Calculating Electrical Power Consumption on your Jeep Wrangler

Quite often we get questions on how many lights can I run on my vehicle or how much power do I need to operate this winch.  We will try to give you a quick lesson on basic electricity 101. 

There are two basic laws of electricity that apply.  The first is Ohm’s Law.  Ohm’s states that Voltage = Current x Resistance.  This is pictured as V = I x R where V = Voltage, I = Current and R = Resistance.  It is important to note that current is measured in amperage. 

When factored out you come up with the following equations:
 V = I x R
I = V / R
R = V / I 

The second equation is Watts Law.  Watts Law states that P = Current x Voltage.  This is pictured as P = I x V where P = Watts, I = Current and V = Voltage.  Once again it is important to note that current is measured in amperage.

 When this basic formula is factored out you come up with these formulas:
P = I x V
I = P / V
V = P / I

To apply either of these two formulas, you will need to know at least two of the variables.  Most standard vehicle electrical systems are 12 volts.  If you had a light that put out 55 watts of power you would be able to determine the current load consumed by using Watts Law where I = V / P.  In this case 55 watts divided by 12 volts equals 4.58 amps.  If there were multiple lights used, you simply add the current draw from each light to come up with a total current load for that particular system.  If you had a two light system, the total current load would be 9.17 amps.  A three light system would have a total current load of 13.75 amps.

 Here are couple of actual light kits to demonstrate how this works. 

The Rugged Ridge 5” HID Light Kit comes with two lights along with all the wiring and hardware to install in your vehicle.  To accurately determine how much current this system uses, we could apply Watts Law to determine this.  The battery voltage is 12 volts.  Each HID light operates at 35 watts for a total of 70 watts between both lights.  70 Watts divided by 12 volts equals 5.83 amps. 

The Rugged Ridge 6” Halogen Light Kit comes with two lights along with all the wiring and hardware to install in your vehicle.  To accurately determine how much current this system uses, we could apply Watts Law.  The battery voltage is 12 volts.  Each Halogen light operates at 100 watts for a total of 200 watts total between both lights.  200 Watts divided by 12 volts equals 16.67 amps. 

These two examples indicate the allowable current needed for each of these systems to properly function.  This example also demonstrates how the HID lights operate at considerably less amperage than the equivalent halogen lights.  This may be something to consider when installing several electrical components where there is a limited amount of  amperage available. 

Always make sure that you install the correct fuse to properly protect the system and your vehicle.