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[Ideas For Design]
Build A Smart Battery Charger Using A Single-Transistor Circuit

Ejaz ur Rehman  |   ED Online ID #1823  |   November 25, 2002


The following automatic battery-charger design is created with a circuit that could qualify as the simplest window comparator ever built around a single transistor (see the figure). It starts charging when the battery voltage drops beyond a preset value, and it stops when an upper preset voltage is attained.

With the help of a precise variable voltage supply, the upper and lower voltage levels were set. The normally connected (NC) lead of the relay isn't joined to the 15-V dc supply, which blocks this voltage from passing to the battery leads. This will accurately set the upper and lower levels. But the charging supply of 15 V dc was connected to the circuit.

First, the variable supply is fixed at 13.3 V dc—the voltage of a fully charged battery—and linked to the battery point of the circuit. The slider of VR1 is turned to the extreme end on the side that's attached to the positive terminal of the battery. VR2's slider should be turned toward the end that's connected to VR1. The transistor turns on, shunting VR1. Then the slider of VR1 is turned toward the other extreme, which is the end connected to VR2.

The test supply voltage is now set to 11.8 V dc, which is the voltage of a drained battery. VR2 is then adjusted so that it just turns off the transistor again. The test voltage is raised to 13.3 V dc again, and VR1 is adjusted so that the transistor turns on. With the upper and lower levels set, the NC point is connected to the circuit (15-V dc charging voltage). Now the battery charger is set and ready to go.

Related Articles:

ifd winners
W. Stephen Woodward, University of North Carolina, "PC And Long-Baseline Chronography Measure Ballistic Parameters Acoustically," July 22, 2002.

Jim Christensen, Maxim Integrated Products, "Speed Control Handles Isolated -48-V Fans," August 5, 2002.

Submit your own Ideas For Design to:
IFD@penton.com


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    Reader Comments

    The circuit is here: http://electronicdesign.com/Files/29/1823/Figure_01.gif

    Anonymous -November 20, 2009

    i can't get this unit to work .do you need to hook up the ac to the cct.to me there is some confusion as how to hook it up.

    thanks for any help

    g

    frustrated -November 06, 2009

    its 9v battery charging 3v battery...can i not use rectifier?

    tp -November 05, 2009

    ok what if i want to recharge the battery with 12v battery? how will that be?

    Anonymous -November 02, 2009

    in ohms or k ohms?

    thnx

    tp -November 02, 2009

    The values in the circuit are ohms not V. I just made it and it works fine.Smart idea by Rehman.

    Anonymous -October 14, 2009

    I LIKE IT

    SHILJITH -October 10, 2009

    i want to a math still model for our school math fair?

    Anonymous -October 03, 2009

    i want to a math still model with picture

    Anonymous -October 03, 2009

    hi would please any one tell me how to down convert ac voltage just thru a resistor and not by transformer?

    Satish -September 14, 2009

    what is the value of VR1,R2 ana R3

    oscar -September 10, 2009

    can u send me the simplified circuit diagram

    ramadhevi -August 29, 2009

    What is the value of the component used in constructing this smart battery chargerbuilt around a single transistor

    Oscar -August 28, 2009

    plz send me the codes

    Anonymous -August 17, 2009

    I need to design a phone charger that uses heat energy from burning charcol to charge a 3.7V battery.

    Dominic -July 31, 2009

    I need simple diagram how to make 90amp,12v battary charger. Hemantha.

    Anonymous -July 14, 2009

    which transistor is equivalent to c1061

    hamid -July 06, 2009

    The resistor values are correct. I just tested circuit and every thing works well. Of course the V refers to ohms, you just can't type Ohms symbol. Use a relay with a 12v coil and one that has a NC(no contact connection)which is a 5 pin device i used a car relay.

    For Vr1 & Vr2 use variable resistors

    Anonymous -July 03, 2009

    I also would like to see some answers to these legitimate questions contained within these posts

    Anonymous -June 24, 2009

    hello

    cdmawin -June 05, 2009

    I WANT 1 NOS. BATTRY CHARGER

    SHAHID ALAM -June 04, 2009

    hgfhfhfhgfh

    vijay -May 19, 2009

    The circuit it is shown that VR1 is 500V is it ohm?also R2 is 290V and R3 is 15V ,should we read this V as Ohm? Please reply me. Thank and regards , Tariq

    Tariq -May 18, 2009

    hi

    I ask for RL1 Whai is ?

    Auose -May 12, 2009

    diagram of battary charging circuit.

    Engineer -May 09, 2009

    circuit digram of single transistor battary charging circuit.

    amal -May 09, 2009

    could u plese talk in tecnical languge.

    KK -May 03, 2009

    Where is Mr. Elaz Ur-Rehman ? He develioped this design, and I want to ask hem about the component values.

    Tom Berge -April 16, 2009

    Please, anybody can help me out. I need circuit diagram 1000 watt inverter for inverter using SG3524 IC with pmw

    farooq ahmed -April 16, 2009

    Where will you print these answers ? I don't know if this is getting through to ANYBODY ? ANYBODY? Please answer me at tberge@gra.midco.net Thanks somebody

    Tom B -April 14, 2009

    PLEASE tell me what the proper values are for this schematic. VR1, VR2, R1,R2, R3, and whats the dweal on the relar RL1. Thank you

    Tom Berge -April 14, 2009

    kindly respond to readers query and lets know through this site the correct values VR1, R2 and R3.Thanks

    Anonymous -April 08, 2009

    good

    Anonymous -April 07, 2009

    in the circuit it is shown that VR1 is 500V is it ohm?also R2 is 290V and R3 is 15V ,should we read this V as Ohm? Please reply me. Thank and regards , Ashok

    Ashok D. Chachad -March 25, 2009

    Your ideya is good but where is the circuit?

    Ashok D. Chachad -March 25, 2009

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