Lithium Iron Phosphate Batteries (LiFePO4 or LFP)
by Tony Clark
(Perth Australia (Hills))
LFP Batteries protected by corrugated polycarbonate sheet
After 7 years of using second hand telecommunications batteries to power our (mainly) solar powered home, I had to bite the bullet and purchased a set of new batteries when a couple of cells failed.
After researching the options, I chose Lithium Iron Phosphate batteries, for their deep discharge ability, combined with long cycle life-time and stable battery voltage.
Where to get them??
I could have purchased them in Australia, but I would not have been able to afford as much battery capacity.
I was able to find a Chinese manufacturer who would ship a small (by their standards) battery.
I wanted to have about 20KWH capacity, which would have lasted ~3 days of overcast conditions. Due to cell availability, I settled on a cell capacity of 180AH, with 2 cells in parallel, 16 pairs in series to give a 360AH 48V (nom.). I paid the factory by international Foreign currency exchange and insured the consignment. I also chose an agent to handle the paperwork (Import duty and GST) at this end.
When it arrived, the Shipping agent contacted me by email and I paid the Government charges. There was an extra delay due to Customs deciding that they needed to xray the consignment to make sure I wasn't importing drugs or other contraband.
When I got the all clear, I drove to the shipping agent who loaded the crate onto my trailer and I took it home, unloading the crate while it was on the trailer.
A week later and the new battery was installed.
Actual battery voltage is between 52 - 54v at most times, dropping below 50V only at very low state of charge.
LFP batteries are easily damaged by over charge or under charge, so a Battery Management System (BMS) is essential. to protect the battery. (It disconnects the charge to prevent over voltage or disconnects the load to prevent under voltage).
I contacted EV Power (Australia) for a suitable BMS which was not expensive.
I used the existing Solar charger, adjusting the parameters to prevent excessive voltage being applied to the battery. I used the existing inverter, battery fuses and battery cables from the Lead Acid bank which this replaced.
This has been in reliable service now for over 6 months.
What do I do when it is overcast for a week or more? I also purchased a 48V 50A charger, for which I had a 15A outlet installed.
OK, I need to explain something else, While we are mainly solar powered, we still have mains power connected (3 phase) as we have pumps which need 3 phase power and our inverter is only single phase. So, if we run out of sun generated power, we can charge the batteries from the mains, using off peak power.