Use the calculator below to find the minimum wire gauge to supply the load with the correct voltage. The default voltage of 13.8 is a common base point for a running vehicle while the alternator is producing a charge. Select a lower voltage drop percentage for critical loads such as electronic control modules (ECM's), motors, user interfaces, alert systems, and any other devices that require supply voltages with minimal drop to work with the best efficiency. When running a positive and a ground wire enter the total length of the run from the power supply. When grounding to the vehicle chassis, enter a length for just the positive wire plus 20%. The 20 percent is a safety margin. If you consider the large metal structure of a vehicle chassis and its cubic area compared to that of even a 2/0 gauge cable, we can see that even though the resistivity of steel is higher than copper, in nearly any case it provides a very low resistance ground path.
Calculator courtesy of http://www.gtsparkplugs.com/WireSizeCalc.html
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage. This is true for many materials, over a wide range of voltages and currents, and the resistance and conductance of electronic components made from these materials remains constant. Ohm's Law is true for circuits that contain only resistive elements (no capacitors or inductors), Use this calculator to solve for an unknown value with just two known values.
Use the calculators below to find out what size resistor to use when adding an LED indicator to your vehicle. Some LED's for automotive use have the resistor installed in the base. But if you want to use an LED in it's raw form to build an indicator panel, you will need to install resistors to drop the voltage to the value required by the LED manufacturer. The Multiple LED calculator is used when you want to connect more than two LED's in series or parallel and want to use just one resistor. Pick one of the three calculators that best suits your design. This is handy for backlighting a panel with multiple LED's.
* Use these calculators as a general guideline. Always check manufacturers specifications on power supply requirements. 12 Volt Connection will not be responsible for any outcome due to the use of information provided by these calculators. Use at your own risk.