vB Easy Archive - Charge BB from AA batteries?

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Charge BB from AA batteries?
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Posted by: tafische

So I decided to make an emergency battery charger using 4 AAA batteries. I have occassions where I have no other power source avaliable.

I am using a 7805 5volt regulator and 4 AA batteries. Note: you can not use recharagables unless you go with 5 because they are only 1.2V, not 1.5

Anyway - I get a great 5v regulated output, however the BB only charges for a few seconds then stops. It is the exact behavor I get when I use my MP3 player's charger. I thought the mp3 charger was bad, but obvioulsy the BB is looking for some type of signal on the data lines or something to keep it charging. I tried my homemade charger on another device and it works perfectly.

Anyone know the details of this? Obviously just 5v across the power lines of USB is not enough, it needs to be fooled or something. I have a car/desk charger from Cingular that work fine, so it is possible.

Posted by: corey@12mile

If I had to guess I would say that the battery solution is not providing enough amps of power. There is no signal involved with the charging process. Car chargers do nothing more than what you have outlined. Did you add a resistor and capacitor to the circuit to handle jumps when plugging in and unplugging the device? You could possibly catch a small spike when plugging in or unplugging that will burn your blackberry unless you have a protective circuit like I mentioned.

cd.

Posted by: GregGebhardt

why go to all this trouble. I think radio shack has a deviice that holds size "D" batteries and a plug (female) that you can stick the car charger in.

DONE|

Posted by: Pennywise

It needs more than just the 5V, you can demonstrate this for yourself by trying to charge via USB cable from a device that doesn't have the desktop client installed. It charges at so slow a rate that it would probably be a full 24 hours to reach a full charge.

Posted by: GregGebhardt

Quote:

Originally Posted by Pennywise

It needs more than just the 5V, you can demonstrate this for yourself by trying to charge via USB cable from a device that doesn't have the desktop client installed. It charges at so slow a rate that it would probably be a full 24 hours to reach a full charge.

I think you have to tell your computer to provide more voltage to the USB connection. Installing the BB software does this. I have charged my BB from a desktop and laptop that did not have the software and it charged it up just as fast. All depends on the voltage comming from the USB.

Posted by: corey@12mile

OK... here's the way USB charging works from a computer.

By default, when a USB device is plugged into a computer, the OS gives the USB device 100 milliamps of power, voltage is *always* 5 volts. In order for a device to receive enough power to charge, or to run at times, the driver has to be installed to tell the OS how much power to send to the port.

When you install the handheld driver for your blackberry, the OS then knows to send 500mA to the port that the blackberry is connected to.

You can see this by going into the device manager in windows, expanding the USB devices branch and going into the properties of any of the 'USB root hub' listings. The second tab over says 'Power'. From there you will see how many ports that root hub has, and what devices are connected to it. I have my MS mouse on 1 port drawing 100mA, my blackberry drawing 500mA and a thumbdrive drawing 200mA.

This is the exact reason I said the AA battery solution wasn't working. Not enough amperage, has nothing to do with voltage. You could, hypothetically speaking charge the device with 3 volts, as long as you have enough amperage. Voltage is the speed that the electricity runs at, amperage is the volume of electricity moving along the conductor (wire, pcb trace, etc.).

In order to charge a battery, you need amps, not neccessarily volts.

cd.

Posted by: jefe

Quote:

Originally Posted by corey@12mile

In order to charge a battery, you need amps, not neccessarily volts.

cd.

That's not exactly correct.

Ameperage is indeed the volume of the current flow. It's analogous to the volume of water flowing through a garden hose.

Voltage is the electromotive force behind the current. It's analogous to the pressure in a water hose.

Current flow has to over come resistance. Thus the amount of current flow is a product of the voltage devided by the resistance, shown in Ohm's law, I=E/R, where I= current in amps; E=electrocmotive force in volts, and R=resistance in Ohms.

The bottom line in simple terms is the charging voltage has to be greater than the voltage of the device being charged or there won't be any current flow in the direction you want it to go. You can't charge a 5 volt battery with 3 volts, or a 12 volt battery with 11 volts.

That AA charter should work if the output is 5v and the regulator can maintain 5v under a load of 500 ma.

So my question to the OP is have you measured the output of the 7805 regulator while it's actually charging the Blackberry for that few seconds? My guess is it's folding back and you're not seeing 5 volts under load.

Posted by: racarusotheoreo

Quote:

Originally Posted by tafische

So I decided to make an emergency battery charger using 4 AAA batteries. I have occassions where I have no other power source avaliable... so it is possible.

Silly rabbit.

This is the BoxWave "Battery Adapter for miniSync".
I've only used it with my Treo; the BB battery ROCKS so much I haven't had to recharge it on the go.
But the BoxWave charger will recharge/run ANYTHING that can charge via USB...

and that ROK's!!

Links:
BoxWave Charger for Purchase

Posted by: tafische

Yes...I have tested the output and definatley 5v. It will charge other USB devices just fine. One posted mentioned I was not getting enough power out. I am sure you can get 500mA out of 4 fresh alkaline batteries. One person suggested since there is not a current limited circuit on it that the BB might be shutting down the charge circuit for protection. I would have thought the bb had its own internal current limited.

It is a plausable reason since I went back and looked at my MP3 charger that acts the same way and it outputs 1000 mA (not the standard 500mA).

racarusotheoreo - can you try that device on your BB and let us know how it works?

Posted by: racarusotheoreo

Quote:

Originally Posted by tafische

racarusotheoreo - can you try that device on your BB and let us know how it works?

Already done, ranger

This is a 7290 GSM locked to Cingular I tried it with (will try to get my hands on a 7100g and t by Sunday to try.)

The BoxWave, with it's 2 batteries, charged the 7290 battery from bone-dead dry to full in about 35 minutes

Yes, it rocks. And it's pocketable too...
I would consider getting a second USB cable for the BB from here, just so that you have a backup. Be prepared

Hope this helps!
The. Caramel. Sensation.

Posted by: tafische

Thx! I appreicate you trying that out for us. I am still going to figure out why mine is not working!

Posted by: jase88

This thread reminds me of the 957 days; when I'd go through an AA battery a week...