Hi guys - its me asking inane questions again.

Why are lipos manufactured at 3.7volts  and nimh manufactured at 1.2 volts ?

I mean why can't they manufacture at some round number to make life easier
for the world.

Could someone care to enlighten please ?

Isn't that directly driven by the chemistry of the materials  used inside (electrolyte etc) ? 

It does not look like the quantity of the materials allow for change in nominal/peak voltages, which is why one can only vary the C rating and mAH capacity with the quantity (to some extent, the type of materials). And when there is too much difference in the material used, you end up with another type of battery (like LiFe), where again the voltage parameters are sort of fixed for that material combination.

In short, cell chemistry determines the voltages.

Quote from: anwar on September 27, 2011, 11:13:01 AM

In short, cell chemistry determines the voltages.

That is absolutely correct.

Anwar, I used the "quote" specifically because of the single line that was of relevance.

You are worried about our (sometimes over-zealous?... including myself) "quote police brigade"

YES!

Yes I had imagined it had something to do with cell chemistry

- what exactly ? could someone go into more detail ?

Hmm... wonder how one can explain it further other than that it is the "natural behavior" (i.e. "property") of particular materials.

PS: Kinda reminds me of the teacher enacted by mimicry artists in the olden days in Kerala. The teacher asks "Why do ships stay afloat?".  No student has the answer.  Finally one of the students asks the teacher to explain "why a ship floats".  The teacher asks "When you were a toddler, did you see any ships?".  The boy goes, "Yes Sir!".  Teacher asks "Were they floating back then?". The boy agrees. The teacher goes "THAT IS HOW THEY ARE... THEY ALWAYS FLOAT!"

Ok - Let me ask a few specific ones to satisfy my curiosity..

what are the chemicals used ? - any variants ? isotopes and such ?
what ratios ?

can one get an equation perhaps ?

I tried searching - but no luck

as the name states that what the battery contains eg: LiPo- Lithium polymer, NiCd- Nickel cadmium, NiMh- Nickel metal hydride. etc

the voltage in theoretical terms is the called EMF ( Electro-motive force) , the force at which the battery drives one charge(electron) around the circuit.

with different chemicals used and the reactions giving loose electrons out (current)changes along with the composition.
as the current  builds up. the force needed to drive the charge increases thus to balance it the voltage increases.
when the charge is used in form of work done(motor in our case), the charge reduces and hence the force required also decreases hence the voltage also decreases.

more info: http://en.wikipedia.org/wiki/Battery_(electricity)

Soikatda, add a LiPO (3.7v) with a NiMH (1.2V) and you get 5 Volt (4.9V) cell. Just need to select same AH and same C Capacity and self discharge rate . Cell chemistry do the trick now.

Cell EMF depends on the electrochemical property of the chemical and active materials of the cell and remains constant till last molecule exist for reaction. Now the reaction rate depends upon the ion concentration and does the internal resistance also. So, internal resistance is the culprit for lowering the voltage theoretically. And during overcharging, when the reaction is over, the excess current just charges like a Capacitor, and the voltage shows little bit higher than EMFs, Sometimes, the excess power does other complex reaction and the power ultimately results into heat.

But the need of us is to make a cell that can give more power with less cell and at higher current rate and at LOWER COST too. You can make using different combination and different polymer and some other advanced technics (Like Porus silicon and Polymer Electrochemistry) the cell of your required voltage, but the cost, utility will determine that it will be practical or using regular battery with voltage converter will be easier.

Ultimate COST - UTILITY - DEMAND will determine the manufacturing of the cell you need.

So, for 12 volt, you can use
3S LiPO,
9NiMH,
10NiCD,
6S LeadAcid, and
8 Alkaline or Zn-Cl battery.

The utility - cost will determine, which you choose, choice is yours.And this determine the research world too. Funny na !