14s bms help

cheetahgod

1 mW
Joined
Dec 1, 2017
Messages
16
Hi im making my own 14s 18650 battery. I bought 102 18650 cells with 2200mah samsung. I plan to use this on a 1000w electric bike that has a max continous draw of 25a. I want to get the electric bike kit mag pie from golden ca motors.. Which bms should I buy?
ebay:
https://www.ebay.com/itm/BMS-PCB-PCM-for-50-4V-14S-Li-Ion-Battery-Pack-45A-Drain-Rate-w-Balance-Function/172971369981?hash=item2845e5a5fd:m:mXMtKdEkl9LiKaQeHUZzbrw
alexiexpress:
https://www.aliexpress.com/item/51-8V-30A-14S-PCM-used-for-51-8-V-lithium-ion-battery/1206415913.html
 
In my opinion, BMS's are useless. I'd manually read voltage of each cell and discharge/charge as needed to balance.
 
alec said:
In my opinion, BMS's are useless. I'd manually read voltage of each cell and discharge/charge as needed to balance.

Have you shared this advice with Tesla, Nissan, Chevy, Zero, Bosch, every laptop manufacturer, every cell phone manufacturer, etc.? If not, why are you withholding this wisdom from the world????
 
cheetahgod said:
Hi im making my own 14s 18650 battery. I bought 102 18650 cells with 2200mah samsung. I plan to use this on a 1000w electric bike that has a max continous draw of 25a. I want to get the electric bike kit mag pie from golden ca motors.. Which bms should I buy?
ebay:
https://www.ebay.com/itm/BMS-PCB-PCM-for-50-4V-14S-Li-Ion-Battery-Pack-45A-Drain-Rate-w-Balance-Function/172971369981?hash=item2845e5a5fd:m:mXMtKdEkl9LiKaQeHUZzbrw
alexiexpress:
https://www.aliexpress.com/item/51-8V-30A-14S-PCM-used-for-51-8-V-lithium-ion-battery/1206415913.html

I'd go with the second one. ANNPower has been around for a while on Aliexpress whereas the Ebay sellers pop up and disappear with regularity. Specs look fine for your application.
 
cycborg said:
alec said:
In my opinion, BMS's are useless. I'd manually read voltage of each cell and discharge/charge as needed to balance.

Have you shared this advice with Tesla, Nissan, Chevy, Zero, Bosch, every laptop manufacturer, every cell phone manufacturer, etc.? If not, why are you withholding this wisdom from the world????

You're entirely valid! It's just my opinion, as a novice and non-professional. I'm really OCD with my cells and prefer to charge, discharge, and balance manually. It's not a hands-off solution. It's not easy or quick. Tesla, Nissan, Chevy, Zero, Bosch, every laptop manufacturer, etc. use BMS's to handle the average end user's abuse. Your sarcasm made me smile though.
 
Either one of those look like they should work fine but personally, I'd go for the first one since it has a higher current rating. In theory, your controller won't draw more than 25A so a 30A rated BMS would be OK, but in the real world, the controller often has a little "overshoot" on the current limit when you are accelerating which might make the BMS trip.

I've had this happen on a couple of them but just added shunt resistors to the BMS board until it stopped tripping.

BTW: I highly recommend using a BMS. I've had numerous pack failures where the BMS prevented further damage or fire.
 
fechter said:
In theory, your controller won't draw more than 25A so a 30A rated BMS would be OK, but in the real world, the controller often has a little "overshoot" on the current limit when you are accelerating which might make the BMS trip.

I've had this happen on a couple of them but just added shunt resistors to the BMS board until it stopped tripping.

If I understand the specs correctly, the trip current is 100 A, whereas 30 A is the continuous operation rating.
 
cycborg said:
If I understand the specs correctly, the trip current is 100 A, whereas 30 A is the continuous operation rating.

That should be good. I didn't read carefully enough.
 
How did this design workout? I'm also running the 1000w GM magic pie and looking at upgrading my battery.
 
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