Hi, im desiging a PWM(boost converter) battery charger for lithuim ion battery cell. Im assuming that the battery will never get to a complete discharge level. so the battery voltage will never have that suddent drop in voltage across its terminals. I want to use the "constant current constant voltage" method. But since the battery will never be discharged fully, i dont have to worry about the constant current part. Now what is it exactly am i sensing to see when the battery is fully charged to eventually stop the charging, the battery voltage terminals wil be constant, so what is it thats gona tell me that the battery is fully charged. keeping in mind that i dont want to get into tempreture sensing.

 

Hi,
First of all,
CHARGING LITHIUM BATTERIES IS DANGEROUS!

You need to follow the makers recomendations exactly. A simple constant current or delta V charger designed for Nicads will not work. Incorrectly charged cells can explode showing everthing with buring lithium.
If you insit doing your own, Maxim ( http://para.maxim-ic.com/cache/en/results/5085.html ) and Linear Thechnology ( http://www.linear.com/pc/downloadDocument.do? )navId=H0,C1,C1154,C1004,C1012,P1220,D4312 do suitable IC's.
Check the specs for the cell you intend to use.

Robert G8RPI.

 

Hi,
First of all,
CHARGING LITHIUM BATTERIES IS DANGEROUS!

You need to follow the makers recomendations exactly. A simple constant current or delta V charger designed for Nicads will not work. Incorrectly charged cells can explode showing everthing with burning lithium.
If you insit doing your own, Maxim ( http://para.maxim-ic.com/cache/en/results/5085.html ) and Linear Thechnology ( http://www.linear.com/pc/downloadDocument.do? )navId=H0,C1,C1154,C1004,C1012,P1220,D4312 do suitable IC's.
Check the specs for the cell you intend to use.

Robert G8RPI.

 

The charger charges the Li-ion battery with constant current until the voltage reaches the final value. During this process the voltage is not constant. Then it switches to constant voltage charging.
The voltage of the battery must be sensed with great precision to avoid overcharching.

 

what about NiMH battery ? I need help for ultra fast smart micro base nicd nimh battery?
I need help for generate negative current pulse between + charge pulse
can any help me?

 

Just a question, what's the difference between that and a regulated voltage (obviously set to the correct voltage) with just a series resistor to limit max current at the start of the charge cycle?

Or one LM317 to fix a constant (max) current followed by another LM317 to fix a max voltage.

 

i feel i get your question, to stop charging for a battery lets say 3.5v nokia battery
and you are using a comparator, all you have to do is to make the reference voltage constant and the battery voltage should be fixed such that the battery gets to 3.6 - 3.8v before it switches off
by this voltage, the battery must have been fully charged and have not changed its temperature.
when you place the stop voltage at 3.5 it won't be completely charged because, when you are using a battery in a phone of 4 bar battery indicator, at 2 or 1 bar, the voltage will still read exactly the same with a 4 bar battery. the difference is in the current.
in other words, you have to charge withe the producer's prescribed current and voltage to charge the battery a little above the original voltage (+0.2 or 0.3)
i have been using this for my nokia battery for up to a year now

 

Please bear with me as I go a little off subject

Robert I am just wondering if you have actually experienced this or are just re-spouting what you have heard. People commonly do just regurgitate this sort of stuff and it is frequently on batteries. Batteries are pretty hardy and personally, despite all the wowsing over 50 years, I have never seen a battery explode or even swell from being recharged.

Thats not ever even one. I have recharged thousands of batteries in that time. No hydrogen explosions or cracking cases or burning anythings !

If you genuinely have seen this then pray re-tell the experience
Oh I'm also a full call

__________________
My Property and my Family are not for Govenments to control.That is not the purpose of Governments.
To stop corruption in Government officials give them three times the penalty. They should, and do, know better. Let them commit to that when first employed

 

And what type of batteries are these "thousands of batteries"?

__________________
Carl
Curmudgeon Elektroniker

 

Of course the charging current for lithium rechargeable cells must be limited.
I have been charging two series 2200mAh cells many times with a 9V/500mA wall-wart to limit the current and an LM317 regulator set to 4.20V per cell (8.4V total).

The wall-wart and LM317 get pretty warm at first then they are cold when the battery is fully charged in 5 hours when the current is almost nothing. The battery stays cold during charging. The battery's load disconnects it when each cell's voltage drops below 3.5V.

__________________
Uncle $crooge

 

Charging Li-ion batteries is not dangerous, it is being done millions of times every day in the planet.
The danger is in lack of knowledge about them. Proper terminology is important; one thing is a cell and another a battery.

Audioguru is doing it the way it is supposed to do, charging each cell of the battery independently on a controlled constant voltage charger.
Limiting the voltage under the maximum limit is convenient. If the maximum is 4.200 V, it is not a sin at all to charge them at a safer ~4.1V. There is no need to push anything to the extremes.

__________________
Abolish the deciBel !

 

Maybe I mis-read his post, but it looks like he is saying he just charges 2 cells in series, at a regulated voltage of 8.4v.

 

Yes, I charge both cells in series at the same time.
I assembled 5 batteries and they all are balanced pretty well. I doubt that I will need to separately charge the cells for better balance.

a serious hazzard will result in a fire if one cell develops a fault like a short then the other cell with it will become way over-charged.

__________________
Uncle $crooge

 

Thousands are mostly lead-acid and some old cadmium-acid . lately Nicads and NiMh.

I thought more about this yesterday and dug out 3 old NiMh 1.5 AAA cells . Measuring them showed two at .700mV and 1 at - .125mV. They had been sitting in a tin of old rechargeables for about 4 years maybe.

So I put each separately on my lab supply at 2.0V and nothing happened . Current was turned up so they could take all they wanted and still nothing happened .
I found I had to go to 10V to start them taking anything then the current gradually rose and when it got to 200mA I backed the voltage down but to get them to take anything at all I had to keep it at about 5 V .This all in about 2 minutes and holding them in my hand , no heat generated I could feel.

Now after about 5 minutes I found one had come up to 1.5V the other two had not . Iĺl continue to test these for a few days to get them to at least 1.3V and then chuck them in the normal plug in charger.

Can anyone suggest why they would need that boost after sitting ,probably flat for that length of time?
I'll have to read up on them , perhaps they sulphate too ?

__________________
My Property and my Family are not for Govenments to control.That is not the purpose of Governments.
To stop corruption in Government officials give them three times the penalty. They should, and do, know better. Let them commit to that when first employed

 

Then you just aren't trying hard enough....

Lithiums can be EXTREMELY dangerous, even if you do everything right. A company called valence Technology made rechargeable LIs for Army night vision goggles. When the batteries would discharge too far, they would short internally and still have plenty of energy to burn up the equipment it was in. That was no myth, the company went out of business because of that problem.

Ask APPLE about their laptops that had LI batteries grow internal shorts sitting on some guy's lap which then cooked his Family Jewels. It happened.

LI's have to be charged by a curent limited CC-CV charger (constant current followed by constant voltage). Final voltage set point has to be accurate to about 0.5% (according to Sony).

Speaking of exploding: If NI-MH (nickel metal hydride) batteries are overcharged hard enough they vent hydrogen gas. remember the Hindenburg exploding? That was hydrogen gas + spark.......

BTW: the reason you don't see batteries explode is because they have vents. And, if the vents get plugged, the battery case is designed with a weak seam for it to fracture and not explode when the internal pressure gets too high. The terminology in the battery business is they MUST "die with honor"......