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Author Topic: DC solar powered fans for Solar kiln  (Read 720 times)

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Offline Paddock Jack

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DC solar powered fans for Solar kiln
« on: March 09, 2017, 01:47:32 pm »
I am looking into building a solar kiln within the next couple of months.  It doesn't seem too difficult to build, but the one thing i am not certain of is the fan to be used.  The property, isn't my main residence, and doesn't have any power (I use a generator when I am there). I was thinking of using a DC Fan connected to a solar panel, so when the sun is shining, it is spinning and when it is night time or cloudy it is not moving.  I am looking to build the kiln so it can fit 16 ft. lengths so the kiln itself would be 18 ft. long so there is a little space on each side.   So my main questions are:
1. Can anyone recommend a brand or specific fan that would work for my scenario that is reasonably priced (like under $100)
2. Do you guys think i might need 2 fans for a kiln that long?
3. Approximately how big should they be?
4. Any helpful insights are greatly appreciated
Thanks

Offline Brian_Rhoad

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Re: DC solar powered fans for Solar kiln
« Reply #1 on: March 09, 2017, 02:57:19 pm »
Here is an article about a solar kiln with solar powered fans.

https://www.homepower.com/view/?file=HP63_pg50_Scanlin

Offline ChugiakTinkerer

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Re: DC solar powered fans for Solar kiln
« Reply #2 on: March 10, 2017, 05:37:50 pm »
Welcome to the forum!

I'd be inclined to start at figuring out how much airflow you need.  Then dial in on a fan type such as the 120mm fans used in computer cases.  They typically run on 12V and have flow rates of 90 cfm and a power draw of ~4 watts.  So let's suppose you need 450 cfm of air flow.  That would take 5 fans and require 20 w of 12v power.

For the solar side I wouldn't try to run the fans directly off of solar panels.  I'd want to add in a 12V battery and solar controller.  Add in a timer or light sensor relay and you can have the fans running during the day even if it's too cloudy to power the solar panel.

Assuming a 12 volt system, the 5 fans would require 1.67 amps and would run for ~12 hours per day.  That amounts to 20 amp-hours.  A deep cycle battery with 100+ amp-hours would probably be adequate.  I'd shoot for around 50 watts of solar panel, and feed that through a simple charge controller.  Assuming I haven't messed up somewhere in my calculations that would recharge the battery in about 4 hours of quality sunlight.

Costs for such a system would be roughly: $50 for the 5 fans, $100 for a 50w monocrystalline solar panel, $35 for a Sunforce 10 amp controller, and $100 for a deep cycle lead-acid battery.
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Offline loganworks2

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Re: DC solar powered fans for Solar kiln
« Reply #3 on: April 20, 2017, 10:19:46 pm »
Hi I'm new here and learning a great deal from reading the many posts on the forest forum. For your fans on the kiln why not use a solar powered attic fan. They are readily available and totally self contained.

Offline GeneWengert-WoodDoc

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Re: DC solar powered fans for Solar kiln
« Reply #4 on: April 20, 2017, 10:45:21 pm »
At what MC will the lumber start in the kiln?  That is, will it be air dried?

For a kiln your length, 3 fans are needed.

The cubic feet per minute is calculated as

Sticker thickness (inches) / 12 x lumber length (16 in your case) x desired air flow (100 feet per minute perhaps) x number of layers of lumber = cfm.  Then add 50% more to account for leaks.  With 3 fans, divide the total by 3 to get the cfm per fan.  Probably will be around 800 to 1000 cfm.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline woodman58

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Offline GeneWengert-WoodDoc

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Re: DC solar powered fans for Solar kiln
« Reply #6 on: April 23, 2017, 07:48:26 am »
There is something funny about these fans.  Look at the huge space between the end of the blade and the housing.  We want there to be very little space for the highest efficiency.  With all the space shown, the efficiency will be poor as the air will go backwards in the space when blowing against some resistance, like a pile of lumber.  Maybe they are ok for an attic that has no resistance on the outside.  I see that other fans from this company do not have the gap.

It is hard to imagine the 3.5" long blades could get 1250 cfm.  Maybe they are using a different method to measure cfm than other fan people use.

Note that with all solar panels, the rating is when the sun is perpendicular.  Most of the time the sun is at a lower angle, so output is reduced.

I note that 120 volt attic gable fans draw around 400 watts to get about 1000 cfm.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more