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 ?
you say you have 4 ichargers but not enough power supply capacity to feed them all ? look into the common rc trick, use server power supplies. they provide 60-100 amps at about 12.33v. because of bitcoin miners most of them are $15-20 each, the best deal in history! i use hp dps 750rb but there’s many out there some with 100 amps, you simply need to google this stuff because they require a jumper or resistor to turn on the supply and trick it into thinking a motherboard is connected
series connect them to provide 24v,36 and 48v
Sounds like you need an AC motor
I actually use a 80a server power supply. looking into 2 in series for 24v. Moving 80a @12v requires big wires .
Hi…I committed an error with my pack voltage computations. various makers have distinctive cell volt information and I got in the weeds. so I modified it and the 144s LTO pack is maybe an exceptionally close match to the 96s LiPo pack at significant voltage states. The LTO thought I’m discussing is supplanting the 48x 7.5v, 65ah 2s2p modules with 48x 7.2v, 3s2p modules of almost equivalent actual size. the cells I connect to are not the correct shape, I was simply attempting to show the market accessibility. From a bundling point of view the stock 2012 modules are 303x213x55 which is 3716cc per module and there seems to be space to grow the cell impression a little, perhaps an inch longer. the amp hour limit of a 6 LTO cells that could find a way into the 4100cc greatest envelope for every module would be around 48 amp hour, for a pack force of 33kwh.