2
GENERAL
5
The DC input circuit of an inverter is required to handle very large DC currents and hence, the size of the
cables and connectors from the battery to the inverter should be properly sized to ensure minimum voltage
drop, minimum heating and minimum power loss between the battery and the inverter. Thinner cables and
loose connections will result in larger voltage drop, increased loss of power and consequent reduction in
effi ciency, poor inverter performance and will produce abnormal heating that may lead to risk of insulation
melt down and fi re.
For safety against overheating and consequent deterioration of the insulation and possibility of fi re, Table
310.17 of the National Electrical Code (NEC) specifi es the maximum current carrying capacity (Ampacity)
of various types of cables for installation in free air. Apart from the consideration of safety as explained
above, reducing the voltage drop as a result of longer distance of the cable between the battery and the
inverter is also important for improving the effi ciency of the DC input side of the inverter system. Longer
distance between the battery and the cable will require thicker cable. Normally, the thickness of the cable
should be such that the voltage drop from the battery terminal to the inverter is as low as possible,
preferably less than 5%.
Inverters are designed to operate normally within a specifi ed lower and upper input voltage range. The
lower operating voltage limit of inverters is normally 10 V, 20 V and 40 V for 12 V, 24 V and 48 V battery
systems respectively. When this limiting voltage is seen at the input terminal of the inverter, it will shut
down due to low input voltage protection. Thus, if there is excessive voltage drop in the input connection
between the battery and the inverter due to thinner cable / longer distance / larger current, the inverter
will shut down even if the battery is fully charged.
As the distance between the battery and the inverter may vary depending upon the user requirement,
10 ft length of cable is provided in the Inverter Installation Kits for convenience. The specifi cations of the Kits
include the
approximate voltage drops for distances of 3, 6 and 10 ft. between the battery and the inverter.
Please note that for the purposes of the calculation of the voltage drop based on the resistance per unit
length, the length of the cable has been taken as twice the distance between the battery and the inverter
to include the overall length of the Positive and Negative cables e.g. if the distance between the battery
and the inverter is taken as 3 ft, the length of the cable has been taken as 6 ft for calculation purposes.
Please ensure that the distance between the battery and the inverter is kept as short as possible to limit the
voltage drop to less than 5%.
Cut off the extra length of cable if the distance between the battery and the
inverter is less than 10 ft.
