More smaller batteries vs. Less bigger batteries

[Green_Primus]

~Hypothetical~
I want to convert my Mountain Bike to electric, I can get my hands on a D-cell sized Battery cartridge that holds 3 rechargeable AA's in series, If I take (lets say 2) 28" "water Pipes" With threaded ends (and caps) with a diameter wide enough to house the batteries/wires (for any leakage) wired in parallel with each other and strapped to the bike and fed into a motor (and any controls) Could this be done? I mean we're talking about 3x1.2v AA's, 3.6v per cartridge, about 2" tall, means ~14 per tube, 50.4v per tube, in parallel, would keep the voltage the same but increase amps meaning the batteries would work longer. So with 50v and a 48v motor it SHOULD work right, yah with a slightly higher voltage it would tax the motor a bite but it should be fine... right?

An Electric bike COULD run on nothing but AA's?

Their cheap used in everything (almost) and don't require any special setups, this can be done?

[2005_rs]

I've read about a guy trying this in a powered bicycle forum who got poor results. The problem is the cheap nimh batteries can't dump amps fast enough to power the motor. This called the C rating, which isn't published on the specs; at least not the ebay ones. C refers to the rated discharge capacity of the battery. A 1000mAh battery rated at 1C can only discharge about 1000mA continuously. Hobby batteries for airplanes etc are rated at 10, 20, 30 and 40C. (maybe more, I don't know)
Once you start looking at batteries that publish a realistic C rating, the price goes way up

[Astro]

Originally Posted by Wilden

Dont worry about not being able to read it. Just my bad drawing. The symbols are meant to represent batteries, and my agument was that, if you can have 48 AA batteries in series to produce 72v at 2.7amps, and you can have 37 batteries in parallel to produce 100amps at 1.5v, surely, if you join those two circuits together you could produce 73.5v at 102.7amps. Or am I talking a load of rubbish?

I know this is an old thread but because this wasn't answered and for anybody reading it in the future.

Adding a series string of cells (72v 2.7A) to a parallel stack of cells (1.5v 100A) will not achieve the desired results. You will end up with a 73.5v battery with 2.7A maximum current.

When cells are connected in series your maximum current draw is limited by whichever cell(s) have the smallest maximum current draw. This is because when connected in series the same current flows through each cell.

To achieve the 72v AND 100A battery you could use the AA cells but you would need to connect them in 37 parallel strings of cells, each of the strings would have 48 cells in series. So you would need 1776 AA batteries. (based on each cell being 1.5v with a maximum current of 2.7amps)

So possible, but practical? That is a huge number of cell connections and points of failure. Also monitoring the state of charge of all these cells would be extremely costly or time consuming. Then if one or more of the cells do go bad, it may prove difficult to locate. Correctly charging and balancing this number of cells would be a nightmare.

[Grant-53]

I have built model car DC permanent magnet motors for years. Motors are designed on the basis of the current flow and the number of loops of wire or ampere-turns. At low rpm a motor will draw maximum current. Ideally to get the max power from a battery pack switching from low voltage/high current at low rpm to higher voltage/lower current for high motor rpm. Since a battery may not be able produce the initial current demand, a capacitor is designed to store a charge and dump it quickly. If you have several large batteries rather than a myriad of tiny ones, less weight will be taken up with casings and cables. The battery pack for starting a diesel tractor engine is typically four large 12v batteries in a 24v parallel/series harness. If you don't have access to heavy gage wire then using several wires in parallel will share the current load. There are a number of different motor configurations and control methods. The local industrial supply house may have a wealth of information on selecting a motor and control system.

[American Viking]

Did anyone discuss LiFePo Batteries, they are smaller and lighter than conventional sealed AGM batteries. They cost only a few $$ more than comparable capacity AGM units, and come with charging ports for balancing.
They are literally 2/3 the size of a same capacity of an AGM cell, can be installed on their sides or on end offering many mounting options so the OP's decision on his blast would not be 2 or 4 batteries but more like 8 to 12 batteries on his blast.
I'm looking at fitting two LiFePo batteries in parallel to increase the Ah capacity on my VFR, and these cells would make it possible to fit roughly where current AGM battery is.