Re: [photo-3d] Ni-MH for Viewers

[Brian Reynolds <reynolds@xxxxxxxxx>]

I'm catching up after being away for a while.

Pixschack@xxxxxxx wrote:
> Has anyone tried NI-MH D cells for viewers like the red button or similar?  
> Are they less bright than alkaline?  Do they last?
> 

I haven't used NiMH batteries in a viewer, but I did just buy a
charger and batteries for a digital camera my wife and I received as a
gift.  I got a set of NiMH cells from Thomas Distributing
<URL:http://www.thomas-distributing.com/>.  I bought some PowerEX
1600mAH AA cells and the MAHA MH-204F microprocessor controlled
charger.  The charger seems to work fine.  I haven't used the
batteries much since I have a set of Lithium Ion (non-rechargeable)
batteries in the camera now.

There are a few things to know about batteries.

Batteries are made up of a collection of cells.  Most batteries in
consumer electronics are single cells (AAA, AA, C, D).  Cells of the
same technology (alkaline, lead-acid, NiCad, NiMH) have the same
voltage.  9 volt "transistor" batteries are actually made up of six
cells within the rectangular packaging.

Cells are rated by their capacity in units of Amp-Hours.  The simple
way to look at this is "how many hours will this cell deliver 1 Amp of
current?".  In reality the relationship is not quite linear.  A 1.2AH
battery may deliver .2A for longer than 6 hours, and may deliver 2A
for less than 36 minutes.  It depends on the type of electrical load
you put on the battery.  This is similar to reciprocity failure in
film.  The world is not as simple as we would like our formulas to be.

The different battery technologies have slightly different cell
voltages, but the big differences are in capacity and discharge rate
(how the cell delivers it's power).  NiCad and NiMH cells are
generally "better" (for various definitions of "better") than Akaline
cells.

If you are using rechargeable cells it is very important that you do
not overcharge the cells.  At best overcharging reduces the capacity
and useful life of the cell.  At worst you will cause a physical
failure of the cell (leak, bursting, etc.).  Charging is done by
applying a high voltage to the cell for a length of time.  After the
cell is at maximum capacity the cell can continue to be charged at a
lower voltage (a "trickle" charge).  A good charger will automatically
switch from a rapid charge to a trickle charge.  At the very least the
charger should automatically shut off after the cell has reached
maximum charge.

It is also important to keep all the cells that make up a battery
together when using and recharging them.  This insures that all the
cells are discharged and recharged at the same rate.  I currently have
two sets of cells (one with magic marker applied to one end so I can
tell them apart).  One set is in the charger and the other is in the
camera.  All four cells in each set get changed together.

NiCad batteries have a reputation for having a "memory" problem
(supposedly if you recharge them before they are fully discharged you
can not reach the full capacity of the battery).  The only detailed
technical explanation of this that I have seen actually points to
overcharging as the main problem.  Overcharging the NiCad cells caused
microscopic internal failures of the cells (described as small metal
whiskers).

NiMH batteries are supposed to lose about 1-2% of their charge per day
just sitting on the shelf.  If you keep a set in a trickle charger
before use you should be OK.

SR Batteries <URL:http://www.srbatteries.com/> makes really good NiCad
battery packs and chargers (in addition to some model airplanes) and
has good information on their site.

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
reynolds@xxxxxxxxx              | "Oooh!"
http://www.panix.com/~reynolds  |    -- Dexter and Dee Dee
NAR# 54438                      |       "Dexter's Laboratory"