DC Voltage drop calculator
This online calculator can be used to estimate the voltage drop (volts), voltage drop (%) and the final voltage after the voltage drop for DC circuits.
Formula for calculating voltage drop
This voltage drop calculator is based on the formula, voltage drop = I * R where:
- I is the DC current flowing in the circuit
- R is the direct current resistance for the wire.
This calculator uses DC resistance from NEC 2017, Table 8 and assumes conductor temperature of 75°C (167°F), uncoated single and 7 strand copper and aluminum wire.
Note: The results of this calculator should only serve as a guide. We shall therefore not
accept any liability resulting from the use of this calculator. Always consult the manufacturer specification’s or a competent professional if unsure.
How to minimize voltage drops in AC and DC applications
Voltage drops result in power wastage along the cable or wire and a reduced voltage which
may cause the appliance not to work properly.
Causes of voltage drops
1.Longer cable runs increase voltage drops
For example, at 13.8V, an appliance drawing 5A over one-way length of 10 feet of 14 AWG wire results in a voltage drop of 2.25%.
Should this distance double (20 feet), then the voltage drop would nearly double to 4.57% increasing the power wastage and may result in the appliance not working properly.
Fix: To maintain the voltage drop (2%) while maintaining the cable length, increase the wire gauge. In this case, using 10AWG would keep the voltage drop to 1.81%.
2.Wrongly sized wire gauges for large appliances increase voltage drops
Larger appliances (larger loads) require more current which results in a bigger voltage drop for the same distance.
To reduce the voltage drop, you need to increase the size of wire (use a lower gauge number).
For example, at 13.8V, an appliance drawing 5A over 10 feet return of 14 AWG wire results in a voltage drop of 2.25%.
Should a larger appliance that draws twice the current (10 A), then the voltage drop would nearly double to 4.57% increasing the power wastage and may result in the appliance not working properly.
1. If this is not possible to move the load (reduce the cable length, you may use a large diameter cable, such as 12AWG). This reduces the voltage drop to 2.9V.
2. Increase the supply voltage to 24V if the load can take it which reduces the voltage drop to 2.6%.
In summary, you can minimize voltage drops by selecting a suitable wire gauge and length for a given appliance (load) such that the voltage at the end of the circuit satisfies the appliance’s requirements.