Using adjustable DC power to restore UPS over-discharged batteries
Fault phenomenon: A SANTAK 500 UPS power supply was damaged due to an unexpected power outage and unattended operation. Connect the AC power supply, there is no response, and the power indicator light does not light up; Disconnect the AC power, there is no response, the indicator light does not light up and there is no alarm. After disassembling and inspecting, there was an open circuit in the copper foil of the circuit board. After restoring it, the machine was tested and the fault persisted. Measure the voltage of two batteries separately, one at 0.5V and the other at 0.75V.
Cause analysis: Copper foil breakage caused the failure of the over discharge protection circuit, resulting in over discharge of the battery.
Solution: The key is to save the battery. Carefully observe the batteries, these are two original CHAMPION brand maintenance free lead-acid batteries from the United States, with performance parameters of 12V/4Ah. From the principle of lead-acid batteries, we know that overdischarging can cause the plates to sulfide, generating coarse lead sulfate crystals. These crystals have poor conductivity, large volume, block the micropores of the plates, hinder the penetration and exchange of electrolyte, and over time, prevent the reversible conversion of electrical and chemical energy, causing the battery to be unable to supply power to UPS.
Generally, overcharging and water washing methods are used to solve sulfurization issues, while maintenance free batteries can only be restored using overcharging methods.
Solution process: Find an adjustable DC power supply, adjust the output voltage to 14V, and charge the two batteries separately. When a battery starts charging, the current is only a few milliamps, and after 10 hours, it only reaches about 200 milliamps. After continuing to charge for 24 hours, the charging current has reached 1.2 amps, indicating that there is hope for recovery. Charge another battery using this method. Measure the series voltage of two batteries to be 26V. Connect the battery back to the UPS power supply and everything will return to normal.
Finally, connect the power supply, continue floating charging for 24 hours, then discharge and charge for 24 hours, and the UPS is back in normal operation.
Summary: Because about 40% of the cost of UPS power is in the battery, it can be said that if the battery is scrapped, the entire UPS power supply will also be scrapped. The method of using an adjustable DC power supply can effectively restore the battery. In addition to extending the charging time during recovery, the charging voltage can also be increased, which increases the probability of recovery (but whether it is applicable should be carefully referred to the UPS manual).
