USB charger.

[vinod chandran]

Hi Friends,
I build this usb charger today. it's working. But i've a doubt. is there any problem with a low battery?. I mean what if the 9v battery gets weaker while charging ?.
-vinod

 

[davelectronic]

USB charger

I can only see one real issue, i would have opted for a higher miliamp hour battery, say four x AA battery's or bigger, four x D, or C, size in a battery pack. other than that, fine.
Dave.

 

[Resqueline]

It will work down to approximately 7V battery voltage (depending on current draw), then the 5V will start to drop. Charging will slowly diminish.
There is only very little current available from non-alkaline batteries like in your picture, better to use alkaline, and preferably 5-6 AA cells.

 

[vinod chandran]

I can only see one real issue, i would have opted for a higher miliamp hour battery, say four x AA battery's or bigger, four x D, or C, size in a battery pack. other than that, fine.
Dave.

Hi Dave,
Thanks for the reply. your suggestions are precious to me.
-vinod

 

[vinod chandran]

It will work down to approximately 7V battery voltage (depending on current draw), then the 5V will start to drop. Charging will slowly diminish.
There is only very little current available from non-alkaline batteries like in your picture, better to use alkaline, and preferably 5-6 AA cells.

Hi Resqueline,
Thanks for the reply. "5v will start to drop ". Does this means the current will flow to opposite direction ?. do i need a diode?. This 9v battery in India costs only 12 Rs(0.240 USD) and the 6 AA batteries costs 60 Rs(1.20 USD). So i decided to work with non-alkaline.
If AA batteries were good for this, i have to rearrange the charger. Here is the total cost of this charger.
9v battery- Rs12(0.24 USD )
USB Female- Rs 5(0.1USD )
5v regulator IC- Rs 5(0.1USD )
2 Capasitors Rs 6(0.12USD )
Resistor Rs0.2(0.004 USD )
LED Rs 1(0.02 USD )
vero board Rs 10(0.2USD )

Total Rs- 39.2(0.788 USD )
-vinod

 

[BobK]

What are you planning on charging with this? If it is a cell phone, you will exhaust the 9V without fully charging the phone. Perhaps it is OK for an MP3 player.

Bob

 

[Resqueline]

The 5v will just simply start to drop, and the charging current will start to drop also, simple as that, nothing more.
This does not mean the current will start flowing in the opposite direction. You do not need a diode.
There is a reason those 9V batteries are cheap. A 9V non-alkaline battery have about 100mAh, while an alkaline have about 500mAh.
Alkaline AA batteries have about 2000mAh. So you figure out what will actually be the cheapest (Rs/mAh) batteries. It's a costly recharge method anyway.

 

[vinod chandran]

What are you planning on charging with this? If it is a cell phone, you will exhaust the 9V without fully charging the phone. Perhaps it is OK for an MP3 player.

Bob

Hi BobK,
I use this charger to charge my mobile phones. But i never charge a phone above 5 minutes from this charger. If so i need to use AA size batteries.
-vinod

 

[vinod chandran]

The 5v will just simply start to drop, and the charging current will start to drop also, simple as that, nothing more.
This does not mean the current will start flowing in the opposite direction. You do not need a diode.
There is a reason those 9V batteries are cheap. A 9V non-alkaline battery have about 100mAh, while an alkaline have about 500mAh.
Alkaline AA batteries have about 2000mAh. So you figure out what will actually be the cheapest (Rs/mAh) batteries. It's a costly recharge method anyway.

Hi Resqueline,
Thanks for the reply. So what if i use 3 AA size batteries ?. In that case do i need the 7805 regulator?.
-vinod

 

[Resqueline]

Hi Resqueline,
Thanks for the reply. So what if i use 3 AA size batteries ?. In that case do i need the 7805 regulator?.
-vinod

With 4.5V input there's obviously no (or rather a negative) headroom for the 7805 to work. It needs 2-3V of headroom, hence 7.5V is the minimum input requirement for its use.
It might work for a while (3 fresh AA batteries, no 7805), depending on the phone charging circuit, but it'll certainly cease to function long before the AA batteries are depleted.

 

[vinod chandran]

With 4.5V input there's obviously no (or rather a negative) headroom for the 7805 to work. It needs 2-3V of headroom, hence 7.5V is the minimum input requirement for its use.
It might work for a while (3 fresh AA batteries, no 7805), depending on the phone charging circuit, but it'll certainly cease to function long before the AA batteries are depleted.

Hi resqueline,
Thanks for the reply. It seems 6 AA batteries is the best choice for this charger.