I've got an Orbit water valve. It appears to be a 24v device and needs to be driven bidirectionally. The goal is to drive it with 5V, or possibly with 3.7V, so I'll use a boost circuit. Here is the very rough circuit:
Now if I drive the circuit with a 24V power supply, instead of the MT3608, and omit the cap, and fire the solenoid for 20ms, everything works great. You can open and close the valve fine, and it gives a nice solid thunk when it does it. But, if I sub in the MT3608 (which generates 24V fine) and the cap for backup juice, it just doesn't get enough juice to fire the solenoid, even if I stretch out the pulse quite a bit. You an hear the valve twitch a little, but not enough juice to kick it over. Commercial Orbit timers do this off battery, and seem to only have a 2200 uF cap, so it must be possible. Any ideas on where I am going wrong? A 10000 uF cap would seem to have enough juice.
My Fluke says the peak current seems to be around 2.5A or so, but that peak is very very short lived.
Any ideas on where I am going wrong here, or possibly where I might go right? Note the solenoid needs to be driven in both directions.