I agree that 3.7 or 3.8 volts per cell is the proper max charging voltage for lifePO4 cells. This is is the recommended maximum charge voltage per cell that Valence and a few of the other more "senior" manufacturers recommend. The 4.25 volts per cell was the standard charge voltage for LiCo2 cells, not LiFePO4. Thundersky should know better.
Amy update on your e-max LifePO4 modification?
the batteries are in and i have since put 700km on them. Theyre holding up fine, my range has increased to a reliable 60km.
The operating voltage was lower than expected, 45v, rather than 48v. This meant my top speed fell to 55kmh, instead of the original 60kmh. To rectify this i wired two of the original batteries in series, which raised my top speed to 65kmh.
To others using LiFePO4, its important to use 16 cells for 48v or 20 cells for 60v.
So far these cells have been quite forgiving, when i first got them i ran them almost dead (2.5v<) due to my dodgy wiring with the original emax charger. turns out it is very important to wire the charger to that black box.
just today, i ran them quite flat, as my timer stopped working and so wasnt charging for 2 days of use. I travelled 65km before i discovered the problem, and even then it was only because i was experiencing greater voltage sag than normal. I initially attributed it to the colder weather, but ruled that one out as the voltage sag became worse with use, rather than better as would be expected with a rising internal temperature.
all in all im rather quite happy with these cells. cant wait for my new ones, so that i can liberate my emax of lead completely.
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
1. Were you using just 14 or 15 cells?
2. Are you using any kind of BMS with your pack?
3. How are you charging them?
I was using 15 cells.
Im using the BMS i bought off rod dilkes here:www.evpower.com.au
the bms is simple, it disconnects the charger or the load when any of the cell voltages go out of bound.
Also, when a cells voltage exceeds 3.8v, it loads that one cell to 0.5A, allowing other, less charged cells to catch up. Thereby maintaining cell balance on charge.
The cells stay mostly balanced by themselves, they just need a helping hand from time to time, so 0.5A is sufficient, even if the charge current is 8A.
The BMS disconnects the charger when a cell voltage exceeds 4.2v, and disconnects the load (if you wire the main contactors through the master BMS module) when a cell voltage dips below 2.5v for 10sec or more (so it doesnt cut out when you just happen to be accelerating hard).
In both cases, the bms has to be manually reset, it wont automatically reset for you.
at the moment im charging with either the original emax string charger, or a 48v 8A charger i bought off ebay, depending on whether im at work or at home.
The charger i bought off ebay was designed for a standard lead pack and terminates charge at 54.2v or in my case 3.61vpc. The emax charger terminates at 59v or 3.93. since the BMS holds the pack voltage at 57v, the emax charger nevers leaves "top off charge", so i have added a timer to the mains side so as not to waste eletricity. Either charger can be left on the pack indefinately without causing damage.
hope this was helpful,
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