We got a lot of really great feedback about low battery cutoff options in the comments section of Monday’s replacement battery post. To refresh your memory, some power tool batteries were replaced by Lithium Polymer units which can be damaged if drained too low before recharging. We had thought that many Lithium cells had cutoff circuitry these days. The consensus is that these batteries didn’t because they’re for RC applications where weight is an issue. But we did get a ton of people sending in commercially available drop-in solutions, mostly from RC hobby outlets, so search around for those if you’re interested.
[Christopher] sent us a link to the cutoff circuit he built for his bike light. You can see the schematic for it above (direct link). He sourced an ATtiny45 to drive a MOSFET which disconnects the battery when it gets too low. This would be easy to adapt to other uses, but note that there’s a voltage regulator involved as well as a few other passives… not a difficult solution but also not all that simple.
This same concept can be adapted. A few commentors mentioned using a transistor (or MOSFET) with the base driven by a voltage divider including a zener diode. This way the voltage rating of the diode would effectively shut off the gate when that threshold was reached.
We also enjoyed reading about [Bill’s] human-controlled cutoff circuit. It also uses a zener diode, but this time in series with a resistor and and LED patched into the trigger of the tool. The LED will shine brightly when the battery is in good shape. It will dim near the end, and fail to light when the critical limit has been reached. Just make sure you’re paying attention and you’re in good shape.
[HammyDude] was tired of buying replacement batteries for his power tools. He had some Lithium Polymer batteries on hand and decided to take one of his dead drills and swap out the dead power pack.
The orange battery pack you see above has a deans connector on it for use with RC vehicles. By opening up the drill housing, [HammyDude] was able to add the mating deans connector. Now the replacement easily plugs into the drill, and it even fits inside the handle body.
This battery is made up of several cells, and an inexpensive charger is capable of topping off each individually for a balanced charge. In the video after the break [HammyDude] points out that the Makita charger applies voltage to all of the cells in series. It’s incapable of balance charging so when one cell dies the battery is toast. We’ve encountered this problem with Makita tools before.
One drawback to take note of in the end of the video: this replacement doesn’t have any low voltage cut-off. Running this battery pack down too low will permanently damage it. There must be a simple circuit that could be added as a safety measure. If you know of one, drop us a tip.
Continue reading “Pros and cons of replacing tool batteries with Lithium Polymer”
It’s no secret that wireless mice can eat through batteries pretty quickly. Rather than keep a fresh supply of AAs on hand at all times, [Phil] decided he would convert his mouse to use a rechargeable lithium polymer battery instead.
This isn’t the first time we’ve seen a cell phone battery crammed into a mouse to increase capacity, but we think this one has been done quite nicely. [Phil] managed to fit a 2.7 – 4.2v Li-Poly battery in the mouse’s palm rest, where there was a little extra empty space. The battery can be charged from any USB port via a custom-built charging module, which he constructed using a MAX1555 charge controller. Another custom-built circuit resides in the space previously occupied by the AA batteries, which uses an MC340063 DC to DC converter to drop the battery’s voltage down to the 1.25v required by the mouse.
The only part of the build that [Phil] is not pleased with is the power switch on the bottom, but since you rarely see that, we could care less. We think it is quite well done, and with a second version already in the works, we anticipate that it will get even better.
Be sure to check out [Phil’s] video tour of the hack, which you can see below.
Continue reading “Wireless mouse Li-Poly retrofit with USB charging”
This Predator costume has an animatronic element in the shoulder cannon. It tracks the movement of the mask, aiming wherever the Predator gazes. [Jerome Kelty] was asked by a friend to help develop the costume and he ended up with an animatronics platform which can be adapted for many different uses.
Starting with an Arduino Pro Mini [Jerome] designed a host board which would breakout the pins of the Arduino and make it easy to connect and drive multiple servo motors. The board is powered by a 3.3v Lithium Polymer battery with charging handled by a MAX1555 that was included in the design. Check out the video after the break which shows off the Predator suit. Looks like [Jerome] got it right, and he’s also put the platform to use with an Ironman suit that has an arm-mounted missle feature.
Need some inspiration for you next costume build? Take a look at this animatronic collection to get you started.
Continue reading “Developing an animatronics platform”
[Matthias] sent us this project where he builds an AVR light controller. He had a halogen bike light laying around, but was unsatisfied with its lead-acid battery. He wanted to use a lithium-polymer battery but found that they can’t be used directly with halogen lamps due to their voltage. His produced 8.5 volts at full charge and can’t be discharged to below 5 volts. He new a power controller would be necessary to try to flatten that out for his lamp, which needed to stay between 6-12 volts.
He used an ATtiny45 doing PWM to change the voltage. Some other cool features he added were the high and low settings and an LED status light for warnings. You can find pictures, schematics and source code on his page as well as tons of great information. Great job [Matthias].