I am using Lithium Iron Phosphate 3.7volt cell @ 4700mA.hour rating. I want to make batteries with output voltages of 24volts and 32volts. They will be recharged from photovoltaic panels only. 7 LiFePo4 cells = 25.4volts and 9 LiFePo4 cells = 33.3volts. Four 12volt photovoltaics are connected in series. The maximum power point voltage is approximately 50 volts. What family of integrated circuits( or design) will individually charge and manage the cells in the batteries while they supply intermittant loads of 7watts and 18watts respectively?
The 7 cell battery will need a DC to DC converter to give a stable 24volt with peaking current of 1amp and the 9 cell battery will need a DC to DC converter with a stable 32volts and a peaking current of 1.5 amps. What DC to DC chip sets ( or design ) can I us?
Advice from anyone will be welcome.
I am not familiar with these type of batteries but in general Lithium batteries need to be charged with a constant current until they reach full charge, and then you scale back the current (CC + CV loop)
This is typically implemented in integrated battery chargers. Unfortunately we do not have a charger than operates at the voltages you specified, so the only thing I can suggest is to design a power supply (buck or SEPIC) depending on the panel voltage range (not just at MPP) and have a dual feedback loop for current and voltage.You can close the dual loop with op-amps (one for voltage and one for current) and diode or them together into the output of the error amplifier of a standard switcher.
Other IC manufacturers may have already integrated chargers or current sources.
Since you are putting batteries in series it is always a good idea to balance and monitor each individual cell to maximize the full pack charge and protect from over charge any single cell.
The AD7280A and the AD8280 are used for this function
Look at this attachment, may be it is helpful.