chas58 wrote:
For a primer, there is a wiki here, but I read everything I could find on electricbike.com. Lots of the articles are written by moderators and long standing members here.

https://www.electricbike.com/lithium-cobalt-manganese/ for instance.

Two things that are critical but not obvious to the beginner:

motor RPM is key

Battery C rate is key.

a cheap battery is 1C, meaning it cant pull more current than its amphour rating.

a 2.0AH battery at 1 C can only pull 2 amps. at 5C it can pull 10 amps.

Yep, you start putting them in parallel, and you are increasing your capacity

That 1C battery at 1p (one set in parallel) can do 2amps

2 parallel packs can do 4 amps

4 parallel packs can do 8 amps, etc.

Motor speed is determined by the motor design (windings) and the voltage. A 24 volt battery will run half as fast as a 48volt battery on the same motor. It is unusual to find a 24v build here because they are slow and don't have much power. Most people here like 48 volts (I've stuck with 36v to keep my weigh down).

I may be a senile old dog (

*and I have been called a lot worse --- sometimes with good reason*) but I can learn new tricks ... just takes a bit longer these days.

EDIT: http://batteryuniversity.com/learn/arti ... the_c_rate

"The capacity of a rechargeable battery is commonly rated at 1C, meaning that a 1,000mAh battery should provide a current of 1,000mA for one hour. The same battery discharging at 0.5C would provide 500mA for two hours, and at 2C, the 1,000mAh battery would deliver 2,000mA for 30 minutes. 1C is also known as a one-hour discharge; a 0.5C is a two-hour, and a 2C is a half-hour discharge."

**So If I am reading this correct (***debateable*):
I will answer my question about the LEEDS battery pack first: They are obviously using the 5C discharge rate cells.

5 x 2.3 = 11.5 amps which is greater than 250 watt / 24 volts = 10.4 amps.

In theory one stack of Panasonic NCR18650B cells rated at nominal 3200mAh should deliver 3.2 amps at a 1C discharge rate.

In theory two stacks of Panasonic NCR18650B cells rated at nominal 3200mAh should deliver 2 x 3.2 amps= 6.4 amps at a 1C discharge rate.

In theory three stacks of Panasonic NCR18650B cells rated at nominal 3200mAh should deliver 3 x 3.2 amps= 9.6 amps at a 1C discharge rate.

I am looking at the spec sheet for Panasonic NCR18650B. Is has a "Discharge Characteristics" chart with curves for 0.2C, 0.5C, 1.0C and 2.0C. So all other things being equal and everything being 100% copacetic 2 stacks of should be able to provide 12.8 Amps at 25 degrees Centigrade.

A 250 watt motor at 24 volts should have a nominal draw of 10.4 amps at leaving a 23% margin.

A 250 watt motor at 36 volts should have a nominal draw of 6.9 amps at leaving a 84% margin.

A 350 watt motor at 36 volts should have a nominal draw of 9.7 amps at leaving a 32% margin

**Of course we all know it ain't a perfect world.**
I am looking at is the middle line and that seems like enough margin for variances, spikes, wear, etc.

Perhaps I should have asked Paul about a 10s2p based on Samsung sdi icr18650-22p cells:

10 x 3.6 volts = 36 volts nominal

2 x 2.3 ah= 4.6 amps nominal

4.6 x 5C = 27 Amps Max draw