4.5 v battery charger.

[vinod chandran]

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

 

[davenn]

and $6million question is....what is the type of battery ?


Dave

 

[CocaCola]

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]

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.

 

[khankll]

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]

Hi khankll,
thanks. Let me try.

 

[Externet]

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*)]

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.

 

[vinod chandran]

 

[vinod chandran]

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