YES, perfect. You got it.
Dear Sir,
My mane is Tom and I am in Venice Florida and have two Gems, the 2002 E825 I converted to lithium ion batteries about 30 days ago. I purchased two 72 volt 50 ah Chevy Volt batteries and bms for each battery, and have them in parallel to achieve 100ah. I first tested the car with my 2 year old Zivan charger withe the setting on gel and the car charged and preformed very well with a 30+ mile range. I had the controller unlocked about two years ago and the car will peak at 34 miles an hour. The first time I charged the car the charger stopped at 75.1 volts. The battery indicator on the car is not accurate with the new batteries. It will show anywhere 65 to 85 % when fully charged. I since purchased a Victron Energy BMV700 battery monitor and installed it with a shunt to have a better idea what the battery level is. The car preformed great except when the level on the dash indicator that is built into the car reaches a certain point, the buzzer on the car sounds off the entire time. Also, when the dash indicator reaches 20% or lower the controller shuts the car down. Is there a way to get around this shut down? I also ordered a new Zivan charger and gave them the battery information and they set the charger for my batteries. When I installed the charger the dash indicator only read 40% and my range dropped to 6 miles and went into shut down. I reinstalled the original zivan and it did fine once again. I was wondering if you had any specs on what the charger should be programmed to? I was told that there are 18 cells at 4.2 volts each and was told not to charge over 75.7 volts. I also own a 2013 chevy volt and love the car.
Any help would be much appreciated,
Tom Royer
The main problem, Gem likes a 72v battery at a minimum. You have a 66 volt battery nominal.
The controller will not let the car start when you have 50% left in battery. Code -15
It will continue to run but will not restart.
Also you will always need to charge 75 volts, which will shorten battery life. 74 volts is a good charge limit for 18s.
You may have dealt with a less than honest seller who claimed they were 72v batteries.
I can tell you how to go the other way. Running with more voltage, but havenât played around with low voltage battery.
You should get 40 miles from your 6kwh on the level at 25mph, without overcharging batteries. Itâs just that the car wonât run on the last half.
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How do I go the other way? Do I have to scrap what I have or can I put a smaller voltage in series to raise the voltage?
Tom
I am so happy I ran across this forum because it has been so difficult to get any straight answers about batteries in general , especially for Gems. Seems as though everyone locally has oposite opinions about them. They act as though a set of batteries no matter what type are inexpensive.
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I hope my frustration didnât come thru in my response. 
You are about the 6th Volt buyer Iâve tried to help with similar problem.
One invested in 48v batteries only to find them 44v nominal.
It might be possible to trick the controller into using more capacity, by operating at lower voltage.
My experience running Gems at higher voltage, leads me to believe running lower voltage is the wrong direction.
The batteries you have should work fine. Just add to them. However that means the bms wonât work. Unless it can be programmed for 20-24 cells.
Itâs hard to build an optimum pack from Volt. Up to 2015 modules are 6s or 12s only.
Thatâs why sellers are free with there 48v and 72v designations. Who would buy a 44v or 66v pack?
There are several ways to go. None easy. But worth the effort.
Setting aside bms for now.
Buy a 6s pack. Electrically separate it into two 3s parallel parts. Add it to your 18s string for 21s total.
21s is considered ideal for gems by many. 77v nominal.
Gem cutoff will be 3.2 volts per cell. Almost dead but enough to get you to a charger.
High volts tolerated by stock gem is about 86v. Or 4.1v per cell. Perfect for long life.
You can test this method by plugging it in and running.
If you are adventurous, buy two. Add parallel 6s to your string for 24s.
It takes a small modification to make the Gem start with high voltage. Cwm just added 1.2 volts to his car yesterday. Iâll invite him to this thread.
In the case of 24s it takes a 15v spoof.
The difference in performance, running another 12-24 volts is amazing.
The parts are cheap. Less than $100 each for bms. Adding two 24s bms not for the faint of heart.
I better leave it at that for now. I tend to ramble.
Where can I purchase the 6s pack? and the approximate cost. I do remember that my batteries are 2015 volt batteries. I thought that each âsliceâ of the batteries was a cell. except for the ends. Each other slice except the ends of the batteries have black marker on them as if they were counted and there are 24 of them.
Tom
My battery dimensions are : 91/2 âdeep, 131/2â tall and 14"tall, if that tells you anything about them. There are no part numbers on them. I have one battery under the rear seat and one in the front under the hood. I relocated the master switch under the front hood. Unless the 6s pack is very large I should have ample space for mounting them.
Tom
Disregard the dimensions I just stated, I will re measure in the morning and let you know.
1kwh modules are 6s.
Should find them on Ebay.
2kwh modules are 12s.
How did you connect a bms to each parallel battery and make it work?
I canât get my head around it.
Each bms would need itâs own charger. Even then the outputs to each battery would be connected together, making the bms useless as a high voltage limit.
The only way Iâve come up with is connecting parallel batteries cell to cell with 1 bms.
The guy sold me a bms for each battery for 500 each. they are little white boxes with a green wire coming out of each one that goes to the negative terminal and the one on the rear battery has a black wire also that comes out of it and the negative wire from the charger hooks to it. Would or should I get two 6s or one 12s? I am not sure how to hook the additional batteries up? Would parallel add to the voltage? He said after I bought them that once the charger was programmed for the batteries I would not need the bms on either battery. I will follow your recommendations on what I should do. Also is there a specific seller on eBay that you use and trust?
Maybe you can make a drawing or take a picture.
Is that 500 for each battery with bms?
Iâll draw a picture of battery connections for you. Bms is another story!
Itâs hard to come in and make things right.
Ok, right , I was thinking that the 6s would have to be in series. If they programmed the charger properly , would I need any bms?
The charger is only connected to one bms?
That kind of makes sense. One bms is not used then. It is balance only.
Nice to see how others do it.
Yes, new battery is connected in series.
Iâll add it to your picture.
I talked to the guy I bought the batteries from to get a price and he suggested that I add a 12 volt 50 ah chevy volt battery in series with its own bms to achieve 84 volts 100 ah with nominal voltage at 77 at 4.1 volts as you mentioned. The cost with shipping is 400 for battery, 275 for bms and 50 shipping which totals 725. that makes my investment around 3600$ the battery is 91/2 " wide, 43/4 " long and 101/2 " tall which would fit in the front nicely. What are your thoughts on this?He was very surprised to find that Gems controller would accept 86 volts.
The price is outrageous.
That is the same connection that I referenced. Not showing the internal modification that he makes.
Again he mis-states the voltage. Total voltage for 21s is 77 volts. Not 86.
However the high voltage limit of a Gem is listed as 86 volts. In practice more like 85.5v.
So all you need to do is stop charge at 85 volts to work as is. A little over 4 volts per cell. Good for long life.
If you want more range I will sell you a device that will allow running at a higher voltage.
It will work so much better at 85 volts you wonât need it.
Youâre pretty much stuck with this guy now. He is the only one modifying Volts for 12v except myself. And I donât have a 1kwh module here.
Do a search here for bms-24 and see what a real bms costs. The ones he sells are about $50 on Ebay. He just adds a Volt harness to them.
For example of pricing.
I just sold a couple 21s volt kits with bms-24 on here for about $1500 each
It is only 1/2 the kwh. So you arenât too bad off if it works.
People interchange the terms cells and modules freely and they shouldnât. With my 20S Leaf setup, I have never gotten near to finding my max distance but i est. 35 to 40 miles. I am happy with my 32mph with stock 2002 2 seater GEM motorâtaller wheels and tiresâŚ
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There is the Las Vegas Hybrid Electric car and car part Ebay dealer that could come in handy. They prefab Leaf and Volt setups w BMS already rigged. But w Inwo/Dave you have someone to hold your hand thru the process.