Just wanted to start posting here and work with others on developing the best Lithium Conversion for the GEM electric vehicles. I am always tinkering with Electric Vehicles and have a passion for reliability and innovation.
Is there many others that have converted to Lithium batteries or considering the swap as the Lead Acid or traditional style are so expensive and have terrible range / reliability.
Would love to hear from everyone as a new poster.
I installed 24pcs of the 130ah 3.2V Lifep04 batteries and have driven the unit just about 100 miles in the past two days. The batteries have only been charged twice. I ordered a 72V Lithium battery gauge to be able to tell the status of the battery packs charge and to be able to install an alarm that will sound when the batteries need to be maintained. I figure in making the system bulletproof to eliminate all the traditional batteries issues with both my gems.
1pc. MiniBMS system with one wire circuit boards.
1pc. QuiQ 1000 W Industrial Battery Charger
24pc. 130ah 3.2V Lifep04 batteries
I will post pictures soon of the installation.
How did you wind up wiring your MiniBMS?
I’ve got mine powered by an aux source (currently a small DC-DC, but may move to a small 12v battery to eliminate the extra drain), but I’m having trouble working around wiring the ignition switch in as the 12v and 86v packs don’t share a ground, and the head board only has one ground input.
You can share ground with separately derived system.
Is this what you have?
Yup, that’s exactly it. So are you saying I would connect both the common ground and the 12v switched ground to the GND terminal on the control board?
I was hesitant to do that since the voltage across the switched 12V leads to the common ground is the pack voltage (70-86v depending on charge level), so the built in DC-DC obviously doesn’t share a ground already.
Post a picture to be sure I understand.
The battery pack is not normally grounded.
The 12v dc converter is.
How are you connected to “key/ign”?
[quote=Inwo;29389]Post a picture to be sure I understand.
The battery pack is not normally grounded.
The 12v dc converter is.
How are you connected to “key”?[/quote]
Sorry, perhaps I’m causing some confusion by using ‘ground’ in place of ‘negative’…
My original thought was to get the +12V for ‘key’ from the fused switched 12v leads that hang down behind the dashboard, but that won’t work because you only get 12v if you use both those specific + and - wires. Using the +12v switched and any common negative doesn’t work.
My constant 12v supply is a 3 wire DC-DC that shares the same - as the battery pack.
A picture wouldn’t do much good since it’s a spaghetti mess ATM, but here’s a diagram of what I have (which doesn’t work, as the control board can’t detect ignition on).
I’m only going by schematic. Not experience.
Is this X correct?
Would not expect 86v pack connection to grd. or board.
Oh, I see that’s your 3 wire converter. Not a good Idea…
What’s not a good idea?
Connecting battery pack negative to ground.
I think we’re talking at cross purposes here - it’s not frame grounded or anything, that’s just how 3 wire DC-DC convertors are wired, common negative, input voltage, output voltage.
Or are you saying 3 wire DC-DC convertors are a bad idea?
In this case it seems to be.
As it would require connecting battery pack neg. to grd terminal of bms.
It doesn’t suggest that connection in anything I’ve seen.
Remember, I haven’t done this. 
Just sharing my opinion. :o
Where else would one connect the bms GND?
Regardless - change that DC-DC out for a 12v battery, and I still can’t see how to wire up both constant and switched 12v, as they will still have different negative sources.
The bms grd is for 12v system only. IMO
As shown in diagram.
[quote=drogers;29397]Where else would one connect the bms GND?
Regardless - change that DC-DC out for a 12v battery, and I still can’t see how to wire up both constant and switched 12v, as they will still have different negative sources.[/quote]
Isolated supplies can share neg sources.
The problem comes from grounding the 86v supply. Controllers are designed to be isolated.
Other than that, you could connect as your diagram.
Starting over. This would be my guess.
I’d like to throw out an alternative here. I have used a Mini BMS system in a previous conversion and now added it to my lithium battery GEM car but so far have decided to use it in my GEM in a different way.
My previous car conversion has the Mini BMS head board (the part you are trying to figure out in this thread) and the Mini BMS boards mounted on each cell. It works great but that car has a 12 volt battery system that my GEM does not.
So, with my GEM, I chose to install a Mini BMS board on each cell and NOT use the Mini BMS head board. The reason is that I did not want to add an additional 12v battery to my GEM simply to run the Mini BMS head board. My lipo CCCV charger will charge and stop when the cells are charged and the Mini BMS protects any cell charging too quickly and provide some balancing of the cells.
By doing it this way in my GEM the thing I’m losing is the monitoring of the lipo cells when the car is in driving mode (i.e., the switched 12v is “on” on the head board) and a buzzer alert when a cell voltage drops below a certain voltage. I don’t feel this is a big deal because I can watch the GEM’s state of charge on the car’s display to monitor battery state. Granted, it is a state of charge display designed for other battery technology but I’ve learned to correlate the display’s % values to the lipo cells.
IMHO, it is good to ask “What are you gaining by using the Mini BMS head board if the GEM display and battery charger will monitor cell voltage during charging and driving modes? And, is that gain worth the cost and hassle of adding an additional battery?” For me, so far so good not using the head board.
RWD
I converted to LiFePO4 four years ago. Link to my info thread is in my sig below.