making a 9 volt battery charger

Thread Starter

gvfc2

Joined Sep 14, 2010
11
I'm trying to see if a usb wall charger will charge a 9 volt battery and be able to charge a phone while its not plugged in to the wall. What I mean is when its plugged in it charges the 9v. When it isn't plugged in it charges the phone.I have a european usb charger I took apart and going to make it usable with us sockets. The circuit board number is 908-55 and it is from courier charger model #TJ-8908<ic>. Please help me
 

Audioguru

Joined Dec 20, 2007
11,251
What chemistry is the 9V rechargeable battery? Ni-Cad or Ni-MH?
Some are actually only 7.2V (six cells) and others are actually 8.4V (seven cells).

USB is only 5.0V so it will not charge a 9V battery.
 

wayneh

Joined Sep 9, 2010
16,102
And a typical 9v battery has many fewer amp-hours than you'll need to charge a modern cellphone battery.
 

Thread Starter

gvfc2

Joined Sep 14, 2010
11
The 9v is nimh. What I was thinking was before the it goes to the usb have it branch off somewhere to have a charger for the battery which then will be connected to the usb to charge the phone at a flick of the switch. Forgot to add I already have a battery powered usb charger that's the simple thing that steps it down to 5v and max amp is 1amp. And I've kind of charged my phone. Its more like an extra battery. But I do have another one of those chips left over if I would need to use it
 

Audioguru

Joined Dec 20, 2007
11,251
What is the mAh rating of the little 9V battery and what is the mAh rating of the battery in the phone?
The little 9V battery has much less capacity so it will not charge the phone much.
 

Thread Starter

gvfc2

Joined Sep 14, 2010
11
The 9v is 200mah. The battery in the phone I don't really know. Ill have to take another look
 

Thread Starter

gvfc2

Joined Sep 14, 2010
11
The phones battery is 1500mah. I could get 2 9v batteries. The charger puts out enough to charge the phone with 2 batterys so all I need right now is a charging circuit for the 2 9v batteries. I should be able to figure out the rest
 

Audioguru

Joined Dec 20, 2007
11,251
The phone needs 1500mAh.
One 9V battery is only 200mAh.
Then you need 7.5 9V batteries to fully charge a dead phone battery only one time.
You also need a 5V regulator to reduce the 7.2V to 8.4V from the 9V batteries to 5.0V.

You need a charger IC to charge 9V Ni-MH batteries.
 

iONic

Joined Nov 16, 2007
1,650
Thats a lot of investment to charge a cell phone battery, more than if you just purchase a second cell phone battery, and you won't have to wait hours to use your phone again.
 
Top