Re: li-poly battery protection for high cell count packs

D from BC <myrealaddress@xxxxxxxxx> wrote in
news:9emme39bjegqqs7tst4rs3gnc3hitj11ol@xxxxxxx:

On Sat, 15 Sep 2007 11:40:02 +0800, budgie <me@xxxxxxxxxxx> wrote:

On Fri, 14 Sep 2007 20:15:34 GMT, D from BC <myrealaddress@xxxxxxxxx>
wrote:

On Fri, 14 Sep 2007 18:22:02 -0000, Michael <nleahcim@xxxxxxxxx>
wrote:

Hi - in the near future I will need to implement a circuit that
monitors and protects a lithium polymer battery pack that has about
12 cells in series in it. There are alot of special purpose chips
designed to protect lithium polymer battery packs consisting of 2-4
cells - but I've never seen anything for this many cells. Does
anybody know of such a beast?

If not - how best would I go about making this? Size is a huge
factor, cost is not nearly as much of one.

Thanks!

-Michael

I'm no expert on Lith batts..
But how about a temperature sensor on each battery.
12 thermistors + 12 comparators + 12 input OR gate + shut down
electronics. Bulky but dodges uC's.

(I hope I don't get too beat up on SED for that suggestion. :| )

you probably should ;-)

The protection modules guard against a number of conditions.
Temperature can be one, but is not always included. The most
important functions of these modules are undervoltage, overvoltage,
excessive discharge current. Often excess charge current sensing is
also included.

Oh crap...
Ok..how about
12 differential amplifiers for V monitoring on each battery.
+
12 I sense resistors..
+
12 differential amplifiers for I monitoring on each battery.
+
A 24 to 1 analog demux to an ADC luckily all in a uC.

But I think this can be reduced..

(2) 12 to 1 analog demux's for differential input A
(2) 12 to 1 analog demux's for differential input B
(1) differential amplifier used for voltage monitoring.

Current sensing will need only 1 12 to 1 analog demux.
(One of the voltage sensing channels will be used as a common. )
So..Only one differential amplifier for current monitoring.

It starts off with something like that....lots of channels anyways...


D from BC


You don't need differential anything, just a number of single ended A/D
inputs connected to each node, calculating the voltage across any two
nodes in software. Since the batteries are in series, there is only one
current path to read, per bank.

If the packs are externally charged, it could be rigged to charge in
series paralell, and discharge in series.
.

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