Follow-up to homemade iPod battery packs

[The Gonif]

A lot of posts were made over the past several months from people who built, were planning to build, or were just curious about a homemade external iPod battery pack.

The most common designs used 8 AA alkaline batteries, 10 NMH AA batteries, and a combination of 2 9v batteries in parallel wired in series with 2 AA batteries (themselves wired in series). The idea behind all of these battery packs was to be able to recharge the iPod when a wall outlet or computer wasn't available -- and by "recharge" this also means that the iPod could be used while it was being charged. The basic idea was to use batteries to simulate the recharger that comes with the iPod.

I was hoping we could re-open that discussion to see what works best. We had a great discussion going there for a while! Some questions:

1) Some people thought that 8 AA's would last the longest (store the most charge), while others felt the 2 AA + 2 9v combo would last the longest. Which is correct?

2) One person thought that wiring the two 9v batteries in parallel was dangerous, because if the voltage ran out on one of them then the stronger 9v would try to "charge" the weaker one.

3) Similar to #2, it was brought up that the 9v batteries would run out of juice before the AA's, and when this happened the overall voltage would drop too low to be userful -- even though plenty of charge remained in the AA's.

4) One person claimed that 9v batteries don't provide a stable current, and their voltage spikes could damage the iPod. Is this true?

5) Some questions were raised (but never answered) regarding what would happen if the voltage of the external battery pack dropped below that of the iPod's internal battery. Is the iPod's charging circuitry smart enough to prevent the backflow of current, or do we have to worry about the external batteries exploding?

6) What cases have people used to house their battery creations? The Altoids box is a great idea, but it's too small for 8 AA's. What commonly found containers are you all using?

Let's build this thread up and get some good information disseminated!

[brted]

I'm glad you brought it up. I just finished my battery pack. It uses 8 AA batteries (NiMH) and a car lighter socket. Then you can plug a car adapter into it (for me the Griffin Powerpod). I found a good case for it too.

I also posted some of what I learned from the various lounge posts before they got wiped out and made links to other people's designs, including some commercial ones:

http://home.speedfactory.net/tcashin/ipodbattery.htm

[Unixmonkey]

All I know is that so far, I haven't had any problems at all with my units based on Drewpy's design.
I will eventually do a thorough test with brand new batteries since I get 2-3 emails a week about it.

[Christophe167]

Maybe this applies only to people like me, but I have pretty much no experience soldering electronics. I'm quite eager to make one of these but I'm scared I'll either a) Kill my iPod or b) Kill Myself.

If someone could make a tutorial for complete idiots I would be forever in their debt.

[brted]

If you have a car power adapter then I think you could make one easily without soldering. The wires attach to the battery holder with a snap connection just like a 9V battery so that end is not a problem. Then the lead wires could just be taped onto the lighter socket with electrical tape instead of solder. With the one I bought the red wire connects to the inner part of the socket and the black wire connects to the outside. Other ways of attaching them might include pop rivets or just alligator clips.

Then you just have to test the polarity which you could do by testing something less expensive than an iPod like an old cell phone if you don't have a voltmeter. You're never working with more than 12 volts from the batteries so you'd have a pretty hard time hurting yourself.

If you want to make one with a Firewire port you might be able to do it without solder by using wire connectors attached to the prongs that come off of the socket (or twisting and taping the prongs and the 9V leads). I'm not sure if those prongs are long enough though since I didn't ever get any firewire sockets.

Maybe someone who is adept with a soldering iron would make some firewire sockets soldered onto one of these 9V connectors. It would be easy to mail that because it would be very small. Then you could go get your own battery holder, batteries, and case.

[Christophe167]

yeah i want to make the altoids tin one, but its not crucial yet. thanks for your help though. i'll defintetely see how feasible these things are

[bdjohns1]

Originally posted by The Gonif


The most common designs used 8 AA alkaline batteries, 10 NMH AA batteries, and a combination of 2 9v batteries in parallel wired in series with 2 AA batteries (themselves wired in series). The idea behind all of these battery packs was to be able to recharge the iPod when a wall outlet or computer wasn't available -- and by "recharge" this also means that the iPod could be used while it was being charged. The basic idea was to use batteries to simulate the recharger that comes with the iPod.

1) Some people thought that 8 AA's would last the longest (store the most charge), while others felt the 2 AA + 2 9v combo would last the longest. Which is correct?

Look at the watt-hour rating. 2000 mAh NiMH AA batteries are available, while 9V NiMH cells come in around 200 mAh.

For 8xAA, you're looking at 1.2V per cell in steady state, so 9.6V x 2000 mAh = 19.2 W-hr.

For 2 9V in parallel, it's about 8.4V in steady state, so 400 mAh x 8.4V is 3.2 W-hr. 2AAs in series is another 4.8 W-hr, so we've got 8.0 W-hr. It's not even close - the 8x AAs rock.

NiMH batteries stay relatively flat voltage-wise across their life, so the 9.6V should be enough to keep charging the iPod through at least 80% of the AA cells capacity.

2) One person thought that wiring the two 9v batteries in parallel was dangerous, because if the voltage ran out on one of them then the stronger 9v would try to "charge" the weaker one.

Yes. How often in consumer electronics do you see an arrangement of parallel cells? And, how often do you see a single device mixing and matching two different cell sizes (aside from battery chargers)? The professionals just might be on to something here.

3) Similar to #2, it was brought up that the 9v batteries would run out of juice before the AA's, and when this happened the overall voltage would drop too low to be userful -- even though plenty of charge remained in the AA's.

Also true. If you're using all NiMH batteries, this won't be too bad, since the internal cell resistance is pretty low. If you were doing alkalines, this would suck, because your 9V cells would turn into a giant resistor.

5) Some questions were raised (but never answered) regarding what would happen if the voltage of the external battery pack dropped below that of the iPod's internal battery. Is the iPod's charging circuitry smart enough to prevent the backflow of current, or do we have to worry about the external batteries exploding?

I'd expect so. Otherwise, the easy thing would be to wire in a diode (the lower the forward voltage drop, the better...although that might be a good case for 10xAA). With the diode in, there's no backflow of power.

Let's build this thread up and get some good information disseminated! [/B]

One great resource for battery charging is by a guy who designs headphone amps. He and his team of DIY designers developed a battery board for a semi-portable headphone amp (about 6 x 4 x 2) which has a charging circuit built in. The section's got build instructions, part lists, and some info on the theory of how battery charging works. Go to:

http://www.tangentsoft.net/audio/ppa/bb/

and read up. I've thought about taking his schematic and basically building a big rechargeable battery pack - put 12 AA NiMH cells in it to get 14.4V at 2000 mAh...that would be enough power to run both an iPod and a low-power headphone amp (PIMETA) for at least 16 hours. Pack it into a small aluminum enclosure, and put a couple DC-out jacks on it, then build a DC-Firewire cord for the iPod and a DC-DC cable to plug into a headphone amp.

Actually, it's too bad there aren't consumer LiIon cells. You could take a laptop battery and make a pretty #### good power pack out of it. The pack in my IBM Thinkpad has 40 W-hr in it, and can source 12V at 1.1 amp. I think LiIon charging circuits are tougher, though.

--Ben

[brted]

I ran a test of my 8-AA battery pack. By itself my iPod gets 7.8 hours of life without recharging before it dies. But I've been testing all week and got 27.7 hours of total life without letting the battery indicator go below one bar (I feel like I could easily add 10 hours to that total if I was willing to go to no bars). I got four hour-long charges out of the battery pack and one partial charge before I started getting odd behavior. But even after that partial charge I still got another couple of hours of additional run time.

I posted details at my website:

http://home.speedfactory.net/tcashin/ipodtest.htm

[Pnkrck83]

I just built an 8 AA pack running to a firewire socket with a small diode to prevent backflow. I measured the current to be about 4 amps at the firewire socket. The AC charger that the ipod comes with measured a current of only .5 amps at its firewire socket. If I understand current right, won't the ipod only draw what it needs, meaning I won't fry it by conencting it to the 4 amp battery pack?

[consumerq]

Hello

Wouldn't the route brted took be the safest? Is there not circuitry in the car-lighter iPod chargers that help regulate voltage and prevent messing up the iPod?

I like it.
cheers!

[brted]

The Griffin PowerPod adapter has a LED and a fuse in it. I'm not sure the fuse is that important because batteries won't generate a surge like a car will. There also seem to be a couple of components on the circuit board including a LED (labeled D1), a resistor (R1), maybe two diodes (D2 and D3), and a capacitor (C1)? So I think you probably are getting some kind of protection there. I guess that was unintentionally smart of me.

[mroats]

http://www.geocities.com/ipodpictures/killer.html

[tanakasan]

Heres the whole thread:
http://ipodlounge.com/forums/showthr...threadid=34241
All 8-AA packs are not killers-some actually work! In fact, this is the first that I can remember that actually BBQ'd a pod! If me and all the rest can make them and use them and even sell them, it looks to be a single case of "operator" error.

If you would like a wiring schematic and p/n of the specific FW connector that I use, email me! I will even send you a cap and case, if you want to go try it again!

[cup0spam]

This is my case... Bought all the parts at radio shack aside from the firewire port. I dismantled the iPod mini firewire adapter to get what i needed... My advice on that is a very sharp knife and a pair of needle-nosed plyers. Works great.... I'm looking for a project case or something to enclose it all inside of. Let me know what you guys think.

[PMazza]

I'm pretty interested in this as well, but I would be making the thing more to see if I can do it more than anything else. I don't know how much it would be used. So I tried cutting the 6-4 pin adapter, and I think I ruined something, and don't think I feel safe using it. Is there anywhere I can buy the port online, other than the un-reliable one posted on a site above? If there are any retailers (such as RadioShack) that sell them, that would be awesome. From what I read on another post, it seems that the iPod will accept anywhere from 7-30 volts, which is quite a bit. I don't know if I would worry about resistance or whatever, however I might try that. If my iPod gets fried, I don't think Apple will replace it due to my error, so I want to do it right (as should everyone else). So if someone can help with a source for firewire ports, please do so. Thanks!