I think Rodney knows the t3 well .
here’s what you need to know . these batteries hold most of their amps between 3.0v and 4.15v . so design the number of cells so they charge too 4.1v - 4.2v each. and on discharge assume 3.1v on the low side . you can go down to 3.0v but there isn’t much power between 3.0 and 3.1v . maybe 1-2 miles real world
Thank you for the info. Looks that you are using three battery per pack,
What range you’ve accomplished with 7.5 hp motor?
the modules are actually a 2s2p layout . I used 10 modules .
range depends on speed . if your doing 25mph , usable range would be over 30 miles . mine set on 34mph gets 26 miles on a 90% charge
I recently completed a lithium battery upgrade to my GEM vehicle. As a member of the Oregon Electric Vehicle Association, I’ve had experience converting a number of cars to lithium batteries, including a 1972 MGB over 5 years ago (with no ev component failures or battery issues in those 5 years). So I used my past experience and satisfaction as a primary factor for my GEM lithium upgrade decisions. I am hoping my GEM lithium upgrade proves to be as satisfying and reliable.
Here’s a summary of parts I used in my lithium battery upgrade:
22 CALB 100ah batteries ($120 ea = $2640)
22 Mini-bms boards for cell balancing ($12.95 ea = $285)
Custom manufactured Charger by Headway Headquarters ($204)
As mentioned in previous posts by others, the bms (battery management system) boards balance the cells at 3.65v each. A bms board is mounted on top of each cell. The charger by Headway needed to be a high enough voltage to allow the cell balancing operation to occur before the charger turns off but not too high, overcharging the battery cells.
A higher amperage charger would be nice and charge the batteries faster but I compromised in this decision of less current (i.e., 10A) so I can charge my GEM vehicle on any standard 15 amp electrical outlet with a little room to spare, in case other devices are plugged into the same electrical branch. The downside here is that a 10A charger is an overnight charger if the batteries are fully discharged (i.e., 80% depleted).
The charger is what is known as a CC/CV charger. This means the charger charges the batteries at a constant current of 10 amps to a point in time then, at that time, the voltage stays constant as the current is reduced toward the end of the charge.
I have a two-seater GEM and placed all 22 cells below the seat. The cells weigh 7.5 pounds each, totaling 165 pounds. Sounds like my solution is heavier than some other solutions but still considerably lighter than the lead-acid batteries that came in the vehicle.
RWD
Hello,
Since my previous post, I have installed my Lifepo4 batteries in my 2002 GEM car.Thought I’d share. The attached pdf file includes a couple pics of the batteries under the seat.
All 22 cells are mounted below the seat (i.e., no batteries under the front hood). I also placed the charger under the seat rather than under the dash. This allows me to read/monitor the charging state based on an LED display on the charger by sliding the seat down to the GEM floorboard. Plus, all battery related components are now located together in one area on the car. Without two lead-acid batteries in the front, I had to manufacture two shock mounts to bring the front end down to its proper height. This shock mount mod also solved a front tire camber issue that was a result of a lighter front end.
Beyond the batteries, I’ve updated the motor/controller with the Ride-4-Fun solution to eliminate the vehicle surging and the 25mph limit. So, being a 2 seater GEM on a lead acid diet via lithium, this makes it a very light GEM.
With this light weight, lithium batteries, and ride-4-fun motor/controller upgrade, the car can accelerate quite quickly and reach 35mph, even with the 10" stock wheels/tires (205/50x10 tires). The light weight will hopefully pay off in driving range too. TBD. Switching the car to “Turf Mode”, the car has a top speed of about 22mph.
RWD
that’s great news . I hope you doing this well also encourage others . what motor are you running ? 35mph with hose small tires well over rev a stock motor unless you have the 8.xx diff . post some pictures would you ? once again congratulations .
Hi kinghappy,
I agree with you. I’m not running the stock motor but am concerned about the rpm I’m reaching with my GEM. Most definitely need to keep monitoring this.
Actually 35mph is faster than the goal I was trying reach. I installed the Ride-4-Fun motor which has a 20% higher rpm spec than the stock motor (4950rpm vs 4100rpm). So I assumed a 20% more rpm would result in around 30mph to 32mph once the controller limit is removed (25mph x 1.2 = 30mph).
The above theory did not take into account several other factors, such that the R4F motor has 50% more hp, the gem vehicle is much lighter and therefore a lighter load on the motor, and I’m running the GEM at ~80 volts rather than 72 volts (fully charged). I believe this combination resulted in a “perfect storm” of achieving higher than expected speed results.
With DC motors on EVs, the voltage impacts the top rpm of the motor. A motor controller controls the motor rpm by delivering pulses to the motor. At slow speeds, the controller is delivering fewer pulses to the motor. At full speed, the pulses are gone and a steady DC voltage is applied to the motor. I’m running 22 cells at 3.65v. So my overall voltage is 22 x 3.65 = 80.3 volts. I believe 80.3 volts is still within spec of the motor controller capability.
So yes, I’m guilty of fudging the voltage up a bit and I justified it in my mind by knowing I have a two-seater GEM with lithium batteries, producing the lowest possible weight and load on the motor.
So what do I plan to do about it? I plan to monitor the motor and controller temp. If I see concerns I can reduce the battery pack from 22 cells down to 21 cells. This will reduce the overall battery pack voltage from 80.3 volts to 76.65 volts. Another thing in my favor is how I use the GEM car. I drive it from my coast property to the beach (about 3 miles). I won’t be driving it full speed for an extended period of time. With no batteries in the front, I have options on improving the cooling to the controller and motor. And finally, I can choose to drive slower than 35mph and only use that speed when I need it to keep up with traffic better. (I would be more concerned if I planned to use the GEM by driving it at a constant 35mph for 40 miles at a time.)
I personally hate the surging aspect of the GEM motor controller limit so I would rather control the speed I’m driving the GEM with my foot rather than some setting inside the controller.
We’ll see how well I can actually manage this. Thoughts? Concerns? Suggestions?
Richard
i’m more familiar with the later t4 controller then the t2 controller you have . a few things . the motor always sends pulses to the controller . your combo could do well over 40mph except the controller is programmed to hold it at your 35 mph . reprogrammed my stock controller and with a stock motor did over 42mph(e4 gem) . to many rpm’s for a stock motor so I pulled it back to 35mph. the ride 4 fun motor well do 35 mph with a 10.44 (assuming that is your gear ratio). but your gem would love bigger diameter tires/rims .
fyi , on my lithium pack I run it @83.0v ( using different lithium chemistry then yours) the controller well handle up to 86v then you get an error . I can charge it to 84v but holding it below max extends the life of a lithium pack . I wouldn’t remove a cell 22 is perfect ( some people run 23)
I run my stock 5hp wide open for miles and haven’t had a problem. your 7.5 can handle top speed for a very long time , wouldn’t worry about it .
if you have a chance get the part number off your diff so we can see what ratio you have . with a lithium pack you can run a lot of gear / tire diameter and it well perform well . also the bigger tires really quiets down your drive train and makes it drive more like a car . my tires are 24.5" diameter with a 10.44 gear ratio .
post some pictures would love to see it. once again congratulations on your setup.
I looked at the diff and could not see any number stamp. Do you know where to look on the diff to tell my ratio?
Not sure what additional pics you’d like to see of my GEM. Attached are two pics of the front of the GEM with the front hood removed. One pic has the front battery tray installed and the other with the battery tray removed. I circled my two upper shock mounts so you can see what I did there.
RWD
In regards to taller tires, I’ve been dragging my feet on that. I’m concerned what that may do is only increase my top speed and the larger diameter would put a larger load on the motor when accelerating. Also, I will be driving this on the Washington State coast beaches. I’m thinking the wider turf tires may be better on the sand and maybe less likely to sink in the sand than a more narrow tread.
Thought I’d wait to see how I like these tires on the beach before purchasing different tires. But your experience about improving the ride quality is certainly worth considering in the decision.
I’m guessing I’ll be driving it to the beach in Road Mode then switching to Turf Mode on the beach.
RWD
there is usually a tag on the top that has a bunch of numbers on it . Rodney can be more help here .you may have the 8.xx diff and then it doesn’t matter .
like your shock brackets . if u choose to put on larger tires , don’t worry about load on motor . again i’m running a 4 seater, with a rack on the back, big tires and stock 5hp motor , accelerates faster then stock because of the lithium pack . the lithium pack drops your weight by about 275lbs , that’s 25% weight of the whole cart ! second lithium doesn’t have the voltage sag of gels/agm’s . so motor gets full voltage under load . don’t know how low r4f set your field current but you should be more then fine .
how about a picture of the battery pack ?
Ok kinghappy, here’s a couple pictures of the batteries under the seat. Not a good way to take a picture and fully see the battery packs but it’s the best I can do.
I sold my 6 lead acid batteries to a gentleman for a solar storage collection system for his hunting cabin.
All 22 of my 100ah CALB lithium cells are mounted under the seat with the charger. The cells are configured in 3 modules due to the car’s framework. I used the original lead acid battery cables to connect the 3 battery modules. The cells within each module are connected via cooper straps.
With the front of the car empty (i.e., no batteries), I’m debating on how to use that space. One option is simply a second storage area. Another option would be to mount a small generator so I can charge batteries at places I drive that don’t offer power (e.g., on the beach).
RWD
You should have about a 40 mile range with those . What charger did u use ? How does it steer without the weight up front
The steering seems fine but I have yet to drive it on loose sand on the beach yet. TBD.
As for charger, I went with a Headway Headquarters charger. Their website doesn’t list exactly what I wanted but was able to call them and have a charger built/modified for my specific needs. With lithium batteries, it is important to have it switch from a constant current to a constant voltage state at a specific point in the charging time. I was able to tell them what batteries I am using (i.e., 22 cells at 100ah) and set the appropriate voltage. The charger cost $204 and took about 2 weeks to receive it. This seemed very reasonable considering it was customized for my specific use.
RWD
is the steering a lot easier with the weight removed ?
Yes! I like the feel of the steering better.
RWD
Ok, I’ve posted a lot lately about upgrading to lithium batteries on this forum. Although this is a great upgrade, I feel the need to post a little disclaimer this time around.
Yes, with lithium technology, you get longer and more consistent range. You should get many more years of life with your batteries. Your vehicle will be much lighter. And yes, the performance will be improved in that the voltage does not drop as much over the charge cycle as lead-acid batteries. It can be a DIY project for your GEM but, in my opinion, you should honestly assess your knowledge and skills to complete such a project.
Although these batteries can last many years, it is imperative that you treat them like gold over the battery life because it is a significant investment. (I converted a 1972 MGB to plug-in electric 5+ years and the car continues to run strong on those lithium batteries.)
In order to have similar experience and satisfaction, here are a few tips and suggestions:
When charging, make sure you use a charging device designed for lithium batteries and the size of your lithium battery pack.
Do not overcharge the batteries.
Do not allow the batteries to get depleted beyond the manufacturer’s specification.
Do not put the batteries on a heavier load than what they are designed to handle.
Have a fuse(s) in the battery pack to protect them and you.
Have a quick release connector or switch in case you need to quickly disconnect the batteries from the controller. Make sure the batteries are disconnected when working on them.
When installing the batteries I tape (insulate) my rachet handle to avoid accidental contact to other batteries or parts in the electrical system.
Double-check and triple-check your work BEFORE you connect the batteries to the controller for the first time. (I even like to jack the drive tires off the ground when connecting the batteries for the first time.)
Re-torque the battery connection bolts after a couple weeks. Then check the torque every 6 months to year.
If you have limited or no experience with lithium batteries, see if you can locate a local experienced person to come and check your work. You may find a person that will check your work for a couple movie tickets or a dinner gift card. That can be a bargain.
You are the best one to assess your skill level, experience, and comfort level on this kind of project.
RWD
I think I have decided to stay with gels. I have read on an rv site about using lithium batteries. There were several concerns they had with the effect of temperature and time that I couldn’t answer for me. 
heat can be a problem . a few years after Nissan released there electric car they had a few customers complain that they weren’t getting full range on their cars . it was less then a dozen people . all of them were in las vegas and the phoenix area . Nissan investigated and found that in those area’s that would get over 115 degrees in the summer and they were heavy users (15k miles/yr) the batteries life spans were shorter . all of these cars hit their 60k warranty mark but the packs were not holding the guaranteed 80% capacity at that time . Nissan changed tweaked the chemistry to tolerate super high heat and , no more problems .
some of the data showed that though it was 115 degrees out , when parked on asphalt the batteries where seeing over 140 degrees !
in the normal world this would not be a problem for us . don’t think many are driving gems around in 115 degree temps. plus these guys were having problems at the 60,000 mile mark . again , not our thing .
if my lithium pack gets me 15,000 miles that would be equivalent to how many gels packs ? 3? 4? @ $1,600 ea. compared to a $1,500 lithium pack . easy decision for me.
kinghappy and others using lithium batteries,
I’m curious, once you changed to lighter lithium batteries, did you keep the original GEM coil over shocks? With a lighter car I’m debating. The ride is not bad but seems stiffer. Is there a softer spring or a softer coil over shock you recommend?
Thanks,
RWD