No BMS.. :)
Hi, I bought an WEL Cruiser Maxiscooter a couple of month's back.
It is Chinese Jonway maxiscooter, 72V, 40Ah, 5Kw Jonway motor, Kelly
controller, no regen (thanks for that) and a pack of big yellow chinese
It works very well so far, with 1000km on it, but I wonder if the lack
of a BMS system is going to be a problem? Are they really needed? ;-)
That sounds like pretty extremely similar to what I am riding, except for I have blue GBS cells in the basement, not the yellow Thundersky/Winston - though they may well have been manufactured by the same company.
Yes, you will badly need a BMS to keep the 24 cells in balance. With battery currents that can easily reach 140A and even up to 200A if the 8kW Kelly is let loose on the motor, those cells will at times be discharged at 4 to 5 x C. This is known to cause cell drift pretty soon, especially on such rather higher impedance cells as we have in our bikes. But finding a dependable and attractively priced BMS is still quite a challenge these days... :-(
No BMS on my 4000li, and at 12,619 miles currently, original set of batteries. Range is down by about 5% from when the batteries were brand new.
I am an engineer who believes strongly in the KISS principle of vehicle design...Keep It Simple Stupid. The hub motor is a brilliant example of simple propulsion technology with only one single moving part. My current 4000li does not have regen either. My previous electric did, and I prefer to not have it. Anything at all to simplify and reduce the chances for breakdown. My preference would be no BMS and no Regen. I plan to check my cells individually again in 2 months, but the last time I checked they were within 0.1 Volts of each other at partial discharge state.
Yes, with no BMS regular cell checking and manual balancing is necessary for keeping the battery happy. But if you have the same body as my scoot does you will not be very keen on stripping down to the battery pack every two months to check your cells. Do not run them down too low, and no trickle charging on LiFePO4 cells, else they will overcharge badly and maybe worse...
I also like to keep things simple, but a WORKING and successfully TESTED BMS is a MUST for me as my pack needs to last at least 5 years of year-round usage, without much range degradation, or else it will not have been worthwhile switching to electric from a TCO point-of-view...
Best of luck ZunZhine! They are awesome bikes. Mine pays for itself every 7 months that I drive it instead of my friggin 12.5 mpg escalade. Tearing them down to check every cell really is a difficult task. I did it at 3913 miles and found the cells in perfect balance. I will be doing it again at the end of my warranty period, when I should be around 14,000 miles.
Zunzhine, here's my under $20 solution:
Route balance leads to each pack of eight cells and connect to a 9-pin connector (1 pin for 1st cell's neg term, 8 pins for the cells pos terms). So you would end up with three cables for 24 cells. Then you could use one or more of these $14 Cell Log 8 to monitor how high the cells charge, how low they discharge, and how balanced the cells are.
They also sell a slightly more expensive version that does data logging and can transfer data to your PC via a USB port: Cell-Log 8S.