I recently undertook a project to add solar heating to my home spa, and as part of this I needed to measure the temperature of the spa water that was completely independent of the existing spa controller. In addition, I wanted the system to interface with C-Bus, so I could monitor it and control it from my iPhone/iPad via Translink. I chose the 5104DTSI but couldn’t find a suitable sensor that was designed for permanent in water use that was also an easy water tight fit. I could have home brewed something, but I wanted it to look as factory fitted as possible. I had a hunch that the temperature sensor supplied with my spa controller might be able to be hacked to work with the 5104DTSI. I had a left over old MK2 version of this sensor (Mk4 is the current version) so I ripped it apart to see what was inside. It took a bit of effort, as it was glued and potted, but after some time I managed to extract the sensor its self, enough to see what it was. As I suspected it was a DS18B20 which is the type of sensor used by the 5104DTSI. So with crossed fingers I ordered a new MK4 sensor (which is listed as not compatible with the MK2 BTW). After it arrived, I cut the plug off and started measuring the various wires and comparing them to a known DS18B20. The upshot of this is I figured out the wiring and after connecting it to a 5104DTSI it works perfectly. So if anybody is looking for a purpose made spa pool temperature sensor that will work with the 5104DTSI here are the details. Davey Spa Power (Spa Quip) Mk4 Temperature Sensor Q915445 available from several online suppliers (shop around as price varies) Cut the Din plug off and you get the following wiring; White - Black + Red Data Green N/C Shield N/C Connect the white and black together (yes this is correct for using parasitic power configuration) and connect to G terminal on 5104DTSI Connect Red to D terminal on 5104DTSI Ignore the rest. Then configure the 5104DTSI via Toolkit as per normal and away you go. I hope that helps someone Cheers Rohan
Nice! It's hard to tell from the picture but it looks like the Davey one is made to fit some standard PVC pipe fitting/thread? What size is it? Is it all plastic? How is the temperature "coupled" to the sensor? Nick
It's designed to fit through a hole in the spa shell. The bit behind the face is a nut that screws up to hold it from behind. The thread might be a standard, but I don't know. It requires a hole about 35mm and the whole thing is fitted from the water side with the nut, cable, etc on the dry side. There is also a foam bit that covers the back not shown in the picture. Based on the earlier model one that I destroyed, the sensor enters from behind, and is stuck to the front face. then the whole inside is potted. It also has a little PCB and a couple of bypass caps as it is not configured to run in parasitic power mode with it's matching controller. They do nothing now that + and - are shorted together. it is actually a 2 part design with an inner that holds the sensor and an outer housing, with a couple of O rings between, but that's not really important as your not supposed to pull it apart to that level. Yes the whole thing is plastic (the earlier one had a stainless centre section) and your probably thinking it wont couple properly, but it does. I have had several different sensors hung in the water whilst testing and they all read to within a degree of each other. The other thing to remember is in this application the actual temperature is not that important. you just learn that the temperature of the water as you like it reads xx on the display and so that's what you set it to. whether it is actually that temperature or +- a couple of degrees is academic. Having said that it does appear to be quite accurate. The only down side is the price, but its an easy solution that just works, and that saves money for sure. Cheers Rohan
Yeah.. it's not so much a matter of "if" it will couple but "when" ie what the lag is. It was more just an observation.. obviously it works because Davey is selling it, but you never know what they've done in their own control system to compensate. Nick
True, but we're talking about measuring the temp change of at least a thousand litres of water, so nothing happens in a hurry. Given I now have 2 identical sensors mounted side by side, I compared the reading I got with the 5104DTSI to the readout from the spa controller and they were the same down to the hundredth of a degree, so I don't think they are pulling any tricks Cheers Rohan
