Originally Posted by evnz
Thank for the replys so main thing i get out of this is as i have less knowlage i will be best to have them so i dont cook them specaily when they cost a 1/3 of my yearly pay
The problem with a BMS is all the added complexity. If you dont understand what it is doing I don't see how it can help you. And if you do understand it then you dont need it.
LiFePo4 is pretty simple to deal with.
1) Bottom balance the cells when you install them. This more than anything else this will prevent you from driving a pack to death. What happens is you are driving along and the battery goes dead. Pretty much every cell at the same time. The car stops. You tow the car home or to a charger and charge it up. No damage. What kills these cells is reverse charging them. A weak cell that goes to zero volts will be reverse charged by the rest of the pack if you keep driving. Bottom balance will cause all the cells to dump at the same time. The car stops because there simply isn't enough voltage to make it go.
2) Deliberately undercharge the pack. All you need to accomplish this is a charger that can turn off when a particular voltage is reached. The first time you charge the pack after the bottom balance you find the weakest cell. You can do this when the pack is nearing full by locating the cell with the highest voltage. Once you have located the weakest cell you monitor that cell until it reaches something a little over 3.5 volts and then read the total pack voltage and set the charger to stop at that total pack voltage. Done!
3) Make certain that there are no connections to the pack except at the endpoints. If there are other connections then these connections are a potential source of pack imbalance.
4) Try not to overdischarge the pack. The pack will last longer if you don't do deep discharges very often. Generally no deeper than 80% is considered a good idea for long life and 70% is better.
5) Avoid extreme discharge currents. Most of the cells can tolerate a continuous 3C discharge and a burst discharge of 8C. If you are going to exceed these levels on a regular basis then you probably need a larger pack.