OT: Cameras, cameras, cameras.. (was Re: Lightbulb police? ...)

Dave Dunfield dave09 at dunfield.com
Fri Jun 11 10:03:42 CDT 2010


> > I find rechargeable batteries to be a pain in gneeral. Unless it's
> > something I'm using all the time, the self-discharge means they're
> > genrally pretty flat when I want to use the device. And then I have to
> > want for a considerable time for them to recharge. For stuff I don't have
> > to carry around I prefer to plug it into the mains.
> 
> Self-discharge isn't really a problem with Li-(ion,polymer) and the 
> "hybrid" NiMH technologies (e.g. Eneloop). Generally speaking I get more 
> use out of my box of Eneloop batteries even though they have a lower 
> rated capacity than a similar set of Energizer NiMHs.

My experience with digital cameras that operate on AA batteries is that
the problem is not so much self-discharge as it is poor design. (This
is also true of many other products)

They design the cameras to run on AA batteries - marketing says it has
to shutdown gracefully when the batteries run out - and they design a
low battery threshold based on 1.5v AA alkaline batteries. Then when they
realize it hogs so much power it only takes 3 shots on dry cells, they
spec. high capacity NiMh cells - which are nominal 1.2v per cell.

I have tested:

Minolta Dimage 7Hi - recommended to use NiMh cells (set came with it),
takes 4 cells (nominal 4.8v), measured low battery threshold is about
5.2v.

Two Cannon A520s - recommended to use NiMh cells, takes 2 cells (nominal
2.4v), measured low battery threshold is about 2.6v.

Hp M(something or other - it's gone now) - recommended to use NiMh cells,
takes 2 cells (nominal 2.4v), measured low battery threshold is about
2.7v.

Sony F42 flash - takes 4 cells (nominal 4.8v), measured low battery
threshold is about 5.1v.

Both the Dimage and the A520 were reviewed to have "excellent battery life"
- the reviews say you can charge a set of cells, and then shoot "all day".
Which is mostly true.

However when you turn it on a morning or two later, after the cells have
settled down to their nominal 1.2v level, they shut down saying the
batteries need to be replaced. In fact this happens even if you didn't shoot
anything - just install freshly charged cells and wait a couple of days.

But... I can take the "dead" cells out of the cameras, and put them in
my 2m handheld - a fairly high current draw device when transmitting,
and they will run it for weeks. I tested once taking the "dead" cells
from my Dimage and drawing a couple hundred ma from them - they lasted
nearly 10 hours - ie: nearly the full capacity of the cells.

NiMh calls when freshly charged exhibit 1.3-1.4v/cell, however they settle
fairly quickly to 1.2v - even if not being used... then the voltage remains
is nearly flat until the cells are depleted, at which point they drop
rapidly. Long term shelf life is poor due to self-discharge, however in my
experience your camera will reject them long before this should be a factor.
Self-discharge takes months, not days.

Hybrid cells like eneloop help with self-discharge, and do slow the
initial drop which makes them more useable in a camera ... but the fundamental
problem remains - the device simply was not designed for 1.2v cells and
shuts itself off when it things the "standard batteries" are getting low.
When my A520 says to replace the eneloops, they are still just at the top
of their discharge curve.


Slight relevence to old computers: Most of the photos on my site were taken
with the Dimage (it's very good in indoor low-light conditions - I got it free
because the original owner "couldn't keep it in batteries")... I struggled for
a while charging batteries every session, but since most of my photos are
taken at a single location, it was easy to provide a power supply and it
hasn't caused me any trouble since.

--
dave09 (at)    Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com            Classic Computers: http://www.classiccmp.org/dunfield/



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