I am sorry, I don't have a lot of experience with electricity, but I'm going to give this a shot. What I'd like to do is utilize a switch, that is part of a large device. When the device turns on, the switch is bridged. I'd like the switch to power a light, as the device turns on. However the switch is limited to 48V 500mA, and I can't change it because it is within the components of the machine.
After looking on the forum I found that 48V 500mA is equivalent to 12V 2A, but I also read it wouldn't be smart to have higher or lower volts running through the switch than it is rated for.
I have uploaded a picture above with a way I thought to create the circuit.
120V 20A comes out of the wall to a 48V 500mA power adaptor. The power would then be consistent with the switch and a simple circuit could be made. I couldn't find a 48V 500mA adaptor online so I was wondering about having a higher voltage run through the light, then through a resistor (to lower it for the switch rating), into the switch, and back to the adaptor.
Does anyone know of a 48V 500mA power adapter out there I could buy? Would the circuit work this way, or would I need a resistor, then an amplifier on the other side of the switch?
Best Answer
Short answer: No, you can't use a resistor to reduce the voltage seen by the switch in your circuit.
It's the voltage difference across the component's terminals that matters, not the voltage at the component.
In your circuit, when the switch is closed the voltage across it is (close to) zero:
When the switch is opened, it will see the full voltage of the source across its terminals, regardless of the resistance of the rest of the circuit:
The purpose of a switch is to extinguish the arc that forms whenever a current-carrying circuit is interrupted. If the voltage and/or current exceeds the rating of the switch, the arc will not be interrupted quickly enough which will cause damage to the contacts of the switch, and eventually cause it to fail. In extreme cases (hundreds of volts and hundreds of amps) the arc will not be interrupted at all and the switch will fail catastrophically (think sparks, fire, molten metal etc).
If you want to operate your light bulb at a higher voltage or current than the switch is rated for you will need to use an interposing relay, like this: