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

[wes@xxxxxxx]

--- In photo-3d@xxxx, Brian Reynolds <reynolds@xxxx> wrote:
> Wes wrote:
> > --- In photo-3d@xxxx, "Dr. George A. Themelis" <drt-3d@xxxx> 
wrote:
> > > Yes, as Brian mentioned, the battery cells in stereo
> > > viewers are connected in series.  The voltages add up
> > > (1.5 + 1.5 = 3V) but the same (high) current goes through
> > > the system.  So if you are testing individual cells
> > > you should try higher currents (minimum of 0.5A).
> > > 
> > > George
> > 
> > If I were to test with a drain of .5 amp for an individual cell, 
that 
> > would be a drain of a full amp for two connected in series (by 
Ohm's 
> > law the currents also ad, or conversely, the current drain will 
be 
> > halved with only one cell in test).  I think that's getting a bit 
too 
> > hefty for most applications.  But what's handy about the chart is 
> > that you can extrapolate a fairly good idea of what to expect by 
just 
> > telescoping the chart out or compressing it depending on your 
current 
> > needs.  Of course, this can't be taken too far or the internal 
> > resistance of the cell will manifest itself more obviously in the 
> > form of a lower service voltage, and such.  But, thanks for the 
> > suggestion.
> > 
> 
> Ohm's Law (Voltage(V) = Current(I) * Resistance(R)) does not work 
that
> way.  It applies to the totals of a circuit (or the portion of a
> circuit under examination).  You'll note that there is nothing in
> Ohm's Law that describes how to total the contribution of components
> with regard to whether they are wired in parallel or serially.
> Kirchoff's Laws (and other rules) describe how to account for 
parallel
> and serial connections in a circuit.
> 
> Here's a viewer example.  The circuit is a 3 Volt battery and a 6 
Ohm
> bulb.  Based on Ohm's Law (I=V/R) the current in the circuit is 500
> milliAmps (0.5 Amp).  If we examine the battery, we find that it is
> made up of two 1.5 Volt cells in series (positive terminal connected
> to the negative terminal of the next cell).  The battery voltage is 
3
> Volts (Vb = V1 + V2).  The battery current (Ib = I1 = I2) is 500
> milliAmps.  In a serial circuit the same current flows through both
> components (in this case battery cells).
> 
> Hi Brian,

I really appreciate your having taken the time for such an 
explanation, and I agree.  But, I feel that I may have been 
misunderstood all along.  It was never a question of whether cells 
are used in series or in parallel.  With regard to the battery test 
chart, I mentioned that I had tested two cells of each kind.  
However, I did not test the two together in the same circuit.  I 
tested two at the same time, but each in its own holder, and each 
with its own matched five-ohm load, to save time.  Using Ohm's law, 
if, by your example, I solve for the current flow by dividing the 6-
ohm load you suggested into the supply of 3 volts you mentioned, 
then, of course we get .5 amps.  But, the same current does not flow 
with a supply voltage of 1.5 volts, when only one cell is being 
drained (6 ohms divided into 1.5 volts now gives a current flow of 
only .25 amps).  I hope that clears it up.  So, in my tests of one 
cell at a time under load (of 5 ohms), I simply mentioned that a 
drain of 300 ma. is fairly practical after all, since I was only 
testing one, and in an application of two cells in series, as in a 
viewer, (now 3 volts, instead of 1.5) the drain would then be 600 ma. 
(still using a 5-ohm load).

As I mentioned earlier, I realize there are far greater drains out 
there, such as the remote-control car I cited, wherein motors often 
having only seven or eight turns of coarse wire in the windings will 
get both the motor and the battery hot in the five or six minutes of 
run-time the battery can deliver.  But that's not in the realm of 
what's needed for a stereo slide viewer (thankfully).

Anyone for a slide viewer with a 3-volt, 30-watt bulb?  Maybe it 
could double as a hand-held projector by holding it up toward a 
screen upside down (and sticking a pair of polarizing glasses in 
front of it).  Thanks again, Brian.

Wes