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# 4.5 v battery charger.

#### vinod chandran

Jun 21, 2011
192
Hi,
I had a 4.5v battery and a 5v (500mA) power supply with me. I want to build an automatic mini LED emergency lamp with these components. All i need an automatic charger circuit which suits these components. plz help.
-vinod

Moderator
Sep 5, 2009
14,039
and $6million question is....what is the type of battery ? Dave #### CocaCola Apr 7, 2012 3,635 In addition to the$6 million question...

Define the battery better, if it's 4.5 volts what is the measured 'full' charge voltage? The 5 volt supply might be too low to bring the battery full charge...

#### vinod chandran

Jun 21, 2011
192
Ha..ha...Davenn..Actually i don't know anything about that battery. I got it from a LED Torch. Anyway i am attaching the image of that battery. If you cannot understand the battery we can leave this project but i had another big battery (12v 7AH). And i need your help to find a charger circuit for this battery. I got this battery from my old ups. And for the charger, i had two transformers., one is 12-0-12 5A and the other is from an old CD player which has so many outputs.(2 yellow wire gives 22v, 2 black wires gives 12v , 2 blue wires gives 12v and 2 green wires gives 3.3v). I don't know how to measure the ampere but i think it is an 1.5 A transformer.

#### Attachments

• Photo-0042.jpg
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#### khankll

Feb 6, 2011
110
post side views mostly its 2 cell lead acid battery.. check if there is some electrolyte..
to charge it u will need realy tiny current say 100-200mA .. these are normally .7-1 AH ..
or 1.3 for a realy good brand battery like leoch etc..

you can attach a quarter watt 5.6 ohm resistor in series with 5 volts and it will slowly chargre it.. in 5-8 hours..

or get a potentiometer as low as possible ( which should provide resistance from 1ohm to 10 ohms) and use that to adjust the current..

#### vinod chandran

Jun 21, 2011
192
Hi khankll,
thanks. Let me try.

#### Externet

Aug 24, 2009
830
Connect the 5 V power supply to the battery with a 1N4001 diode in series.

+5.0V-----------------|>|------------Bat(+)
Common----------------------------Bat(-)

If the battery needs 5.0V to charge, just connect directly without the diode.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Some form of current limiting should be used.

Also with this you need to monitor the battery voltage and disconnect it when it reaches a full charge.

Note that this voltage varies with temperature for lead acid batteries.

Also, if you do this without a diode, and you're using something like a computer (USB?) to charge this, when you turn the computer off the battery may try to power the 5V rail of your computer. This is probably not what you want.

Jun 21, 2011
192

#### vinod chandran

Jun 21, 2011
192
Hi
Thanks Externet and steve. . How about this circuit ?. What if i connect my 5v power supply (actually it's a mobile charger) to this circuit. How can i monitor full and low battery ?
-vinod chandran

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