[Help] Building a reparable and upgradeable battery

[romeupaz]

Hello !
I am new here and searched around the forum for information but could not answer all my questions. I ask the help of experienced users this forum, to help me properly build a battery for my electric bike. THANKS

What i have:
The "bike" http://gingabike.pt/pdfs/MANUAL%20NEXON.pdf

25km/h limit (not true it goes 32km/h flat)
250w Motor
48v 12ah battery (4xSLA series original)
The controlor:

48v Input
Max Current: 30A
Low Batt Protections 42v
The charger (original for SLA)

The New Battery:
Objective 48v 12ah

What i want to use:
Cell's - NEW Sony Konion US18650V3
Mounts:


I know I do not advise to use springs but I intend to make an assembly similar to the image below or can i use the original Fittings(Springs). I have no way to weld the cells without too much heat. Considering that the bike uses a low current I think there is no problem.



Build 13s5p (48v 11ah) or 14s6p (51,8v 13.5mah) if its better for batt health?

I intend to create groups 5-6 cells in parallel and in series with connecting wire (Parallel Mounts back to back 3+3):
Scheme:

http://postimg.org/image/bsh63wqux/
I left an empty space on purpose to later add more cells. The sets will be packaged with tape.

Questions:
It will be absolutely necessary an BMS? I think it adds later (1-2 months)

Can I use the same charger of the SLA? What charger should I purchase? type?

It will be better 13s5p or 14s5p?

give your opinion, any help is welcome. thank you

 

[Nobuo]

Build 13s5p (48v 11ah) or 14s6p (51,8v 13.5mah) if its better for batt health?

yes, more Ah means lower C rates for each paralleled group at the same Amps output

Questions:
It will be absolutely necessary an BMS? I think it adds later (1-2 months)

Can I use the same charger of the SLA? What charger should I purchase? type?

It will be better 13s5p or 14s5p?

If you don't add a BMS you need to manually balance the cells one in ten cycles at least, if you want healthy chemistry over time and not any paralleled group on harming low (discharging) or high voltages (if you charge all the cells in series). You will need to add a fuse to avoid a dangerous short circuit. You also need to check carefully discharge rates in order to doesn't overload the cells and destroy the chemistry. The controller will be the only one to prevent a under-voltage situation, and doesn't for each paralleled group, this will be your manually balancing work

You shouldn't use a SLA charger for lithium-ion cells. The max voltage is different (however you could maybe adjust the pot to fit lithium-ion). The stages of charge are different, there are not float charge needed for lithium-ion. Once you charge the battery you need to disconnect it, and is better to use the soon as possible. You need a lithium-ion charger that fits your max voltage, thats all. Just make sure the charging rate is equal or below 0.3C if you want a very high life span / cycling life.

14s just give you 8% more torque path and more top speed (also more range if you fit the same speed as with 13s, but this does not happen in real life :lol: ), another paralleled group (6p) will make you an appreciable ~25% more range (20% in capacity, ~5% on increased efficiency)

 

[romeupaz]

by the away! THANKS for the quick response

What i need to know its good for the cell not changing to the top?
Ex:
14s = ~51v and charge it only to 48v (nominal) ?

What it is the maximum A used by my ebike? 5 to 6A? more?

Will this BMS and Charger be ok?
http://www.ebay.com/itm/48V-2A-Char...R-10AH-12AH-/141672624630?hash=item20fc58b1f6
or
http://www.aliexpress.com/item/48V-...est=201526_5,201527_4_71_72_73_74_75,201409_4

http://www.ebay.com/itm/Batterie-Pr...ell-Max-25A-/121713481986?hash=item1c56b05902

 

[Nobuo]

Yes, is indeed very good to not charging to the "top" for lithium-ion chemistry. Each 0.1V less per cell will translate in x2 cycle life.

The problem about charging a 14s battery with a 13s charger is that the voltages differences are to broad.

A 13s battery needs 54.6V (4.2V per cell) to fully charge. A 14s battery needs 58.8V in order to fully charge.

If you charge a 14s battery with a 48V (13s) charger you will charge each cell to 4.03V (56.4V / 14) that's around the 80% of SOC

Your controller can pull peaks of 30A but it will sustains around 15A max, only when you push the motor hilling up probably (taking into account the max speed and the medium Kv of your motor)

Those chargers will work the BMS is a little limited, but it will probably work good, both are for a 13s battery

 

[romeupaz]

on the way

I will keep posting my build

 

[romeupaz]

How many amps will be drawn from each cell if peak 30A in pack total?

 

[Nobuo]

30 / number or paralleled cells = peaks for each cells

peak for each cell / 2 = ~max continuous discharge for each cell