DIY Li-Ion: do I need a balancer?

[Momato]

Hi All.

I am thinking of DIY'ing a Li-Ion pack for my bike light (4 * 18650 cells). Do I need to use a balancer (and thus wire the batteries accordingly)? Or is a "normal" PCB ok? 4 cells are fairly cheap.

BEst regards, Morten in Denmark

 

[VidPro]

for long life, best capacity, and total assurance a balance charger is money in the bank , if your cells are cheap , well then its more nessisary cause the cheap ones will do more things to fall out of capacity .

but 4 cell protection ONLY that connects to all the cells using center tap methods, OR 4 protected cells in the pack, is sufficent to prevent danger, and will keep the cells in spec, just not balanced. so its still SAFE.

price of balancing is getting cheaper and cheaper, you can get a 4 cell charger that does some sort of balancing for less than 100$ now .
and if your a real chepskate (like me) you can just seperate the cells and balance them, or use 4 cheap chargers that stay in spec, connect it up manually or make up a connection.

you could seperate them and balance them only as needed, too, as opposed to EVERY charge.

getting out of balance occurs over much time, unlike ni-mhy and ni-cd, li-ion can not be overcharged slowly to balance out the cells on charging. so without it, in TIME they WILL get wacked, protection doesnt prevent it, and there is nothing to balance without it.
so you CAN get away with it, and everything will seem peachy and fine, then things start getting bad.

 

[Momato]

does this mean that I will not need a PCB built in if I use balanced charging? These are the cells I thougt of using: http://www.batterycity.eu/cgr18650_...__with_solder_tags_-p-1063.html?cPath=239_206

I was looking at a hyperion balancer:LBA10net 6S+

 

[VidPro]

you still have to have protection on the PACK (like a 4 cell protection curcuit) or on the cells to prevent deep discharges of a single item in the series pack.
----3.5---3.5---2.0---3.5--
because this can happen during discharge, it is less likly to happen when balanced during charge, but can still happen from offset capacity, or when a cell is becomming weak or has gotten damaged. when a cell goes below the specs for discharge voltage , it becomes damaged, then of course gets worse and worse because it gets lower even faster.
so the situation spirals.

http://www.batteryjunction.com/oneli18322ma.html
this cell here is a great cell, if you dont get stuck for high shipping. the dealer gives 5% discount to cpf, by using a Code, CPF07 or something.
tabs are optional.

 

[Momato]

thanks! On batteryspace, they write that only packs with >4 cells needs a balancer? True or false?

I also noticed that they have combined protection/balancer boards for about 40$, then I can use a standard charger. Maybe thats the way to go? However, I do not want to spend 40$ if I can just buy a 5$ PCM

 

[VidPro]

thanks! On batteryspace, they write that only packs with >4 cells needs a balancer? True or false?

I also noticed that they have combined protection/balancer boards for about 40$, then I can use a standard charger. Maybe thats the way to go? However, I do not want to spend 40$ if I can just buy a 5$ PCM

ummm, i dont want to argue with battery space or battery univercity even , but any SERIES set of cells can get out of balance, and with li-ion there is only one way to full charge each cell, and balance it, with something that does that. there is no magic that i know of. because you cant overcharge it, even slowy.

----3.5----2.0---- <--- still a ruined cell.

the more there is, the more it can occur, but we have it go bad here with 2Xparellel 2Xseries, where one parellel set gets out of balance with the set its in series with., also happen in the 2 cell li-ion flashlights.

combined protection balancer ??? hey now that is magic and about time, do you have a link, i want one.

 

[Momato]

combined protection balancer ??? hey now that is magic and about time, do you have a link, i want one.

this one for 4 cells: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3324

shipping to denmark is just stupid................................ :sigh:

 

[VidPro]

this one for 4 cells: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3324

shipping to denmark is just stupid................................ :sigh:

that is awesome, except for the discharge short protection, whats it for an electric Car
put that on a bike , and crash (like i would) and short out your wires, and nothing will stop a bad short.
but its also about time they had a high amperage protection, just kinda overdid it.
mabey its for this battery http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4058



if a person could go with 5 cells, this one is at a more logical 10amps
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3387

 

[VidPro]

reading all the spec sheets, the 40amp one doesnt stop till like 60 amps , by then most of my wires are gone hey a simple fuse or resettable breaker, will fix that, soooo no problem at all, next issue.

how does it balance and at what rate.

To achieve balance, each cell in battery pack must have equal voltage within tolerance of 0.2V. After charger LED turn Green, unplug charger and wait 30 minutes before use. This is for the pack to perform balance function

Whaaaat? oh come on, surely they could do a simple cutoff of charged cells and continue to pass some current to the rest, that doesn't make any sence.

then the rate for balance is some 50ma ? ya sure, only 5% of a 2500 would take 2 hours to balance, and BY discharging a cell?

so if all that was true, then the overcharge protection of 4.35 could be reached via sloppy charging, say then a battery is at ~4.30 (still completly alive) THEN after unpluggin it discharges that one back down to the ~4.25.
that works.

but still, why not watch the cells singularly they have a microcontroller for that, if any one reaches 4.20 , disconnect that one, resister down the whole input, and keep feeding 100ma through till the next one reaches 4.2 ,disconnect it and so on. at the end of charge , all cells were brought up to 4.2 ON the power supplied.
isnt that electronically feasable?

 

[Momato]

I am way below being able to answer that last question - I did not even notice all the problems I think I will just go with a normal package and wire a balancer cable into it. That should be OK, right? I have not found any packages with balancer cables already attached?????

Does anyone know of such a package (4 cell i think is sufficient).

And if not, is there any problems invovled in soldering a balancer cable in myself??

Best regards, Morten

 

[VidPro]

I am way below being able to answer that last question - I did not even notice all the problems
Best regards, Morten

and SO AM I , it just seem to me like they use a method that isnt the greatest method.
it seems to be "stuck in a box" of what chips are available , how they know to use them, and what purpose the curcuit would be used for.
this one for radio controlled high torq motors.

 

[VidPro]

Does anyone know of such a package (4 cell i think is sufficient).

And if not, is there any problems invovled in soldering a balancer cable in myself??

Best regards, Morten

many RC and batteryspace themselves, have and will assemble packs using the batteries they sell with balancing taps now.
getting a finished 4cell pack with balancing taps should be easy.
also Luxluthor is assembling packs.

also if you can get a good LG or Sony cell to go in the packs.

i would check out batteryspace first for that. they have sold protected packs for years, and now have ones with balancing.
you could even get li-poly if you wanted, there is more li-poly packs due to RC use. li-poly would have advantages of small tight bundle, disadvantages of not as durable because no metal can around it.

myself, if i had the skill, and i DO i make my own, to insure the cell i wanted is in it.

 

[rizky_p]

i always recommends balance taps for individual charging, feels safer and you can read each cell voltage kinda cool!