This is how to prevent voltage losses: • Use as short as possible cable lengths • Use cables with sufficient cable thickness • Make tight connections (but not too tight, follow torque recommendations in the manual) • Check that all contacts are clean and not corroded • Use quality battery isolator switches • Reduce the amount of connections within a cable run • Use DC distribution point or busbars
It is good practice to measure the system voltage drop. But Remember that a voltage drop only occurs at high current events. This is when an inverter is loaded with maximum load or when a battery charger is charging at full current. This is how to measure voltage drop: • Load the DC system with maximum power. • Measure with a voltmeter in the negative cable between the connection inside the unit and the battery pole • Repeat this for the positive cable In case of the battery and the unit being too far away or in a different room or enclosure: • Load the DC system with maximum power. • Measure with a voltmeter across the DC connections inside the unit • Measure arcos the battery poles • Compare these readings 2.6DC ripple One of the negative effects of high voltage drop in a system is ripple. Ripple appears in a system were the power source is a battery (DC) and the load is AC device. This is always the case in a system with an inverter. The inverter connects to batteries, but it powers an AC load. Ripple is directly related to the voltage drop over the DC cables when a system is under load and the battery currents are high. A high current causes a high voltage drop and this means that there will be a high ripple in the system.
The mechanism that causes ripple is an alternating voltage drop. The voltage drops when the system is feeding a load. And once the load is turned off the voltage recovers. And then drop again, recovers, drops and so on and on…. The voltage drop can be made worse if lead acid batteries are used, especially when these are too small or
when they are too old or when they are damaged. This process is depicted in the drawing on the right. 1. The voltage measured at the inverter is normal. In this example 12.6V 2. When a large load is turned on the battery voltage drops to 11.5 V 3. When the load is turned off, the battery voltage usually recovers back to 12.6V
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