Twoprops’ hot tub, wonderful as it is, has no remote control features. That became an issue when we went off-grid as having the hot tub power up in the middle of the night risked depleting our stored charge when the sun wasn’t shining. After considering a lot of other options, including designing my own controller from scratch, I ended up just putting a Kauf smart outlet (pictured below) on the tub (enclosed in a weatherproof box) and a wireless Ecowitt temperature probe (pictured above).
The result was functionally useful, but it had an anomaly that bothered me. The temperature probe was somewhere around 2½° higher that what the tub itself showed. I tended to believe the temperature probe, as the hot tub circuitry seems to employ some clever hacks, but when I tested it against my kitchen thermometer it appeared that the Ecowitt probe was just… wrong. And not really consistently wrong, either. The variation from reference seemed to vary.
I tried to figure out a way to re-calibrate the Ecowitt or fix the problem in software when it occurred to me that I was doing a lot of thinking and messing around when the obvious answer was probably just to buy a new ($12) probe and see if it worked better. I did. It did. I was happy until yesterday when the new probe quit working (just totally dead). It’s been raining a lot, and I suspected water intrusion.
Continuing the theme of investing hundreds of dollars in engineering time to troubleshoot a $12 device, I disassembled it and discovered that, yes, it was really wet inside. I dried it all out, but broke the two power leads in the process. I tried two different soldering irons: one had rechargeable batteries that had died, the other asked for a firmware update (!). I decided that the “twoprops need hot poker” soldering iron would probably work even with outdated firmware. I repaired the broken leads, let the device thoroughly dry out, and it worked!
I then re-installed it in the hot tub, but put the electronics in the same weatherproof box that holds the Kauf plug. I was concerned about the box and its location (down low right next to the tub of water) possibly affecting the wireless range, but it seemed to work. Except, now this new one is also reading several degrees too high.
What could possibly explain this? It was working well.
My current theory is this: The probe claims to be “waterproof” but, having disassembled the case, it clearly is not. I think when they say waterproof they are referring only to the actual thermistor, not the main electronics unit to which it is attached. I got lucky with the first one, though I noticed that the display window had condensation on it the device continued to operate even after being rained on. I’m now thinking that the erroneous readings are the result of water damage to the electronics in both cases. So I’m probably just going to get a third unit, and put it in the weatherproof box from the outset.
By the way, except for the fact that the product description isn’t clear that “waterproof” doesn’t apply to the entire unit, the Ecowitt device is pretty cool. I haven’t found the limits of its range, but I once had the thermometer more than 100 yards from the base station (sold separately) through walls and dense jungle and it worked fine. The original unit is on its first set of two AA batteries and it has been running on them for nearly a year. So they’re inexpensive, long-range, and power frugal. Just keep the electronics dry.
—2p