New Lithium Iron Phosphate (LiFePO4) Battery for Off-Grid Ham Radio Shack
This is the screen of battery management system of my Lithium Iron Phosphate (LiFePO4) Battery. It has a rated capacity of 105 Ah and nominal voltage of 12.8V. There are four cells inside, well compressed in a metallic case to prevent expansion of the cells. Good compression is essential for long life of the LiFePO4 battery. It has an energy capacity of 1.38 kWh and maximum charging voltage is 13.9V, with discharge cut off at 12V. Maximum charging current is 50A and maximum continuous discharge 100A. In my usual ham radio operations, I am unlikely to reach the limit. I am relying on the battery management system to prevent over discharge and over charging. This battery management system is rated for 100A.
The display shows 58% residual charge and present battery voltage of 13.0V. Temperature is shown as 29°C and individual cell voltage as 3.264V. Charging current is 4.0A. I am using a 180W Monocrystalline PERC solar panel at a distance of 6m, kept on the roof. Charge controller is a 200W Pulse Width Modulation charge controller which was here earlier. The time was 9.30 am local time when this image was captured. When I got the battery, it had 99% charge and I had used it for a few days to run a 55W pedestal fan with a 200W rated car inverter.
Image captured a few minutes later showed charging current of 3.8A, battery voltage of 13.0V, state of charge of 59%, temperature of 29°C and the individual cell voltage of 3.266V.
About one hour later, at 10.40 am local time, charging current had increased to 5.8A, possibly because of better illumination of the solar panel. Battery voltage was 13.2V and charge 63%. Temperature was static at 29°C. Individual cell voltage, possibly an average value, was shown as 3.318V.
Here you can see that the charging current has come down to 1.2A. That was because I had switched on a 55W pedestal fan connected to a 200W car inverter from the battery. Voltage is steady at 13.2V and temperature is stable at 29°C. Individual cell voltage is 3.313V and battery charge 63%. I am monitoring the functions closely as recommended by the manufacturer for the initial period to make sure that everything is in the safe limit. That is mandatory when you start using a new battery, especially so for LiFePO4.
Now I have connected my FT-710 radio also to the battery and this is the situation when the radio is delivering full output power. Current is shown as -16.6A, meaning that battery is discharging. Voltage has dropped slightly to 13.1V. Individual cell voltage is 3.289V and temperature is stable at 29°C. Earlier when the fan alone was connected, the battery was still charging at 1.2A. Currently it is draining at 16.6A. Battery charge is stable at 63%.
After disconnecting the car inverter running the pedestal fan, the current drain was 12.1A with the radio delivering full output power, and battery voltage 13.1V. I expect the current drain to be even more at night when the solar panels will not be working.
Kept the radio in receive mode, with the pedestal fan running, for about another 40 minutes or so. Charging current is just 0.8A and the voltage is 13.2V. Individual cell voltage is 3.304V. Temperature and battery charge levels are unchanged. So I can make out that the current 180W solar panel will take a very long time to charge the battery to full state of charge. When I was using 65Ah sealed lead acid battery with the same solar panel, battery used to become fully charged when I was away from the radio room for a few hours in the peak sunlight periods. This LiFePO4 certainly has a much higher charge holding capacity and that is why I have bought it for the first ever trial of LiFePO4 battery!
This could be the peak charging current which I can expect with the current setup when there is no load connected. That is 6.6A. Temperature has gone up by one degree to 30°C. Shall keep on monitoring and post updates, for the benefit of new users of LiFePO4 battery like me. It will also serve as a reference value for me, to see if the parameters change in future.