I’m building a simple garage door circuit that have two solenoid locks. Each solenoid lock is rated at 12V/3Amps and is only supposed to be activated during 3 seconds each time the “open door” button is pressed.
I'd like to use a power supply that can feed 12V/4.5Amps, so it will not be able to provide the required current for both solenoids.
I was wondering if I could add a (big) capacitor to the Power supply output that could supply the extra energy during these 3 seconds, so I wouldn’t need to buy a new power supply. Basically this capacitor would have to provide (rough figures) 12V*1.5A=18W in 3 seconds. I could easily implement a protection delay in the button so that the solenoids are not activated before the capacitor re-charges.
Would this be possible? How could I calculate the value of the capacitor?
Thanks for all the comments. This was question was a mix of real need and a theoretical exercise. I could understand its theoretically/technically possible, but not really feasible/economical due to the high value of the capacitor, afecting its price.
From a CAPEX (investment) point of view, I could understand that investing in a 12V/10A power supply could be the cheaper option. However, from a OPEX (operating expenditure) perspective would that still be the case?
My point here is that having such a powerfull power supply turned on, standing-by, 24/7 just to activate a pair of solenoids a couple of times per week would have a small but continuous electricity cost that could change the business case on the long-run. Even though the 10A aren't being drawn, the residual consumption would be bigger than a smaller PSU, right?
What I'm evaluating now is to use the original circuit to activate a relay instead of the solenoids, and that relay will turn on a bigger power supply that is directly connected to the solenoids. This way, the PSU is turned off most of the time. This seems a good approach, but I'm concerned because the PSU will "boot" everytime with a huge load - not sure if it wouldn't hurt it.