I'm building this circuit:
I'll be use a 12v DC power supply (same as pictured), but with a 220uF electrolytic capacitor because of the 400 ohm 12v relay I'll be using (instead of 220 ohm).
But looking through the toggle switches available, there are tons. I guess I need a SPST, or a SPDT wired to act like one? Also, it should be On-On?
My main question is on the ampere rating required. Would a 3A switch do? How can I calculate the amps required?
I tried Googling, but can't find any info. More info on the circuit itself is in my other questions.
Best Answer
Your diagram shows SPDT, so that's what you need. SPST isn't going to work.
The peak current through the switch will be the same as if you connected the relay coil directly to the 12V supply without the capacitor in place. (The capacitor merely causes the current to decay down to zero from this peak value.)
Therefore, if your 12V relay has a coil resistance of 400 Ω, the peak current will be 12V/400Ω = 0.030A.
With a 220 µF capacitor, the relay will activate for roughly 50-100 ms each time the toggle switch changes state. The exact value depends on the holding-current requirements of the relay.