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.

[ADBrown]

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?

Electonics in general, and PocketPCs in particular, usually have a viable range of voltages, and if the voltage is off they just won't run. There are exceptions to this, of course--enough voltage and it really won't matter. Don't plug a 5 volt device directly into a 12 volt source, or a 110 volt adapter into a 220 volt outlet. But if it runs off 6 volts, you're probably pretty safe. Be alert to whether or not the PPC gets overly warm--if it does, then the power regulator might be working too hard, and you should step down the voltage.

You can't overcharge a LiIon battery. Once it's full, it will stop charging and just run off the external batteries. I believe that there's a small risk of a reverse flow, the PPC battery trying to charge the AAs, but I'm not sure. You'd have to ask somebody more knowledgable about EE matters.

Theoretically, if something went wrong, you could fry the entire PDA. It's not very likely, and the only time I've ever heard of it happening was some guy who plugged his iPaq directly into a 12 volt battery.

[uzetaab]

Some suggestions on what you could do to make sure you won't have any problems:
1. buy a 5v voltage regulator (from Radio Shack etc)
2. A diode will prevent reverse charging (from Radio Shack etc)
3. google for a circuit diagram to make a proper charger
4. use a torch or something to partially drain the battery until they register 5 volts
5. put a resister into the circuit to lower the voltage (from Radio Shack etc)

If I were you I would go for 3. There are some really simple circuits out there for chargers & the parts could easilly be bought from a electronics shop like radioshack. Actually, you could probably buy a kit to make a charger from them.

As for your questions, I'm not an expert, but I can say that although the 6v charger will work fine, it is overworking your device & will probably shorten it's life expectancy.

An overcharge would damage the battery & effectively give you a shorter battery life between charges.

I would expect that the long term results would be that the battery life would shorten & eventually the inbuilt voltage regulator might give out.

Mind you this assumes that you use this device as your primary charger. Most likely you will only use this in an emergancy & therefore only infrequently. If this is the case I would not worry to much about it.