Extra Battery Life

fogus · Post by **fogus** » Sat Mar 12, 2005 12:11 am

Hello,

I’ve been enjoying things very much so far here at PCA. I have a question about my palm pilot now. As we are aware, with the advent of the LCD screens, palms chew up a lot more power than they used to.

I was thinking that it would be nice to have an external battery charger. However, I don't want to blow my Tungsten E anytime soon. I was thinking that although my palm charges at 5.5 V DC, that I may want to charge at a lower voltage. I thought that four AA batteries would do nicely, (as NIMH batteries carry a charge of 1.2 volts, making 4.8 volts total). I assume that this voltage is safe. (What voltage do USB ports carry? My palm also charges off these) The only question is whether the amps of the battery would be safe. I'm sure that four AA batteries could carry a lot of energy. Think of how long my palm would last! If the amps is too high, could I hook up a resistor some how?

I got started on this whole idea because I found a little jack that would fit my palm’s charger port. Apparently the Tungsten models are fairly universal. They have the regular USB ports, and regular charger ports. Its very annoying to have special cables for all my devices. My dad got a Treo, and it has all the *special* cords that no one but palm one sells. I think that special cables are stupid! Why are USBs everyone's favorite for connecting devices? Because they are UNIVERSAL serial buses. My rant of the day.

What's your opinion? Is it safe? I'm always running out of battery because I do a lot of reading off of it. (text files are small, and I have documents to go and Adobe reader for palm. (adobe is great, and I have the full version of acrobat 5.0, so I can make all my documents into PDF. Its lots of un)). I do have my screen dimmed to the lowest possible setting, and I assume that this saves power, plus it is much easier on the eyes.

Thanks all,

Badmojo · Post by **Badmojo** » Sat Mar 12, 2005 1:24 am

I remember an old digi cam site where the author used to make battery packs out of multiple AA or whatever equvilant size for the voltage needed. Best advise was an LED to limit feedback/reverse polarites etc.
Usb is 5v and most cables have black,red lines for power.

The site also had info about how to charge the batteries or something to regulate power from interal to external sorce which i think was the main objective. also you can get 5v capcitors or limitors??? at radio shack so you could use 5.5/6v source.

fogus · Post by **fogus** » Sat Mar 12, 2005 3:31 pm

Very cool. I would like to check out that website. I have heard that if you use 1/10th the total watts to charge the batteries, that you would be safe (same goes for discharge. if you have a 2100 milli amp nimh, then you can draw 210 milli watts safely, and charge at the same). So how would I go about checking how much power I am charging with? (I have a multi meter, but I think the ammeter might be broken. When I shove it in at wall socket it reads irrational numbers, like 0.02 milli amps, on a 15 amp circuit. Should I buy a little ammeter?) An LED would be nice to have, at least for the initial setup, just to make sure things are safe. Will my batteries charge fully if I use slightly under the regular charge voltage? I suppose it would, since USB charges at 5V.

If someone can give me a few more details on this it would be helpful. My palm gives me the polarity that I'm supposed to charge with, but how do I check if I've got the batteries hooked up to the right imput? I can’t get inside the little charger port thing, because its too narrow. Should I compare the outside with ground? My multi meter has two wires, one red, one black, so I should just hook up the positive one with the outside and the negative one with a ground source and see what it reads when I have my batteries hooked up. Has anyone else done anything like this before for a PDA? PDA is a bit different than a camera, because the camera has a separate battery. Could my lil PDA motherboard get fried if I give the PDA battery too much current? Would it just go “pop” or would it be a slow process?

Badmojo · Post by **Badmojo** » Sat Mar 12, 2005 6:16 pm

http://www.dansdata.com/cambattery.htm
this seems like it

http://www.hackaday.com/entry/1234000520028239/

google links http://www.google.com/search?hl=en&q=ma ... gle+Search

Post by **FlyingPenguin** » Sat Mar 12, 2005 6:55 pm

A Palm PDA should run for almost a week before the battery dies. My Sony Clie does and it's 2 years old.

If yours doesn't I'd say you have a bad battery.

You SHOULD be docking the thing every night and under normal usage (this assumes you're not using it 9 hours a day as an MP3 player) it should EASILY last a day.

Simple solution otherwise is to buy a spare car or AC charger and charge it at work/school/in the car whatever.

I carry around a data cable for my laptop that also charges my Clie off the USB port.

I definately would not mess around with do it yourself batteries without getting detailed specs. Most PDAs run on NiMH batteries or Lion batteries. The charge rate for these batteries is can be VERY fussy. Under the wrong circumstances you could easily damage the PDA or the batteries. At the extreme end you could cause the batteries to catch fire or explode (unlikely since most have internal short protection, but possible).

fogus · Post by **fogus** » Sat Mar 12, 2005 7:34 pm

So basicly, I can charge with a USB port adapted with a 9V battery with a resistor to cut the current (amps) and a diode to cut the voltage, or I could use four 1.2 volters. my second option is to go with my origional option and just make sure that i dont blow too much current in, which shouldent be a problem if im just using AAs and not a car battery. Sounds like a very cool project, I think I will try both, and maybe give one away to someone with an iPod. I think i will try to exactly match the charger that i have that plugs into the wall. I mean, if that doesnt work, then something is very screwy. Does anyone happen to know the average amp output of a AA NiMH? And then how do I calculate what resistor to tone it down with?

And my PDA runs out of charge in 3-5 hours of screen time (it lasts double when just playing music with the screen off). This seems consistant, because digi cams will run out in even less than this usualy, and they have relativly small screens. A tungston hand held has a big screen, and draws alot of power. Plus the battery must be tiny, because it is as thin as the average pocket calculator, and has a screen that nearly covers the whole front of it. A Tungston E is MUCH smaller than a Sony Clie.

PDAs are such wonderful things...

Pugsley · Post by **Pugsley** » Sun Mar 13, 2005 12:56 am

Well its no where near that simple. A resistor is a waste since it will convert energery into heat to dissipate it.. so you will loose there. And diodes simply prevent current from going in one direction. You want a voltage regulator. and if your charging them fancy batterys you need some sort of monitoring circuit so you dont over charge them. As FP said they are verry picky about charging.

fogus · Post by **fogus** » Sun Mar 13, 2005 1:06 am

According to "hackaday"

" the zener diode conducts in the reverse direction when its breakdown voltage of 5.1 volts is reached, and the voltage across the diode will be that same 5.1 volts, so it acts to limit our 9 volt supply down to roughly 5 volts, which is what usb powers devices at."

so they claim that the diode is the limiting factor for volage. I was going to protest, because diodes control direction of flow, but then i remembered about magentic gate stuff, and thought better of it. Who is wrong here?

Also, i realized that my fuze on my multimeter was blown. I replaced it and presto, i can measure amps. My AA batteries give about 800 Ma, so I better do some serious limiting before i connect them up.

Guys, I know that its complicated, but if my multimeter reads less than 5.5V and exactly 500Ma, then what can go wrong? That is all there really is to DC voltage, right?

I seriously want this upgrade. I read a LOT off of my palm, on long drives and stuff. The battery life sucks though, so I need something to help. Failure is not an option.

Post by **FlyingPenguin** » Sun Mar 13, 2005 1:56 am

You don't want to use a zener. Again, like a resistor, any extra energy is just being converted to heat through the zerer. An innefficient use of batteries - and depending on how much current is diverted through the zener (and in this case it's a lot if you're starting with 9 volts), you'll also be heating up the batteries. You want a true voltage regulator if you want to go from 9 volts to 5 volts.

You don't use a zener to brig a 9 volt circuit down to 5 volts. That's 4 volts that's being shunted through the zener as heat. You'll probably burn up the zener.

Zeners are used when the voltage differential is small - like bringing a 5.5 volt circuit down to 5 volts.

fogus · Post by **fogus** » Sun Mar 13, 2005 11:57 am

Yes, I will not be using a 9V though, just 4 AAs NIMH, so it wont be nessisary to cut the voltage at all. All I need is to cut the current. How can I do this while wasting the least amout of power?