why 1.2V on rechargeabels

Why does a rechargeable cell only supply 1.2V and not 1.5V like regular
cells?

 

Because that's the terminal voltage of that kind of battery technology.

Ni-Cad and Ni-Mh 1.2V
Zinc-Carbon and Alkaline 1.5V
Lead-Acid 2.0V
Lithium (watch batteries)3.0V

 

The chemistry can be changed to create a voltage of 1.5V. Adding more (or
stronger) electrolyte will increase the voltage. I doubt the fact that
someone made the cell and it became 1.2V by coincidence. There must be a
reason for this standard

 

---
Top posting is usually a sign of rude and inconsiderate behavior.
Please don't top post.

Adding more electrolyte won't change the voltage. Adding a different
electrolyte or changing the plate materials will, but there are
compatibility problems like corrosion of the metals by the electrolyte
which creep up, rendering some systems useless for some applications.

There are also economic considerations like if it costs $1 to build a
1AH 1.5V secondary cell VS 25 cents to build a 1AH 1.2V secondary
cell, guess what? If you need 6V either buy an extra cheap cell to
get the battery voltage up to 6V or design your stuff to work on 4.8V
if you can only fit 4 cells in the box.

1.2V is not a standard, per se, it's a consequence of the combination
of metals and electrolyte used and is determined by nature. We just
found it, that's all.

 

almost as bad as not trimming your posts lol


Tim

 

John:
I'm no chemist, and certainly no electrochemist, but I had the idea
that the voltage was determined more-or-less entirely by the
electrodes, given an "adequate" electrolyte (whatever that may be).
I seem to recall seeing tables of voltages for electrodes, with no
mention of electrolyte. Does electrolyte really affect the voltage
(other than in a pathological case), or is it more related to other
issues like longevity, current capacity, etc, etc. ??? Thanks!


Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

I had thought that the type of electrolyte made a difference, but I
was wrong in that it's not the electrolyte itself which makes the
difference but, I believe, its concentration. As I understand it, as
long as you've got the same concentration of ions capable of giving up
electrons in a solution of HCl and water as you do with, say, NaOH
and water, the voltages on the metals will be the same. I think the
trick is finding a set of metals for the electrodes and an electrolyte
that won't eat them up when there's no load on the battery...

Here's a good link:

http://www.tu-darmstadt.de/fb/ms/student/fs/german/lab/w10/mse10-1.htm

Bill Beaty also has a nice description of the process somewhere, but I
lost it... :-(