Re: [EVDL] 24 cell BMS

[Lee Hart via EV]

Cor van de Water via EV wrote:

There may be reasons to have a large balancing current, but they escape
me.


1. To deal with cheap old mismatched cells.

2. To allow you to replace one cell without replacing the whole pack.
   The new cell is likely to be significantly different than the rest.

3. To stop a cheap, stupid, or non-networked charger that hasn't cut
   back its current from overcharging cells.

4. So it can balance faster, as when commissioning a new pack with
   cells that arrive at different states of charge.

5. To be able to balance *while driving*. If you top-balance and the
   cells have different amphour capacities, they will go dead at
   different times. If the BMS can transfer charge from stronger
   cells to weaker ones, then you can increase the effective capacity
   of the pack, and thus your range.

That said... I don't think this particular BMS can do any of these 
things. It does not appear to have any way to deal with the heat 
produced by many cells bypassing at 1.5 amps, nor to be able to transfer 
charge between cells rather than just burning it up as heat.


--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com/balancer.htm
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Re: [EVDL] 24 cell BMS

[Cor van de Water via EV]

I am surprised at people wanting an extremely large balancing current
as that should never be needed unless your cells are either defective
(too high self-discharge in some cells) or you are drawing current
at inappropriate places (tapping the pack).
As an example, the Leaf BMS has 10 mA (0.01 Amp) balancing current
by using 430 Ohm balancing resistors.
All 96 series cells are only connected to the BMS which apparently is
guaranteed to draw extremely low current (everything is designed for
very low current in their BMS, even the voltage reference works with
microAmps of power supply) and the cell quality is apparently so good
that their self-discharge does not vary enough to need more than this
extremely low current.

There may be reasons to have a large balancing current, but they escape
me.

BTW, even though the Leaf BMS is part of the vehicle, it is
self-contained in the battery box with only OBD coming out for status
and it works and balances stand-alone as long as all 24 BMS front end
chips are powered (4 cells per chip). With the (free) Leaf Spy you can
monitor the BMS stand-alone, as long as you connect a Bluetooth ELM327
OBD interface.
There is a way to use the BMS on anything from 48 to 96 cell packs,
because the BMS has opto-isolation mid-pack, so you can overlap the BMS
inputs if you have less than 96 cells (but at least 48 cells). The only
thing you lose is the ability to break the pack midsection, unless you
add another opto coupler in the RS232 data line that daisy-chains all
front ends together.

Regards,

Cor van de Water 
Chief Scientist 
Proxim Wireless 
  
office +1 408 383 7626Skype: cor_van_de_water 
XoIP   +31 87 784 1130private: cvandewater.info 

http://www.proxim.com

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-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of ken via EV
Sent: Wednesday, July 27, 2016 11:02 PM
To: paul dove; Electric Vehicle Discussion List
Subject: [EVDL] 24 cell BMS

 I haven't see the prices yet but I see this as a Advanced version of
cell
log. with very good features.

Smart Balancer & BMS series

http://www.chargery.com/BMS24.asp it balances at 1.5 amps.!!

they have other smaller cells version also.

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[EVDL] 24 cell BMS

[ken via EV]

 I haven't see the prices yet but I see this as a Advanced version of cell
log. with very good features.

Smart Balancer & BMS series

http://www.chargery.com/BMS24.asp it balances at 1.5 amps.!!

they have other smaller cells version also.

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