Charging Li-ion packs with protection circuitry

[mrme]

I have some Li-ion packs for Qualcomm 820 phones I would like to try on a headlamp project. They have 2 li-ion 18650 cells. I don't want to elimnate the protection circuitry.

How do I charge them? Everything I have found has been on how to charge bare cells, not packs.
I don't have a phone, just some batteries and a car charger that I think is for a phone the battery is compatible with. The charger only puts out 8 V open circuit, which is incapable of putting a full charge on the cells. I got them to take some charge DD, but not anywhere near full and it was charging REALLY slow.

Can I just build a charger like bare cells require and use it with the circuitry? I saw an article for a charger I would like to build. I have most of the parts.

What should I know? I really don't want to make a bomb. This thing will be worn on my head (most often on a helmet, but not always).

 

[SilverFox]

Hello Mrme,

This charger will work, but depending on the capacity of your cells, it is not what I would call fast. You can just clip the charger to your phone pack and let it charge. Universal Li-Ion Charger

I have some Sony 18650's from a phone battery pack. I tested them at a 1.5 amp draw (thinking to use them in my U2) and was very disappointed in their performance. They do not have the capacity listed on them but it is well below that of a Pila 168a or a bare LG 18650 2400 mAh cell.

Good luck.

Tom

 

[mrme]

They are 1400 mah cells (acording to the package).

Thanks for the link.
I can't afford that charger right now, although it looks really good. I have all the parts to make my own LM317 based charger except the perf board (only a couple of bucks), so that is what I want to do. Even if I could buy it, I would prefer to use the parts I have to make my own.

I just need some more information about charging protected packs.

 

[andrewwynn]

from my understanding the protection circuitry just drops a little voltage.. so.. i.e. rather than getting a full 4.2 to the battery maybe you'll only get 4.1.. I would get a chip from Linear designed for a two-up LiON.. i use the 1-up (4.2 chip) and it is incredible, i wouldn't look elsewhere.

The chip is under $2, but shipping is like $7. I will be ordering another 50 or more chips of the 4.2 variety soon and i think i might get some double cell chips so i can try some series solutions.. if you aren't in a hurry i could pick up some spares and save you as much as $7 shipping.

I can build a full charger (just needs power) on top of a proto board in a matter of 10 min or less... i have pictures of them sitting on top of a penny, they are very cute.

 

[mrme]

[ QUOTE ]
andrewwynn said:
from my understanding the protection circuitry just drops a little voltage.. so.. i.e. rather than getting a full 4.2 to the battery maybe you'll only get 4.1.. I would get a chip from Linear designed for a two-up LiON.. i use the 1-up (4.2 chip) and it is incredible, i wouldn't look elsewhere.

The chip is under $2, but shipping is like $7. I will be ordering another 50 or more chips of the 4.2 variety soon and i think i might get some double cell chips so i can try some series solutions.. if you aren't in a hurry i could pick up some spares and save you as much as $7 shipping.

I can build a full charger (just needs power) on top of a proto board in a matter of 10 min or less... i have pictures of them sitting on top of a penny, they are very cute.

[/ QUOTE ]

So what exactly does this chip do?
Does it trickle charge unp to 3 V per cell, then pump it full? I assume it would make a smart charger.
Are you saying it doesn't require any external components?

Whether I am in a hurry or not is complicated. I am starting grad schoolin a couple of weeks, maybe sooner. I have flashlight building time now, but how much I will have later is not at all clear. I doubt I will be able to finish this project in the week or so I have anyways. I would like to know if the batteries will do what I need to know whether to scrap it now.

So I will go ahead and build a LM317 based charger. No one has told me making my own charger for protected cells is especially unwise. I will check the voltage drop across the circuitry and report back.

I may take you up on your offer to order me a chip or two, but only if the batteries will do what I hope they will. Mechanical barriers are worse than electrical ones when palying with headlamps.

Charger size is not an issue. A through hole chip would be preferd to a SMD. Are any Li-ion chips avalible that are easy to solder?

 

[SilverFox]

Hello Mrme,

I have a set of Sony 18650's that may be close to 1400 mAh. What do you think the draw of your light will be? I can dial that in to my tester and give you a graph of the performance.

Tom

 

[andrewwynn]

If the protection on your cells is for both under and over charging you have very little to worry about, expecially if you build a charger designed for LiON from a plan.

The LTC4054 chip is a very smart charger.. it knows what to do and not to do.. pretty much the holy grail of charger chips for LiON.. it knows how to trickle charge an overly dead battery (i've brought batteries back from the dead with it).. and knows not to charge already charged batteries.. also.. how to re-charge 'stale' batteries.. (i.e. if you left it on the charger for a month or something and it drained over time)..

'easy to solder?' i actually prefer the SOT-23 form factor now.. even though it's about 1/2 the size of a rice.... i'm just used to it now... i will solder one on a proto board and sell them to people if they want something a little bigger to work with.

my latest LiON charger is shown here

here is a preview: