14s bms help

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cheetahgod
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14s bms help

Post by cheetahgod » Dec 04, 2017 12:38 am

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-fo ... aQeHUZzbrw
alexiexpress:
https://www.aliexpress.com/item/51-8V-3 ... 15913.html

cheetahgod
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Re: 14s bms help

Post by cheetahgod » Dec 04, 2017 6:23 pm

Anyone?

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alec
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Re: 14s bms help

Post by alec » Dec 04, 2017 7:02 pm

In my opinion, BMS's are useless. I'd manually read voltage of each cell and discharge/charge as needed to balance.
"Black Widow" Greyborg [v.2] | Cromotor [v.3] | Greentime 1440 | 24s EIG cells 12kW peak (thread coming soon)
Project(s) in works: FatCON (& DIY Serial/USB to Bluetooth)

cheetahgod
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Re: 14s bms help

Post by cheetahgod » Dec 05, 2017 1:18 am

then why do a lot of people use them?

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cycborg
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Re: 14s bms help

Post by cycborg » Dec 05, 2017 1:05 pm

alec wrote:
Dec 04, 2017 7:02 pm
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????

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cycborg
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Re: 14s bms help

Post by cycborg » Dec 05, 2017 1:07 pm

cheetahgod wrote:
Dec 04, 2017 12:38 am
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-fo ... aQeHUZzbrw
alexiexpress:
https://www.aliexpress.com/item/51-8V-3 ... 15913.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.

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alec
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Re: 14s bms help

Post by alec » Dec 05, 2017 1:45 pm

cycborg wrote:
Dec 05, 2017 1:05 pm
alec wrote:
Dec 04, 2017 7:02 pm
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.
"Black Widow" Greyborg [v.2] | Cromotor [v.3] | Greentime 1440 | 24s EIG cells 12kW peak (thread coming soon)
Project(s) in works: FatCON (& DIY Serial/USB to Bluetooth)

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fechter
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Re: 14s bms help

Post by fechter » Dec 05, 2017 3:30 pm

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.
"One test is worth a thousand opinions"

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cycborg
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Re: 14s bms help

Post by cycborg » Dec 05, 2017 3:57 pm

fechter wrote:
Dec 05, 2017 3:30 pm
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.

cheetahgod
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Re: 14s bms help

Post by cheetahgod » Dec 06, 2017 2:07 am

Im thinking of buying the one on ebay as it is cheaper and higher amp rating

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fechter
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Re: 14s bms help

Post by fechter » Dec 06, 2017 8:59 am

cycborg wrote:
Dec 05, 2017 3:57 pm
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.
"One test is worth a thousand opinions"

cheetahgod
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Re: 14s bms help

Post by cheetahgod » Dec 06, 2017 10:32 am

Yeah bought the 45a one on ebay

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