Battery Questions

[ironwill8282]

I was wondering if someone could explain to me the difference between a 24V and a 36V battery? And the difference between a 13AH and 8AH battery pack? That is in reference to NiMH batteries as I feel at the moment they are the best battery option.

[CarlsEbike]

n simple terms: The difference between a 24 volt battery and a 36 volt battery is simple the voltage potential.  A system would be designed to work with a specific voltage.  The 13AH and 8AH refer to the capacity of the battery. A 13 amp hour battery would have more capacity than an 8 amp hour battery.  However, the useful capacity (driving distance) would the joules or watt/hour capacity the battery can deliver.  This is calculated from multiplying the voltage times the amp hour rating.  Thus a 24v/13AH battery could have 24 x 13 = 312 watts of driving capacity.  Where as a 36v/8AH battery system would have only 36 x 8 = 288 watts of driving capacity.  If you were to use a 36v/13AH battery system then you could get 36 x 13 = 468 watts of driving capacity.
There are many tradeoffs why a designer would select either a 24 volt or 36 volt battery system for an application.  See my next post for what I did and why.
...CarlsEbike

[CarlsEbike]

When I was evaluating what size battery system to install I considered several factors.  The most important being the cost to operate the bike. Battery cost, expected lifetime and driving distance.  So I measured my bike for where I could make the largest battery fit.  I decided the weight issue was not a big factor for me since I'm a heavy guy and I thought I could cut my weight back by the difference the batteries added. I purchased the 36v/500w kit, so it was given that I needed 3 (12v) batteries to install.
One of the considerations was how many recharge cycles the batteries would be good for before needing replacement.  If you look at vendor data, PowerSonic (http://www.batteryplex.com/sheets/PSH%2D12180%20FR.pdf) is a good one to look at, they have cycle life vs. discharge depth.  So basically if you fully discharge a battery you might only get 200 recharge cycles out of it before needing battery replacement.  Whereas if you discharge it only about 30-50% you can get upwards of maybe 1000 discharge cycles out of it before needing replacement.  Consider the fact that doubling the capacity is roughly 2x the cost but it could get you 5x the driving life for the same distance.  So I chose the PSH-12180 FR, which is a 12v/21AH high rate battery.  I figured in the long run this was the best bang for the buck.  I'll see...
The battery vendor is also an important factor.  I have personal experience with several brands and my choice by far is PowerSonic.  I have seen them outlast any other brands I have tested by far.

I'm sure other people have their inputs as well.  Ask 10 people and I'm sure you'll get 10 different answers.
…CarlsEbike