Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Mobile charger to charge LiIon batteries, Usng Voltage Divider to drop voltage

Status
Not open for further replies.
K

khankll

Junior Member level 2
Joined
May 23, 2010
Messages
24
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Location
usa
Activity points
1,442
hii have a lot of mobile phone charges that say "output 5v .7A" i want to use it to charge a liion battery..both prismatic and cylindrical 18650.i have few question..

What does the figures in output mean ? does it means its a CC/CV output ?

Can i use a Voltage Divider Circuit to Drop the extra voltages and get 4.2volts and then connect those 4.2 volts to the output of protected 18650 cell or unprotected liion cell ( saftey against over charge is gauranteed by firstly the fact that when the battery voltage equals the charger output voltage no more current flows and secondly i will be constantly observing it..) while reading about Voltage divider network in the book "Electic Circuits" by Nilsson it mentioned that the as long as the Load Resistance is very very greater then R2 ( wheare as r1 and r2 are the two series resistors and r2 is the resistor accros which i will be geting output ) ..the output voltage remains fairly constant.. ? so in my case the load is cell what should be its resistance ?


Thanks
 

Absolutely not!

Sorry to be so blunt, but you don't want to mess with those cells, even with the protection circuits on them. Charging LiIon cells, while not complicated, needs control and precision. The fact that you are asking the questions you are, means that you don't (yet) have the knowledge to do it safely. Seriously.

The voltage divider will not give anything like a constant voltage when connected to a charging cell, nor will it be able to provide enough current without using massive power resistors and wasting a hundred times more current than the cell gets.

I regularly recycle 18650 cells from laptops and, even though I know what I'm doing, I won't charge them in anything but a proper charger. LiIon cells can burst into flame long after you have misused them due to internal crystal growth.

You can buy single cell charger integrated circuits that simply need a couple of components and a 5V input. Maxim make some, I can't remember any part numbers off the top of my head. That's the way to go if you don't want to buy a full charger.

The 5v .7A PSU means that it gives 5V, and can safely provide up to 0.7A - it will only give what current is taken by the circuit.

Do a search here, for LiIon charger and similar key words. You will find a lot of posts about it, and probably the part number that I can't remember.

P.s. don't take anything I said to be derogatory or anything like that - I'm thinking of your safety and just tend to speak plainly. Feel free to ask more questions about this after doing a quick search as I suggested.
 

FoxyRick said:
Absolutely not!

Sorry to be so blunt, but you don't want to mess with those cells, even with the protection circuits on them. Charging LiIon cells, while not complicated, needs control and precision. The fact that you are asking the questions you are, means that you don't (yet) have the knowledge to do it safely. Seriously.

The voltage divider will not give anything like a constant voltage when connected to a charging cell, nor will it be able to provide enough current without using massive power resistors and wasting a hundred times more current than the cell gets.

I regularly recycle 18650 cells from laptops and, even though I know what I'm doing, I won't charge them in anything but a proper charger. LiIon cells can burst into flame long after you have misused them due to internal crystal growth.

You can buy single cell charger integrated circuits that simply need a couple of components and a 5V input. Maxim make some, I can't remember any part numbers off the top of my head. That's the way to go if you don't want to buy a full charger.

The 5v .7A PSU means that it gives 5V, and can safely provide up to 0.7A - it will only give what current is taken by the circuit.

Do a search here, for LiIon charger and similar key words. You will find a lot of posts about it, and probably the part number that I can't remember.

P.s. don't take anything I said to be derogatory or anything like that - I'm thinking of your safety and just tend to speak plainly. Feel free to ask more questions about this after doing a quick search as I suggested.
Click to expand...

thanks brother i realy appreciate your concerns for my saftey.. and ur frank advice..

i did reasonable research on charging liion.. and when looking at most products in the market (on the net) it boils to the fact that most liion chargers are simply CV sources which continiously pumps charge to cell and when the cell voltage equals the charger voltage the current flow stops and hence charge done...

i have few chargers but here in my country firstly most of the ics are not available ... cant buy it from net online ... as the shipping cost to my countery is exhorbitatnly high.. and also me poor guy not credit card.. hahaha here deals are made hand to hand..

also power loss with proper resistors is not an issue if i can get a good choice of resistors.. and also i red in nilsson book that vdrs are extensively used to obtain multiple voltages in electronic circuits instead of using seperate power supplies...

and i have charged liion cells manually using bench power supply using CC/CV outputs of the supply...

so i want to mod these chargers or somehow its output to get what i want...
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top