bms

15 Articles

Integrated BMS Makes Battery Packs Easy

March 26, 2025 by 40 Comments

[Editor’s note: The hacker requested that we remove the image for legal reasons, so it’s blurry now. We hope all’s well!]

Lithium technology has ushered in a new era of batteries with exceptionally high energy density for a reasonably low cost. This has made a lot possible that would have been unheard of even 20 years ago such as electric cars, or laptops that can run all day on a single charge. But like anything there are tradeoffs to using these batteries. They are much more complex to use than something like a lead acid battery, generally requiring a battery management system (BMS) to keep the cells in tip-top shape. Generally these are standalone systems but [CallMeC] integrated this one into the buswork for a battery pack instead.

The BMS is generally intended to make sure that slight chemical imbalances in the battery cells don’t cause the pack to wear out prematurely. They do this by maintaining an electrical connection to each cell in the battery so they can charge them individually when needed, making sure that they are all balanced with each other. This BMS has all of these connections printed onto a PCB, but also included with the PCB is the high-power bus that would normally be taken care of by bus bar or nickel strips. This reduces the complexity of assembling the battery and ensures that any time it’s hooked up to a number of cells, the BMS is instantly ready to go.

Although this specific build is meant for fairly large lithium iron phosphate batteries, this type of design could go a long way towards making quick battery packs out of cells of any type of battery chemistry that typically need a BMS system, from larger 18650 packs or perhaps even larger cells like those out of a Nissan Leaf.

Disposable Vape Batteries Power EBike

November 7, 2024 by 15 Comments

There are a lot of things that get landfilled that have some marginal value, but generally if there’s not a huge amount of money to be made recycling things they won’t get recycled. It might not be surprising to most that this is true of almost all plastic, a substantial portion of glass, and even a lot of paper and metals, but what might come as a shock is that plenty of rechargeable lithium batteries are included in this list as well. It’s cheaper to build lithium batteries into one-time-use items like disposable vape pens and just throw them out after one (or less than one) charge cycle, but if you have some spare time these batteries are plenty useful.

[Chris Doel] found over a hundred disposable vape pens after a local music festival and collected them all to build into a battery powerful enough for an ebike. Granted, this involves a lot of work disassembling each vape which is full of some fairly toxic compounds and which also generally tend to have some sensitive electronics, but once each pen was disassembled the real work of building a battery gets going. He starts with testing each cell and charging them to the same voltage, grouping cells with similar internal resistances. From there he assembles them into a 48V pack with a battery management system and custom 3D printed cell holders to accommodate the wide range of cell sizes. A 3D printed enclosure with charge/discharge ports, a power switch, and a status display round out the build.

With the battery bank completed he straps it to his existing ebike and hits the trails, easily traveling 20 miles with barely any pedal input. These cells are only rated for 300 charge-discharge cycles which is on par for plenty of similar 18650 cells, making this an impressive build for essentially free materials minus the costs of filament, a few parts, and the sweat equity that went into sourcing the cells. If you want to take an ebike to the next level of low-cost, we’d recommend pairing this battery with the drivetrain from the Spin Cycle.

Thanks to [Anton] for the tip!

Xiaomi M365 Battery Fault? Just Remove A Capacitor

October 1, 2024 by 11 Comments

Electric scooters have long been a hacker’s friend, Xiaomi ones in particular – starting with M365, the Xiaomi scooter family has expanded a fair bit. They do have a weak spot, like many other devices – the battery, something you expect to wear out.

Let’s say, one day the scooter’s diagnostics app shows one section of the battery going way below 3 volts. Was it a sudden failure of one of the cells that brought the whole stage down? Or perhaps, water damage after a hastily assembled scooter? Now, what if you measure the stages with a multimeter and it turns out they are perfectly fine?

Turns out, it might just be a single capacitor’s fault. In a YouTube video, [darieee] tells us all about debugging a Xiaomi M365 battery with such a fault – a BQ76930 controller being responsible for measuring battery voltages. The BMS (Battery Management System) board has capacitors in parallel with the cells, and it appears that some of these capacitors can go faulty.

Are you experiencing this particular fault? It’s easy to check – measure the battery stages and see if the information checks out with the readings in your scooter monitoring app of choice. Could this be a mechanical failure mode for this poor MLCC? Or maybe, a bad batch of capacitors? One thing is clear, this case is worth learning from, adding this kind of failure to your collection of fun LiIon pack tidbits. This pack seems pretty hacker-friendly – other packs lock up when anything is amiss, like the Ryobi batteries do, overdue for someone to really spill their secrets!

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Ryobi Battery Pack Gives Up Its Secrets Before Giving Up The Ghost

August 14, 2024 by 44 Comments

Remember when dead batteries were something you’d just toss in the trash? Those days are long gone, thankfully, and rechargeable battery packs have put powerful cordless tools in the palms of our hands. But when those battery packs go bad, replacing them becomes an expensive proposition. And that’s a great excuse to pop a pack open and see what’s happening inside.

The battery pack in question found its way to [Don]’s bench by blinking some error codes and refusing to charge. Popping it open, he found a surprisingly packed PCB on top of the lithium cells, presumably the battery management system judging by the part numbers on some of the chips. There are a lot of test points along with some tempting headers, including one that gave up some serial data when the battery’s test button was pressed. The data isn’t encrypted, but it is somewhat cryptic, and didn’t give [Don] much help. Moving on to the test points, [Don] was able to measure the voltage of each battery in the series string. He also identified test pads that disable individual cells, at least judging by the serial output, which could be diagnostically interesting.  [Don]’s reverse engineering work is now focused on the charge controller chip, which he’s looking at through its I2C port. He seems to have done quite a bit of work capturing output and trying to square it with the chip’s datasheet, but he’s having trouble decoding it.

This would be a great place for the Hackaday community to pitch in so he can perhaps get this battery unbricked. We have to admit feeling a wee bit responsible for this, since [Don] reports that it was our article on reverse engineering a cheap security camera that inspired him to dig into this, so we’d love to get him some help.

Open Source DC UPS Keeps The Low-Voltage Gear Going

December 22, 2023 by 26 Comments

We all like to keep our network gear running during a power outage — trouble is, your standard consumer-grade uninterruptible power supply (UPS) tends to be overkill for routers and such. Their outlet strips built quickly get crowded with wall-warts, and why bother converting from DC to AC only to convert back again?

This common conundrum is the inspiration for [Walker]’s DC UPS design, which has some interesting features. First off, the design is open source, which of course invites tinkering and repurposing. The UPS is built for a 12 volt supply and load, but that obviously can be changed to suit your needs. The battery bank is a 4S3P design using 18650 cells, and that could be customized as well. There’s an ideal diode controller that prevents DC from back-feeding into the supply when the lights go out, and a really interesting synchronous buck-boost converter in place of the power management chip you’d normally see in a UPS. The converter chip takes a PWM signal from an RP2040; there’s also an ESP32 onboard for web server and UI duties as well as an STM32 to run the BMS. The video below discusses the design and shows a little of the build.

We’ve seen a spate of DC UPS designs lately, some more elaborate than others. This one has quite a few interesting chips that most of us don’t normally deal with, and it’s nice to see how they’re used in a practical design.

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LiPo Replacement Keeps Portable Scanner In The Action

November 21, 2023 by 8 Comments

If there’s anything people hate more than being locked into a printer manufacturer’s replacement cartridges, it’s proprietary batteries. Cordless power tools are the obvious example in this space, but there are other devices that insist on crappy battery packs that are expensive to replace when they eventually die.

One such device is the Uniden Bearcat BC296D portable scanner that [Robert Guildig] found for a song at a thrift store, which he recently gave a custom LiPo battery upgrade. It came equipped with a nickel-cadmium battery pack, which even under the best of circumstances has a very limited battery life. Using regular AA batteries wasn’t an option, but luckily the space vacated by the OEM battery pack left a lot of room for mods. Those include a small module with BMS functions and a DC-DC converter, a 2,400 mAh 4.2 V LiPo pillow pack, and a new barrel connector for charging. With the BMS set for six volts and connected right to the old battery pack socket, the scanner can now run for seven hours on a one-hour charge. As a bonus, the LiPo pack should last a few times longer than the NiCd packs, and be pretty cheap to replace when it finally goes too. There’s a video after the hop with all the details.

If you’re looking at a similar battery replacement project, you might want to check out [Arya]’s guide to everything you need to know about lithium-ion circuitry.

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Fail Of The Week: Car Starter Motors Aren’t The Best Fit For EBikes

April 14, 2023 by 40 Comments

A lot of what real engineering is all about is designing to the limits of your materials, with a healthy margin for error. On the other hand, seat-of-the-pants engineering often takes the opposite tack — working with the materials you have and finding their limits after the fact. While the former is more rigorous and better suited to anything where life and limb are on the line, there’s something to be said for the flexibility that informal engineering offers.

[Austin Blake]’s latest eBike is a case study in informal engineering. [Austin] started out wondering if a starter motor from a car engine would make a decent electric bike motor. Our first instinct before watching the video below was to answer that question with a resounding “No!” Yes, starter motors seem like a natural for the job, delivering high torque in a compact package. But starting a car engine is the very definition of a low-duty-cycle application, since it should only take a second or two of cranking to get an engine started. Pressing a motor designed for such a task into continuous duty seems like, well, a non-starter.

And to be fair, [Austin] fully acknowledges this from the start. He even retrofits the motor, wisely replacing the shaft bushings with proper bearings in an attempt to get a better duty cycle. And it works, at least for a while — with the motor, a homebrew battery, and an ESC mounted to a bike frame, the bike was actually pretty peppy. But bearings aren’t the only thing limiting a starter motor to intermittent duty operation. The short drive really heated up the motor, and even with a few ventilation holes knocked in the motor housing, it eventually released the Magic Smoke. The video has all the gory details.

As always, we like to stress that “Fail of the Week” is not necessarily a badge of shame. We appreciate it whenever someone shows us the way not to go, as [Austin] did here. And let’s keep in mind that he’s had success with this approach before, albeit with a much, much bigger starter motor.

Continue reading “Fail Of The Week: Car Starter Motors Aren’t The Best Fit For EBikes” →