Replace Batteries With USB Power

[Mark Bog] thought it was a waste to use batteries for his desktop touch pad. Quite frankly we agree that if you can avoid using disposable cells you should. He ditched the dual AA batteries inside of his Magic Trackpad and built a battery-sized adapter to feed it some juice. It consists of a dowel of similar diameter with a screw in each end. He scavenged a USB cord, connecting hot and ground wires to the corresponding pole of the adapter. Now his Trackpad is USB powered and never in need of a battery replacement or even a recharge.

We’re not familiar with the inner workings of Apple’s Magic Trackpad. We assume there’s a voltage regulator inside and we hope it doesn’t have a problem working with the 5V regulated power coming in from the adapter. If you’ve got the skinny on the hardware we’d love to hear about it in the comments. One last thing: because the forum linked above requires a login to view the images in the post, we’ve embedded the rest of them after the break for your convenience.

[Thanks to Patrick for the tip and the images]

47 thoughts on “Replace Batteries With USB Power

  1. I was going to make some sny remark about how he spent ENTIRELY too much money on his setup there…
    While thats still true, i just realized its all running off his macbook, thats pretty cool. The fact that apple didnt even make it an option to use external power on those is kinda stupid in my opinion for just this reason.

  2. This thing is wireless?? O.O

    I always thought i’d be wired. (Don’t blame me pls. No Apple products in my house except for an iPhone 3G so no need to lookup the info on this…mouse/tablet thingy)

    BTW: Another Apple design failure. I bet they made it wireless because otherwise it wouldn’t look good in their minds. I’m still wondering that it’s that easy to make a wired power supply for this. Who would have thought, Apple didn’t design it to work only with batteries with some Apple chip inside them ;D

  3. I too am suprised he got away with simply hooking the USB power into a device that runs off two AA’s and not using any voltage reduction bits, 4 and perhaps 3 AA/AAA powered devices can usually cope with plain USB voltage.

    I would’ve added 3 diodes into the USB wire to drop the voltage down by ~2.1v (3×0.7v) to 2.9v, as I’ve seen USB bluetooth adaptors that use two diodes to drop the voltage down to ~3.6v to run a 3.3v board.

  4. My logitech mouse is a wireless mouse that when I charge it I plug it into the USB. Unfortunately my logitech wireless keyboard still uses 2 AA batteries, although it says up to 3 years on the pair. I was thinking about making a charging circuit for it so it can do essentially what my mouse does. Just gotta make a circuit that can charge a 3.7v 1A LIPO battery from 5v and about 20mA, and then hide it in they keyboard with only a little microusb connector sticking out. Then, one usb cord for keyboard, mouse, AND cell phone. On a roll.

  5. Nifty trick. This would be useful for a lot of older devices that run only on batteries which is what I pictured in my head before opening the rest of the article. Then I saw the new Apple hardware. Kind of a funny combination, but hey, it works!

  6. I use this for some of my guitar pedals, which the adapters usually don’t come with the pedal. I took the end off a power adapter and wired it to USB. It works even though the pedal requires 9v battery’s and a 9v DC.

    Don’t ask how since the USB is only 5v :s but it works.

  7. I did that with a cordless phone once. It was always running out of charge right in the middle of the phone conversation. So I took some wire (I round this really cool coiled wire) and connected the charging jacks on the phone base to the metal contacts on the bottom of the cordless phone. Now I can talk for hours – and I’ve found that the coiled charging cord is really fun to twirl around and play with.

    1. What a brilliant idea, a phone that never needs charging. You should consider getting a patent for this design. I especially like the idea of a coiled cord that offers a little extra mobility and then retracts to a compact size.
      Now, if somebody would just come up with a wired phone system for use when there is little or no cell service.

    1. @Osgeld and others who pointed out price,
      If you want multitouch input for your PC, wacom’s latest bamboo series have touch features as well as multi level pen input. The device alone might cost a little more depending on what size you get (yeah, choices are great aren’t they?) but your entire rig will be cheaper. I’ve also usually seen linux drivers for wacom devices.

  8. Why not put an induction charger on the backside and on the bottom of the table , that way your devices allways get charged when the stay in the region of the induction coil.

    just an idea ;)

  9. @Reaper, check out the MAX1551 & MAX1555 chips out there, they’re all-in-one solutions to charging single cell lithium-ion & lithium-polymer batteries from USB & other power sources. Sparkfun sell the individual ICs and fully made-up boards with various connectors on.

  10. ^^^Diodes dissipate most of the .7 Volts as heat, so really probably not much more efficient than an LDO regulator. Personally I would have use a step-down regulator, diode, inductor, and filter cap instead. Great idea, though, and it is a shame that Apple didn’t, at least, add a coaxial DC power jack…

    Also, it seems like I remember this type of thing being sold back in the ’80s. If I remember, they were made of black injection molded plastic, with a thin cable coming directly out of the housing leading to a DC wall-wart. I know Radio Shack did sell a 9 Volt battery replacement kit that consisted of a wall-wart with the cable terminating into a 9 Volt type battery snap connector wired up in the opposite polarity of that of a battery…

  11. You could also use a cell phone chager, Same voltage as USB without the hazard of drawing all of the amps your PSU can put out on the 5v rail.

    Every wall charger I’ve seen for phones and hair clippers etc, has been 5v @ 1 amp.

  12. @Lathos, I bought an iRiver H140 many years ago when they were still being made, I still use it daily because it’s such an excellent mp3 player, but I remember seeing many postings on from very disheartened users who used Nokia phone chargers, because the connection plug was identical, and discovered the charger fried their beloved player.
    Though today I think almost all current mobile phones use 5v.

  13. I did the same sort of thing with a surround sound headphone adapter I got. I wanted surround sound for my xbox, but wanted to use headphones, so I figured it was the best option. When I got it, I was disappointed to fine it only worked from 2 AAA batteries and had no external power jack (the international version of it did).

    I took apart an old NiCd AAA and got the ends from it, soldered a wire to each, then epoxied them to the ends of a pair of dowels. I found a smt 3v3 regulator and put it on a circuit board and regulated the 5v usb down to 3v3, so I wouldn’t fry it. It works quite well and I’ve never had to buy any batteries for it.

  14. Sweet, I wonder if it could be modified to use the neodymium magnet type cord that the Apple laptops use, then it would look sleek and you could pop it loose if you need to.

  15. Are you Apple detractors so full of free time? Why complaining on something you don’t even know… i mean: while this (ghetto)hack seems to be ok, no need to say “another apple design failure”; my logitech bluletooth mouse’s batteries have been changed once in 6 months: probably that damn trackpad could run for a year in typical usage with plain (non rechargeable) batteries. No problem in changing/charging batteries at this rate in my opinion, we’re no more in the early “1 day battery cycle” era anymore.

  16. there is some thing in the air(referring to macbook air)
    but thats that guy’s burning house
    oh ____, that idiot is using 5v to overvolt it and exploit a top secret vulnerability to explode his house , and the after math will cost me money which as you all know is something i hate (that is why im living off disneys share)
    steve jobs

  17. Wanted to warn people to double check the polarity of any USB cable , DO NOT RELY ON THE RED BLACK WIRE COLORS. I have found some USB cables where the factories just used them for power wires without regard to colors.

    If people at the plant just put whatever color wire in the bin for a wire the machines feed it and assemble the cable . The machines do not care what color the wire is and both ends are assembled in one run so if red is in the ground slot it will run as that from end to end and the cable will work, but someone who cuts it and re-purposes it could end up in trouble.

    I destroyed a good LCD interface with one of these mis-colored cables.

  18. 5VDC is okay to power most portable devices like mp3 players through the battery connector . They usually contain chips that act as DC-DC converters and every DC-DC converter chip on the market I have seen in the last couple years has a max input of at least 5.5V and some as high as 6.6V.

  19. @cgmark that was some good advice there, thanks for the warning

    To the posters advising wacom: I love wacom tablets but all the tests and reviews say the touch part of the new touch&pen ones isn’t that hot, it’s a cute extra but it’s not what you’d hope for, so be aware of that.
    But for pen use wacom is great though, and the touch is a nice extra, just not a reason to buy.
    But maybe the next generation though?

  20. i have one of these magic trackpads, i have a set of 8 of the same rechargeable NiMH’s that ive been using for almost 4 years. i can’t remember the last time i bought batteries for anything at all. really a great investment, if you’d even call $20 an investment.

  21. help needed! lol

    i am not electrically skilled and want to do something that seems easy, but want to ask all of you experts first. thank you.

    i would like to replace battery power for a device with an AC/DC converter. putting out the same Dc volts (and i think it must also be the same amps.)

    im ok with the votage, since the device is now using four 1.5v AA batteries, wired in series.

    does this mean i need a Dc power supply that puts out 6Vdc, and about 2400Ma? (I read that 1.5V AA batteries are about 2400Ms.)

    or, do i need 6vdc and FOUR TIMES 2400Ms, that is, 9600Ma.

    i think it is the former since i read that the amps do not cumulate when batteries are wired in series, only the voltage does.

    finally, if it is a 6cdc, 2.4amp transformer i need, where can i get one? if i find one with 6vdc, but only 2amps, is that ‘close’ enough to run most devices, or do you have to be right on the numbers.

    sorry if some of these questions are stupid, but i am not skilled in this area.

    thanks very much.

    send reply to my e mail,

  22. I have the magic track pad that is in use for hours every day. The original batteries have been in it a month and are still at 14%. When they are gone, I have rechargeable batteries with even higher capacity (2450 mAh vs 2000 mAh) that I expect will keep me going for many recharge cycles.

    One of the reason Apple products cost more is Econ 101. Price, vs value. Macs last longer, the software is cheaper, the resale value is higher, the repairs less frequent, and the wasted down time for system crashes is non-existent.

    But I wouldn’t expect Windows fan bois to understand that. If they were capable of of[comprehending facts, they would be using Macs.

    1. Mr. Smith in Brazil, the 90’s called and they want their anti-Windows doggerel back. I could care less about your stupid Apple whatever. I’m still running a Windows machine from 2006 and a Windows laptop from 2002. The software is cheaper? What software are you talking about??? Half the software on my system was free. The stuff that wasn’t free I got on sale. Resale value??? Who wants to buy your old P.O.S. Apple anyway? Repairs? WTF are you even talking about? Seriously. System crash down time??? Uhm… most of that went out with in the era of Windows XP in the early 2000’s. Failures now mostly come from tweaking, fiddling, incompetence, or ignorance. Apple is a niche product–hence the reason for the price/value nonsense. Linux is for DIY-ers. Apple is for artists and posers. Windows remains the vehicle that drives the entire PC industry. As much as I hate Microsoft, if I want a machine that will kick your old man’s @55 in any of a dozen current mindblowing games, it will be running Windows. Put that in your pretentious pipe and smoke it, Sonny.

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