Author Topic: Evolution of the Hillybilly hot tub continues! Now with less milk crates!  (Read 4138 times)

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madlabs

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The evolution of the Hillbilly Hot Tub continues! Now with 50% less milk crates!

In order to keep the hot tub running this winter there were a number of things to be done. As it was the tub was an ad hoc arrangement, simply thrown together this summer. If it was to survive the winter and keep providing the delightful, relaxing soaks that I have come to expect, much work needed to be done. I was going to need more thermal power, a better lid and freeze protection. Where I live in Northern CA, I get about 30 nights of frost a year. The original PV panels rack was just a few sticks and not going to survive winter storms. Plus I needed a place to keep the wood burner out of the weather and a place to store firewood.

So, for starters I built a combination PV panels rack/wood burner / firewood shed thingy. Also added a third thermal panel.

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The next step was to provide freeze protection. None of the available freeze protect valves will work right, since there is no pressure in the water system when turned off. So I went for active freeze protection. I dug out the controller from my last hot tub at my old place and was pleased to find that it still works. It has a PIC 16F88 for a brain, a 12 bit ADC and a 74HC595 coupled with a ULN2003 to expand outputs. So I have lotsa ADC channels and plenty of outputs to drive stuff.

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I made some sensors from LM34's in a TO-92 package. These fit nicely into 1/4 stainless tubes with one end welded closed. I inject some thermal grease into the bottom for good contact. The wire is just outdoor phone wire and I used a waterproof heat shrink to seal it up.

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One of them lives at the bottom of the tub near the pump. The other is inserted into the system with a compression fitting.

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So, the system waits until the thermal panel temp. is at least 5 degrees warmer than the tub and then continues to pump until the output temp. is less than 2 degrees warmer than the tub. For freeze protection, the pump is also run if the thermal panels temp. drops below 40 degrees. I chose 40 because thermal panels can have a lower temp. than ambient, due to their ability to radiate heat.

We have had some rain and some frosty night and so far the system is working great! It may still be an above ground dough-boy pool filled with hot water, but I'll tell ya on a clear night soaking under the stars the girls don't seem to mind!

Jonathan

Bruce S

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Re: Evolution of the Hillybilly hot tub continues! Now with less milk crates!
« Reply #1 on: November 21, 2013, 11:12:00 AM »
I kinda miss the milk crates ;-).
Nice use of the LM34's! I use them to keep a cheaper eye on my indoor grow center.

NICE!!
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madlabs

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Re: Evolution of the Hillybilly hot tub continues! Now with less milk crates!
« Reply #2 on: November 22, 2013, 10:26:45 AM »
Don't worry, the drink table is still made of milk crates. ;-0

LM34's are great little sensors. Used a lot of them and never a failure. Super easy to read to at 10mV a degree.

Was given a Morningstar 10 amp charge controller by a buddy yesterday. I was going to use a Ghurd controller but can't pass that up. Works out well because now I can use the Ghurd controller to charge the battery on the electric fence around my apiary. The bears would love to get in there!

Jonathan