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Author Topic: Fresh solar kiln build... 12 charging question  (Read 759 times)

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Offline ray299

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Fresh solar kiln build... 12 charging question
« on: May 19, 2017, 07:26:33 am »
Hi All, I'm building my first solar kiln. and yes, it's portable :o) I have plywood exterior with house wrap underneath and then foam insulation on the interior. I was going to plug up any gaps with spray foam and paint the inside black... any comments on that process are welcome as this is my firs time...
But the main reason I'm posting is to ask if anyone uses a solar panel to charge a 12v car battery for a circulating fan (I'm using an automotive cooling fan). I'm wondering what wattage to buy.... I see 100 watt on sale for $100 at homedepot... Suggesitons on that?
TIA! Looking to build this and get it done within the next couple weeks.

http://www.forestryforum.com/gallery/displayimage.php?pid=226326

Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #1 on: May 19, 2017, 07:27:12 am »

Offline grouch

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Re: Fresh solar kiln build... 12 charging question
« Reply #2 on: May 19, 2017, 09:08:26 am »
100 watts sounds like a lot. How big of an array do you plan for charging that battery?

You're not trying to cool an engine pulling a loaded car or truck down the road. I may be wrong, but it seems like that will move 'way more air than needed. Hopefully someone with experience will be along shortly.

Offline btulloh

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Re: Fresh solar kiln build... 12 charging question
« Reply #3 on: May 19, 2017, 01:04:05 pm »
You need to calculate the watt/hours (or amp/hours) you'll be using for the fan.  Size the batteries to fit the amp hour draw over the time the fan will be running.  Generally you don't want to run the batteries down below 50% charge or you'll lose battery life.  Choose batteries that will supply the necessary amp hour for the period the fan is running. Then you can figure out what size panel is required.  You'll need a charge controller as well, but they're pretty cheap for small systems.

Before you get too far, you may want to figure out the cfm for that auto fan.  It may not be the best solution.  You really need to use the most efficient fan/motor combo if you're running off solar or your costs will go up pretty fast.  I wonder if one fan will give you the proper air flow through the whole stack?? 

There are some good solar sites out there with tutorials and calculators that can help.  I'll see if I can dig up some links and post them.

==

By the way - I'm looking forward to seeing how you make and hang your doors.  I'm planning a kiln about the size or yours and I like what I'm seeing so far.  I planned to have it finished by now, but it keeps getting pushed down the list. 

What is the length of the kiln?

Good luck and keep us informed.

BT
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Offline btulloh

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Re: Fresh solar kiln build... 12 charging question
« Reply #4 on: May 19, 2017, 01:13:32 pm »

Offline GeneWengert-WoodDoc

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Re: Fresh solar kiln build... 12 charging question
« Reply #5 on: May 20, 2017, 06:38:41 pm »
Did you nail or screw the exterior plywood?  The reason I ask is that the plastic is usually on the inside.  When on the outside, water can condense and get trapped in the wall. 

If you put plastic both in and out, then it will work ok, until there is a hole on the inside....In this case, install exterior weep holes at the bottom of each 16" or 24" wall section and floor sections.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline GeneWengert-WoodDoc

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Re: Fresh solar kiln build... 12 charging question
« Reply #6 on: May 20, 2017, 06:45:20 pm »
For a kiln your size, you might use two or three 20" fans that use 300 watts each.  This is for green lumber.  If well air dried, this size is a little large.

A battery can run a cooling fan in a car for perhaps 5 hours until it dies.  Two batteries, ten hours...give or take...or two fans for 5 hours.

We need to consider the volume flow, cubic feet per minute.  Previous postings give a calculation technique.  Total cfm is often around 1500 - 2000 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 Darrel

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Re: Fresh solar kiln build... 12 charging question
« Reply #7 on: May 20, 2017, 09:23:41 pm »
My plan is to not use batteries. Sun comes up and shines on solar panels fans turn. Sun goes down fans stop. Simple.
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Offline GeneWengert-WoodDoc

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Re: Fresh solar kiln build... 12 charging question
« Reply #8 on: May 21, 2017, 03:26:43 am »
In the early morning, the sun will not yet heat the air in the kiln until the sun has been shining for an hour or two.  So, it is best to delay the start until maybe 9AM.  So, consider a timer on the solar fans.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #9 on: May 22, 2017, 07:23:53 am »
Tools and info:   http://www.solardesigntools.com/system_sizing.php

Thanks for the link. The doors will just be two 3/4 plywood on hinges with a frame built behind for strength... I'll post more pics when I get further. As with everything else, it seems to be taking longer than anticipated...

Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #10 on: May 22, 2017, 07:28:23 am »
Did you nail or screw the exterior plywood?  The reason I ask is that the plastic is usually on the inside.  When on the outside, water can condense and get trapped in the wall. 

If you put plastic both in and out, then it will work ok, until there is a hole on the inside....In this case, install exterior weep holes at the bottom of each 16" or 24" wall section and floor sections.
Plywood is screwed... on the inside I was planning on sealing around the insulation panels and gaps and painting everything.... I thought the moisture would be coming out of the bottom vent holds in the doors after the fan pushed the air through the stack... anything that collects on the inside will eventually evaporate and get cycled out with the moving air. I was hoping the sealing and painting would protect the wood on the inside.

Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #11 on: May 22, 2017, 07:29:22 am »
My plan is to not use batteries. Sun comes up and shines on solar panels fans turn. Sun goes down fans stop. Simple.
I was thinking that too but then I don't think you could use a timer like GeneWengert-WoodDoc suggested

Offline Darrel

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Re: Fresh solar kiln build... 12 charging question
« Reply #12 on: May 22, 2017, 09:13:56 am »
That is probably true, but you still would only need enough battery to run the timer.
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Offline WV Sawmiller

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Re: Fresh solar kiln build... 12 charging question
« Reply #13 on: May 22, 2017, 11:59:55 am »
   What would happen if you just used the circular house vent fans? They only spin when the temperature reaches a certain point and the hotter it is the faster they spin? No power requirements at all for them.

   Just wondering.
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Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #14 on: May 23, 2017, 07:38:11 am »
   What would happen if you just used the circular house vent fans? They only spin when the temperature reaches a certain point and the hotter it is the faster they spin? No power requirements at all for them.

   Just wondering.

That is a really interestign idea... I'd like to try that! Anyone else have an opinion on this?

Offline WLC

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Re: Fresh solar kiln build... 12 charging question
« Reply #15 on: May 23, 2017, 10:26:28 pm »
   What would happen if you just used the circular house vent fans? They only spin when the temperature reaches a certain point and the hotter it is the faster they spin? No power requirements at all for them.

   Just wondering.

That is a really interestign idea... I'd like to try that! Anyone else have an opinion on this?

Wouldn't those require open intake vents in order to work?  If so, in my mind they would serve to lower temps in the kiln too much. Too much air flow??? I dunno.  Interesting idea though.
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Offline Darrel

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Re: Fresh solar kiln build... 12 charging question
« Reply #16 on: May 23, 2017, 11:51:50 pm »
WLC, I was thinking the same thing.
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Offline YellowHammer

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Re: Fresh solar kiln build... 12 charging question
« Reply #17 on: May 26, 2017, 11:52:29 pm »
Are these the mushroom fans in top of a house?  If so I don't think they would work very well.  They are designed to remove hot air, and in the solar kiln, it's necessary to circulate and sometimes recirculate the hot air though the stack.  Lots of times I have my vents almost closed to limit the amount of air lost, to keep the heat up.  So the mushroom fans would be removing the hottest air in the top of the kiln at a pretty high rate, as they are designed to do, instead of pressurizing it and pushing it through the stack.

They would be venting and pulling ambient air through the stack so would be working more like a solar powered air drying shed than a kiln.  That being said, any time air can be moved over a stack of wet wood, it will accelerate the drying process, for a while at least, until the moisture levels in the wood drop lower, then the the effect of air movement decreases. 
 
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Offline ray299

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Re: Fresh solar kiln build... 12 charging question
« Reply #18 on: May 30, 2017, 07:28:30 am »
Are these the mushroom fans in top of a house?  If so I don't think they would work very well.  They are designed to remove hot air, and in the solar kiln, it's necessary to circulate and sometimes recirculate the hot air though the stack.  Lots of times I have my vents almost closed to limit the amount of air lost, to keep the heat up.  So the mushroom fans would be removing the hottest air in the top of the kiln at a pretty high rate, as they are designed to do, instead of pressurizing it and pushing it through the stack.

They would be venting and pulling ambient air through the stack so would be working more like a solar powered air drying shed than a kiln.  That being said, any time air can be moved over a stack of wet wood, it will accelerate the drying process, for a while at least, until the moisture levels in the wood drop lower, then the the effect of air movement decreases.

I was considering the little fans that are held into the window sill by the sash... but as someone stated the temps would probably be too hot for them to last inside the kiln and if I put them outside the kiln they may not judge the temp right and would be intaking all fresh air.... I think I'm going back the automotive cooling fans idea....