Hi all ;
This is a post to understand the phases of the charge process of a brand new « vanilla » Lithium Vectrix Li +.
First I have to introduce myself : I am an electric scooter addict ; I have been using different electric scooters professionally for almost five years now and I've felt ready to buy my first Vectrix : a brand new beautifully white Li+. I go and see my scooter at night in the garage in admiration... Now I ride in comfort and as I travel almost 10 000 miles a year on a scooter (going back and forth in the centre of a town to meet my clients) it is easier and quicker for me to work and a much more pleasant experience. As you might have guessed I expect much from my V, and I rely on it a lot.
I have read many posts on Lithium conversions here but I've learnt little about Vectrix' own batteries. Few people have a Vectrix Li to report on V is for Voltage. I feel ignorant on recharge phases, temperatures and batteries as far as it concerns LiFePo modules.
Here is my concern. Although I can reliably get over 100 km of range on a single charge, I would like to take care of my batteries to keep them in a perfect shape as long as possible. I have read many things on LiFePo batteries ans if I am not mistaken, these modules are known to be reliable, strong, light and resistant to temperature to some extend. Best allaround modules technology can provide today with a long service life. How about GP Batteries modules in particular ?
When I plug in my Vectrix, I can read several phases : CC146, CV146 and EO146. Correct me if I'm wrong : constant current, constant voltage, end of charge ? 146 for 146 V overall ?
When I just plug, charging current goes up to 10 A (needdle reading 100km/h) I read for example : hi 331, lo 331, and on the left (where « est range » is usually) 130 V. I understand : « hi » for highest voltage module reported by the BMS, and « lo » for lowest voltage module reported by the BMS. Is it ok ?
Every thing appears to be ok, and all modules seem to be in balance.
After several hours of charge here are the readings :
hi lo charge voltage Amp temp C min-max
339 338 CC146 136 10 24 – 25
364 355 CU146 141 1,5 27-29
364 343 CU146
364 342 CU146
364 341 CU146
365 340 CU146 138 1 28-30
365 338 CU146 137 0,5
365 337 EO146 137 0,5 28-29
365 346 EO146 145 0,5 31-33
When the CC charge ends at 10 A, the low cell is at 355, as soon as the charge drops down to 1 A gradually, its voltage goes down to 337.
Clearly : the pack is not in balance anymore. There are two options. Or a module is weak, damaged, dead, or it has to be balanced and is far behind the others in the chargecurve.
If you take a low module and apply to it 10 A, I think it will go up and reads as much as its buddy modules ; but if you drop the current to 0,5A (CV and EO) if it is not as charged it will drop significantly its voltage, because it is late in the charge process. Thanks to the BMS, other modules stay at 3.65v waiting for it, giving up heat. I hope after a few other charges, it will catch up.
I would like your opinion on that...
When I read the GP batteries modules specsheet, 3.65 v seems to be pretty high for an end of charge : 3.65 x 40 = 146 v. My Vectrix takes loooong to get there ; and I don't think this is good for my modules to get up there each time and get as hot doing so.
Why is such an imbalance and can I deduce I have a weak cell ?
If I could open the batteries, the best thing to do is to take appart the lowest cell and do a charge in order to get a top balanced pack (or better yet : a bottom balanced pack). But as long as I can't do it (warranty and absence of knowledge – yet) I have to rely on the BMS to do so ; and it seems each charge my low module is going up a bit.
For the moment I hope each charge will bring the lowest cell onpar with the others, and I intend to charge up to 146v no more than once a month or less and go down to 3.1 maximum as far as I can.
Here is in insight on the Vectrix Li+, and I hope to hear what you think and recommend about it.
Thank you all.
Hi Paco,
Let me talk about balance for a bit:
No Lithium cell is made the same,
each will have slightly different capacity (in Ah) and internal resistance.
When we say the pack is balance, we mean all the cells in a battery are at the same state of charge for *one* specific state of charge
For a brand new set of batteries, that usually means all cells pass through 50% SOC simultaneously
So for a battery, when the smallest/weakest cell reaches full (3.65v in this case) the largest/strongest cell will have the lowest voltage.
The same is true at the other end, when the smallest/weakest cell reaches 2.5v at load, the largest strongest one will probably be still 3.xx V
Brand new cells are all charged to 50% so that when they are assembled into a battery, the capacity difference is spread evenly at both sides of the charge curve, minimising the risk of overcharge/overdischarge
When using a BMS that works at the cell level, we normally move to balanced at 100% as it is easiest to achieve. That is, all cells reach 100% state of charge simultaneously.
However, the smallest cell will still deplete first
Thats part of the reason on my conversion kits, I leave such a wide margin between rated capacity, and the amount actually used.
The official Vectrix lithium bike limits lowest cell voltage to 2.5v
Holding cells at 3.65v for extended periods is not ideal, but if its only for a few hours its ok
The fact that there is a temperature rise indicates current is being shunted across the full cells
If you charge a lithium cell by itself, there is no temperature rise until the voltage exceeds ~4.3v (and the damage is permanent).
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km