Coin Cells: The Mythical Milliamp-Hour

Just how much metaphorical juice is in a coin cell battery? It turns out that this seemingly simple question is impossible to answer — at least without a lot of additional information. The problem is that the total usable energy in a battery depends on how you try to get that energy out, and that is especially true of coin cells.

Energizer specs its 2032s at 0.2 mA

For instance, ask any manufacturer of the common 3 V lithium 2032 batteries, and they’ll tell you that it’s got 230 mAh. That figure is essentially constant across brands and across individual cells, and if you pull a constant 0.2 mA from the battery, at room temperature and pressure, you’ll get a bit more than the expected 1,150 hours before it dips below the arbitrary voltage threshold of 2.0 V. Just as it says on the tin.

What if you want to do anything else with a coin cell? Run an LED for a decade? Pull all the energy out right now and attempt to start a car? We had these sorts of extreme antics in mind when we created the Coin Cell Challenge, but even if you just want to do something mundane like run a low-power radio sensor node for more than a day, you’re going to need to learn something about the way coin cells behave in the real world. And to do that, you’re going to need to get beyond the milliamp hour rating. Let’s see how deep this rabbit hole goes.

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Ask Hackaday: Preserving Electronic Devices

Conventional wisdom holds that we no longer make things to last for the long haul, and that we live in a disposable world. It’s understandable — after all, most of us have a cell phone in our pocket that’s no more than a year or two old, and it’s often cheaper to buy a new printer than replace the ink cartridges. But most of that disposability is driven by market forces, like new software that makes a device obsolete long before it breaks down, or the razor and blades model that makes you pay through the nose for ink. It turns out that most electronic devices are actually pretty well engineered, and as long as they’re not abused can still be operating decades down the road.

But what happens when you want to put an electromechanical device away and preserve it for a rainy day? What can you do to make sure the device will operate again a few years down the road? Are there steps one can take beyond the typical “keep it in a cool, dry place” advice? In short, how do you preserve electronic devices?

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Welding Batteries With Batteries

Welding equipment is always expensive and bulky, right? Heavens no! [Jaromir Sukuba] is making a welder for battery tabs which can fit in a pocket and gets its power from a coin cell. It may be expensive to power compared to a mains welder, but for the sake of portability this is quite the hack. Not only that, but it uses 555 timers in the charging circuit.

His entry for the 2017 Coin Cell Challenge saps every bit of power from a coin cell and stores it up in a 100F supercapacitor bank. All that stored energy takes a long time to get into the supercapacitors but it comes out in a flash. In fact, it can take 12 hours to fully charge. For the convenience of size, we have to trade the convenience of speed. This should be a strong contestant for the Supernova and Heavy Lifting categories.

We see a quick demonstration of a successfully welded tab which shows that using coin cells to weld metal to coin cells is equally ironic and apropos. Other welders on Hackaday feature a quicker way to control your battery tab welding, safety-rich spot welding, or just go off the rails completely and use an arc welder to make a coil gun.

Smart DC Tester Better than a Dummy Load

Testing DC supplies can be done in many ways, from connecting an actual load like a motor, to using a dummy load in the manner of a big resistor. [Jasper Sikken] is opening up his smart tester for everyone. He is even putting it on Tindie! Normally a supply like a battery or a generator would be given multiple tests with different loads and periodic readings. Believe us, this can be tedious. [Jasper Sikken]’s simulated load takes away the tedium and guesswork by allowing the test parameters to be adjusted and recorded over a serial interface. Of course, this can be automated.

In the video after the break, you can see an adjustment in the constant-current mode from 0mA to 1000mA. His supply, meter, and serial data all track to within one significant digit. If you are testing any kind of power generator, super-capacitor, or potato battery and want a data log, this might be your ticket.

We love testers, from a feature-rich LED tester to a lead (Pb) tester for potable water.

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DIY 9V Battery

Volta’s pile — the first battery — was little more than silver and zinc discs separated by paper soaked in salt water. A classic classroom experiment is to build a pile from copper pennies, tin foil, and vinegar or lemon juice. [Omars2] has a different take on this old experiment. He creates a 9V battery using some zinc screws, copper wire, and salt water. There’s a video of the battery, below.

A syringe piston serves as a substrate for the cells, and each cell is just a screw with paper wrapped around it and then 35 turns of copper wire on top of that. The battery is soaked in salt water, although we suspect vinegar or lemon juice would work even better. Heating the electrolyte is also a good idea.

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Hackaday Prize Entry: Modular, Rapid Deployment Power Station

After a disaster hits, one obvious concern is getting everyone’s power restored. Even if the power plants are operational after something like a hurricane or earthquake, often the power lines that deliver that energy are destroyed. While the power company works to rebuild their infrastructure, [David Ngheim]’s mobile, rapid deployment power station can help get people back on their feet quickly. As a bonus, it uses renewable energy sources for power generation.

The modular power station was already tested at Burning Man, providing power to around 100 people. Using sets of 250 Watt panels, wind turbines, and scalable battery banks, the units all snap together like Lego and can fit inside a standard container truck or even the back of a pickup for smaller sizes. The whole thing is plug-and-play and outputs AC thanks to inverters that also ship with the units.

With all of the natural disasters we’ve seen lately, from Texas to Puerto Rico to California, this entry into the Hackaday Prize will surely gain some traction as many areas struggle to rebuild their homes and communities. With this tool under a government’s belt, restoration of power at least can be greatly simplified and hastened.

Power Through a Hurricane

When living in an area that is prone to natural disasters, it’s helpful to keep something on hand for backup power. While a large number of people chose to use generators, they are often unreliable (or poorly maintained), noisy, produce dangerous carbon monoxide, or run on a fuel supply that might not be available indefinitely. For truly reliable backup power, [Jay] has turned to a battery bank to ride through multi-day power outages.

While the setup doesn’t run his whole house, it isn’t intended to. One of the most critical things to power is the refrigerator, so this build focuses on keeping all of his food properly stored through the power outage. During the days following Hurricane Irma, the system could run the refrigerator for 10-11 hours, and the thermal insulation could keep everything cold or frozen overnight. Rather than using solar panels to charge the batteries, the system instead gets energy from the massive battery of his electric vehicle. [Jay] was out of power for 64 hours, and this system worked for him (and at a better cost) than a generator would have.

With the impact of major storms on many areas this year, we’ve been seeing a lot of interesting ways that people deal with living in areas impacted by these disasters. Besides riding through power outages, we’ve also seen the AARL step in to help, and also taken a look at how robust building codes in these areas help mitigate property damage in the first place.