My Lithium Conversion

Hello,

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:

  1. 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?
  2. 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-

Thank you. I will look into this post. I appreciate your help.

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.

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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.

Daly BMS also will manage the high temp.

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Thank you for your thoughtful reply.

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.

Sounds like a great upgrade. When completed post some pics.
And don’t forget to come back with range data.

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I will continue to report on my progress and the outcome. Thank you.

Check these out for top balancing. One across each cell.
Made specifically for LiFePo4. $5 each.
Led “cell full” indicator.

balance board