Lithium Ion charging ICs

[Mohamed Najiullah]

I am currently trying to make a solar cum hand cranked charger... As I wish to make it portable, I thought of using a Lithium Polimer battery to store the charge... Can u recommend some possible Lithium Polimer Charging ICs for a 4.2v, 150-200mA output?

 

[Hero999]

I wouldn't recommend lithium batteries because they're really sensitive to overcharge and can explode or catch fire if only overcharged a bit. You'll need a pretty complicated charger circuit to monitor the charge going to and from the batteries and stop them charging when they're fully charged, if you're running them off a hand crank. A mains powered lithium charger is much easier because it has a reliable and steady power, not hand cranking which produces a wide and unpredictable amount of current.

I'd recommend using NiMH cells because they can tolerate overcharge so the chances are your circuit will be as simple as connecting a diode in series with the dynamo.

What capacity do you require?

Three NiMH cells in series will give a similar voltage to a single lithium cell, you can get small NiMH button cells.

 

[Diver300]

There are a lot of Li-Ion and Li-Polymer charger ICs. One is a LTC4053. However, they are all tiny, as they are designed to go in cell phones etc. They all limit the current, limit the current to a much lower value when the battery is really low, and limit the voltage. They also prevent charging if the temperature isn't right. With one of those in the way, and wired correctly it is quite difficult to damage the battery.

Most of the charger ICs can charge with the current either being limited by the supply or by the IC. It is also not normally necessary to actually do anything to switch between what is limiting the current, so all you need to do is to limit the voltage to the IC's maximum. You can set the current limit to the maximum for the battery, and if your generator / solar cell isn't producing that much, it does't matter, the battery will just charge slower. The charging ICs don't usually discharged at battery that they are connected to, so you don't need a diode to isolate them when not charging.

 

[Hero999]

To charge a lithium battery most simple chargers do the following:

1) If the voltage is below 3V, charge at a lower current typically 0.1C, otherwise skip to step 2.
2) Charge at 0.5C until the voltage reaches 4.1V per cell.
3) Hold the voltage at 4.1V per cell until the current taken by the battery drops to towards 0A, say 0.05C, then terminate the charge.

The problem it become is the above become difficult next to nearly impossible if the supply current and voltage vary continuously or the load is often connected to the battery. To properly charge a battery under the aforementioned conditions, the the charge and discharge current needs to be accurately monitored to ensure the battery never overcharges or overdischarges.

 

[Mohamed Najiullah]

I wouldn't recommend lithium batteries because they're really sensitive to overcharge and can explode or catch fire if only overcharged a bit. You'll need a pretty complicated charger circuit to monitor the charge going to and from the batteries and stop them charging when they're fully charged, if you're running them off a hand crank. A mains powered lithium charger is much easier because it has a reliable and steady power, not hand cranking which produces a wide and unpredictable amount of current.

I'd recommend using NiMH cells because they can tolerate overcharge so the chances are your circuit will be as simple as connecting a diode in series with the dynamo.

What capacity do you require?

Three NiMH cells in series will give a similar voltage to a single lithium cell, you can get small NiMH button cells.

Actually I plan to use a voltage regulator IC in between the solar cell or crank dynamo and the Lithium IC.. That is to limit the voltage going to the LiPo IC.. Will that be a good idea?

 

[Diver300]

Actually I plan to use a voltage regulator IC in between the solar cell or crank dynamo and the Lithium IC.. That is to limit the voltage going to the LiPo IC.. Will that be a good idea?

You need to limit the voltage, but you also need to limit the current.

The scheme that Hero999 quoted is what you need. The only thing that I would add is that the charging current doesn't have to be be 0.5 C, it can be anything up to 0.5 C

 

[Mohamed Najiullah]

You need to limit the voltage, but you also need to limit the current.

The scheme that Hero999 quoted is what you need. The only thing that I would add is that the charging current doesn't have to be be 0.5 C, it can be anything up to 0.5 C

I have two things to say...

First, the input current will definitely be near to 250mA if not lesser... And I'l chose a regulator IC that limits the current i/p to the LiPo IC to around 100-200mA and nothing greater... Is that ok?

Secondly I don't understand what u mean by 0.5C... What does the "C" stand for? I thot the unit for current was always Ampere??

 

[Mohamed Najiullah]

NiMH cells

I wouldn't recommend lithium batteries because they're really sensitive to overcharge and can explode or catch fire if only overcharged a bit. You'll need a pretty complicated charger circuit to monitor the charge going to and from the batteries and stop them charging when they're fully charged, if you're running them off a hand crank. A mains powered lithium charger is much easier because it has a reliable and steady power, not hand cranking which produces a wide and unpredictable amount of current.

I'd recommend using NiMH cells because they can tolerate overcharge so the chances are your circuit will be as simple as connecting a diode in series with the dynamo.

What capacity do you require?

Three NiMH cells in series will give a similar voltage to a single lithium cell, you can get small NiMH button cells.

The NiMH cells in series give the same voltage but they have really low current o/p... The range is usually from 5mA to 20mA per cell... The discharging speed will be very slow, don't u think?

 

[Ubergeek63]

The NiMH cells in series give the same voltage but they have really low current o/p... The range is usually from 5mA to 20mA per cell... The discharging speed will be very slow, don't u think?

hmmm tell that to the people making 3AHr RC packs with 20A continuous drain rates

seriously though, you would be much better off using LiFePo4 cells

 

[Diver300]

Secondly I don't understand what u mean by 0.5C... What does the "C" stand for? I thot the unit for current was always Ampere??

C is an abbreviation for the battery capacity. So if you have a 5 Ah battery, charging at 1 C means charging at 5A. Charging at 0.5 C means charging at 2.5 A.

You haven't said how big the batteries are that you are charging, we can't say what current to charge them at as a number of amps. So what we do is say to charge no faster than 0.5 C.

That also means at least 2 hours to a full charge.

 

[Mohamed Najiullah]

Something to add to my question

Does the battery require a special circuit for transferring the charge to a mobile phone? What i mean is, can i simply connect the +ve and -ve terminals to the cellphone i wish to charge?


Or do i have to use a special circuit to maintain the LiPo battery's temperature while discharging?

 

[Mohamed Najiullah]

C is an abbreviation for the battery capacity. So if you have a 5 Ah battery, charging at 1 C means charging at 5A. Charging at 0.5 C means charging at 2.5 A.

You haven't said how big the batteries are that you are charging, we can't say what current to charge them at as a number of amps. So what we do is say to charge no faster than 0.5 C.

That also means at least 2 hours to a full charge.

I was thinking of using a Cell Phone LiPo battery... U know, like a Nokia, or sony ericsson battery...

 

[Hero999]

A mobile phone will have the charge circuit already built in to the phone, there is no need to make an additional circuit, just supply the phone with 5V and it'll charge the batteries.

 

[MrAl]

Hi there,


Li-ion cells are a little more problematic than NiMH if they are not handled properly. They must be charged correctly and can not be discharged too much or they will get ruined. NiMH cells are a little problematic too in that they really need the correct charging method, but they are safer to use overall.

An Li-ion cell requires a charge algorithm similar to a lead acid battery. Luckily, there is an easy way to get this with fairly common parts. For example you can build a Li-ion charger from a common LM317 voltage regulator with a few parts and charge the Li-ion cell fairly accurately. You do need to get the max voltage setting correct however, or at least set it close to the max.

The circuit looks like a standard LM317 voltage regulator circuit, with one exception: there is a small power resistor in series with the input. The power resistor is there to limit current while the cell voltage is under about 4.200 volts.
The drawback to this or any other linear circuit is that it isnt that efficient for voltages far above the output voltage, but then again many other Li-ion charging chips work like this too (although their max input voltage is not very high to begin with).
It's also a good idea to set the max output to about 4.15v instead of 4.20v just in case your meter doesnt read correctly.

If you'd like to see a circuit drawing i can post one with all the details.

 

[Mohamed Najiullah]

A mobile phone will have the charge circuit already built in to the phone, there is no need to make an additional circuit, just supply the phone with 5V and it'll charge the batteries.

No. I meant the LiPo battery i'm using to charge the mobile phone.. U know, the battery i charge using the Solar and crank shaft. Does it require any special circuit to discharge without getting heated?

I've attached a rough schematic.. I'm talkin abt the one highlighted in yellow.


I know i'm asking too many questions.. I'm a beginner in electronics u see...

 

[Mohamed Najiullah]

Hi there,


Li-ion cells are a little more problematic than NiMH if they are not handled properly. They must be charged correctly and can not be discharged too much or they will get ruined. NiMH cells are a little problematic too in that they really need the correct charging method, but they are safer to use overall.

An Li-ion cell requires a charge algorithm similar to a lead acid battery. Luckily, there is an easy way to get this with fairly common parts. For example you can build a Li-ion charger from a common LM317 voltage regulator with a few parts and charge the Li-ion cell fairly accurately. You do need to get the max voltage setting correct however, or at least set it close to the max.

The circuit looks like a standard LM317 voltage regulator circuit, with one exception: there is a small power resistor in series with the input. The power resistor is there to limit current while the cell voltage is under about 4.200 volts.
The drawback to this or any other linear circuit is that it isnt that efficient for voltages far above the output voltage, but then again many other Li-ion charging chips work like this too (although their max input voltage is not very high to begin with).
It's also a good idea to set the max output to about 4.15v instead of 4.20v just in case your meter doesnt read correctly.

If you'd like to see a circuit drawing i can post one with all the details.

Yes please... If u do, it'l be of gr8 help.

 

[Mohamed Najiullah]

Is there any IC for charging NiMH button type cells? And what happens if NiMH cells are over charged?

 

[audioguru]

Ni-MH cells get warm or get hot when overcharging. A battery charger IC should be used that detects when they are fully charged and turns off the charger so that the cells will have a long life.

 

[Mohamed Najiullah]

Ni-MH cells get warm or get hot when overcharging. A battery charger IC should be used that detects when they are fully charged and turns off the charger so that the cells will have a long life.

Can u recommend any such ICs?

 

[Diver300]

View attachment 39977

No. I meant the LiPo battery i'm using to charge the mobile phone.. U know, the battery i charge using the Solar and crank shaft. Does it require any special circuit to discharge without getting heated?

I've attached a rough schematic.. I'm talkin abt the one highlighted in yellow.


I know i'm asking too many questions.. I'm a beginner in electronics u see...

What we mean is that there is no need to have a battery between the cellphone and the regulator.

The cellphone has its own battery and charging control. If you supply it with 5 V it will charge, and it won't overcharge.

If you want to store power in a battery, and at a later time charge a cell phone from the battery, it is a lot more complicated.