14s bms help

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cheetahgod   1 mW

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14s bms help

Post by cheetahgod » Dec 04 2017 12:38am

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   1 mW

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Re: 14s bms help

Post by cheetahgod » Dec 04 2017 6:23pm

Anyone?

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alec   10 W

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Re: 14s bms help

Post by alec » Dec 04 2017 7:02pm

In my opinion, BMS's are useless. I'd manually read voltage of each cell and discharge/charge as needed to balance.
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cheetahgod   1 mW

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Re: 14s bms help

Post by cheetahgod » Dec 05 2017 1:18am

then why do a lot of people use them?

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cycborg   1 kW

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Re: 14s bms help

Post by cycborg » Dec 05 2017 1:05pm

alec wrote:
Dec 04 2017 7:02pm
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   1 kW

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Re: 14s bms help

Post by cycborg » Dec 05 2017 1:07pm

cheetahgod wrote:
Dec 04 2017 12:38am
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   10 W

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Re: 14s bms help

Post by alec » Dec 05 2017 1:45pm

cycborg wrote:
Dec 05 2017 1:05pm
alec wrote:
Dec 04 2017 7:02pm
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.
❝ With great power comes an even greater PG&E bill.
12kW+ Greyborg, Cromotor V3, SSC96150
sabvoton.wire.bike [unofficial user's guide]
wire.bike [personal projects]

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fechter   100 GW

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Re: 14s bms help

Post by fechter » Dec 05 2017 3:30pm

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   1 kW

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Re: 14s bms help

Post by cycborg » Dec 05 2017 3:57pm

fechter wrote:
Dec 05 2017 3:30pm
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   1 mW

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Re: 14s bms help

Post by cheetahgod » Dec 06 2017 2:07am

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

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fechter   100 GW

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Re: 14s bms help

Post by fechter » Dec 06 2017 8:59am

cycborg wrote:
Dec 05 2017 3:57pm
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   1 mW

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Re: 14s bms help

Post by cheetahgod » Dec 06 2017 10:32am

Yeah bought the 45a one on ebay

Capedbandit   1 µW

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Re: 14s bms help

Post by Capedbandit » Aug 17 2018 7:52pm

How did this design workout? I'm also running the 1000w GM magic pie and looking at upgrading my battery.

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