Li-ion charging IC - 12.6V

[domas]

Hello folks.

I have a few devices around that are powered by battery packs salvaged from laptop batteries.

First one is a cordless drill, powered by some 3 flat li-ion batteries (connected in series), as it did not have any original battery. Works well, they give little over 12V, while the original was rated at 14.4V, but it just works, whatever. The controller for the battery was discarded long time ago.

Another device is self built small ventilation system in my appartment (a fan, 2 switches and few components for a timer) that are powered by 4.4Ah battery pack. It is laptop batteries

two of them are connected in paralel X 3 and then all 3 packs are connected in series.

I am charging both devices by adjustable ATX, but i have to check the temps constantly, as well as current and voltage (it has to be adjusted every 10 minutes)..

I want to build an IC based charger circuit that would control pre-charge, constant current and constant voltage itself. Most of those chips are rated at 4.2V (for charging one battery at a time or more of them in parallel - just multiply the current by number of batteries).

I know that laptop controllers have connections between the cells, but does it mean that they can use 4.2V controller? Not sure.

The problem is that i am not able to find suitable IC for that. Most of them are rated at 4.2V, the ones that are able of charging in higher voltage are too complicated for me, they have a shitload of pins and adjustments), and again they are rated either for 12V or for 14.4V. My pack has a charging voltage of 3 x 4.2V = 12.6V. Then again most of them are smd components that I do not like soldering. Aren't there any 12.6V old school 8, 14 or so pin chips that would work for amateur like me?

[mariushm]

Re: Li-ion charging IC - 12.6V

You can't find such charger ICs because it's not normal to charge them like that.

You normally charge each cell separately, you don't charge them connected in series.

Each cell charges at its own speed, there's variations between cells, so if you charge all three at same time, some would get more abused then other cells.

You can buy a charger like the one in this teardown video : http://www.youtube.com/watch?v=3LfU4mjgpyM

or if you watch the teardown and the explanations you can build one yourself.

[Th3_uN1Qu3]

Re: Li-ion charging IC - 12.6V

You can't find such charger ICs because it's not normal to charge them like that.

You normally charge each cell separately, you don't charge them connected in series.

Really? Then why do *all* laptops charge the cells in series?

Sure, it *is* less than optimal, and is part of the reason why laptop batteries die so quickly, but for the most part, it works.

Charging a Li-Ion pack isn't rocket science actually, and you could cook your own controller if you wanted to. You need to charge the pack with CC->CV (Constant Current -> Constant Voltage). The current should be limited to 1C (max charge current in mA = the capacity written on the cells in mAh). Charge at this constant current until you reach 4.2v/cell (just monitor the voltage of the whole pack), and then switch to constant voltage (hold this 4.2v/cell voltage level) until the current reaches (almost) zero, then the pack is charged.

Sounds a bit complicated, but it isn't. All you need to do is have a current limited voltage source. The implementation is up to you. You could simply attach a LM317 configured as a current source to the ATX power supply you're using. It won't be very efficient (it'll burn up quite a bit of power, will require heatsink), but it's gonna serve the purpose.

It is of course a good idea to monitor the voltage of each cell, to stop charging if any one cell goes over 4.4v or something. This can be done easily with a few resistor dividers going into a comparator.

You shouldn't need temperature monitoring, except as a safety feature. Temperature measurement does not play a part in the charging method of Li-Ion batteries.

[budm]

Re: Li-ion charging IC - 12.6V

You can study these info.

[delaware74b]

Re: Li-ion charging IC - 12.6V

The Craftsman LI-Ion 19.2Vbattery packs only have 4 posts on them, same as their NiCad packs. 2 pins are used for temp monitoring during charging and the other 2 are + - 19.2V.

Obviously, they're charged in series. Dewalt and Black&Decker are the same setup.

[domas]

Re: Li-ion charging IC - 12.6V

LM3420 Battery Charger Controller part of document snva557_Ti.pdf posted by budm is the money.

The current limitation might be an issue as for now, but surely I will make it. Until now I would simply adjust voltage of ATX power supply to adjust current.. The higher the difference of current batt. pack voltage and atx supply voltage, the higher current battery is charging at.

I am not sure how to limit current in SMPS, but I think it is self regulating according to load, isn't it? Would it be necessary? As far as I know, current is dependent on voltage and resistance, therefore adding resistors in series between PS and charger load would make a trick, wouldn't it?

[tom66]

Re: Li-ion charging IC - 12.6V

Careful, at higher currents, you must balance the cells! Which means monitoring each cell voltage and discharging any that are significantly out of balance.

I use something very similar to this:
http://www.hobbyking.com/hobbycity/s...idproduct=7028

For a made in China product, it is pretty good, the software is stable, the readings are accurate, it is capable of 5A (given a decent power supply), it can balance the cells (up to 6 in series), and it's $23. You're going to struggle to make a charger cheaper than that.

[domas]

Re: Li-ion charging IC - 12.6V

You can't find such charger ICs because it's not normal to charge them like that.

You normally charge each cell separately, you don't charge them connected in series.

Each cell charges at its own speed, there's variations between cells, so if you charge all three at same time, some would get more abused then other cells.

You can buy a charger like the one in this teardown video : http://www.youtube.com/watch?v=3LfU4mjgpyM

or if you watch the teardown and the explanations you can build one yourself.

Laptop battery controllers charge them in series i guess, but they monitor separate voltages as they have leads going to pcb from in between the cells. I am not sure if those are used for monitoring purposes only;

I have seen some Li-ion charger circuits with special charging state called balancing.

[domas]

Re: Li-ion charging IC - 12.6V

Careful, at higher currents, you must balance the cells! Which means monitoring each cell voltage and discharging any that are significantly out of balance.

I use something very similar to this:
http://www.hobbyking.com/hobbycity/s...idproduct=7028

For a made in China product, it is pretty good, the software is stable, the readings are accurate, it is capable of 5A (given a decent power supply), it can balance the cells (up to 6 in series), and it's $23. You're going to struggle to make a charger cheaper than that.

Nice one. And you are right about the price, it is really hard to beat that apart from the fact that in warehouse i have access to it is 39.99usd.

I thought I would make something more simple, but now I feel like incorporating a balancing circuit. I assumed it would be a smart IC, few resistors for programing / pre-setting charge current and voltage, few transistors and caps.

[budm]

Re: Li-ion charging IC - 12.6V

I used LM317 to feed the charging circuit for constant current source to limit the charging current for overnight charging. I know I can buy charger cheap, but I want to learn and experiment with the circuits.

[ben7]

Re: Li-ion charging IC - 12.6V

I see you guys have the right ideas about charging the lithium batteries, except for the atx charger. PLEASE be careful, that is very dangerous in my opinion! The cells could overcharge or overheat in those 10 minutes. Lithium batteries have a high energy to weight ratio. Lithium metal itself is very reactive.

[domas]

Re: Li-ion charging IC - 12.6V

I used LM317 to feed the charging circuit for constant current source to limit the charging current for overnight charging. I know I can buy charger cheap, but I want to learn and experiment with the circuits.

Agree. I would love to build one myself, just for sake of learning something new.
I would like to build one with automatic charging circuit, including pre-charge, CC, CV and balancing stage.

I see you guys have the right ideas about charging the lithium batteries, except for the atx charger. PLEASE be careful, that is very dangerous in my opinion! The cells could overcharge or overheat in those 10 minutes. Lithium batteries have a high energy to weight ratio. Lithium metal itself is very reactive.

Everything is just a question of selecting right voltage. As from my experience, battery packs can not pull extreme currents with a small voltage difference on ATX and battery pack. And yes, when I charge I monitor the current going to battery pack, i have my DMM connected in parallel all the time. That is the reason why I want to build a smart charger with IC for charge control.
Just try (actually please don't) to charge for example a 9V battery with ATX connected directly to it supplying 12V and being able to supply 15A of current, it would kabooom withing first 10 minutes of charge, i guess.

[budm]

Re: Li-ion charging IC - 12.6V

That why I set my to low C of 0.2~.3 at the beginning of the charge and let the IC takes care of the rest when it is fully charge, plus it is on timer for protection. Never leave the charger in place when I am not home either.
But some people does not believe so:
https://www.badcaps.net/forum/showth...t=28508&page=2

[domas]

Re: Li-ion charging IC - 12.6V

for my particular pack the limit is 0.7C according to manufacturer (panasonic), I keep it a little bit lower anyway, approx. 0.5-0.6. Batteries 3.7V nominal 4.2V charge, each cell is capable of 2200mAh, but they are 6, connected in 2P3S, so due to 2p they (whole pack) can be charged at maximum 2200*2*0.7=3.08A of current @ 12.6V

During my ATX charge current would constantly drop, as ATX is capable of supplying CV not CC, so I had to increase the voltage constantly to keep CC, I would increase voltage so current increases to ~3A, then is slowly reduces to 2A, then I increase it again, so the average charging current was about 2.5A = 0.57C

But I do know that it is a dangerous game, actually once I found my pack pretty hot, probably over 70 deg. celsius that time in the end of charge, didn't have an IR thermometer around, so not sure how hot was it exactly, and that happened even though I was around, it got hot over some 10 minutes.

That is why i need a smart charger.

and that thread is effin hilarious.