Decided to have a little fun a do some comparison testing . I did the first Leaf conversion about 5 years ago (Probably first one ever done) and still have that gem . About a year ago bought a 2014 gem and built the first LTO lithium gem , This is my daily driver . Unfortunately i didn’t plug in my hardly used gem and damaged the leaf battery pack . Inwo has been asking me ( begging me) to test his Lifepo4 cells in a gem and since he pays very well i couldn’t say no . So yesterday a set of cells showed up and i started charging / balancing them . The first test well be running 25 cells charged to about 85v , 3.4v / cell which is perfect . This is the same voltage the leaf and lto banks were charged to so a fairly comparable test . After i may add more cells and do a high voltage test .
2 ichargers charging/balancing banks of 5 cells . i have 4 ichargers but not enough power supply capacity to feed them all . FYI the big cells on the left are 260ah Lifepo4 cells
Do your chargers top balance ok?
What voltage and how close when finished charging?
I only charge to 3.5v for testing. Don’t even attempt balancing on the top, but discharge all to 3v.
Should have another batch later today.
so far Icharger is doing a great job at the difficult job of top balancing lfp cells . Cell #5 is max charge of 3.5v . The charger is holding it there but still putting in 18.26a into the rest of the cells . The cells were in low voltage storage mode about 80mv apart . charger now has them to 58mv . The pack has already taken 62.7ah and based on the amps it is still taking they should go over 70ah , impressive .
The first icharger has them balanced down to 3mv and still working . the 2nd icharger here has them down to 1mv . That is very tight .
also the first pack which was at a lower start voltage took 72ah , this pack started higher and took 64ah . These cells are under rated @60ah
@chris1 may try making 5s packs. How did it go for you?
so i was waiting for Inwo’s check that is "in the mail " ( ) to start my testing but couldn’t wait any longer. So i finished testing and balancing all 25 cells . They were all way above their 60ah rating . Set them up as 5 strings and installed 5 sets for a total of 25 cells . These cells after charging fall back to 3.334 volts per cell and are very close to each other . 25 cells showed 83v . dropped them in this afternoon , easy to do . 3 sets fit between frame rails and then i put 1 set on the outside of each rail , easy . hooked them all up and then hooked up a bluetooth monitor / balancer . Didn’t spend a lot of time making it look good , wanted to get it in with monitor wire hooked up and start testing . This is in a 2007 e4 with a high speed 10.3x diff and an old 2002 5hp rusted motor . ( this motor has been used for 5 years on all my lithium testing , also ran with oversize tires , beat to hell )
Cart accelerates hard and spins tires . Speed is limited to 38 mph and it got there quick . Drove it full throttle start and hard stops around neighbor hood . Was watching each cell during testing . Cells stayed very close in voltage . 140 mv during hard acceleration and stayed about 40mv during high speed cruise . One of the cool things about Lifepo4 lithiums is that they have a narrow voltage range 3v dead , 3.334v full . so voltage on the gem stay mostly in the 80v range . Gem was consistently fast .
around 14 miles started smelling something and gem acceleration slowed down . Speed was still mid 30’s but it accelerated slowly , voltage was still holding high . Pulled over and checked battery and connection temps , all good . Continued to drive it for 20 miles and brought it home . Smell was coming from motor , 265 degrees .
Batteries were still very tight in voltage . Even when soc was low they stayed tight under load . So far i like these batteries . They seem to work pretty well with the stock gem charge gauge .
So first response is very good . Will charge pack tomorrow when i can monitor and see how tight it stays . Then take it for a long cruiser ride and see what it does , hopefully motor is still good and it was just protesting from being abused for the 100 time .
here are the voltages of the first 24 cells after 20 miles and a 2 minute rest . They are with in 6 one thousand’s of 1 volt . very very close . Pack still shows enough voltage to run and the turtle had not come on yet . The gem was still doing 30+ mph at this point . Further testing tomorrow .
Hi…It will be interesting to see if the weight will be prohibitive for transportation. I can always go back to Lipo if it fails. Like I said, high number of cycles with high power is important to me to reduce cost of ownership.
Battery and tires are the most expensive cost of ownership for an ebike: 4000 miles on a $400 battery is 10 cents a mile. I now plan to get over 40000 miles out of LTO for about $400 in cells and BMS…that’s a huge reduction in cost by a factor of 10.
There’s no way can get that usage cost with Lipo.
@LionHo do you know you posted about an eBike to the GEM forum?
Which lto cells are you using ?