MP3Car.com - View Single Post - Connecting wires to switch, dumb electrical question

AVGeek · 01-06-2003, 10:53 PM

There is a simple formula to determine current, wattage or amperage when the other two are known. the formula is P=IE (power in watts equals current in amps time voltage) For example, a switch rated at 25 amps at 12 VDC would be good for 300 watts.

I strongly recommend the use of relays for heavy duty switching needs. This is how I have my Epia system wired so that it will only boot when the radio is on. I used the 12V amplifier trigger wire, which is only rated at about 1a. I connected one end of the coil to the trigger wire from the head unit, and the other end to ground. The other two terminals are wired inline from my amplifier ditribution block to the positive input on my PC. Whenever the radio is on, current flows through the coil, creating a magnetic field which causes the heavy duty metal contacts to close, allowing power to flow the input terminal on the PC. I used a standard Bosch type SPST relay (there is also a SPDT which is identical except for an additional terminal labeled 87a) that I had left over from some old alarm installations.

01-06-2003, 10:53 PM	#15
AVGeek Maximum Bitrate Join Date: Dec 1999 Location: Buena Park, CA Posts: 468	There is a simple formula to determine current, wattage or amperage when the other two are known. the formula is P=IE (power in watts equals current in amps time voltage) For example, a switch rated at 25 amps at 12 VDC would be good for 300 watts. I strongly recommend the use of relays for heavy duty switching needs. This is how I have my Epia system wired so that it will only boot when the radio is on. I used the 12V amplifier trigger wire, which is only rated at about 1a. I connected one end of the coil to the trigger wire from the head unit, and the other end to ground. The other two terminals are wired inline from my amplifier ditribution block to the positive input on my PC. Whenever the radio is on, current flows through the coil, creating a magnetic field which causes the heavy duty metal contacts to close, allowing power to flow the input terminal on the PC. I used a standard Bosch type SPST relay (there is also a SPDT which is identical except for an additional terminal labeled 87a) that I had left over from some old alarm installations.