As we have seen before, a cable has a certain amount of resistance.
When current flows through a resistor, the resistor heats up. These are called cable losses. Power is lost in the form of heat. The lost power can be calculated with the following formula:
Power = Resistance x Current 2 P = R x I²
Another effect of cable losses is that a voltage drop will be created over the cable. The voltage drop can be calculated with the following formula:
Voltage = Resistance x Current V = R x I
We now will add cable resistance to the system we used previously. In the circuit diagram on the right we have added two cables with a 1.6 mΩ resistance. The current that flows through each resistive element in a series electrical circuit remains the same while there will be a voltage drop over each element of which the sum equals the total voltage. This is called the Law of Kirchhoff. Knowing this we can calculate the voltage drop over one cable: • A 2400W load at 12V creates a current of 200 A • The voltage drop over one cable is: V = I x R = 200 x 0.0016 = 0.32 V
Because we have two cables, the total voltage loss in this system is 0.64 V
This also means that the inverter does not get 12V anymore, but 11.4V
The load is a constant in an inverter system, so the battery needs to deliver more current to compensate for the losses. In this example this means that the current will increase to 210 A.
Powered by FlippingBook