[Barry] sent us a tip about a video from [electronupdate], describing an experimental cell phone charger. It’s a familiar issue: Your cell phone battery is low, and you aren’t in a position to plug it in for hours to charge. Some phones, including the one in his video, have swappable batteries, but that isn’t always an option either. As he explains in the video, a wall outlet can deliver the joule capacity of a high-end battery in a matter of seconds, but it is impossible to charge a battery that quickly. Capacitors, on the other hand, charge near-instantly.
[electronupdate] decided to look at the possibility of using super capacitors to power a typical usb plug. It would allow you to charge a secondary power supply in a short period of time, and then get on your way, letting your phone charge slowly from the device.
His experiment wasn’t entirely successful, possibly because he used 2.7V capacitors, which required a boost regulator and limited the useful voltage range. We think he might have had better success using 120V capacitors and a switching power supply, but it would be nice to see the various options compared.
Oh, [electronupdate] describes using this circuit as you are rushing to your airplane. We aren’t convinced carrying a couple super capacitors through a TSA checkpoint would be the best idea… YMMV.
Continue reading “Supercap-Based Cell Phone Charger”
Cordless power tool battery replacements are expensive: you can easily spend $100 for a NiCd pack. [henal] decided to skip nickle-based cells and cut out the middleman by converting his old cordless battery packs to inexpensive hobby lithium cells. These batteries appear to be Turnigy 3S 1300mAh’s from Hobbyking, which for around $10 is a great bargain. As we’ve explained before, lithium batteries offer several advantages over NiMH and NiCd cells, but such a high energy density has drawbacks that should be feared and respected, despite some dismissive commenters. Please educate yourself if you’ve never worked with lithium cells.
[henal] gutted his dead battery packs and then proceeded to prepare the lithium replacements by soldering them to the cordless pack’s power connectors. To keep charging simple, he also branched off a deans connector from power and ground. After cutting some holes in the pack for access to the balancing connector and deans connector, [helan] went the extra mile by soldering on a DIN connector to the balancing wires, which he then securely glued to the side of the case.
We’ve featured lithium power tool replacements before, and these Turnigy packs pose the same problem: they don’t appear to have any low voltage cut-off protection. Check out some of the comments for a good solution.
A team of researchers from Georgia Tech unveiled their findings yesterday at the Blackhat conference. Their topic is a power charger exploit that installs malware on iOS devices. Who would have thought that there’d be a security hole associated with the charging port on a device? Oh wait, after seeing hotel room locks exploited through their power jack this is an avenue that should be examined with all device security.
The demonstration used a charger and an BeagleBoard. Plugging in the charger is not enough to trigger the exploit, the user must unlock the screen while charging for it to go into action. But once that’s done the game is over. Their demo removes the Facebook app and replaces it with an infected impostor while leaving the icon in the same place on your home screen. They notified Apple of their findings and a patch will roll out with iOS7. So when would you plug your device into an untrusted charger? Their research includes a photo from an airport where an iPad is connected to the USB port of a public charging station.
The summary on the Blackhat site has download icons for the white paper and presentation slides. At the time of writing we had a hard time getting them to download but succeeded after several tries.
Calling this a boom box is at least slightly ironic. Instead of high explosives it now carries high decibels in its new life as a self-contained sound system.
Despite the conspicuous power cord a peek inside reveals a big enough battery to keep the tunes playing for hours on end. [King Rootintootin] kept the cost on the build down since he was given the used speakers and amp by his girlfriend’s dad. The amp kicks out about 25 Watts with the battery rated at 7.2 Ah. He added a charger and routed the controls to the side of the ammo box so that it can be charged without removal. The only external component is the audio jack which connects it to the music source.
One of the suggested improvements from the Reddit thread is to add baffles inside of the enclosure so that sound from the two stereo channels doesn’t interfere with each other.
Power outage? For the average citizen it’s very easy to take electricity for granted. Go a few hours or more without it though, and you’ll suddenly be reminded just what a luxury it is. During an emergency situation, sometimes you have to come up with alternative methods to get the job done. This human powered cell phone charger is a great example.
Using just a few ordinary around the house items, [The King of Random] turned a cordless electric drill into a human powered electrical generator. If the drill is run in reverse and cranked by hand, the generated energy can be transferred through the battery terminals to a connected device. So, he cut a USB charger cable in half and wired it up to the terminals to be able to charge his cell phone. Some yarn, a salad fork, a mixing beater, a scrap 2″x4″, some aluminum foil, and scotch tape were the only other materials he used. Using this technique, a totally dead phone battery was charged in around 3 hours.
Remember that this method is only intended to be used in an emergency, not as every day practice. Using these methods could potentially overheat or damage your gear, so be careful.
Check out the MacGyver worthy video tutorial after the break.
Continue reading “Human powered emergency cell phone charger”
Here’s a USB charging center which [Kenneth Finnegan] built using parts from his junk bin. We’d like to reiterate our claim that he must have the most magical of junk bins (the last thing we saw him pull out of it was a 24-port managed Ethernet switch).
The jack on the side accepts the barrel connector from a 12V wall wart. [Kenneth] mentions that the 2.1mm jack is a standard he uses in all of his projects. Inside there’s a switch mode power supply that provides the regulated 5V to each USB port. We really like the fact that he added some protection; diy is no fun if you end up frying your beloved multi-hundred dollar devices. The yellow components are polyfuses which will cut the power if 600 mA of current is exceeded. This works great for almost all of his devices, but his iPod 4G doesn’t like the system. It sees the voltage dip just a bit and stops charging entirely.
[Kenneth Finnegan] took the focus of a great design and redirected it to solve his own problem. What results is this lead acid battery charger based on the 555 timer. It’s not a top-of-the-line, all the bells and whistles type of charger. But it gets the job done with a readily available IC and no need to code for a microcontroller.
The original idea came from a solar battery charger entered in the 555 timer contest. The main difference in application between that and [Kenneth’s] application is the source. A solar array or wind turbine is limited on how much juice it can produce. But mains power can push a shocking (har-har) amount of current if you’re not paying attention. Herein lies the alterations to the circuit design. To control this he’s using a Laptop power supply as an intermediary and only implementing the constant current portion of the tradition 3-stage lead acid charging profile (those stages are explained in his write up).
He did a talk on the charger at his local radio club. You can see the 90-minute video after the break.
Continue reading “555-timer charges lead acid batteries”