Home-made battery extender for pda’s

[cmavr8]

Hi, I have been seeing those “Battery extenders” around ebay for a long time. As I understand it is just a battery case with a led, a switch and an adapter. Some have a circuit that prevents overcharging.

My question is; why pay $30 when I can make one of these for almost nothing?
Well, I tried it. I connected a battery case, with a cable and an adapter that fits my Toshiba e570 pda.

I plugged it in and… BOOOOOM!

No, it worked. The red led on the pda went on, and the indicators where showing charging…

But I didn’t let it there, I was afraid. My stock-original adapter gives 5Volts but as I connect 4 AA batts I get 6 when fully charged. So, Qs:

1. Will this +1 volt harm the battery or the pda?
2. What happens if overcharge occurs? (no protective circuit here…)
3. Generally, what can happen? Damage just the battery or the whole pda?



Thank you.

[Demens]

I just build a one for me too.

I used 4.5V battery and usb female-cable.
http://koti.mbnet.fi/mads/webbi/LATURI2.jpg


I think that it's not wise to charge 5V with 6V. Can be harmfull. Consider buying a "regulator" to drop the voltage... When i get mine i'll change the 4.5v to 2x9v.

[thatcloud]

Do you need a capacitor to prevent the external from draining the internal battery? (OR does the machine itself prevents that?)

[Tam Hanna]

Hi, i would say that you should use a shottky diode for this purpose.

[strider_mt2k]

IMO there are three schools of thought here.

1. A diode.
A diode will drop a little voltage(.6 or so +/-), and for sensetive/low current devices this is usually just fine.

2. A voltage regulator (like an 7805 or similar)
A voltage regulator is great, but you have to run a sigificantly higher voltage into it for it to operate properly, so for 5 volts, a battery of 9 volts is probably where you want to be.
Why 9 volts?
(Without resorting to a bunch of figures that I don't know off the top of my noggin)
The battery's voltage will drop as it's being used, but the 5 volt output will remain the same, because your usable voltage stays above where the regulator needs to be for proper operation.
As the battery drops below useable voltage, the regulator will simply drag the voltage down further, and finally the device being charged will stop charging as the battery voltage drops below a certain level and switches over to it's own internal battery.

The voltage regulator also won't shed much heat only regulating down 4 volts from a 9 volt supply.

You can run higher voltages into regulators, but they will have to work harder thus shedding more heat, which will have to be carried away by a heat sink or else the regulator will overheat and either go into thermal shut down, destroy itself, or a combination of both, depending on the regulator and the circumstances.

(What you want is higher CURRENT for longer running time.)

Now...

#3. To be honest, I think running one volt higher is NOT going to harm a thing.
DISCLAIMER:
NOT RESPONSIBLE FOR 1 VOLT HIGHER HARMING A THING.
RESEARCH YOUR DEVICES AND WORK CAREFULLY!

The electronic components involved here generally have wider tolerances that 1 volt.
More voltage than 1 volt that COULD harm the device in question, but 1 volt?
Doubtful.

I became a licensed ham radio operator in 1990, and soon after built an uninterptable DC power supply into an ammunition box using a lead-acid battery, charger, and a light-weight (and available) digital power supply.
I built it to run my portable communications rig.

When my "N2NLQ Power Box" is pugged into an AC outlet, the power supply provides the DC output while the battery is kept maintained by the charger, but when in the field, or in the event of AC power loss, the battery supplies the DC ouput.
(Automatic switchover in the event of power loss, hee! :) )

Something very similar to this could be constructed on a smaller scale so that you could get the best of both worlds.
EDIT
(for 5VDC I envision USB connector(s) for easy fabrication from off-the-shelf components, and ease of custom cable fabrication.

If you're into that kind of thing.

[strider_mt2k]

Here is a great link I just found that gives better info than mine on voltage regulators.

http://www.rc-cam.com/dc-dc.htm

Hope it helps.

[JAmerican]

I decided to be safe and order one :)

http://jamerican.net/1src/UX50/batteryextender.jpg

I call it my EB50.

JAmerican

[carson]

If you want to use a 6V battery with 5V out, use a Low Drop Out regulator (LDO). You just need to choose one that will handle the current, and operate within the 1V overhead. Most standard 7805 type regulators require 2V of overhead. However, I'm not sure if you also need a charging circuit which controls the current or not. A charging circuit may be built into the Clies.

Hope that helps.

[naborcb]

Hi I make a home Battery extender with a Circuit 7805 and 4 AA Ni/Cd 850 Mah battery but it did´nt work so I try with 6 AA Ni/Cd mah and.... nothing . It´ll be safe to try whith 2 groups of five AA Ni/Cd in serial join in parallel ?

(a)5AA ser = 6V
(b)5AA ser = 6V
(a)+(b) par-------6V+ 2 (850mah)????

[egadgetguy]

You guys must be forgetting that the voltage supplied to most of these devices is approximate anyway. Most of them can charge from any old ~5VDC as the internal battery is connected through a complex regulated charging circuit which can work with 5V+- 1.5V

[Kessler]

You guys must be forgetting that the voltage supplied to most of these devices is approximate anyway. Most of them can charge from any old ~5VDC as the internal battery is connected through a complex regulated charging circuit which can work with 5V+- 1.5V

So.. is it safe to just grab a 4 pack of AA's and use a battery holder then solder a palm cable on? I just don't want to destory my T3. All the battery packs online specify that they have an IC chip to prevent damage.

[cheys03]

Why not use NiMH rechargable batteries instead? Usually run at 1.25-1.3v each, four would give you 5.0-5.2v...ideal with the bonus that you'll save on regular AA batteries in the long-run (once you've paid for the charger!)

I would also agree with alot of the comments above and would be happy charging at 6v.
Besides, if you measure the actual output of the official mains charger, it's generally not 5v anyway. Mine reads @ 5.4v.

[MrGadgets]

Hi, i would say that you should use a shottky diode for this purpose.

which kind of diode? :confused:

[_Em]

Look it up on digikey.com :)

I agree with the +-1.5v statement above; I've always used this tolerance level on 5v digital electronics and have never had a problem.

Actually, because of the way Palm/Clie devices work, they'd probably tolerate all the way up to 8v... and if you push it too high, they have a built in failsafe that will break the loop. I think powering down completely for 5 min is generally enough to bring it back up (yay for automatically resetting fuses!).

Just make sure you watch your amperage; you could probably do some damage pushing too many amperes through that circuitry. My Palm states "5.2V - Max 1A" on the back.