li-poly battery protection for high cell count packs

You can do it with a uC and 12 channels A2D. The important thing is to monitor shorts in any one cell and disconnect charging. Otherwise, you have a good detonator.

I'm no expert on Lith batts.. But how about a temperature sensor on each battery.

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

D from BC

There is an application note on the Maxim site, for using their single cell monitor IC, to monitor multiple cells. The same techniques can be applied using one of the four cell monitor IC's, to handle larger packs. Some applications using packs with large numbers of cells like this, actually split the pack, for charging, so having the pack in (for instance) three 'four cell' modules, and charging these with their own monitor IC. This is also useful, since it allows charging off lower voltages. Most people doing this 'in circuit', will almost certainly use a cheap micro, to do the whole job.

Best Wishes

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

• 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

D from BC wrote in news: snipped-for-privacy@4ax.com:

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.

:P ... Ok...I'll try again ..How about?

Let's say each battery is individually charged so that each cell current can be monitored.

---cell1-+-Rsense-+ | | | Com Vcheck Charge Isense

ewwww.... This looks aweful... Glad I don't have this problem... :P

D from BC

(snip)

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.

I don't think this is true. If I used 1% precision resistors for my voltage dividier, my measured voltage would be accurate to +-500mV or so, assuming a perfect ADC with infinite resolution.

-Michael

future I will need to implement a circuit that

I can't seem to find this app note. Can you point me to it? Thanks,

-Michael

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:

- but that part appears to hold true to the Maxim standard - it's not available - anywhere.

-Michael

interpose

charging

sort

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.

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) - = 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.