Materials on batteries

ECEN 4517/5517 Spring 2008

battery cutaway

Manufacturer's data on batteries

The batteries used in this lab

The batteries used in this laboratory are valve-regulated absorbent glass mat (VR-AGM) sealed lead-acid batteries, intended for deep-discharge solar power system applications. They are rated 56 amp-hours and 12 V: a fully-charged battery can be discharged at a constant 2.33 A rate, and will last for 24 hours before becoming fully discharged, for a total capacity of (2.33 A)(24 hrs) = 56 A-hrs. The batteries contain six series-connected cells; each cell voltage is 2.4 V when fully charged and 1.75 V when fully discharged (at 25 deg C).

When charging the battery, one applies the available charging current until the terminal battery voltage reaches the "charge voltage". Further charging at high current then risks overcharging and damaging the battery. The battery may then be held indefinitely at the "float voltage", to trickle charge and maintains the battery at full state of charge. Battery chemistry during charging and discharging.

Battery life, or the number of charge/discharge cycles, is a function of the depth of discharge. It is undesirable to fully discharge the battery, because this reduces the battery life. On the laboratory PV carts, a buzzer will sound when the depth of discharge reaches approximately 50%; please do not discharge the battery beyond this point.

Battery state of charge (SOC) vs. terminal voltage
100% SOC12.80 volts or greater
75% SOC12.55 volts
50% SOC12.20 volts
25% SOC11.75 volts
0% SOC10.50 volts

At the end of the lab period, you should dock your PV cart underneath your lab bench, disconnect the battery cable from the cart, and connect it to the battery charger