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

On Mon, 17 Sep 2007 13:38:37 -0000, Michael <nleahcim@xxxxxxxxx> wrote:

On Sep 16, 2:04 am, budgie <m...@xxxxxxxxxxx> wrote:
On Sat, 15 Sep 2007 15:54:10 GMT, Gary Tait <classic...@xxxxxxxxx> wrote:

(snip)

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

in which case a readily available 4-cell chip would provide the basis for the
monitoring side of protection.

One complication is the readily available protection modules normally interpose
a series "switch" as their method of protection/intervention. For S/P charging
that would be fine, but for series discharge you would (probably) wind up with
N/4 series switches, all of which present a finite impedance, and which is sort
of suboptimal. Generally these switches can't be isolated from their driver
which ties them back to their group of cells, and the drivers can't readily
interface with a common switch.

How readily available are these chips? I had thought that I had seen
them before - but now I'm going through all the usual suspect's
websites and I'm turning up essentially nothing. The only chip I've
found that looked reasonable was the MAX1666: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2022
- but that part appears to hold true to the Maxim standard - it's not
available - anywhere.

Ironic, that old maxim ;-)

As an aside, we used a Maxim controller chip in one lithium charger design, and
had the devil's own job getting supplies. Wound up using an offshore supplier
who could source them well ahead of the next Maxim scheduled run. It appears
that maxim's policy is to design/develop/prototype achip and then announce it.
When/if enough orders are to hand, a run will commence. until then, it is
really vapourware.

On protection modules, we looked at TI/ Benchmarq but wound up using
preassembled modules (Powerlogics PLM4005) from a Korean fab, the Powerlogics
PLM-4005. (www.powerlogics.co.kr) which used a MM1294A from Mitsumi and a
Vishay S14431DY power MOSFET as the series switch.

From my notes and their doco at the time:

"The PLM-4005 is designed to open circuit the pack terminals in the event of:
· undervoltage (on discharge) - <2.35 +/- 0.1V [hysteresis 0.7V]
· overvoltage (on charge) - >= 4.35+/- 0.05V [hysteresis 0.2V]
· excess pack current (charge or discharge) - > 5 +/- 0.5A.
· voltage difference between cells exceeding (sorry, indecipherable)
These parameters are not user adjustable.

The protective action of the module is non-destructive. The connection between
cells and external pack terminals is re-established when the condition causing
the intervention is no longer "out-of-bounds". To achieve this, the module
continues to monitor the external load condition and cell voltage while the
"open circuit" condition exists."

Another lead was the PS401 from Powersmart.

One version we considered but never actually evaluated (if the difference makes
sense) was from International Components Corporation. Another used the Mitsumi
MM1414 chip, might pay to look at their range if you are planninga possible
build of your own module.

I hope those give you some leads.
.

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