Heat Mat Thermostat Question

thomasshawn(Z8 TX tyler)February 21, 2009

I did some experimenting and created a heat mat from rope lights I found at HD.

Initially I used just one 18' rope and it seemed to do OK but there were some cold spots as some of the heat escaped out the bottom of the shelf I had them sitting on.

So I cut a scrap of plywood to fit the shelf and then mounted the rope lights to the wood.

It works probably too well. surface temp on the cells is 80-85 but with a kitchen probe into the soil some are in the 90s. So Currently I have it set to 2 hrs on and 2 hours off via a timer. I was considering just putting a heat mat thermostat on the setup but I was wondering how that would work. does the device turn the heater OFF if the temp gets too high and back on if it gets too low? Or does it adjust the output like a rheostat (i.e. adjusting how warm the mat actually is).

I assume the on/off function would work just fine with the lights but not sure about the rheostat. I plan on sticking the thermostat prob into one of the warmer cells and using that as the basis for the thermostat and then setting it a few degrees cooler

any ideas?

here is my setup

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thomasshawn(Z8 TX tyler)

I forget, this setup cost $18 and allows me to keep three 72-cell trays toasty.

    Bookmark   February 21, 2009 at 9:31AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

The thermostats are expensive but would work with some fine adjusting - lights off and the heat slowly drops.

You can accomplish much the same thing by making spacers to raise the trays off the lights. Small wood chips for example or anything similar (I use wood "L" shaped brackets) that create a 1/2-1" airspace between the lights and the bottom of the trays. Test your soil temps to determine how much of a airspace you need.


    Bookmark   February 21, 2009 at 10:42AM
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thomasshawn, I know of no rheostat type thermostat. They probable exist but would be special electronic type. Most thermostats are the on/off type. Not sure what the new electric blanket controls are though. How about a water bed heater one? Hope this helps,

    Bookmark   February 21, 2009 at 11:32AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

If you want a rheostat thermostat then most greenhouse suppliers sell them - $45 and up. Check Charley's Greenhouse Supply.


    Bookmark   February 21, 2009 at 3:01PM
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thomasshawn(Z8 TX tyler)

weird for some reason I didn't get notification this had been replied to.

I guess I needed to make myself more clear in the 1st post. I was looking for an on/off type timer not a rheostat simply because that was the method I was using at the time. on for a while then off to keep the temp under control. It was working but was not as well as I liked so in the interim here is what I did:

I took the rheostat idea and ran with it. I went to Lowes and got a plug in lamp dimmer. Then I just dialed back the intensity of the lights to 75% (this had my trays all running in the mid-high 80s) so I backed it down to about 50% and now we're sitting in the 75-80 degree range pretty uniformly and I have seedlings galore.

so I'm at about $24 ($32 if you count my shop light) but I have 3 seed trays well heated/lit.

thanks for the input


    Bookmark   February 23, 2009 at 5:41AM
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