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From: SMS on 8 Jul 2010 21:55
On 08/07/10 6:42 PM, MothboyHunter wrote:
> In article<p4sc36loqs36jnan7ml9hinhd8hok0k68i(a)4ax.com>,
> TomTom<ttom697921(a)hotmail.com> wrote:
> I guess we should be thankful this is only your third nym shift in this
> and it is nice to see a new one "TomTom" added to the mix. Some of those
> others were getting over used.
Is Garmin next? or Magellan?
From: Outing Trolls is FUN! on 8 Jul 2010 22:04
On Thu, 08 Jul 2010 18:42:37 -0700, MothboyHunter
>In article <p4sc36loqs36jnan7ml9hinhd8hok0k68i(a)4ax.com>,
> TomTom <ttom697921(a)hotmail.com> wrote:
>I guess we should be thankful this is only your third nym shift in this
>and it is nice to see a new one "TomTom" added to the mix. Some of those
>others were getting over used.
What? No information about cameras, camera gear, nor photography from you?
Ooooops! The MothboyHunter troll trimmed groups, typical signs of 100% pure
troll. Must restore groups.
From: David J Taylor on 9 Jul 2010 02:20
"John Navas" <spamfilter1(a)navasgroup.com> wrote in message
> Attention students -- note how SMS is trying to quietly, hoping nobody
> will notice, change his story on measuring remaining Li-ion capacity as
> a result of my pointing out the basic nonsense he had posted in the
> first place, a classic example of Baloney Maximus.
Not much of an encouragement to learn from you, then? Do you not praise
the student who learns rather than disparage them?
From: SMS on 9 Jul 2010 09:58
On 08/07/10 11:20 PM, David J Taylor wrote:
> "John Navas" <spamfilter1(a)navasgroup.com> wrote in message
>> Attention students -- note how SMS is trying to quietly, hoping nobody
>> will notice, change his story on measuring remaining Li-ion capacity as
>> a result of my pointing out the basic nonsense he had posted in the
>> first place, a classic example of Baloney Maximus.
> Not much of an encouragement to learn from you, then? Do you not praise
> the student who learns rather than disparage them?
LOL, no story is changing. You can look at the various application notes
from the companies that make fuel gauge chips and they will all explain
that capacity is a function of mainly of voltage, with dependencies on
temperature, and discharge rate. They will even have graphs showing the
voltage versus capacity at different discharge rates and temperatures.
This is one of the ways the temperature sensor inside a Li-Ion pack is used.
If you Google "li-ion fuel gauge application note" you can find plenty
of evidence that what I wrote is correct (and that what Navas believes
is wrong--as usual), not only on fuel gauging, but on self-discharge.
"SOC�Because of a strong correlation between SOC and OCV for particular
Li-ion battery chemistry, the SOC can be estimated from the OCV of the
battery. The OCV I <sic> measured when the cells are in relaxation mode,
which is defined as the state of the battery when its current is below a
small threshold (such as 10mA) and when the cell voltage is stabilized."
For self-discharge rates, the Maxim app note at
"http://www.maxim-ic.com/app-notes/index.mvp/id/3958" has a table that
shows the following:
Table 1. The Self-Discharge Rates of Common Battery Types
Lead-acid 4% to 6%
NiCd 15% to 30%
Lithium 2% to 3%
For a camera pack that lacks a CPU for coulomb counting, this rate is
accurate, and actually it's incorrect to call it self-discharge for
Li-Ion batteries, it's actually a combination of two things, 1) the
voltage monitoring circuit uses some power all the time, and 2) a
fully-charged Li-Ion pack loses about 20% a year of capacity.
BTW, this Maxim application note also includes a nice chart, figure 5,
that shows the linear decline in voltage of a Li-Ion cell for most of
the capacity, i.e. an 8AH cell has a linear decline between around 1AH
and 7AH (depending on the discharge rate). They also state that using
solely voltage to measure capacity "purely voltage-based monitoring is
unlikely to provide charge-level accuracies better than 25%." That's why
you need to also know the discharge rate (well characterizes in a
digital camera, and the temperature (monitored via a temp sensor in the
While coulomb counting (keeping track of coulombs-in (during charging)
and coulombs-out (during discharging), combined with voltage and
temperature monitoring (along with keeping track of charge cycles and
age) is preferred for the most accurate gauging, this is not done in
most camera batteries because of the cost. It's done in consumer
products like the iPhone which uses a smart fuel gauge chip.
The problem with NiMH cells is that the voltage difference between 90%
charged and 20% is nearly flat. You would need a set of very accurate
voltage references to use with comparators and A/D converters to
accurately gauge NiMH and the other types of AA batteries that can be
used in the low end cameras that use AA batteries. That's not going to
happen in a $100 camera. Even the SX20IS, probably the best super-zoom
on the market, does not have a way to set the type of AA battery being
used. If you install CHDK then you can set some voltage thresholds which
give you more information on the state of charge, but it's still
dependent on voltage.
The MB-D200 vertical grip for the Nikon D200 can take six AA batteries
or two EN-EL3E batteries. In order to ensure a more accurate battery
level indicator, there is a way to tell the camera which type of
batteries you are using, Li-Ion, or one of four types of AA batteries
(all of which have different characteristics).
I've updated the web site "http://batterydata.com/" with more
information on how fuel gauging works. It's been one of my areas of
expertise over decades in the semiconductor industry.