I now have my Evader scooter powered by two YESA 48V, 20AH LiFePo4 packs wired in parallel, and I have run them through about 20 charging cycles to date. I am charging them with a Taiwan made 48V, 8A SLA charger I purchased on Ebay and all seems fine(the slighly lower charging voltage will probably extend the life of the batteries somewhat). Today I rode 25 miles and still had power left to go a few more miles. The parallel arrangement seems to work well (I am charging and discharging in parallel), and I expect even more range when it warms up here in Rochester, NY (it was 50F today when I rode).
I have had a good experience with YESA but not with the shipping of these packs from China. The first pack came through with the package damaged and one of the cells dented, but it still worked ok. The second pack came through with the package damaged and one of the cells shorted out. YESA quickly sent me a free replacement cell, but I had to pay for shipping. I consider this fair treatment under the circumstances. Replacing the bad cell turned out to be pretty easy.
FYI, the Evader is a 48V large scooter which came originally with 48V, 40AH of SLA's. Replacing the SLA's with the LiFePo4 packs reduced the weight of the scooter by about 100 lbs. The exchange went off pretty easily but the Evader doesn't use a voltage converter to get 12V for the accessories. Instead it simply grabs 12V off of one of the SLA's, so I had to tap off one of the LiFePo4 packs 4 cells into the pack to get the 12V I needed. Top speed is about 32 mph. I expect that range will be above 30 miles when the temperature here rises to 80F or so.
Thanks for your report of the Yesa cells. I look forward to more performance reports. It is also nice to know that Yesa customer service did not leave you hanging. Hopefully, they will improve the packaging to make this less likely in the future.
I am very concerned about you getting 12V from within one pack to run the accessories. This will likely make the battery management system (assuming there is one) work harder to balance the cells during charging. If the BMS does it's job then your maximum range will surely be reduced. If the BMS fails or does not exist, on a long ride these cells may go much below 2V or even reverse leading to premature failure. A safer thing to do would be to just buy a 48V to 12V DC-DC converter with enough rated power to run all the accessories, or alternatively a small 12V battery that would last about 2-3 hours could be used instead and charged separately.
Thanks for the comment. I am also a bit concerned about tapping off one of the packs to get the 12V, but that is the OEM design on the scooter and the battery gauge on the scooter may also be reading off the tap as well. Both packs do have BMS on them. I had previously used powercheks on the SLA setup to balance the batteries.
According to the stated claims for LiFePo4 cells, they can be fully discharged without damage. Of course this claim, like the statement that they operate as well in cold weather as they do in warm (which is not true), may be overstated.
Is the battery gauge on your scooter just an analog voltmeter? If it is then it will not be very reliable anyway for lifepo4 given the flat discharge curve. By the time the voltage dips significantly at the end you will almost completely be out of juice. This is the reason why some people use devices (drain brain, paktrakr, etc.) to monitor how much capacity they are actually using. There are only a few scooters that have this capability built into their battery gauge (like the Oxygen Lepton and Vectrix) and they are generally pretty expensive.
Modifying the OEM design to get 12V a different way should not be too hard and not take very much time especially if you have a wiring diagram. You will have to find some extra space on the scooter somewhere (under the seat, under the floor board, on the floor board, etc) and do a little fabrication with the wiring. Your battery pack (especially the BMS) will likely reward you with more longevity and range which you probably want after paying >$1000 for it.
It's a very bad design. You could run the wires of just the battery gauge to a 12v section and this would probably not cause problems.
Do you still have the old Evader batteries? One could be used to power the 12v system, and it would need a separate 12v SLA charger. Batteryspace sells some cheap smart lead-acid chargers. Otherwise, 48 to 12v DC-DC converters are pretty common, even though they might be somewhat expensive. Trust me, it's worth the expense, especially with the batteries you have.
[url=/forum-topic/motorcycles-and-large-scooters/587-my-kz750-electric-motorcycle-project]KZ750 Motorcycle Conversion[/url]
[url=/forum-topic/motorcycles-and-large-scooters/588-fixing-my-chinese-scooter]900 watt scooter[/url]
Pic from http://www.electri
Yesterday was a beautiful day and I decided to do a real range test. I went 29 miles and returned home with some(but not a lot) of juice in the tank. The battery gauge showed 2 bars out of 8 at standstill but went down to zero as soon as I accelerated. One thing to note about these LiFePo4 packs - they have nonzero internal resistance (in my case about 200 milliohms for each 48V 20AH pack), and that tends to drag down the voltage across the motor at high amp levels. Putting two packs in parallel as I have done halves the effective resistance, so the operating voltage at load is higher with the two packs in parallel than with one alone.
One nice thing about these battery packs is that the voltage holds up pretty well throughout the discharge cycle, which means the scooter's speed also holds up well.