How to decrease the output current and voltage from this DC to DC converter?

[audioguru]

I will be busy in gardening. Hehe

Good, then you will be safe.

Will battery explode with charging voltage up to 4.2V, then can't use this (above) circuit and monitor its charging voltage mannually and disconnect after it reaches 4.2V?

A Lithium rechargeable battery protection circuit disconnects the load if the voltage of a cell drops to about 3.2V. If the voltage drops lower then the cell will probably catch on fire the next time it is charged. A battery charger IC senses that a cell has a voltage lower than normal and begins charging it with a low current to avoid a fire. If it does not begin charging or if it develops a short circuit then the charging is terminated with a warning indication.
The circuit you found does not sense voltage so it will cause a fire if it tries to charge an over-discharged cell.

Be careful. Another thread has a Chinese ad posted for FAKE protection circuits that look identical to the REAL protection circuits on some Lithium cells.
When will you begin gardening?

But almost every Li-ion cell has its own built-in tiny chipset look like this (uploaded below, sorry for bad pic. It was a round shape Li-ion cell by LG). Is it a Li-ion charger chip you were talking about? Then can I apply any supply of 5V in the chip then will it limit everything needed for its Li-ion cell?

It is Korean and looks identical to the FAKE one. It might protect but I do not think it is a battery charger circuit.
My toy helicopter has a tiny protection circuit on its tiny Li-Po battery something like that.

-But I think each cells inside laptop battery pack has no its own differents chip. I guessed all cells have single chipset, called battery system circuit.

Two laptop batteries I opened had one battery system protection and balancing circuit.

 

[MrAl]

Hello,

The circuit you have posted is not good enough because it does not limit the voltage as audioguru pointed out. Ideally you could do it if you had to, but there are problems so please read on.

Yes it is true that you could charge a Li-ion cell with a pure power supply with no voltage regulation, but you would have to be very very very very very very careful because if you allow the voltage to get above 4.2 volts then the cell could explode. Ideally if you watch the cell voltage constantly with a good meter you would see it rise up as it charged:
3.60v, 3.61v, 3.62v, 3.63v, then later 3.9v, 3.91v, 3.92v, etc., and went you see it get to 4.15v you should stop the charge.

But you can see how boring this would get, and if you get distracted by someone or something else and you miss the termination voltage and it goes much over 4.2v you might come back to find a pile of ashes and whatever else around could be ashes too.
That's why we use a circuit to monitor the charge so that we dont get distracted and allow the cell to overcharge and cause big problems.

Yes you could use that chip in that circuit you posted, but it would have to be connected differently. There is another cheap very low cost charger that you could build using an LM317. Just a couple parts and you have a decent charger. If you are interested i'll post a circuit.

The current limit for a given cell is specified by the manufacturer. Looking at the data sheet for your cell you find out the max current and that's really the only way to be sure. You could estimate i guess but you should then err on the low side.
For example, a typical AA size Li-ion cell takes a max of about 330ma, but an 18650 cell takes 700ma or more up to maybe 1 amp. But again it is best to read the data sheet for the particular cell.

For a couple real world examples, i have AA cells that take 330ma and 18650 cells that take 1 amp max. The charger i built a long time ago can switch between the two current levels.

 

[Willen]

When will you begin gardening?

Let me to explode few cells, may be after then I will begin it. But don't worry I will use a 100 meter wire and will keep the cell 100 meter far from me, like NASA explodes its each space shuttle for International Space Station Because I have to charge and wake up laptop battery. It was good and it was able to operate my laptop more than two hours. But Voltage Regulator Module of motherboard shorted so battery discharged fully. So I am almost sure cells are in good in condition. I will check their condition first, will check thire voltage specially and will start to charge with VERY low current then will monitor its status. Then will increase little more current. Will use 4.2V charger circuit (didn't find till now). If i got success to explode them will start gardening. I have no garden so I will do it by going to neighbour's garden.

Two laptop batteries I opened had one battery system protection and balancing circuit.

Oh Yes, did you repaired then?

 

[MrAl]

Hi,

You posted right after me, so i hope you did not miss post #22.

 

[Willen]

Yes you could use that chip in that circuit you posted, but it would have to be connected differently. There is another cheap very low cost charger that you could build using an LM317. Just a couple parts and you have a decent charger. If you are interested i'll post a circuit.

Wow, I am really searching it! I have bought three brand new LM317 chips too, so post everything, say everything about it!

 

[audioguru]

Let me to explode few cells, may be after then I will begin it. But don't worry I will use a 100 meter wire and will keep the cell 100 meter far from me

55 years ago my friends and I made rockets that all blew up and we made very powerful bombs that flew very high. Some of our bombs blew up by themselves. We all survived somehow with no injuries.
But one friend died from absorbing a fuel ingredient (I think it was nitro-benzene) in the skin on his hands.

Oh Yes, did you repaired then?

I disconnected the cells from the protection circuit and used the best ones in an RC model airplane. They performed poorly and were very heavy.
Here is an American modern small lightweight Li-Po battery for an RC model airplane that comes without a protection circuit. Look at its continuous output of 189A! It can provide 378A for a few moments. It can be fully charged in 5 minutes.

 

[Willen]

Hi,

You posted right after me, so i hope you did not miss post #22.

Hi,
I am reading all posts by audioguru and by you. I am waiting a circuit by LM317 as you said...

 

[Willen]

55 years ago my friends and I made rockets that all blew up and we made very powerful bombs that flew very high. Some of our bombs blew up by themselves. We all survived somehow with no injuries.
But one friend died from absorbing a fuel ingredient (I think it was nitro-benzene) in the skin on his hands.

Then I knew you tried almost everyting But I knew that each and every humans are dangerous in his youth. Oh God how danger the experiment was....... You lost your friend. Yesterday I explode a 1watt resistor on a SMPS, my heart beat was 150beats per second. Then I used goggles and helmet of my motor bike for further reparing process.

Here is an American modern small lightweight Li-Po battery for an RC model airplane that comes without a protection circuit. Look at its continuous output of 189A! It can provide 378A for a few moments. It can be fully charged in 5 minutes.

OH GOD!!! I never heared about Li-Po battery and about its power!!!!!!! How tiny and how POWERFULL!!!! Why cell phones and laptop and cars are not using these Li-Po?

 

[MrAl]

Hi,

Ok well you did not reply so i was not sure if you wanted a circuit or not.

Here's a circuit that is pretty simple, but i have another one too that is even simpler. Note the IC can be a LM317 with a max current requirement of 1 amp.

Note you need at least 7vdc at the point shown in the diagram for this to work.
You should also make sure that the power can not be disconnected or the cell will be discharged over time which is not good.

 

[Willen]

*same post deleted!

 

[Willen]

Hi,

Ok well you did not reply so i was not sure if you wanted a circuit or not.

Here's a circuit that is pretty simple, but i have another one too that is even simpler. Note the IC can be a LM317 with a max current requirement of 1 amp.

Note you need at least 7vdc at the point shown in the diagram for this to work.
You should also make sure that the power can not be disconnected or the cell will be discharged over time which is not good.

Wow it's so simple and tricky! But how to choose current output? like you said 1A, 2A or 2A but I need amlost 400mA. Generally for 1500mAh cell, 1A output is too much high isn't it? May be I have to apply 1 or two ohms current limiter resistor R4 to get 0.3 or 0.4A current, isn't it?

And another- may I can use 7V to 30V as an input in LM317 (?)

 

[audioguru]

For an output of 4.2V then an LM317 needs a minimum input of about 5.7V. Any higher input voltage increases the heating of the LM317.
If the input is 30V and the current is 0.8A then you might not be able to cool the resulting 20.64W.

 

[MrAl]

Wow it's so simple and tricky! But how to choose current output? like you said 1A, 2A or 2A but I need amlost 400mA. Generally for 1500mAh cell, 1A output is too much high isn't it? May be I have to apply 1 or two ohms current limiter resistor R4 to get 0.3 or 0.4A current, isn't it?

And another- may I can use 7V to 30V as an input in LM317 (?)

The current limit resistor value is chosen to give a voltage drop of about 0.6v at the required current. So for a 1 amp current limit you would try 0.6 ohms first. The formula is simply R=0.6/Imax.

The current limit to choose could be estimated by the cells ampere hour rating divided by 2. So a 1 ampere hour cell would have a max current of 500ma. That's if you cant find the data sheet. So a 1500mAh rated cell should be charged at 750ma max as a rough guide.

I like to have about 2 to 2.5 volts of overhead across the LM317 but if you want to try lower you can try that too. As long as the cell gets the required current, and the regulator limits the voltage to 4.15 volts as a set point, and the LM317 does not get too hot with the heat sink you are using.

 

[Willen]

The current limit resistor value is chosen to give a voltage drop of about 0.6v at the required current. So for a 1 amp current limit you would try 0.6 ohms first. The formula is simply R=0.6/Imax.

The current limit to choose could be estimated by the cells ampere hour rating divided by 2. So a 1 ampere hour cell would have a max current of 500ma. That's if you cant find the data sheet. So a 1500mAh rated cell should be charged at 750ma max as a rough guide.

I like to have about 2 to 2.5 volts of overhead across the LM317 but if you want to try lower you can try that too. As long as the cell gets the required current, and the regulator limits the voltage to 4.15 volts as a set point, and the LM317 does not get too hot with the heat sink you are using.

Hi,
Few basic question again-

- Will it stop the charging process if battery charged fully? No chance to over charge? (I think yes)

- What is the chance of explode battery during charging, if battery is internally shorted? Will the circuit protect or will the circuit stop the current instantly?
- May be I can apply general purposes any NPN like BC547B there, isn't it? (but also I have 5 pieces of 2N4401 sent by Charles)
Thaks!

 

[audioguru]

- Will it stop the charging process if battery charged fully? No chance to over charge? (I think yes)

No.
The battery keeps charging at a low current and it becomes over-charged.
The Battery University says "Terminate charge when current <3% of rated current". The University also says, "Li-ion cannot absorb overcharge, and when fully charged the charge current must be cut off. A continuous trickle charge would cause plating of metallic lithium, and this could compromise safety".
Why didn't you read it??

- What is the chance of explode battery during charging, if battery is internally shorted? Will the circuit protect or will the circuit stop the current instantly?

The Battery university says that if a cell is discharged to a voltage too low and is charged then it becomes unstable. Nobody and nothing flammable should be near unstable Lithium.
Some protection circuits prevent charging a cell with a voltage that is too low.

- May be I can apply general purposes any NPN like BC547B there, isn't it? (but also I have 5 pieces of 2N4401 sent by Charles)

The current is low so ANY little NPN silicon transistor will work.

 

[Willen]

As I said before various cell has its own internal tiny chipset.
I think it is good and normal to apply this 4.2V supply for cell through that built-in internal chipset for max protection. Or will that chipset need overhead voltage too like 5V?

 

[MrAl]

Hi,
Few basic question again-

- Will it stop the charging process if battery charged fully? No chance to over charge? (I think yes)

- What is the chance of explode battery during charging, if battery is internally shorted? Will the circuit protect or will the circuit stop the current instantly?
- May be I can apply general purposes any NPN like BC547B there, isn't it? (but also I have 5 pieces of 2N4401 sent by Charles)
Thaks!

Hello again,

The circuit charges the battery with the usual Li-ion charge profile where the current starts out at the max and then when the voltage gets very close to the set point the current starts to taper off until it reaches a very very low level. For all practical purposes, the cell does not overcharge when the voltage set point is set correctly.

We have to be careful when reading some other web sites because they assume certain things and make conclusions based on those assumptions. If you remove even one of the assumptions, then you invalidate the conclusions. If the voltage is set to 4.15v then the cell can never overcharge because the voltage has to reach something like 4.25v before it begins to overcharge.

Also, stating that the cell can not absorb overcharge is not that informative of a statement in all cases. Yes it is true that it can not absorb overcharge and this is a reference to a comparison with other types of cells that can like NiCd. But what we want to know is not just whether or not it can absorb overcharge (which we know it can not) but also what conditions can cause an overcharge. We need to examine these conditions and how they relate to our charge circuit to know if the cell can overcharge.

So we know that comparing these cells to other cells that they are less flexible during the charge phase, but we also need to know the limits of that flexibility or else we'll call every charger out there 'bad' for the cell.

Commercial chargers turn off after the current reaches a low level related to the maximum current level. This is to protect their own but also because they often attempt a higher termination voltage. We could build this into the charger too, but it would be a waste of time and energy.

That said, a good set point for the charge termination voltage is 4.15 volts not 4.20 volts. What this does is it sets the maximum voltage for the cell at 4.15 volts, meaning that if you connect a cell that is 4.2 volts to the circuit it will probably actually DISCHARGE. Also, the slightly less voltage makes up for any meter inaccuracies, but you should use the best meter you can find to set this voltage, and check it often.
The drawback to using 4.15 volts is that the cell capacity is slightly reduced for that charge cycle, but it's not enough to worry about. The good thing is that the cell has a longer life and runs safer.

For a cell that has been discharged too low however it is a different story. Low cell voltage could cause an 'almost but not quite yet' short internal to the battery which may not show itself until the voltage across that 'almost short' increases. That's when the current jumps the now closer gap and causes a high current discharge which causes rapid and intense heat buildup which causes fire, smoke, and loud sound. So the only way to test if there is a short is to charge the cell and wait for fire, smoke, and loud sound <chuckle>. That's why you cant charge a cell that has been discharged too low. Of course it is entirely possible that this 'almost short' did not form yet, and then the cell can work fine for years to come. But it is that risk that is what tells us not to do it. It is also possible that there is a delay between the time we charge and the time we see fire and smoke. That delay would be caused by an 'almost short' that was less than that required to cause current to flow immediately but then happens at a later time just the same. Normal everyday mechanical stress applied to the outside of the package could cause that 'almost short' gap to become closer, thus initiating a sudden and intense high current discharge. This also tells us something about the proper everyday handling of the cells even when not charging them.

As for a cell having an internal short, if that happens all bets are off. It doesnt matter if it is being charged or not. If it shorts inside it could cause an explosion depending on how much energy there is left in the cell.

A good idea is to charge the cell inside a metal container of some type maybe with an open top so that the pressure cant build up inside.

I will also add that this charge methodology is based on leaving the cell on charge for 24 hours or less but it's best to never leave the cell alone when it is being charged no matter what charger you use.

 

[4pyros]

As I said before various cell has its own internal tiny chipset.
I think it is good and normal to apply this 4.2V supply for cell through that built-in internal chipset for max protection. Or will that chipset need overhead voltage too like 5V?

Some batteries may have a built in discharge protection circuit.
Lithium-ion batteries need to be charged with a charge controller circuit which can be in the device used or the charger for the batteries.

We are talking about two different circuits.

The discharge protection circuit built into some batteries will not control charging.

If your charge circuit does not have a timer then you will need to time the charging and pull the plug your self.

 

[audioguru]

As I said before various cell has its own internal tiny chipset.

Didn't you see the thread here with a photo of FAKE protection chips that are sold by a Chinese company? The FAKE circuit looks identical to the real one.

We do not have the datasheet for the protection chipset in your battery cells to see what protection it provides:
1) Refuse to charge or begin charging with a low current a cell with a low voltage.
2) Disconnect when the charging current is too high.
3) Disconnect when it senses a full charge.
4) Disconnect when the temperature of the cell is too high.
5) Disconnect when the pressure inside the cell is too high.
6) DISCONNECT WHEN THERE IS A FULL MOON?
Notice that I said many disconnects because a linear controlled charger produces heat in a circuit. The protection circuit is too small to dissipate heat so it has only on-off Mosfet switches that do not get hot.

I think it is good and normal to apply this 4.2V supply for cell through that built-in internal chipset for max protection. Or will that chipset need overhead voltage too like 5V?

I don't know because my cells had a system protection circuit. I used the cells with no protection. I made my own pretty big charger circuit from an LM317.

 

[Willen]

I made my own pretty big charger circuit from an LM317.

Few of you I meet here, I can believe fully!

Do you have the schematics till now?