Solar Light Shows Why Replacing NiMH With Li-Ion Is Dangerous

November 2, 2026 by Maya Posch 49 Comments

Recently [DiodeGoneWild] got his paws on a purportedly IP44-rated outdoor solar light with PIR motion sensor that also contains an 18650 Li-ion cell. Since it’s being sold in Czechia in a supermarket by a Czech company you’d expect it to meet at least some quality standards, but once he got inside the device a true horror show unfolded.

The best guess here is that someone took an originally cheap NiMH cell-based solar light circuit and simply replaced said NiMH cell with an – unprotected – Li-ion 18650 cell, as there is absolutely no charging management or cell protection. This is important as while NiMH will throttle charging current by rejecting it as heat the more it is in a charged state, Li-ion is not as tolerant.

Even ignoring that the ‘IP44’ enclosure has more gaps and holes in it than the average slice of Swiss cheese, the 5.5 V-rated PV solar panel happily tried charging the Li-ion cell at around 6 V. This raises the potential that on a particularly sunny day with an already charged Li-ion cell sitting at 4.2+ V, it’ll effectively grenade this cell.

During an outdoors test the 18650 cell was charged to 4.8 V before the sun vanished behind the building, which probably isn’t an amazing sign if you are expecting for this light to keep working for more than a few weeks. Or not violently explode/catch on fire on the side of your house for that matter.

Of course, treating a NiMH cell better than in this particular circuit will extend its lifespan as well, but the failure mode of that battery chemistry tends to be a bit less aggressive. Hence why people keep getting away with dodgy circuit designs like this.

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Solar Fueled Emergency Power Pack

August 15, 2021 by Chris Lott 23 Comments

Heavy rainfall in Northern Europe last month caused disastrous flooding in several countries. [Daniel Jedecke] was on assignment in the North Rhine-Westphalia region of Germany during the floods and saw the damage firsthand. He was struck by the lack of emergency power, and set about the task of designing a simple, portable power pack.

[Daniel] wanted his system to be as simple and maintenance-free as possible, and well as inexpensive. He passed by the traditional solutions such as gasoline fueled generators or advanced chemistry battery packs. Instead, he settled on the ordinary car battery — they’re easy to obtain in a pinch, and he found a used 45 Ah one sitting in his basement. To keep the system portable, he decided on a single 80 W monocrystalline solar panel which comes with a smart battery charge controller. An inverter provides standard (for Germany) 240 VAC in addition to the +12 VDC output.

The whole thing, except the panel, is installed in an off-the-shelf toolbox with the pieces secured to a custom-made wood frame. We think [Daniel]’s goals were met: made from standard materials, long-lasting without excessive maintenance, portable, and providing both DC and AC outputs for everyday use. Way back in 2015 we wrote about an emergency battery pack using rechargeable drill batteries. Do you keep an emergency power pack handy in case of outages or disasters?

Big Power, Little Power, Tiny Power, Zap!

August 9, 2018 by Roger Cheng 4 Comments

Our Hackaday Prize Challenges are evaluated by a panel of judges who examine every entry to see how they fare against judging criteria. With prize money at stake, it makes sense we want to make sure it is done right. But we also have our Hackaday Prize achievements, with less at stake leading to a more free-wheeling way to recognize projects that catch our eye. Most of the achievements center around fun topics that aren’t related to any particular challenge, but it’s a little different for the Infinite Improbability achievement. This achievement was unlocked by any project that impressed with their quest for power, leading to some overlap with the just-concluded Power Harvesting Challenge. In fact, when the twenty Power Harvesting winners were announced, we saw that fourteen of them had already unlocked the achievement.

Each of the Power Harvesting winners will get their own spotlight story. And since many of them have unlocked this achievement, now is the perfect time to take a quick tour through a few of the other entries that have also unlocked the Infinite Improbability achievement.

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High Efficiency, Open-Sourced MPPT Solar Charger

July 31, 2018 by Donald Papp 28 Comments

A few years ago, [Lukas Fässler] needed a solar charge controller and made his own, which he has been improving ever since. The design is now mature, and the High Efficiency MPPT Solar Charger is full of features like data logging, boasts a 97% efficiency over a range of 1 to 75 Watts, and can be used as a standalone unit or incorporated as a module into other systems. One thing that became clear to [Lukas] during the process was that a highly efficient, feature-rich, open-sourced hardware solution for charge controllers just didn’t exist, at least not with the features he had in mind.

Data logging and high efficiency are important for a charge controller, because batteries vary in their characteristics as they recharge and the power generated from things like solar panels varies under different conditions and loads. An MPPT (Maximum Point Power Tracking) charger is a smart unit optimized to handle all these changing conditions for maximum efficiency. We went into some detail on MPPT in the past, and after three years in development creating a modular and configurable design, [Lukas] hopes no one will have to re-invent the wheel when it comes to charge controllers.

Open Hardware Takes Charge In Papua New Guinea

July 10, 2018 by Kristina Panos 29 Comments

You probably don’t think much about charging your phone. Just find an outlet, plug it in, and wait a while. Can’t find a cable or wall wart? A rainbow of cheap, candy-colored options awaits you down at the brightly-lit corner drugstore.

This scenario couldn’t be further from reality in third world countries like Papua New Guinea, where people living in remote jungles have cell phone coverage, but have to charge their phones by hooking them up directly to cheap solar panels and old car batteries.

[Marius Taciuc] wants to change all of that. At the suggestion of his friend [Brian], he designed an intermediary device that takes any input and converts it to clean 5 volts with a low-cost, reliable buck converter. The inputs are a pair of alligator clips, so they can be connected to car battery terminals, bare-wire solar panel leads, or 9V connectors.

Mobile phones mean so much to the people of Papua New Guinea. They’re like a first-world care package of news, medical advice, and education. At night, they become simple, valuable lanterns. But these dirty charging hacks often lead to house fires. Someone will leave their phone to charge in the morning when they go off to hunt, and come home to a pile of ashes.

This is an open, simple device that could ultimately save someone’s life, and it’s exactly the type of project we’re looking for. [Marius] hopes to see these all over eBay someday, and so do we. Charge past the break to see [Marius] discuss the Brian Box and the people he’s trying to help.

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Hackaday Prize Entry: Arduino MPPT Controller

May 23, 2015 by Brian Benchoff 17 Comments

Imagine you’re building a small solar installation. The naive solution would be grabbing a solar panel from Horror Freight, getting a car battery and AC inverter, and hoping everything works. This is the dumb solution. To get the most out of a solar you need to match the voltage of the solar cell to the voltage of the battery. How do you do that? With [Debasish]’s entry for The Hackaday Prize, an Arduino MPPT Solar Charge Controller.

This Maximum Power Point Tracker uses a buck converter to step down the voltage from the solar cell to the voltage of the battery. It’s extremely efficient and every proper solar installation will need a charge controller that does something similar.

For his MPPT, [Debasish] is using an Arduino Nano for all the math, a DC to DC buck converter, and a few MOSFETs. Extremely simple, but [Debasish] is connecting the entire controller to the Internet with an ESP8266 module. It’s a great example of building something for much less than it would cost to buy the same thing, and a great example for something that has a chance at making the world a little better.

The 2015 Hackaday Prize is sponsored by:

Beach Buddy Is A Boombox, Phone Charger, And Sunburn Warner

August 18, 2014 by Marsh 6 Comments

When you venture out onto the beach for a day in the sun, you’re probably not preoccupied with remembering the specifics about your sunscreen’s SPF rating—if you even remembered to apply any. [starwisher] suffered a nasty sunburn after baking in the sunlight beyond her sunscreen’s limits. To prevent future suffering, she developed The Beach Buddy: a portable stereo and phone charger with a handy sunburn calculator to warn you the next time the sun is turning you into barbecue.

After telling the Beach Buddy your skin type and your sunscreen’s SPF rating, a UV sensor takes a reading and an Arduino does a quick calculation that determines how long until you should reapply your sunscreen. Who wants to lug around a boring warning box, though?

[starwisher] went to the trouble of crafting a truly useful all-in-one device by modifying this stereo and this charger to fit together in a sleek custom acrylic enclosure. There’s a switch to activate each function—timer, charger, stereo—a slot on the side to house your phone, and an LCD with some accompanying buttons for setting up the UV timer. You can check out a demo of all the Beach Buddy’s features in a video below.

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