Hi guys. I’m new here.
I am doing a master degree in Electrical Engineering in the area of Power Electronics. I am researching and constructing a wireless power transfer charger for a Twizy (2016 Model).
I need some information that is unfortunately not easily found. According to the vehicle user manual, the traction battery’s voltage is 58 V (so far I don’t know whether it is nominal or maximum voltage). That’s all the information I can get about the battery from this manual
(link: http://gb.e-guide.renault.com/sites/default/files/pdfs/eng/X09/Twizy-913-12_ENG.pdf). I don’t know about other EV’s manual, but this one is ridiculous. It doesn’t tell anything about the ac voltage range (220 right?), energy, current drawn from the grid (it does tell me the protection = 16 A). I hope Renault upgrades it.
With that being said, I found a brochure from UK
(link: https://www.cdn.renault.com/content/dam/Renault/UK/brand-and-editorial/Brochures/Vehicles/twizy-brochure.pdf) that contains way more information regarding technical information than the manual itself (mind, a brochure!).
Battery’s information are:
Capacity = 6,1 kWh
Battery type = Lithium Ion
From 0 to 100% = 3,5h
Slow charge = 10 A
The AC voltage = 230 V (brochure from UK)
Now, let’s do the math. Usually, a lithium cell is about 4.2 V to 4.1 V maximum voltage
I found a video of a guy using a “power box” to hack/tune the Twizy. It could be seen, indeed, that the maximum voltage was at 4.135 V. Of course you don’t wanna over charge a lithium-ion cell, so probably the charger will charge up to 95 ~ 99%. Nevertheless, round up to 4.2 V.
In the video, it was shown the amount of series cells s = 14.
14 x 4.2 = 58.8 V. Which means, that the information that is given in the manual is apparently related to the maximum voltage of the battery pack, and not the nominal.
Searching even further, the Wikipedia says that the battery pack is supplied with LG Chem modules. Then I found this datasheet (link: https://www.s-power.cz/wp-content/uploads/lg-chem-resu-datasheet.pdf).
For a specific power module, it exactly states:
Energy 3.3 kWh
Capacity 64 Ah
Nominal voltage: 51.5 V
Voltage range: 42 to 58.8 V
Weight: 28 kg
So, in this case, my guess is 14 cells in series (14 x 4.2 = 58.8 V) and 22 cell in parallel (taken the Panasonic lithium-ion cell’s capacity = 2.9 Ah = > 64/2.9 = 22).
Considering all guesses are correct =>
6100/51.5 = 118.44 ah (Hopefully they have informed the energy (kWh) using the nominal voltage, and not the maximum voltage)
118.44/2.9 = 40.84 cells in parallel => 41 cell in parallel in the Twizy battery pack.
Total amount of cell = 14s x 41p . Can anyone confirm if this guess is correct? I really need to know the capacity of each cell from the Twizy.
Now, coming back to the brochure information:
Consider V ac = 220 V.
If it can charge from 0 to 100 % in 3,5h the amount of 6100 Wh
=> 6100/3,5 = 1742 W delivered to the battery considering power is constant.
Consider now efficiency of the power converter = 85%
=> 1742/0.85 = 2050 W. Therefore, the battery charger is designed to be able to operate at 2kW.
However, charging a battery uses 2 modes (constant current and constant voltage) and not constant power. So, there might be a peak power (Suppose 2.2 kW), which yields:
220 V x 10 A = 2,2 kW
Therefore, the information in the brochure (10 A - Slow charge) is related to the current drawn from the ac grid, and not the battery!
2200*0.85 = 1870 W delivered to the battery at peak power condition.
1870/51.5 = 36.31 A (avg) = constant current to the battery pack.
Iconstant = 36.31/41 = 0.885 A. for each cell
Usually, constant current Iconstant charges between 0.5C. The Panasonic example was 0.7 C
=> C = 0.775/0.5 = 1.55 Ah
C = 0.775/0.7 = 1.1 Ah
You see, it is important to know the capacity of each cell to be able to manage the power the way you want(charge quicker, discharger quicker… and so on).
Which means that my previous guess on the capacity C = 2.9 Ah is not very correct…
Well, these were all guesses that I hope someone can help me or at least I hope it can be helpful for the community