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Kaos DIY Heated Propagator

KAOS

KAOS

After running into "space" issues using a single mini greenhouse on a brewing heat pad this year I have decided to upgrade my setup for next season.
 
My options were to buy a second heat pad (for a second mini greenhouse) or buy a store seedling heatmat (to hold two mini greenhouses).
 
Ignoring options of buying something it's back to the DIY and this will be a short thread on my build.
 
The given dimension I worked with are the two mini greenhouses (Bunnings) due to being a good product at a good price.
 
I found a sturdy plastic tray (with acceptable dimensions) at the local plastic shop and had some silicon resistance wire ordered some months back (0.6 Ohm/m)
 
Keeping things simple and using only electrical tape and clear silicone progress so far...
 

 
Prop2.jpg

 
Prop3.jpg

 
 
Did some testing and it comes out at a reasonable 8.8 Ohms. It will be powered by either a 12V or 19V adapter (still to decide) and this will give a final power output of 16W or 41W.
 
It houses the two greenhouses perfectly and I am now deciding on a thermal mass as a filler between the heating wire and the bottom of the mini greehouses. Any suggestions ???
 
Thanks for stopping by and update to follow. :party: 
 
 
How bout a copper sheet? It produces pretty even heat without worry of cold or hot spots.
 
Hi Ed
 
It's not so much hotspots I'm concerned about. What I'm looking at is a medium to accept the heat from the wire and transfer it through to the base of the mini greenhouses. There is about a 25mm gap between the two.
 
What I've settled on for now is a mix of sharp sand and pumice dust.
 
Hopefully this provide the bridge between the two for heat transfer and also act as a heat mass to reduce thermal cycling (it will be thermostatically controlled)
 
Are the cables designed to be in open air or embedded in a solid mass like concrete?
 
salsalady said:
Are the cables designed to be in open air or embedded in a solid mass like concrete?
Click to expand...
 
Timing of this question is good ...
 
Mixed up a 6:1 sand:tile adhesive dry mix which should be equivalent to hand crushable sandstone (only holds its form)
 
Lined the heater box with cling film in case I change my mind and  filled with dry mix
 
Now just the wait to see if it sets off as expected ....
 


 
Prop5.jpg

 
Prop6.jpg

 
 
Looks good.
I placed a heat mat in a plastic container like yours and topped it with tile cement and tiles for thermal mass and heat distribution and waterproofing the heat mat.
 
I'm wondering if the heat cables will melt the plastic.  We install a lot of heat cables in concrete and some mylar heat mats that are designed to be in free air.  The sand mass will hold the heat, I'm just wondering if the heat cables will burn out if they are supposed to be encased in mortar/concrete or such.  Might want to check the specs of the heat cable and their intended use.  Don't want to hear about any accidents~
SL 
 
Thanks for the info SL.
 
I don't think it will be an issue, but will check for any heat stress on the plastic over the weekend.
 
I've decided on the 12V (16W) option based on initial test run as this has a 1degreeC/hr temperature increase which is fine for the intended purpose.
 
That also results in a max of 1.2W/m and the cable is rated to 20W/m
 
Will report back on any issues.
 
Did some testing overnight and hit an equilibrium temperature of 26.3C at 12V.
 
I upped the voltage to 16.5V and it's cycling nicely now.
 
Power on at 26C / Power off at 28C.
 
I'll run it like this until tomorrow night and then check for and cable or plastic container stress.
 
 
 
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