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.
This is a scratch-build meter for measuring the internal resistance of Lithium Polymer cells. [Bleuer Csaba] uses the LiPo cells for RC vehicles and thet take quite a beating from the motors they’re supplying. This means that he only gets about 100-200 cycles out of each cell. To figure out where one is in its life cycle you can measure the internal resistance where a rising resistance indicates greater age. [Bleuer] mentions that you can buy a meter to do this for you, but what fun is that?
Since he’s rolling his own tool he defined his own parameters for the readings. After experimenting with different loads driven for different test periods he was able to extrapolate an equation that estimates the resistance measurement. As you can see in the clip after the break, this happens very fast. All he has to do is connect the cell and press one button. The measurements are made and various data points are displayed on the quartet of 7-segment displays.
Continue reading “LiPo internal resistance measurement tool”
Here’s a project that let [Rick Pannen] try his hand with an OLED display and a rechargeable power source. He calls it OLEDuino which is a mashup of the display type and the Arduino compatible chip running the whole thing. He figures it will serve nicely as a geeky name badge but also ported a Breakout type game to play when he’s bored.
The project is an inexpensive way to attempt a more permanent trinket than simply using Arduino and a breadboard. [Rick] sourced the OLED display and USB LiPo charging cable on eBay. The ATmega328 hiding below the display is being driven from the 3.7V LiPo cell without any power regulation. The four buttons at the bottom provide the only user input but it should be more than enough for a few simple tricks.
Head over to his code repo for a bit more information. The schematic and board are both Eagle files. We generated an image of the schematic and embedded it after the break if you want to take a quick look at how simple the hardware really is.
Continue reading “OLED name badge with rechargeable LiPo cell”
Want mobile power for your Stellaris Launchpad development board? [Philipp] was looking to add some lithium power for the Launchpad. He used an off the shelf single cell LiPo battery and connected it to the 5V rail of the Launchpad board. It didn’t work.
So [Philipp] started looking through the schematics and noticed that the regulator was working fine, but the Stellaris wasn’t starting up. He tracked down a voltage supervisor connected to the Stellaris reset pin. After some investigation, it was clear that this supervisor was holding the device in reset.
The solution is a quick and dirty hack: cut the trace that connects the reset line to the voltage line. With this modification, the device starts up from the LiPo without any issues. [Philipp] does note that you should be careful about battery under-voltage and over-voltage. This hack doesn’t handle charging the LiPo battery, but we’ve discussed that in the past.
If you’re building solar vehicles at a competitive level you’ve got to know exactly how the storage batteries will perform. To that end [Matthew] built a Lithium Polymer battery tester for use by the McMaster University Solar Car Project. It worked well, but could only test one battery at a time. He just finished up a second version, which can test battery specifications on up to eight units at once. It saves a lot of time, but still takes fifteen hours to test just one set of the units used by the vehicle.
The most important aspect being measured is the discharge curve. Sure, there’s a datasheet that includes this information, but how can be sure that what you received will perform at spec? Each of the eight channels can be disconnected from the system using a relay. This is just one of the safety features which watch for things like over-voltage and over-current conditions. Remember, Lithium batteries can heat up fast if there’s a problem. Data is sampled on a 12-bit ADC and can be pushed to a computer via USB for graphing.
When [Soo-Hyun]’s friend had an Apple Macbook Pro battery that began to swell, his friend did the reasonable thing and donated it to be used in a robot. Now [Soo-Hyun]’s kiwi drive robot is powered by a gigantic LiPo battery, giving it a huge range and a very fast top speed.
The defunct laptop battery that formerly powered a 15″ macbook pro is three battery packs of two cells in parallel, delivering 12.6 Volts. To get the power to the robot, [Soo-Hyun] etched a simple PCB that fit into the slot in the battery. A little bit of soldering later, and mounting the battery as a shark fin because of the 8×8 inch limitation of maze-solving robots, the power plant was complete.
Using a bulging LiPo battery probably isn’t the smartest idea (listen for the great line, “it got the camera and my face” at 4:08), but as long as [Soo-Hyun] keeps an eye on the battery as it’s charging, it should be alright.
Check out the video of the robot zipping around on 12.6 Volts after the break.
Continue reading “Powering a robot with a macbook battery”
[Brian Knoll] still uses his Super Nintendo with relative frequency, and he just can’t get enough Super Scope action. If you never owned one, the Super Scope can be a ton of fun, but it’s also an incredible battery hog. It eats through AA batteries by the caseful, so [Brian] wanted to make the switch to rechargeable cells. Since NIMH AA batteries just don’t cut it in the Super Scope, he put together a rechargeable solution of his own.
He started off by calculating what sort of battery he would need for 8 hours of game play, then he started work on designing his circuit. The board he built contains both a DC/DC converter to provide the 9V required by the Super Scope, as well as built-in LiPo charger. He had his board made by BatchPCB, and after working through a small production error, he put everything together and gave his revamped scope a shot.
Things worked great, and while he says that he really should have built a low-voltage shutoff into his circuit, he is very happy with the results.