter vents with a control arm. To control them I plan useing a 1/4 scale servo that are used in model airplanes to proportionally control the venting. I will use a PIC controller to make all this happen. Probably over kill from what I have seen with other solar kiln designs but I like over kill.... Also plan to monitor temp and humidity and log it to a PC.

Looking for cheap solar panels......

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Doc

No such thing as cheap solar panels. Even retired used ones sell high. I have been looking for some as well, but for a different reason, and the info I have found says that the big resellers of solar gear buy the damaged/used ones and resell those as well. They pay top dollar and have the connections to get them before you doso you pay top dollar to them to get them.

The harbor freight units are about as cheap as it gets, and be prepared to buffer that collector through a battery.

Doc

Jason_WI

I think that eBay will be somewhat reasonable. Hafta watch the auctions close. I am planning on using a 24 battery system.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Larry

Don't know if feasible or not but could ya do anything with a wind powered generator?

Larry, making useful and beautiful things out of the most environmental friendly material on the planet.

We need to insure our customers understand the importance of our craft.

Ianab

A different thought...

I bet those car / attic fans are not very efficient.
Both in motor and in fan design.
What about taking one of those motors, or maybe a geared down version, and building up a laminated propellor (airplane style). I'm thinking about the big blades on power windmills and solar powered aircraft.  If you can get twice the airflow from the same power input, you only need 1/2 the solar cells, and they seem to be the main cost. The fan / prop could be wooden, 3 or 4 ft dia, put in a chicken wire safety cage. Weight isn't so important as it doesn't have to fly, it may just take a minute to get up to speed. Maybe look at how model / homebuilt airplane builders make them?

Just an idea anyway  :P

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Doc

I was looking at attic ventilator fans last night at Home Despot. they had the gable units there that woudl move 1500cfm or so for about $100 bucks and they are thermostatically controlled on the motor. I did not get a good look at one, but I am thinking this may be the way I go, and set them on a timer.

may run up the cost of drying a bit, and the cost of building my solar kiln a bit, but it is still cheaper than the 4k or so I am seeing ont he Nyle units (I can't afford that ....yet).

Doc

Jason_WI

So far the best price I could find is if I were to build my own panels with solar cells purchased for $2.35 a watt.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Randy

I already have the solar panels and charge controllers and the 12volt attic fans and the batteries and the power inverters---------------All I need is some plans on how to build it and how to operate it after it is built. Where can I find some detailed info?? Do I need a humidifier or a de-humidifier?? Thanks Randy

Jacar

Jason,

I have been operating my solar kiln for 3 years now.  It is 12'x8', and can hold around 1000 bdft.  I used salvaged materials for the majority of my construction.  The whole idea for using a solar kiln is it's simplicity and low cost of operation.  Like you I am into overkill, but I did not have the finances for it. 

There are really only two things you can control on a solar kiln:  how much air you move in the kiln by the capacity of your fans, and how much outside air you exchange thru the vents.  I have two 18" fans that came out of A/C units.  I have six vents that have doors on the inside that I open and close as needed.  I use themostats that came off attic vent fans.  I insert one  remote temp probe into the wood stack.  The thermometer records high and low temps that I track daily. 

Anything much more complicated rules out the efficiency of a solar kiln.  Depending on where you live determines how many loads you can dry in a year.  If I plan it right and have the wood available I can dry 7-8 loads/year NW of Houston, IF the lumber goes in airdried at less than 20 % mc.  If I start with green lumber then everything changes.  If I have a cloudy summer month, then everything changes.  Between Oct and Feb I usually can plan on drying one load. 

There are many variables to be considered in selecting a drying method.  I chose solar kiln because of the low intitial cost.  It is also very cheap to operate, but I am soley at the mercy of the weather.  I cannot depend on it to produce a timely product to maintain production.  But for my use for part time woodworkers and serious hobbiest, it works great.  You might find the cost of going totally solar not cost effective,  depending on your production needs.

These are just my two cents.  Hope it helps. 

Jacar
Jack Watkins

Jason_WI

If I can dry 2 to 3000 bf a year that is really all the capacity that I need.

I have some small solar cells, enough to build a 12 volt 6 watt panel. I know its far from the 150 or so watts that I need but I want to see it it is feasible to build my own panels. The cells I have are polycrystaline which are not as efficent at monocrystaline or ribbon grown cells. I have most of the pieces gathered up except for a aluminum sheet about 1/8" thick. I am planning to make all my panels 36 cell which will perform bettter if its cloudy.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

Just bought two 94 watt panels on Ebay for $3.80 a watt and that includes shipping. 188 watts should be plenty with 3, 12 volt fans pulling about 6.5 amps total. Need to get a charge controller and a deep cycle battery yet and I'll be all set with the electrical.

What insulation is recomended in a solar kiln. I know fiberglass batting isn't recommended. 2" pink foam at Menards is about $20 each.  It is R10 rated so 2 layers would be needed for R20.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Randy

Hello Jason
I am not sure what experience you have with solar, but I would reccomend using two 6volt golf cart batteries over a deep cycle battery. I bought GOOD(check them with a battery load tester)used golf cart batteries for $25 each 3 years ago---they are still working. You can buy New T-105's golf cart batteries here for less than $60 each.  I went to Walmarts and Bought 2 of The Heaviest Duty Deep Cycle they had last summer----------one is already bad the other is ok, but they don't perform no where as good. Also keep in mind if you are using 12 volt fans to not let them run untill the batteries are almost dead-----------that will destroy the batteries if its done over and over. It would be the best to never let the battery voltage drop below 10 volts under load. If you need a simple low voltage disconnect idea, holler back at me. Randy

Jason_WI

I will have a low voltage cutoff circuit. Basically a voltage comparitor with some hystersis to prevent oscillations. Output of the comparitor will go to a 2N3904 which will control a relay. Voltage cutoff can be programmable with a multiturn pot. Simple stuff. If I find the right charge controller it may already have that feature built in. Also everything will be going through a fuse panel just in case something bad happens like a rotor lock on a fan motor.

In addition to the main voltage cutoff I will have a microcontroller monitoring the battery voltage while the fans are on. If the voltage reaches a critical level I can switch off a fan or two to save power and let the solar panels catch up on a cloudy day. My plans are to use 4 temp/humidity sensors to monitor and control the fans and proportional vents. Probably overkill but that's my style.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Randy

Jason
Sounds as though you have some electronic experience talking about building your own Comparator Circuits. Let us know how everything works out---------Take some pic's. I just got to get some Good info on how to Operate one once its built. You know---when and how much to run the fans, how much air exchange etc. I hadn't searched hard for this info yet. Got any good info---web sites?? Randy

Dan_Shade

i use the thermostat that came with the attic fan I use.  I don't control the vent openings.  I'd really like to know a better way to do it, but this works, I think.... :)
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Jason_WI

Basically the fans are on when the internal temp is 20 deg above the morning low. I will track this with a microcontroller. An easiier way is to have the fans on 2 hours after sunrise and off two hours after sunset. I will be using the more scientific method along with vent control. I still need to get info on venting . My solar panels arrive on Friday.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

I am planning on using t&g aspen in the inside and outside for the walls. I am going to coat with aliminized roof coating on the inside. Do I use latex or oil flat black over the roof coating? My gut tells me to use oil base.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

The solar panels are in. The fans and louver vents I bought from surplus center are in. The fan puts out a fair amount of air at 2.5 amps current draw.  I have purchased the pink insulation for the kiln and the other misc materials. I will post pics of the progress as I build the kiln. Hopefully I can get pictures of the wagon/running gear I am going to use along with the solar panels that are 6' long by 3' wide. I have the solar charge controller on order. I need two, 6 volt deep cycle batts yet.

Lots of work needs to be done for the controller yet....


Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

Here is the picture of the wagon running gear. It is an old chopper box 16' by 8' with a 2" doug fir deck. I am going to remove  the top and sides which will be used for sawdust storage from the output from the mill.








The solar kiln itself will be 14' long by 8" wide. Long enough for 12' material to dry. Two large doors will be on the tall back side to load the kiln with a loader. It would be easier to build without the doors but the thought of carrying every stick of wood in and out to dry it doesn't sound too appealing.

The 2 feet of extra space will be for the control room. The solar panels will be mounted above the control room.

I have all the parts in for my custom controller. This needs lots of work yet. 1 external temp/humidity sensor and 3 internal. The external will allow me to determine when I should turn on the fans inside the chamber. I have the servos for the shudder vents and have to fabricate a bracket for the servos. The servos will allow me to control proportionally  from 0 to 100% of the vent opening.


I was hoping to have it done this spring but spring is almost over ::) ::)


Jason



Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

Here is a partial schematic of the controller:

http://my.vbe.com/~jbirnsch/Kiln/Solar_kiln_controller.bmp

I have to add the temp/humidity sensors yet and the servo controller for the proportional shutter vents.

I will post source code when I have it.
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

caryr

Hi Jason,

Here are a couple of comments.

Whenever I see .1u and 10u bypass caps spread around a little alarm goes off in my head. Those value are fairly standard for general circuits, but many modern high performance circuits will find them inadequate. Make sure you have good power and ground planes and that you read the manufactures bypassing recommendations. My biggest concern is the bluetooth module. I can provide other help if you need it.

It would also be best if you posted your schematic in a different format (gif, png). Bmp files are not compressed. Though make sure you use a lossless setting.

My planes for kiln automation is to peruse the Omega, Automation Direct, etc. catalogs and build it up with standard modules. Hook them together, write a bit of code and I can check on the kiln with my laptop sitting by the pool  ;D.

Take care,

Cary

Jason_WI

Cary,

The bluetooth module that I am using is from A7 Engineering. It is fairly straight forward to use and I have already had it communicating with my PC which is using a USB bluetooth adapter set up as a serial port. I am using it for remote data logging as my PC will be in a different building close to where the kiln is.

Omega modules are a bit pricy and take all the fun out of designing your own controller ;D

The Microchip PIC16F877 doesn't consume much power. I will be building my circuit on a gold plated pad per hole perf board. No gnd or power planes. I have built many circuits like this without problems. The sprinkling of bypass capacitors around the schematic helps. The 6V servo power supply for the shutters will be on a different regulator.

For the regulator I am using a 3A, 5V Power Trends DC-DC converter module. I have experience with switching power supplies and know all the tricks to snub the noise. PI filter ;D

Jason

Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

caryr

Sounds good Jason. I didn't know how much of the RF chain was integrated on the module. You are correct that prebuilt modules do take some of the fun out of it, but I have had over twenty years of fun, so sometimes I just want to get it done and get back to the forest.

Perf board is great stuff. I have a couple of circuits that are over 15 years old and still working perfect.

Cary

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