- Common solenoid valves require a 24VDC supply, and (say) 100mA holding current to stay on. They are relatively cheap (about AU$21 at Bunnings).
- Latching solenoid valves can use much less power because they only need a brief pulse to switch from one state to another (on or off). They tend to be more expensive, though: Cheapest non-junk I could find was AU$35.
- 9V battery discharge rates is tricky but suggests that it becomes exponentially bad for high currents.
- Specs for my latching solenoid: 6–12VDC; 3/4″ (≈19mm) male BSP threaded on both ends; not sure about pulse current or any other specs yet, though.
- Info on how latching solenoids work.
- Latching pulse width is typically 20–50mS?
- I intend to switch with 9V, or something close to it. Anything at 6V or above should do.
- Not sure what the pulse current will be, but I've seen various numbers: 300mA, 333mA, 1A, 3A. It depends on the resistance of the coil, and the respective voltage I guess. At a guess, from looking at other datasheets, a 6–12V coil might be about 20Ω, so at 6V it needs 300mA?
- If we assume 2A pulses of 50mS, but two required per occasion (on, then off) that's 2000mA × 0.1S = 200mAS, and divided by 3600 seconds gives 0.0556mAh. At a discharge rate of 2A, a 9V battery drains much faster. It might fall below 6V after discharging about 20mAh, but this still works out to 20 ÷ 0.0556 = 360 on/off cycles, or about 1 year. In fact, since the pulse is so brief, it might get better performance than this? We still need to factor in the ESP8266 though and loss resulting from its voltage regulator. ESP8266 light sleep supposedly uses only about 0.4mA, while Deep Sleep uses about 0.02mA. Since this is a very small drain on the 9V battery, it might deliver more like 100mAh, and if we factor in some losses we should be able to get about 140 days. A 6V torch battery would blow this all out of the water, incidentally :)
- Discussion about latching solenoid with Arduino, here.
- Do I already have any L293D H-Bridge Motor Driver ICs or could I pull them from other boards/shields that I have? Alternatively I can make an H-Bridge. I've ordered Darlington transistors and MOSFETs.
- Other interesting info: https://electronics.stackexchange.com/questions/456025/how-to-trigger-a-latch-solenoid-valve-from-an-arduino