low cost li-ion batterry charger with stage detector - not necesary

1270

1d 01:26:47

Charges in two stages
1 - Quick charge, charges with almost constant current untill 4V, red light
2 - precise charge, charges with decreased current untill 4.2V. green light

This will not overcharge your batterry so you dont have to worry about time. Commercial chargers work like this. At beginnig of 2nd stage battery is charged at about 90% of its capacity. 
v1.1 - one op amp used

published 12 years ago

Secuture

12 years ago

Great and simple design

hacsav

12 years ago

If i want to use 5 volt input what should i change ?

stanke

12 years ago

Nothing, but first part wil not gave you that much current :) itll charge your battery anyway but much slower

stanke

12 years ago

Youll need step up before circuit because you need at least Ud+2Ube (~7V) to open transistors to let circuit work properly.

hurz

12 years ago

And 2Ube depend highly on temperatur, so be careful to not overload your Bomb ;-) and keep the darlington stage constant in temperatur.

stanke

12 years ago

Its very good point but in the second stage it is only mAmps flowing through emmiter, so be carefull but dont worry about explosion.

hurz

12 years ago

I would save the seconde OpAmp and power it with 12V to save one hidden 7805. Both LEDs in serie and at the middle point the comparator out. Keep on constructive circuit design

stanke

12 years ago

But left OP amp is precise current limiter and right op amp is voltage limiter :) thats the way how lions should be charged :)

hurz

12 years ago

Sorry, the circuit i see is different. The opamps have the same input information. 1pin for a referenz derived from 12V and one zener voltage. Only +- is swapped how switch from green to red is made. They do nothing really different

stanke

12 years ago

My god i was in mind in another circuit. I used two op amps because theyre usuallyin one package :)

hurz

12 years ago

Ahora si, now the LEDs in serie. From plus to minus, LED R, comparator out, LED R. Comparator output to low 0V and 12V rail to rail. Voila

methane2k

9 years ago

I see some confusion in the comments as to which circuit was posted. Is the circuit posted now the complete circuit? Looks good just hoping I don't have batteries exploding on me when I try to use it.

ETJAKEOC

9 years ago

One thing comes to mind, rough math would state that to represent a 3.5Ah cell it would take a 1.3Mf capacitor, yikes lol

stanke

9 years ago

Sure its only for illustration of charge. Also the circuitry should be safe from plain design :)

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