Squeeze More Juice Out of a Dead Battery!
Squeeze More Juice Out of a Dead Battery!
榨干废旧电池的最后一点能量！
You’re walking the dog at night, and your little flashlight, which has been getting dimmer, conks out. Instead of stumbling home in the dark, wouldn’t it be great if you could somehow eke a little more energy out of the batteries inside? 你正在夜间遛狗，手里那把光线越来越暗的小手电筒突然熄灭了。与其在黑暗中摸索着回家，如果能设法从电池里再榨出一点能量，那该多好啊？
That’s not as crazy as it sounds. When a battery-powered device stops working, we say the battery is “dead”—but it’s not really. It still contains chemical energy, and the voltage isn’t zero; it’s just not high enough to run a current through the light bulb or LED (or whatever load you have). 这听起来并不疯狂。当电池供电的设备停止工作时，我们说电池“没电”了——但事实并非如此。它内部仍然含有化学能，电压也并非为零；只是电压不足以驱动电流通过灯泡、LED 或其他负载。
But with a little physics chicanery, you can indeed get that light to run longer. Much longer! I’m going to show you how to build a simple electrical circuit, pairing a transformer and a transistor, to tap that residual energy. It’s waggishly called a “joule thief” circuit. Get it? 但只要耍一点物理学上的“小花招”，你确实可以让灯亮得更久。长得多！我将向你展示如何构建一个简单的电路，通过搭配变压器和晶体管来利用这些残余能量。这种电路被戏称为“焦耳小偷”（joule thief）。明白了吗？
It’s not only fun to build and kind of mind-blowing, it’s also a great illustration of Faraday’s law of induction, the same principle that’s used in electric generators—and induction cooking stoves, for that matter. Let’s do this! 这不仅制作起来很有趣，而且令人大开眼界。它还是法拉第电磁感应定律的绝佳例证，这一原理同样被应用于发电机，甚至电磁炉中。让我们开始吧！
Basic Battery and a Light Bulb
基础电池与灯泡
I’ll start with a very simple circuit. This is a 1.5-volt AA battery connected to a small incandescent light bulb using a single copper wire. 我先从一个非常简单的电路开始。这是一个 1.5 伏的 AA 电池，通过一根铜线连接到一个小型的白炽灯泡上。
It’s a complete circuit. Electric current comes out one end of the battery, runs through a bulb with a tungsten filament inside, and then returns to the other end of the battery. Because that filament is super thin, the current heats it up—to like 4,500 degrees Fahrenheit—so that it glows white-hot. (Luckily, tungsten has the highest melting point of any pure metal.) 这是一个闭合电路。电流从电池的一端流出，穿过灯泡内部的钨丝，然后回到电池的另一端。由于钨丝非常细，电流会将其加热到约 4500 华氏度，使其发出白炽光。（幸运的是，钨是所有纯金属中熔点最高的。）
As long as the circuit is complete—which in a flashlight means the switch is left on—current will continue to flow, gradually using up the battery’s chemical potential energy. As the voltage drops, it produces less current. At some point, there won’t be enough to produce any light. 只要电路保持闭合（在手电筒中意味着开关处于开启状态），电流就会持续流动，逐渐耗尽电池的化学势能。随着电压下降，产生的电流也会减少。在某个临界点，电流将不足以产生任何光亮。
In a way, this circuit is also a joule thief. If you leave the switch on, current will continue to flow even after the light goes out, and it’ll use up the battery’s remaining energy. But who cares about a joule thief that drains a battery and doesn’t produce light? 从某种意义上说，这个电路也是一个“焦耳小偷”。如果你一直开着开关，即使灯灭了，电流仍会继续流动，耗尽电池剩余的能量。但谁会在意一个既耗尽电池又不发光的“焦耳小偷”呢？
LEDs vs. Incandescents
LED 与白炽灯
Today, most devices use LEDs instead of incandescent bulbs. An LED doesn’t produce light by making things hot; instead, it’s a solid-state device with an energy gap. When electrons in the current fall to a lower energy level, they release the extra energy as light. It’s way more efficient, because you don’t have all that wasted thermal energy. The only downside is that a white LED requires 3 volts, so now we need two of those AA batteries. 如今，大多数设备使用 LED 而非白炽灯泡。LED 不是通过加热来发光的；它是一种具有能隙的固态器件。当电流中的电子落入较低的能级时，它们会将多余的能量以光的形式释放出来。这效率高得多，因为你不会浪费那么多热能。唯一的缺点是白色 LED 需要 3 伏电压，所以现在我们需要两节 AA 电池。
As the batteries run down, they’ll eventually drop below the 3-volt threshold. You might still have 2.8 volts, but you get zero light. This is where the magic of the joule thief comes into play. In fact, we can get a 3-volt LED to turn on with just a single 1.5-volt battery! But first, there are two things we need: a transformer and a transistor. 随着电池电量耗尽，电压最终会降至 3 伏阈值以下。你可能还有 2.8 伏的电压，但灯却完全不亮了。这就是“焦耳小偷”的神奇之处。事实上，我们仅用一节 1.5 伏的电池就能点亮 3 伏的 LED！但首先，我们需要两样东西：变压器和晶体管。
The Transformer
变压器
There’s more than one way to make an electric current. Yes, a battery does the job, but you can also use a magnetic field. This is Faraday’s law. It says that if a loop of wire sits in a region with a changing magnetic field, a voltage will be induced in that wire. 产生电流的方法不止一种。没错，电池可以做到，但你也可以利用磁场。这就是法拉第定律。它指出，如果一段导线环位于一个磁场不断变化的区域内，导线中就会产生感应电压。
Well, that’s exactly how a transformer works. It has two coils of wire wrapped around a common core. The wires are insulated so they aren’t in contact—it’s two separate circuits. But if you run a current through one coil, it generates a magnetic field, and when that field changes in any way, it creates a current in the second coil. 这正是变压器的工作原理。它有两个绕在同一个铁芯上的线圈。导线是绝缘的，所以它们互不接触——这是两个独立的电路。但如果你让电流通过其中一个线圈，它就会产生磁场；当该磁场发生任何变化时，就会在第二个线圈中产生电流。
Just to be clear: It’s not the magnetic field per se that induces a voltage in the second coil. It’s the change in the magnetic field. When you turn the current on or off in one coil, you get a voltage spike in the other coil. If you turn it on and leave it on, that voltage falls to zero. 需要明确的是：并不是磁场本身在第二个线圈中感应出电压，而是磁场的变化。当你开启或关闭一个线圈中的电流时，另一个线圈中就会出现电压尖峰。如果你开启电流并保持不变，电压就会降为零。
In fact, the strength of the induced voltage depends in part on the rate of change. Reduce the magnetic field slowly and you get a low voltage; turn it off quickly and you get a high voltage. You can also get a higher voltage by having more turns of wire in the secondary coil. 事实上，感应电压的强度部分取决于变化率。缓慢减小磁场，你会得到低电压；快速切断磁场，你会得到高电压。你还可以通过增加次级线圈的匝数来获得更高的电压。
That’s the secret to this whole magic trick. With a transformer, you can get a higher voltage in the secondary circuit, which is attached to the LED, than you started with in the battery. So all we need now is a way to turn the primary circuit on and off repeatedly and quickly. That’s where the transistor comes in! 这就是整个魔术的秘密所在。利用变压器，你可以使连接 LED 的次级电路获得比电池初始电压更高的电压。所以现在我们只需要一种方法来反复、快速地开关初级电路。这就是晶体管发挥作用的地方！
The Transistor
晶体管
At the most basic level, you can think of a transistor as a valve for electricity. It can turn the current off or let it pass through. And the transistor gate is controlled by … wait for it … an electric current. Yes, it’s a little mind-bending. It’s as if you need a stream of water to open a spigot and create a stream of water. 从最基本的层面来看，你可以把晶体管想象成电力的阀门。它可以切断电流或让电流通过。而晶体管的栅极是由……（屏住呼吸）……电流控制的。没错，这有点令人费解。这就好比你需要一股水流来打开水龙头，从而产生另一股水流。
But that’s pretty much all you need to know about how the joule thief works. The transistor switches the current on and off thousands of times a second, essentially creating an oscillating current so that the transformer produces a higher voltage. 但这基本上就是你需要了解的关于“焦耳小偷”工作原理的全部内容。晶体管每秒钟开关电流数千次，本质上产生了一种振荡电流，从而使变压器产生更高的电压。
The Joule Thief
焦耳小偷
Now we’re ready for the full circuit. There are many tutorials online for building one of these, but I’m going to use a very simple version. 现在我们准备好组装完整的电路了。网上有很多关于制作这种电路的教程，但我将使用一个非常简单的版本。
So the battery pushes a current through the primary (blue) coil in the transformer—creating a magnetic field and thus a burst of current in the secondary (red) coil. This induced current then goes into the transistor and switches off the primary current—but that again causes a jump in the magnetic field. Each time, there’s a spike of 3 volts in the second coil, lighting up the LED. 电池推动电流通过变压器的初级（蓝色）线圈，产生磁场，从而在次级（红色）线圈中产生一阵电流。这种感应电流随后进入晶体管并切断初级电流——但这又会导致磁场的跳变。每一次跳变，次级线圈中都会产生一个 3 伏的电压尖峰，从而点亮 LED。