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IS THIS SENSIBLE? OS 3.3 Latch with 6x Hunter latching valves, powered by a 25W solar panel and charger with 6x 18650 batteries that produces nominal 12V DC output.
Hi, appreciate some advice if I am doing the right thing. My goal is to have a solar-battery operated sprinkler controller that integrates with Home Assistant over WiFi.
Q1. My assumption is the right way to do this is to use latching valves to minimise power usage. Is that correct? Or would the USB DC controller also be fine to run off battery?
Q2. I understand only the “OS 3.3 Latch” module will work with latching valves. Is that still correct? The USB DC controller can’t also handle latching valved?
Q3. For power I was going to use a 25W Solar Panel with MPPT and charge controller for 6x 18650 batteries which produces 12V DC output. 25W might be overkill, but the sun exposure will not be great, so I expect low yield. If controller uses 1W to 1.5W, then 57Wh of battery should be good for 40-60 hours between solar charging. Is that suitable for the “OS 3.3 Latch”? I read that 12V DC would not be a problem for the 7.5V DC “OS 3.3 Latch”, is that correct?
Q4. Does the “OS 3.3 Latch” measure the input power voltage so I can monitor the battery charge?
Q5. The simple integrated solar charger and panel I was looking at is in image attached. Is there a better quality product I could use instead?
Q6. Will there be a “v3.4 Latch” at some point I can upgrade to, is is the “OS 3.3 Latch” a dead-end product?
Q7. Is what I am doing sensible? Should I be doing something else?
Attachments:
Q1: Both Latch and DC controllers use the same WiFi chip (ESP8266) so the controllers consume about the same amount of power. The main difference is that Latching valves themselves are more power efficient as they only draw power when opening or closing valves, but don’t draw power if the valve remains stable. Whether DC controller will run fine on battery depends on how much power is drawn when valves are on, which in turn depends on how many valves you plan to run a day, and for how long.
Q2: Correct: only Latch controller can operate latching valves, because they require the so-called ‘H-bridge’ to operate. DC controllers do NOT have h-bridges so cannot operate latching valves.
Q3: Latch controller can work with 12VDC, that’s not a problem. In fact, the voltage sent to the valves come completely from the internal boost converter, so the input power supply is never connected directly to the valve, therefore the controller can work with a wide range of input voltages.
As I said, how much power is sufficient depends on how long and how many valves do you operate a day. Here is a ballpark calculation:
– The controller itself draws somewhere around 80mA to 150mA constantly (this also depends on WiFi signal strength). Latch controller uses completely linear regulators so the total power is whatever input voltage multiplied by the current consumption. If we assume 100mA current, 12VDC input, that means 12V * 100mA = 1.2 Watt just to power the controller itself. Lower input voltage reduces the power consumption, for example, 7.5VDC means 7.5V * 100mA = 0.75 Watt.
DC controllers are slightly more efficient here in comparison as they use switching regulator internally so are a bit more efficient, but as you will see below, since they need to provide constant power to valves to keep them on, they also draw a lot of power when any zone is open.
– Because latching valves only draw power at the moment of opening and closing, the power consumption of the valve itself is negligible compared to the controller’s power draw.
In comparison, for DC controller, this depends highly on your usage. Let’s say you have 1 valve, which you turn on for 2 hours a day, and the valve draws about 200mA when it’s on, that means a total of 200mA * 2h = 400mA*h. Again, if input voltage is 12VDC, then this is 12V * 400mAh = 4.8Wh. If you run valves for longer, or you have multiple valves, you can multiply them to get the total energy consumption.
Q4: No, neither Latch nor DC controller monitors the input battery charge. This is because ESP8266 has only one analog sensing pin, which is used for current sensing on DC controller and for boost voltage control on ESP8266. There are no other spare analog pins for sensing other voltages.
Q5: I am not familiar with solar panel and batteries, so I am not qualified to answer this question. But honestly generative AIs should answer this question very well.
Q6: There is no current plan for Latch v3.4 — the demand for Latch controller is significantly smaller than AC and DC controllers. There is no incentive currently to redesign the Latch controller, especially since we still have v3.3 in stock. Even if there is a v3.4 in the future, it will be largely the same design except the enclosure change.
Thanks for the answers Ray. I’ve ordered the parts and I am going to give this a go and will report back here in a month to two for other people who might need a mains-free controller.
Various other brand controllers generally only offer mains with smart (usually cloud), or dumb with battery, or just one zone smart with battery. So a smart multizone controller that runs off battery (or battery and solar) is a gap in the market IMO. A well documented build and/or FAQ could help. Certainly latching controllers are very common.
“only Latch controller can operate latching valves, because they require the so-called ‘H-bridge’ to operate. DC controllers do NOT have h-bridges so cannot operate latching valves.”
If a future DC design v3.6 included H-bridges, it could be the one model to do everything! Plus it could appear in science fiction shows, since you can reverse the polarity 🙂
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