For our project “2nd Life for GEL batteries” we converted two 140Ah GEL batteries from a UPS system. These batteries, which had to be replaced due to their age, should be given a second chance at the Shack. Our procedure is explained step by step here.
The start: voltage test and charging process
After collection, the batteries were subjected to a voltage test and both showed around 12.7V – a positive starting point. With GEL batteries, the voltage gives a good indication of the capacity:
- 100% charge level: Approx. 13V resting voltage
- 50% charge level: Approx. 12.1V resting voltage
- 0% charge level: Around 10.5V
Each battery was then charged individually using a 5A charger and left on the charger for an additional 5-6 hours to ensure maximum charge. This was followed by a rest period of 24 hours.
Construction of the circuit and preparation of the wiring
While the batteries were resting, we prepared the wiring. We mounted a 40A DC circuit breaker, a measuring shunt and a battery capacity display on a stable plate. The 16qmm and 25qmm cables in stock ensured low power loss.
Capacity test: How much energy is left?
After assembly, the voltage was measured. Both batteries showed around 12.9V resting voltage, which indicates full charge. To accurately determine the capacity, we used a discharge device with a fixed load of 5A and a final discharge voltage of 12V. The result: around 800Wh or 68Ah could be removed – a remarkable value for the batteries, suitable for use in the shack.
Use in the shack: flexibility and independence
The first battery was installed on a trolley at Michael OE8YML and connected in parallel to the power supply. This enables uninterrupted operation of the radio system in the event of a power failure. It should be noted that when switching from mains to battery operation, the voltage is adjusted so that the power supply is not overloaded.
Conclusion: Old batteries in new use
With little effort and a little creativity, we were able to breathe new life into older GEL batteries. As reliable power sources in the shack, they now offer additional independence and flexibility.