LIPO are great cells during great environment conditions as we know.
BUT I would like to remind everybody here that winter
might change a bit these great performances your LiPO have during summer
I thought it would be great to share the experience someone on E-S shared with me recently.
Leaving your ebike outdoor during temp under -10 celsius might give you unattempted performances and damage your lipo cells.
( i'm not talking about the nanotech wich are another category of LiPO... but most about the normal lipo... 15C, 20C and 25C)
That person explained me that normally he leave his ebike indoor during winter but that time he visited some friends at 30km from his home with his ebike, he left his ebike outdoor that time.
When he wanted to return home and started using his ebike he observed a big voltage sag and very poor performances. He also observed voltage drop down to 87V with a 24s pack but hi still ahd enough Ah left in the pack.
For him, it was like his pack have a big voltage sag eventhough it have enough Ah left.
In fact the Internal resistance of lipo are excellent in warm temperature, but that change alot with cold temperature!
Unlike LiFePO4, lipo are more affected by cold temp.
LiFePO4 cells have better performances and tolerance with with cold temperature ( i mean under freezing point)
You must remember to let your lipo warm enough before using them or charging them.
In fact it is NOT the capacity that decrease with lithium cells.. it is internal resistance that increase, making more heat lost during discharge.
ex: an 1Ah cell in cold temp, might just output 0.4Ah electrical output and 0.6Ah in heat meaning very poor energy efficiency transfer!
The 1Ah cell still have 1Ah inside... but cold temp make his internal resisatance too high and to dissipate too much energy thru that resisatance and not in pure output.
it's like puting a resistor in serie with a cell in normal warm temperature use... the electrical energy output after the resistance connected in serie will be lowered.
LiPO, LiCo and LiMn internal resisatance is more affected than LiLePO4
with cold temperature.
For the same C-rate the cold temp is at least the area where LiFePO4 outperform any other lithium cells. A123 are great exemple of that.
Your 180Wh/kg lipo might deliver just 50Wh/kg.. compared with LiFePO4 that will have just a bit Wh/kg lost
so be carefull during this winter... You dont want to see your cells too having the blues of winter!