Comparing Making To Buying A Lithium Ion Battery Pack

At Hackaday we’re all about DIY. However, projects can have many components, and so there’s sometimes a choice between making something or buying it. In this case, [GreatScott!] wondered if it would be cheaper to make or buy a lithium-ion battery pack for his new eBike kit. To find out, he decided to make one.

After some calculations, he found he’d need thirteen 18650 cells in series but decided to double the capacity by connecting another thirteen in parallel. That gave him a 5 Ah capacity battery pack with a nominal voltage of 48.1 V and one capable of supplying a constant current of 40 A. Rather than connect them by soldering the nickel strips, he purchased a kWeld battery spot welder, adding to the cost of the build. He charged his new battery pack using his bench power supply but being concerned about uneven charging of the cells over the battery pack’s lifetime, he added a Battery Management System (BMS). The resulting battery pack powers his eBike motor just fine.

After adding up all the costs, he found it was only a tiny bit cheaper than prices for comparable battery packs on eBay, which were €24.4 per Ah (US$29.5 per Ah). The only way it would be cheaper is if he made multiple packs, spreading out the one-time cost of the battery spot welder. So that means it’s really up to your preference. See his video below to judge for yourself if you’d rather do it the DIY way. And then let us know what you’d do in the comments below.

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Vastly Improving The Battery Life On Cheap Action Cams

At one time, GoPro was valued at over eleven Billion dollars. It’s now on the verge of being a penny stock, because if surfers can make action cams and video editing software, anyone can. Action cams are everywhere, and one of the cheapest is the SQ11. It’s a rip-off of the Polaroid Cube, has a non-standard USB socket, a tiny battery, and the video isn’t that great. It only costs eight dollars, though, so [pixelk] decided to vastly expand the abilities of this cheap camera for a Hackaday Prize entry.

The major shortcoming of the SQ11 action cam is the tiny battery. Reportedly, it’s a 200 mAh battery, but the stated 1-2 hours of runtime bears no resemblance to reality. The solution to this problem, as with most things in life, is to throw some lithium cells at the problem.

[pixelk] disassembled the SQ11 action cam and 3D printed a much longer enclosure meant to fit a single 18650 battery. There’s a protection circuit, so that’s fine, but there’s still a problem: the charging circuit in the camera is tailored for a 200 mAh battery — charging an 18650 cell would probably take a day. That’s no problem, because this enclosure leaves the battery removable, for easy recharging in an external device.

Does this make the SQ11 a good camera? Marginally, yes. If you need to record video for hours and hours, you won’t be able to do better than an eight dollar camera and four dollars in parts.

Assemble Your Own Modular Li-Ion Batteries

Low-voltage DC power electronics are an exciting field right now. Easy access to 18650 battery cells and an abundance of used Li-Ion cells from laptops, phones, etc. has opened the door for hackers building their own battery packs from these cheap cells. A big issue has been the actual construction of a pack that can handle your individual power needs. If you’re just assembling a pack to drive a small LED, you can probably get by with spring contacts. When you need to power an e-bike or other high power application, you need a different solution. A spot welder that costs $1000 is probably the best tool, but out of most hackers’ budget. A better solution is needed.

Vruzend v2 Battery Caps.

Enter [Micah Toll] and his Vruzend battery connectors, whose Kickstarter campaign has exceded its goal several times over. These connectors snap onto the ends of standard 18650 cells, and slot together to form a custom-sized battery pack. Threaded rods extend from each plastic cap to enable connection to a bus bar with just a single nut. The way that you connect each 18650 cell determines the battery pack’s voltage and current capability. There are a couple of versions of the connector available through the campaign, and the latest version 2.0 should allow some tremendously powerful battery pack designs. The key upgrade is that it now features corrosion-resistant, high-power nickel-plated copper busbars allowing current up to 20A continuous. A side benefit of these caps instead of welded tabs is that you can easily swap out battery cells if one fails or degrades over time. Continue reading “Assemble Your Own Modular Li-Ion Batteries”

Cross-Brand Adapter Makes for Blended Battery Family

Even though he’s a faithful DeWalt cordless tool guy, [Richard Day] admits to a wandering eye in the tool aisle, looking at the Ryobi offerings with impure thoughts. Could he stay true to his brand and stick with his huge stock of yellow tools and batteries, or would he succumb to temptation and add another set of batteries and chargers so he could have access to a few specialty lime green tools?

Luckily, we live in the future, so there’s a third way — building a cross-brand battery adapter that lets him power Ryobi tools with his DeWalt batteries. [Richard]’s solution is a pure hack, as in physically hacking battery packs and forcing them to work and play well together. Mechanically, this was pretty easy — a dead Ryobi pack from the recycling bin at Home Depot was stripped down for its case, which was glued to a Dewalt 20-v to 18-v battery adapter. The tricky part came from dealing with the battery control electronics. Luckily, the donor DeWalt line has that circuitry in the adapter, while Ryobi puts it in the battery. That meant simply transplanting the PCB from the adapter to the Ryobi battery shell would be enough. The video below shows the process and the results — Ryobi tools happily clicking away on DeWalt batteries.

While [Richard] took a somewhat brute-force approach here, we imagine 3D-printed parts might make for a more elegant solution and offer other brand permutations. After all, printing an adapter should be easier than whipping up a cordless battery pack de novo.

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Repairs You Can Print: Nintendo DS Lite With New Battery And Case

The problem with hanging on to old consumer products is that the original batteries no longer hold a charge. To make matters worse, replacement batteries ordered online have likely been sitting on a warehouse shelf for years and are no better. [Larry G] faced this issue with his old Nintendo DS Lite. Luckily he remembered a hack from his youth where a friend’s Dad had duct-taped a massive alkaline D-cell battery pack to the back of a Gameboy to give it a longer life. And so [Larry] gave new life to his Nintendo DS Lite by designing and 3D printing a case for a battery with an even larger capacity than the original.

He first obtained a 2400 mAh 18650 lithium-ion cell, one with over voltage and under voltage protection. With that as a guide, he designed and 3D printed a case for it made up of four printed parts. The case was needed because the 18650 doesn’t fit in the NDS Lite’s battery compartment. Instead, one of the parts, which he calls the fake battery, fits in the compartment and has copper strips glued to it for connecting to the NDS Lite. From there, wires go to another part wherein sits the 18650. The remaining parts secure it all in place.  Charging is done using the NDS Lite’s built-in charger. Even though the new case adds significant bulk, it actually fits well in the hand.

No doubt many of you have your own old NDS Lite sitting around that can benefit from this repair. The project details and STL files can be found on his page using the above link.

This is also [Larry]’s entry for our Repairs You Can Print contest which puts him in the running for one of two Prusa i3 Mk3s plus the multi-material upgrade.

Build a Tiny Hot Wire Foam Cutter

Let’s face it: cutting foam with a knife, even a serrated plastic knife meant for the job, is a messy pain in the ass.  This is as true for insulation board as it is for the ubiquitous expanded polystyrene kind of foam used for everything from coffee cups to packaging material.

Those stick-type hot wire cutters from the craft store that plug into the wall aren’t much better than a knife. The actual cleaving of foam is easier, but dragging a long, hot flexible wand through rigid foam just right, without making burn marks, is pretty frustrating. It’s not like you can hold the other end to keep it steady. A foam cutter built like a coping saw but held parallel to the wire would offer much better control.

[Techgenie]’s handheld hot wire foam cutter is a simple build based on a single 18650 and a piece of nichrome wire. While this is probably not the most Earth-shattering hack you’ll see today, it’s a useful tool that can be made in minutes with items on hand. Laptop chargers are full of 18650s, and nichrome wire can be sourced from old toasters, hair dryers, or space heaters.

You shouldn’t use just any old wire for this, though, or the battery will get hot and potentially explode. Nichrome wire has a high resistance, and that’s exactly what you want in a tool that essentially shorts a battery to make heat. [Techgenie] used a momentary button instead of a switch, which is a good way to stay safe while using it. It wouldn’t hurt to add some protection circuitry and take the battery out when you’re done. Burn past the break to watch him build it and cut a few tight turns with ease.

If you have bigger, more complicated foam-cutting jobs in mind, why not build a CNC version out of e-waste?

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Roll Your Own Rotary Tool

Rotary tools are great little handheld powerhouses that fill the void between manual tools and larger shop machines. They’re also kind of expensive for what they are, which is essentially a power circuit, a switch, and a high-RPM motor with a tool coupling on the shaft. If your tooling needs are few and you have the resources, why not make your own?

[DIY King 00] built himself a cordless rotary tool for less than $10 out of commonly-available parts. It doesn’t run nearly as fast as commercial rotary tools, but that’s not necessarily a bad thing. He made the body out of 2″ diameter PVC and mounted a 12 V, 400 RPM DC motor directly to one of the fiberglass end caps. Tools are chucked into a collet that screws into a coupler on the motor shaft.

For power, [DIY King 00] built a 7.4 V battery pack by wiring two 18650 cells from an old laptop battery in series. It isn’t the full 12 V, but it’s enough power for light-duty work. These 2200 mAh cells should last a while and are rechargeable through the port mounted in the other end cap.

Drill down past the break to see the build video and watch the tool power through plywood, fiberglass, and inch-thick lumber. Once you’ve made your own rotary tool, try your hand at a DIY cordless soldering iron.

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