Are my calculations correct using this l-ion battery?

electrowheelz · #1 09-25-2009, 07:25 PM

I have a Unite 24v scooter motor and am exploring an alternative to SLA batteries. This battery is 3.7v 2600maH. I did simple calculations and calculated it would take 7 of them to power the motor at 25.9v and get about 18ah. It just sounds too cheap and simple to be right. Not to mention the super light weight. It seems too good to be true. Am I missing something?

Panasonic Li-ion Lithium 18650 3.6V/3.7V 2.6Ah/2600mAh! - eBay (item 270411043052 end time Oct-16-09 09:52:21 PDT)

myocardia · #2 09-25-2009, 10:54 PM

Well, first of all you'll have to use eight of them, because your stock battery charger is built where you will have 14V in each of your SLA batteries after it has finished charging, so you'll need to be able to hit 28V pack voltage. Then just multiply those eight batteries by the number of ampere hours of storage you'd like to have. Every eight batteries will give you 2.6aH of storage.

Realize also that you will have to do all of the soldering that will be required, to turn all of these batteries into one large battery pack. Spending the money to buy a charger meant to charge lithium-ion batteries is also something you should consider, if you're going to own L-ion batteries.

deacon · #3 09-26-2009, 11:59 AM

I did math on it last night but the reply it didn't post. I came up with 56 batteries for a 20ah pack. Almost four hundred dollars without shipping. around 450 with shipping. Plus you would have to soldier the whole thing together. It would be cheaper to buy the lithium phosphate pack from china. I'm not sure if you would need a circuit to balance the cells or not.

electrowheelz · #4 09-26-2009, 04:50 PM

Yes, I realized later that I was forgetting one critical thing. I was multiplying ah by number of batteries but when you wire in series, the amps stays the same. It would be much too complicated and expensive to bother with. I'll just stick with the old dinosaur SLA batteries. I guess we'll all be dead by the time they finally have an affordable, fast charging battery solution.

myocardia · #5 09-27-2009, 03:08 PM

Quote:

Originally Posted by electrowheelz

I guess we'll all be dead by the time they finally have an affordable, fast charging battery solution.

Possibly, but nothing's for sure in this business. We may all be using EEstor's ultracapacitors very soon. Then again, they may also be a figment of someone's imagination. Only time will tell, I suppose.