So... You're sitting there looking at a stack of cells. They look pretty 'happy' siting there - and you'd like to find a way to keep them happy and give them a long life once you put them to work. One way to look at battery management is a way to ensure you have a good return on investment.
I use the Robert Kiyosaki definition of 'investment' here - financially, an investment is something that puts money into your pocket on a regular basis. I put a fair amount of money down to purchase the cells - I want to guarantee that they'll repay me each time I ask them to work, and I want a guarantee that they'll have a very long life.
The Datasheet is your Friend
The first place to start, since you can't interview the cells on the table, is to spend some 'quality time' with the datasheet for your cells. Some of you are using cells from A124-Systems, some from PSI, some from Thunder Sky, and others. Each company gives high and low temperature limits, voltage limits for charge and discharge, and current limits. Some companaies will also list a range of voltages - absolute maximum before damage is certain, along with more conservative limits that give longer life. You may have to put on your detective hat for some of this - because quality of information will vary just as cell quality varies from manufacturer to manufacturer.
The Thunder Sky Battery Manual is available for their cells. A123-Systems publishes data sheets for their cells, as do the folks at Phoenix Silicon International (PSI).
Important Numbers
Some of the things we'll need to think about when deciding how to manage our battery is what our goal for pack is. If long life is the number one choice, we'll manage the pack differenly than one that's builting a pack for a drag racer. Basically we'll have to look at all the possibilities then decide what we want to trade to get our goal. It will be fairly easy to manage the cell once we have our goal in mind.
For example - take a look at the low voltage levels. For a maximum discharge, we can take the cell down to 2.1V. But for max cycle life, we may choose to follow PSI's lead and stop when the cell reaches 2.3V. Thunder Sky lists 2.5V for their long-life choice.
In general, the more conservative we are with the cell, the longer it will last. For example - if we move from using 100% of the energy to using only 70% we can move from 1500 recharges to more than 2500. In this example, we choose to trade range each trip for battery pack life. Worst case is operating the cell at max temperature, with max discharge rate, after charging the cell to 100% and discharging to 2.1V.
Do note, though, that the 2000 or so cycle 'end of life' doesn't mean the cell is dead - it just means that the cell is down to 80% of it's new power capacity. The cell that starts at 10Ah will be down to about 8Ah after 2000 well-managed cycles (or 1500 more difficult cycles). The cell will continue to work beyond that point.
A log of charge and discharge experiments with rechargeable 40138 LiFePO4 cells. These cells are easily connected into complete batteries and are being used in hybrid cars, electric bicycles (ebikes), scooters, car starter batteries, and ham radio field batteries.
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