I'm designing automatic watering system for my garden. I've bought these bistable electromagnetic valves.
But specs are somewhat confusing: voltage range is 3.6-6 V, current consumption is 200-300 mA, coil resistance is approx 9 Ohms. I've measured the latter parameter for all valves bought and got mean resistance of 9.08 Ohms with SD = 0.13 Ohms so coils have pretty much the same resistances.
But I can't figure out numbers for volts/amps - seems like "datasheet" and description are simply contradictory. Given that coil resistance is valid I've got the following current values for boundary voltages (assuming R = 9 Ohm): 400 mA @ 3.6 V and 667 mA @ 6.0 V; while the specs are 200-300 mA.
As I remember from my previous practice with relays the device itself (relay switch) is just rated for some voltage (at which I guess it's safe to use it without insulation breakage, arcing etc) but the coil is characterized with resistance and working current. As soon as bistable valve is just a coil it's performance should depend only on current value and not the voltage directly.
I've conducted small test: feeding SN754410 with 10.9 V and powering my coil in series with 2 parallel 47 Ohm 1 W resistors I've got that for 9.8 V drop on the whole circuit (coil + 2 par. resistors; -1.1 V due to drop on SN's outputs) I'm getting 265 mA and valve works well (I've tried to change pulse polarity too). At the same moment voltage drop across the coil is just 2.4 V. Seems like it is the current which specified right in valve datasheet and not the voltage!
And the question is for what reason the seller has specified 3.6-6 V range? Will I get any troubles/glitches with valves using them undervolted? Or it will be ok while current is enough to stay in specified 200-300 mA range?