Four years ago i did the first leaf cell / gem conversion ( hard to believe it was that long ago) somewhere on the old site the details exist . Since it hadn’t been done there was no info available so i had to start from scratch . First i looked at all the different lithium cells that were available and their chemistry , then the what would be required to put it all together ( charging , programming of controller , fit , battery meter , weight …After dozens of hours on research i decided on the leaf cells .
one of the hardest things was deciding what voltages to charge and discharge to , not a lot of info available .
so i finally went for it , the results exceeded my expectations .the cart got real fast ( 40 + mph with a stock 5hp motor) , range was low 20 miles @ 35mph cruise and acceleration/ handling was a blast .If Porsche made a gem , this would be it .
After a few years i noticed range started dropping , after some testing it had become apparent the cells were losing capacity. i had read that nissan was having problems with them in hot climates and i live in south florida so they saw hot a lot . Also they were being charged to 4.13v , below their maximum but as later discovered a long term voltage that would reduce their capacity . so Nissan made some changes and produced a cell that is refereed to as the Alligator cell because of the casing . Got a set of those , dropped charge voltage to 4.08 ran those for 2 years . same thing happened . Now i’m run my stuff hard so that probably contributed to it . this pack is still in my gem and runs well , range has just dropped to about 14 miles again at about 35+ mph . The good news is that after all of these years the cells have stayed balanced within 1/100 of a volt ( i dont use a bms) ., after the initial lose of range they seem to have stabilized . i still love this conversion and would recommend it . Gm uses the same Chemistry in their cells but uses a water cooled thermal management system in their cars . plus they undercharge the batteries and as they age increase to charge voltage to retain mileage . this combo has kept owners happy but in our installations will probably have similar results as Nissan.
here are some tips:
keep max cell voltage to 4.05v , 4.0v if you can . try to keep them as cool as possible . dont use 2011/ 2012 cells if possible . if you need more range just do a double pack.
So 4 years later i started looking for the next generation update and found LTO (because of inwo)
Lithium Titanate is an amazing chemistry , you can :
charge an entire pack in 10 minutes
it is highly stable and wont catch on fire if over charged
can be rapidly discharged
can be discharged down to zero volts and left there without damage (this is a big one because multiple people have accidentally over discharged their gel or lithium packs and ruined them , expensive mistake)
has a 25+ year storage life
estimated to have 20,000 discharge cycles @100 dod
nothing else comes close.
the disadvantages are:
a little heavier then other lithium
lower cell voltage so you need more cells
they are expensive
and they’re used in commercial applications and not usually available to the public, until Dave came along .
so Dave got his hands on a bunch of test cells last year and sent me some , i tested them and knew this was it . But i didn’t react quick enough and couldn’t get all that was needed . A few months ago Dave came across some more of them and these were new . so we bought them all, 8 pallets worth, some 53ah and some 11ah.
These come in pouch form so you have to design a way to make them into a battery ( nowhere nears as easy as a leaf conversion) This is what we are doing right now , Dave has come up with couple of prototypes and they work awesome . I am currently trying to make to create a simpler version.(out doing Dave is not an easy thing to do )
hopefully this week i will receive the parts i need and will start assembly . will post some pictures shortly and update as we go.
mike
