Page 95 - Solar Power in Building Design The Engineer's Complete Design Resource

STORAGE BATTERY TECHNOLOGIES 65

of the cabinet to avoid anyone having to reach over the cells. Always use the
manufacturer-supplied connection diagram to ensure the open positive and negative
terminals when charging the cells. In the event of installation schedule delays, if pos-
sible, delay delivery.

BATTERY SYSTEM CABLES
Appendix A provides code-rated dc cable tables for a variety of battery voltages and feed
capacities. The tables provide American Wire Gauge (AWG) conductor gauges and volt-
age drops calculated for a maximum of a 2 percent drop. Whenever larger drops are per-
mitted, the engineer must refer to NEC tables and perform specific voltage drop
calculations.

CHARGE CONTROLLERS

A charge controller is essentially a current-regulating device that is placed between the
solar panel array output and the batteries. These devices are designed to keep batter-
ies charged at peak power without overcharging. Most charge controllers incorporate
special electronics that automatically equalize the charging process.

DC FUSES

All fuses used as overcurrent devices, which provide a point of connection between PV
arrays and collector boxes, must be dc rated. Fuse ratings for dc branch circuits,
depending on wire ampacities, are generally rated from 15 to 100 A. The dc-rated fuses
familiar to solar power contractors are manufactured by a number of companies such
as Bussman, Littlefuse, and Gould and can be purchased from electrical suppliers.
Various manufacturers identify the fuse voltage by special capital letter designa-
tions. The following are a sample of time-delay type fuse designations used by vari-
ous manufacturers.

Bussman
Voltage rating up to 125 V dc and current ampacity range of 1 to 600 A– Special
fuse designation for this class of fuse is FRN-R.
Voltage rating up to 300 V dc and current ampacity range of 1 to 600 A– Special
fuse designation for this class of fuse is FRS-R.

Littlefuse
Voltage rating up to 600 V dc and current ampacity range of 1 to 600 A– IDSR.

Photovoltaic output as a rule must be protected with extremely fast-acting fuses. The
same fuses can also be utilized within solar power control equipment and collector boxes.
Some of the fast-acting fuses used are manufactured by the same companies listed before: