[ydsouza]

Hey Guys,
I'm new to the forum. I'm building a battery pack for my EV, i need a 48V 100Ah pack which can discharge at 3C. I plan on using NMC batteries for the same. I plan on making 5 packs of 48V 20 Ah each and then connecting them in parallel(yes, i know 13s NMCs will give me 46.8v but that's ok with my motor controller) . My questions are:-
1. I will be needing 1 bms per pack. That means I'll be needing 5 bms' in total. Am i right or i need to consider something more than this?
2. What do i need to consider while selecting a bms (as per my calculations i will need a 13s 60A(to handle 3c discharge) bms)?
3. Are bms' battery chemistry specific?
4. What do i need to consider while selecting the charger, in my case I'll be needing a 54.6v charger.
5. Can anyone suggest me a good, reliable BMS or a BMS vendor, one that's not very expensive, perhaps one which is tried and tested by any of yall?

Thanks.

 

[Solarsail]

Hi - Some of these issues are discussed in the thread http://www.diyelectriccar.com/forums/showthread.php/18650-13s10p-project-48v-x-34ah-188618.html

I would suggest going 14s because that gives you more options to expand vertically.

1- depends on config. Let's assume you are using 20Ah pouch cells, then 13s5p would need one 300A BMS, while 5p13s would need 5x 60A BMS.

2- the BMS should obviously have protection. At 300A total, you would want to go to the 5x BMS config, which is 5p13s with 60A BMS. Or if you are bold enough, go to 13s5p with boards wired in parallel. I am not sure if it is possible to put BMS boards in parallel - something may croak. I found this BMS on eBay but it is only good to 45A, so you would need 7 of these in parallel with 13s5p.
https://www.ebay.com/itm/For-48V-13...642990?hash=item36166f8bae:g:Gv8AAOSw3ZRY9Utg

3- BMS are voltage specific, so LFP and NMC are different BMS. But within the varieties of NMC and NMA and LiPoly, I am not sure if BMS becomes specialized. Some newer 4.35V LiPoly would need their own BMS.

4- The charger can be a separate charger and power supply. You would need a step-up 60V CCCV charger, and let's say a 48V/36V/24V power supply. Or an integrated unit. Time to charge - thus a 0.9 kW charger will take 6 hours - can put multiple in parallel, I believe.
https://www.ebay.com/itm/BST900W-DC...d=401320880903&_trksid=p2047675.c100005.m1851

5- eBay and AliExpress stuff is cheap - and are used in Chinese ebikes, but quality can be questionable.

 

[ydsouza]

Thank You so much Mr. Solarsail. I appreciate your time and the help.

"I would suggest going 14s because that gives you more options to expand vertically."
could you please elaborate on this please, i didnt quite get it.

 

[Solarsail]

Well, this is my own theory. It seems propulsion motor voltage ratings are 48V or a multiple of 48V. 48V can be either 13s or 14s. 96V would be two of these in series and so on.

On the other hand EVs from auto manufacturers are 96s or 345.6V, which is not a multiple of 48. So let's say you build a number of 48V packs which will give you 48V and 96V and 144V. But what if you want to get 345.6V or 96s by putting them in series? Then if you had chosen 13s as your building block, and you put 7 of them in series, you only get 91s and then you need to build a 5s for a total of 96s. However, if you choose 14s, then 7x 14s is 98s, and you can always reduce the voltage by undercharging to match 96s. My pack is intended to address such a possibility, so I have chosen 14s.

 

[ydsouza]

Ok, Got it,, Thank you so much Mr. Solarsail.