LiPo Replacement Keeps Portable Scanner In The Action

November 21, 2023 by Dan Maloney 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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Cheap Power Supplies With Fake Chips Might Not Be That Bad

November 10, 2023 by Dan Maloney 33 Comments

We all know the old maxim: if it’s too good to be true, it’s probably made with fake components. OK, maybe that’s not exactly how it goes, but in our world gone a little crazy, there’s good reason to be skeptical of pretty much everything you buy. And when you pay the equivalent of less than a buck for a DC-DC converter, you get what you pay for.

Or do you? It’s not so clear after watching [Denki Otaku]’s video on a bargain bag of buck converters he got from Amazon — ¥1,290 for a lot of ten, or $0.85 a piece. The thing that got [Denki]’s Spidey senses tingling is the chip around which these boards were built: the LM2596. These aren’t especially cheap chips; Mouser lists them for about $5.00 each in a reel of 500.

Initial testing showed the converters, which are rated at 3 to 42 VDC in and 1.25 to 35 VDC out, actually seem to do a decent job. At least with output voltage, which stays at the set point over a wide range of input voltages. The ripple voltage, though, is an astonishing 400 mV — almost 10% of the desired 5.0 V output. What’s more, the ripple frequency is 18 kHz, which is far below the 150 kHz oscillator that’s supposed to be in the LM2596. Other modules from the batch tested at 53 kHz ripple, so better, but still not good. There were more telltales of chip fakery, such as dodgy-looking lettering on the package, incorrect lead forming, and finger-scorching heat under the rated 3 A maximum load. Counterfeit? Almost definitely. Useless? Surprisingly, probably not. Depending on your application, these might do the job just fine, especially if you slap a bigger cap on the output to smooth that ripple and keep the draw low. And keep your fingers away, of course.

Worried that your chips are counterfeits? Here’s a field guide for fake chip spotters. And what do you do if you get something fake? A refund might just be possible.

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Buck Converter Takes 8V To 100V

September 17, 2023 by Bryan Cockfield 40 Comments

For those living before the invention of the transistor, the modern world must appear almost magical. Computers are everywhere now and are much more reliable, but there are other less obvious changes as well. Someone from that time would have needed a huge clunky machine like a motor-generator set to convert DC voltages, but we can do it with ease using a few integrated circuits. This one can take a huge range of input voltages to output a constant 5V.

The buck converter was designed by [hesam.moshiri] using a MP9486 chip. While it is possible to use a multipurpose microcontroller like something from Atmel to perform the switching operation needed for DC-DC converters, using a purpose-built chip saves a lot of headache. The circuit was modified a little bit to support the higher input voltage ranges and improve its stability and reliability. The board is assembled in an incredibly tiny package with inputs and outputs readily accessible, so it would be fairly simple to add one into a project rather than designing it from scratch.

Even though buck converters, and other DC converters like boost and the mysterious buck-boost converter, seem like magic even to us, there is some interesting electrical theory going on if you’re willing to dive into the inner workings of high-frequency switching. Take a look at this explanation we featured a while back to see more about how buck converters, the more easily understood among them, work.

Minimizing Stress On A Coin Cell Battery

August 10, 2023 by Bryan Cockfield 20 Comments

When it comes to powering tiny devices for a long time, coin cell batteries are the battery of choice for things like keyfobs, watches, and even some IoT devices. They’re inexpensive and compact and a great choice for very small electricity needs. Their major downside is that they have a relatively high internal resistance, meaning they can’t supply a lot of current for very long without decreasing the lifespan of the battery. This new integrated circuit uses a special DC-DC converter to get over that hurdle and extend the life of a coin cell significantly.

A typical DC-DC converter uses a rapidly switching transistor to regulate the energy flow through an inductor and capacitor, effectively stepping up or stepping down the voltage. Rather than relying on a single converter, this circuit uses a two-stage system. The first is a boost converter to step the voltage from the coin cell up to as much as 11 volts to charge a storage capacitor. The second is a buck converter which steps that voltage down when there is a high current demand. This causes less overall voltage drop on the battery meaning less stress for it and a longer operating life in the device.

There are a few other features of this circuit as well, including an optimizer which watches the behavior of the circuit and learns about the power demands being placed on it. That way, the storage capacitor is only charged up to its maximum capacity if the optimizer determines that much charge is needed. With all of these features a coin cell could last around seven times as long as one using more traditional circuitry. If you really need to get every last bit of energy from a battery, though, you can always use a joule thief.

Converting On-Grid Electronics To Off-Grid

May 11, 2023 by Dave Rowntree 54 Comments

Husband and wife team [Jason & Kara] hail from Canada, and in 2018, after building their own camper, sold up their remaining earthly goods and headed south. If you’re not aware of them, they documented their journey on their YouTube channel, showing many interesting skills and hacks along the way. The video we’re highlighting today shows a myriad of ways to power all the DC-consuming gadgets this they lug along with them.

LiFePO4 batteries are far superior to lead acid for mobile solar installations.

Their heavily modded F-550 truck houses 12kWh of LiFePO4 batteries and a 1.5kW retractable solar array, with a hefty inverter generating the needed AC power. They weren’t too happy with the conversion losses from piles of wall warts that all drained a little power, knowing that the inverter that fed them was also not 100% efficient. For example, a typical laptop power brick gets really hot in a short time, and that heat is waste. They decided to run as much as possible direct from the battery bank, through different DC-DC converter modules in an attempt to streamline the losses a little. Obviously, these are also not 100%

efficient, but keeping the load off the inverter (and thus reducing dependency upon it, in the event of another failure) should help stem the losses a little. After all as [Jason] says, Watts saved are Watts earned, and all the little lossy loads add up to a considerable parasitic drain.

One illustration of this is their Starlink satellite internet system consumes about 60W when running from the inverter, but only 28W when running direct from DC. Over the course of 24 hours, that’s not far off 1kWh of savings, and if the sun isn’t shining, then that 12kWh battery isn’t going to stretch as far.

There are far too many hacks, tips, and illustrations of neat space and power-saving solutions everywhere, to write here. Those interested in self-build campers or hacking a commercial unit may pick up a trick or two.

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LED Driver Circuit For Safety Hat Sucks Single AAA Cell Dry

January 19, 2023 by Donald Papp 21 Comments

[Petteri Aimonen] created an omnidirectional LED safety light to cling to his child’s winter hat in an effort to increase visibility during the dark winter months, but the design is also great example of how to use the Microchip MCP1640 — a regulated DC-DC step-up power supply that can run the LEDs off a single AAA cell. The chip also provides a few neat tricks, like single-button on/off functionality that fully disconnects the load, consuming only 1 µA in standby.

[Petteri]’s design delivers 3 mA to each of eight surface-mount LEDs (which he says is actually a bit too bright) for a total of about 20 hours from one alkaline AAA cell. The single-layer PCB is encased in a clear acrylic and polycarbonate enclosure to resist moisture. A transistor and a few passives allow a SPST switch to act as an on/off switch: a short press turns the unit on, and a long press of about a second turns it back off.

One side effect is that the “off” functionality will no longer work once the AAA cell drained too badly, but [Petteri] optimistically points out that this could be considered a feature: when the unit can no longer be turned off, it’s time to replace the battery!

The usual way to suck a battery dry is to use a Joule Thief, and while this design also lights LEDs, it offers more features and could be adapted for other uses easily. Interested? [Petteri] offers the schematic, KiCAD file for the PCB, and SVG drawing of the enclosure for download near the bottom of the project page.

Toddler EV Gets Big Boy Battery Upgrade

July 29, 2022 by Ryan Flowers 13 Comments

No matter the type of vehicle we drive, it has a battery. Those batteries wear out over time. Even high end EV’s have batteries with a finite life. But when your EV uses Lead Acid batteries, that life is measured on a much shorter scale. This is especially true when the EV is driven by a driver that takes up scarcely more space in their EV than a stuffed tiger toy! Thankfully, the little girl in question has a mechanic:

A 3d printed adapter sends go-juice to the DC-DC converter

Her daddy, [Brian Lough], who documented the swift conversion of his daughter’s toy truck from Lead Acid to Li-Ion in the video which you can see below the break.

Facing challenges similar to that of actual road worthy passenger vehicles, [Brian] teamed up with [bitluni] to solve them. The 12 V SLA battery was being replaced with a 20 V Li-Ion pack from a power tool. A 3d printed adapter was enlisted to break out the power pins on the pack. The excessive voltage was handled with a DC-to-DC converter that, after a bit of tweaking, was putting out a solid 12 V.

What we love about the hack is that it’s one anybody can do, and it gives an inkling of what type of engineering goes into even larger projects. And be sure to watch the video to the end for the adorable and giggly results!

Speaking of larger projects, check out the reverse engineering required in this Lead Acid to Li-Ion conversion we covered in 2016.

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