[Trac #596] inconsistent battery charge state indications

[Zarro Boogs per Child]

#596: inconsistent battery charge state indications
------------------------------------+---------------------------------------
 Reporter:  Quozl                   |        Owner:  mfoster
     Type:  defect                  |       Status:  new    
 Priority:  blocker                 |    Milestone:  BTest-2
Component:  hardware                |   Resolution:         
 Keywords:  ray.tseng at quantatw.com  |  
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Changes (by jg):

  * keywords:  => ray.tseng at quantatw.com
  * owner:  ray.tseng at quantatw.com => mfoster
  * component:  embedded controller => hardware
  * priority:  low => blocker

Old description:

> All three units were taken for a one hour 40 minute walk over outback
> terrain.  During the walk, psu_0/capacity_percentage was logged along
> with wireless signal and noise level.  The other battery monitoring
> parameters were not logged.  Each unit experienced the same usage pattern
> as part of a structured coverage test, beginning with fully charged
> battery, according to the monitoring parameters.
>
> On unit Quozl 3, the battery capacity remained at 100% throughout, and
> when it was returned to AC adaptor power showed a green battery light,
> and the battery status showed "full".
>
> On unit Quozl 2, the battery capacity declined as expected, and when
> returned to AC adaptor power showed a red-orange battery light, and the
> battery status showed "charging".
>
> On unit Quozl 1, the battery capacity declined as expected, and when
> returned to AC adaptor power showed a light-orange battery light, and the
> battery status showed "charging".
>
> All three units are on build 193 with A62 firmware.

New description:

 All three units were taken for a one hour 40 minute walk over outback
 terrain.  During the walk, psu_0/capacity_percentage was logged along with
 wireless signal and noise level.  The other battery monitoring parameters
 were not logged.  Each unit experienced the same usage pattern as part of
 a structured coverage test, beginning with fully charged battery,
 according to the monitoring parameters.

 On unit Quozl 3, the battery capacity remained at 100% throughout, and
 when it was returned to AC adapter power showed a green battery light, and
 the battery status showed "full".

 On unit Quozl 2, the battery capacity declined as expected, and when
 returned to AC adaptor power showed a red-orange battery light, and the
 battery status showed "charging".

 On unit Quozl 1, the battery capacity declined as expected, and when
 returned to AC adaptor power showed a light-orange battery light, and the
 battery status showed "charging".

 All three units are on build 193 with A62 firmware.

Comment:

 Mary Lou and I had noticed much lower battery life than one might expect
 (even giving the large power consumption of the CaFE FPGA, which will
 become a low power device in the next build as an ASIC).

 Mike Bove has measured a power consumption of approximately 7 watts
 at the moment (no power management work has been done to speak of,
 and CaFE is an high power consuming FPGA), when running idle.

 I sent mail yesterday on the topic, since we'd predict about a 3 hour
 life.

 Thanks for the report; a day or two earlier and you'd have beaten
 us to the punch!
                                         - Jim


 Here's the answer:


 Hi, Jim & Victor,

 The battery life is indeed WAY off, and the EC code is the primary
 contributor.  Just as you say, including the capacity that we are
 reserving for 2,000 cycles, the battery life should indeed be almost 3
 exactly hours.

 The pack capacity is 24.4 WH, and the current ON power without power
 management is ~7W.  The EC should be reserving ~14% of the pack's
 capacity, meaning that the effective capacity should be 21 WH.  If this
 were being done properly, the battery life would be 3 hours.  Instead, it
 is about 1/2 this long.

 The EC is reserving FAR more capacity than it should, plain and simple.
 The core problem is that the EC is currently computing the battery life
 from the battery sensor, rather than reading an actual gas gauge.  I
 learned only after the fact that the "gas gauge" chip chosen by Quanta and
 Gold Peak isn't a true gas gauge - it's just a
 voltage/current/temperature sensor.

 The battery sensor in the pack should be changed to a true gas gauge in
 the next build.

 Best Regards,
 MarkF

-- 
Ticket URL: <http://dev.laptop.org/ticket/596#comment:1>
One Laptop Per Child <http://laptop.org/>