I am upgrading my 2018 GemCar E2 from it’s original AGM batteries to Lithium.
Range anxiety is a great motivator. My 3 year old cart has a useful range of about 35 miles. Empirical testing over several months has shown it uses between 2 and 3 amp hours per mile depending on the ambient temperature and driving conditions. This measured with a Victron shunt.
I purchased 16 EVE 304 amp hour (3.2 nominal voltage) batteries via Alibaba. The cost was about $2421 delivered to my house. Order to delivery was 10 weeks.
When they arrived, I tested each battery and found them to be remarkably well matched at 3.29 volts each. Not a single outlier.
For the past 6 days I have been charging the batteries (all connected in parallel) using a 10 amp bench power supply delivering about 9 amps at 3.6v. My intention is to charge them in this way up to 3.5V. Assuming a 50% charge on arrival, I will need to provide around 2,432 amp hours. At 9 amps per hour, this will take something more than 11 days. As the voltage of the batteries increase, the charge rate will decrease. Charging the batteries in this way will result in a top balanced set. If some adjustment to individual units need to be made after the initial charge, they will be charged (or discharged) individually.
My plan for constructing the pack is to connect them in series, standing like soldiers 4 deep and 4 wide resulting in a unit that has a voltage of around 52 when discharged and 56 when fully charged. Each set of 4 batteries will be compressed using threaded rod and a front and back plate made of 1/4" thick aluminum. I will post photos as soon as the packaging is constructed. This unit will fit nicely in 1/2 of the space currently occupied by the AGM’s.
I have 2 questions for the forum regarding the packaging:
Shock absorption. Should I be concerned about placing these batteries directly on the existing Aluminum battery rack in the Gem? I will provide a 1/8" sheet of PVC for them to rest on to prevent any possible short circuiting from the bottom of the batteries to the rack). Should I consider using some form of rubber or other soft material?
Overheating: I am planning to pack these batteries rather tightly. I do not believe the wimpy 16-17 amp charger provided by Polaris will overheat the batteries but I am a bit concerned about the discharge rate in the summer heat here in Central Florida. Maximum current draw when accelerating up a hill while fully loaded has been tested multiple times and has never exceeded 310 amps (and only for a few seconds). Normal driving rarely causes more than a 60 amp discharge and only for a few seconds at a time.
I also have questions about charging these units with the factory charger. My plan is to run the charging and discharging through a 400A Daly BMS to prevent overcharging and overdischargeing. If I want to charge the batteries to 3.5V each this will require a charger capable of producing 56v or more. Does anyone know what the factory charger is capable of? If not, any idea how to find out? When my current AGM’s are fully charged the Victron shows a voltage of 52vdc.
Thank you for reading this post and any advice you can provide.
304 Ah??? Wow. What does your typical day look like? Do you really need 100 mi between charges?
Looking at past builds in the archives I never saw too much of a concern over vibration. I don’t think it will be an issue.
Heat won’t be an issue either. I think typical use will be barely taxing the batteries.
You may run into issues with the onboard charging system tho. Not so much with the charger, but rather the onboard BMS controls the charger.
This popped up just last week-
Not gonna lie… I’ve seen these cells and thought about it too. I could drive up from my house to visit @AssyRequired . Not that I ever would but would be nice to know I could!
There is a reason Chinese FePo4 are low cost.
Very safe, but heavy and hard to keep balanced through normal methods.
For example, active balancing. As the voltage is constant, it is near impossible to determine state of charge at any point other than full or empty.
The best way is to use high current shunt balancers and a charger that goes to at least 3.65v/cell.
I have killed many a LiFePo4 battery with conservative charging.
I believe charger can be reprogrammed.
Daly BMS will Balance them but the balance current is very low, so make sure to start with a balanced pack its also a good Idea to leave them connected in parallel for a few days so they can self balance.
I wouldn’t be worried about the heat, Lifepo doesn’t like to be charged when its cold thats why its very important to have a BMS with low temp charging protection.
Thank you for your interesting reply. I am hoping the Victon shunt will help me pinpoint the number of amps used. It auto resets each time it senses a full charge has occurred. I am planning to use only the middle 80% of the charge, never charging past 90% capacity or discharging below 10%. I understand this will give me the greatest number of cycles before battery replacement is needed.
I agree 304 amp hour batteries are a lot. But… they will fit in 1/2 the space the current AGMs use, only weigh 198 lbs and cost only slightly more than the next smaller size. We live in a retirement community that has over 700 holes of golf and several town squares. We have found it to be pretty easy to drive 50 miles in a busy day.
I also live in your retirement community, have a 2018 E2 and I’m looking to switch to lithium. Were you successful in getting your cart up to ~100 miles range? Can you share whether you have had any problems with the batteries after 2+ years of use?
New guy here, looking for a DIY tutorial vid or post for a step by step DIY Lithium battery steup for a 2002 GEM? I’ve searched but have only seen posts where its done or just pics but no step by step. I bought the GEM with dead batteries so figured I should go lithium and not spend the money on standard lead acid. Can someone please point me in the right direction, or supply links etc?
I am confused by your request because the archives contain quite a few examples on various builds. Sure, since there are so many it may be tough to sort through, but this can still be all part of the education.
If you haven’t found the archives yet, Tap on the magnifying glass in the upper right of the page and enter a few keywords in the pop-up box. It will give you an idea on where this group has come from and what is involved.
Be aware that much of this info may be a bit outdated (mainly around advancing battery tech), but you still pick up on the concept and theory and it is good for it to become part of your education. Look for the ones with a recent freshness date and you will begin to target in on more of where we are focusing energy today.
A Step by Step Guide is a bit tough to target because there a few different ways to do it. Other than the wish to “go Lithium” you have not specified what this means to you.
Are you going to build this from scratch? (acquire parts, assemble, etc) but want to be told how to do it?
– or –
Are you looking for more of a drop in solution? (of which there are a few here that have put together a package that has a high degree of success)
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Actually, what I see here is that you are in a tough spot (not really wanting to spend money on LA batteries) but you are a new car owner, and bought a car not even knowing if it is even functional. This puts you in a position of doing a fairly radical mod and if it has issues during the build, you need to figure out if it was an issue before or after the mod.
Experience tells most here that successful build has far better odds if applied to a known working car. Even better if it is done by someone that is a bit more familiar with the somewhat complex workings/wiring of the Gem Car.
Question to you: Do your original batteries have any life left in them at all?
What is the condition of the rest of the car?
How are the brakes?
What is the condition of the driveline? (gearbox, half shafts, motor)
Hey Joe, 00-04 have doecial considerations for the suspension design. You have to load them over the motor or they become pogo sticks. Hit up @LithiumGods and @Inwo they have custom packs that fit up there
