Batteries for the GM kit

[kickabear]

Okay, I'll be the first to admit that I'm a bit dense about batteries, so if I say something stupid, or wrong, or stupid and wrong, please feel free to correct me. 

I know the motor/controller are 36V.  I know that Ah controls the range of the bike.  So, that a 36V 15Ah battery pack has better range than a 36V 10Ah pack.  I'm cool so far.  Here's where I get a little fuzzy...

If I have two 36V 15Ah packs, wired in parallel, does that give me 30Ah?  I know it gives me about 36V, but I'm unclear on the Ah calculation. 

I see that there is a 36V 15Ah LiFePO4 pack on the GM website.  If I had two of those, and a couple of chargers, would I be all set? 

Am I thinking right, or did I miss something?

Thanks, everyone...  I am very excited to get started. 

[myelectricbike]

Yes and yes. Be sure NOT to connect then in series.

[29a]

Yes paralell does add the Ah
But theres a lot more to it !
The different tecnologies can be drained to different levels without damage so if you used a 15Ah SLA (Sealed Lead Acid) you wouldn't require a 15Ah Lipo (Lithium Polimer)for the same range.
and the AH ratings are not based on the same parameters (discharge over time)
Its a very complex subject and I still do'nt know what the max volts/amps the motor/controller can handle so I can't even start.

The best bang for the buck Lipo at the moment I hear are the milwakee tools 36V 3Ah packs that come with life time warrenty and are rated 10C-30C
The C rate is the multiplication factor of the Ah, so 36V 3Ah @10C-30C would tranlate to 36V that can discharge at 30-90Amps without damage.

That said my personal prefernce is for Nicd 3C for the extremly high recharge cycles (half the weight of SLA) even though more expensive than SLA but a fraction of the price of Lipo should last five years daily use before damage as opose to noticable SLA damage in 3 months.

[kickabear]

so if you used a 15Ah SLA you wouldn't require a 15Ah Lipo for the same range.

That said my personal prefernce is for Nicd 3C for the extremly high recharge cycles (half the weight of SLA) even though more expensive than SLA but a fraction of the price of Lipo should last five years daily use before damage as opose to noticable SLA damage in 3 months.

Thanks for the advice! 

How can I compare the range differences between SLA, NiCd, NiMH, and LiPo?  Or even LiFePO4?  Is 12 Ah of SLA equivilant to 9 Ah of NiMH?  11?  The more I look at this, the more I don't know.   

[myelectricbike]

A lot depends on the control circuit in control of charge and discharge rates. An Ultra capacitor for instance can charge and discharge fast. The rates are not linear however. Do a Google image search on capacitor charge and discharge rates and you will probably find some curves. All batteries have charge and discharge curves according to there raw characteristics and as permitted by their control circuit. Internal resistance is the reason for the need for control. A high potential discharge rate when paired with technology that has high internal resistance can skyrocket the temperature under high discharge rates unless the control circuit is there to limit discharge. Sort of like what happens if you use speaker wire to jump-start a Mac truck. You may be able to find Google images of raw and controlled charge and discharge rates for all battery types.

What happens then when you connect different types of batteries in parallel with the same voltage rating is that the over all charge and discharge rates blend  abd compensate in terms of rate for each other. The curves for each type merge into a curve of equilibrium,  like doing a least squares fit. The curve of equilibrium will however be closest to the curve of the battery type (according to its control circuit) which has the greater power to maintain a particular volt.

[29a]

For ebike applications under average use conditions, 1 ah of Li or Nimh or Nicd = 1.5 X ah of SLA, so 8ah of Nicd = 12ah SLA roughly

Regarding weight SLA is heavy Nicd is half weight of SLA, Nimh is slightly lighter than Nicd and Lipo is half the weight of Nimh

A lot of retailers blatently lie about battery's and cycle life so be carefull and research.
this link should explain a lot

http://www.batteryuniversity.com/partone.htm