Hi. Why do we ever use AC
嗨 为什么家庭用电从来都是用交流电
to power homes instead of DC?
而不用直流电呢？
Haven’t I showed you that AC is typically more dangerous than DC?
我没有告诉过你交流电通常比直流电更危险吗？
被电到的疼痛 （对比交流电与直流电）
Can we run everything on DC?
我们能在直流电上运行所有东西吗？
Yes!
没错！
In fact pretty much every device at home
事实上 几乎家里的每一台设备
has to rectify AC into DC first before you can use it
在使用之前都要先将交流电转换成直流电
so why？
所以为什么呢？
Why am I angry?
我为什么生气？
The reason is elementary.
原因很简单
Once there was a fight
历史上曾有一次高手过招
between a guy named Nik ola Tesla being AC
一方是尼古拉•特斯拉 他主张用交流电
and Thomas Edison being DC
另一方是托马斯•爱迪生 主张用直流电
and Tesla won the contract for his employer Westinghouse company
最终 特斯拉为其雇主西屋公司赢得了供电合同
to provide power with AC
供应交流电
no matter how hard Thomas Edison tried
不管托马斯•爱迪生多么竭力地
to expose the dangerous nature of AC
在公共场合以电死狗和大象的方式
by electrocuting dogs and elephants in public.
来揭露交流电的危险性 他还是输给了特斯拉
[WOW]
[哇]
Now I remember why I’m angry
现在我记起来我为什么生气了
this Edison guy was an animal!
爱迪生这家伙就是一头禽兽！
He even invented the electric chair to execute with AC
他甚至发明了用交流电来行刑的电椅
not because it was a cleaner or better way to execute
不是因为那是一种更清洁或是更好的行刑方式
because he wanted to deface AC
而是因为他想要抹黑交流电
by forever associating it with death.
手段就是 让它永远和死亡联系在一起
Nikola Tesla very rightfully won this battle.
尼古拉·特斯拉理所当然地赢得了这场对决
yes, AC can be more dangerous than the same level DC
没错 交流电可能比相同电平下的直流电更危险
but a higher level DC can be as dangerous if not more
但高一点的直流电同样危险 绝不亚于交流电
and just because something is dangerous
我们不会仅仅因为某个东西危险
we don’t stop using them
而停止使用它们
like for example if you live in a high-rise
举个例子 如果你住在高楼里
you are not in a constant risk of jumping off the window.
你不会时时处于从窗户跳下去的危险
But is there an advantage of using AC?
但是使用交流电有没有优点呢？
I mean, back then all they wanted was light using incandescent lights
我的意思是 那时候他们想要的只是用白炽灯照明
and those don’t care about AC or DC.
他们才不在乎是用交流电还是直流电
Here I’m running a regular light bulb on AC as usual
现在我像平时一样 把一个普通灯泡接入交流电
and here I……
然后我……
I killed it.
我弄坏它了
Don’t short .
小心别短路了
Anyways with this I’m converting the AC into DC using
不管怎样 我正在把交流电转换成直流电
It’s a single diode,
这是一个单二极管
but it will do,
但它也可以用
and if I measure the voltage at the output
如果我测量它的输出电压
the capacitor
这个电容……
Anyways i’m reading around……
总之 我测出了大概……
170 volt DC
170伏特的直流电
and although it’s still quite dangerous
虽然这仍然很危险
I can still touch it
我还是可以触摸它
and it’s not as remotely as painful as touching the 120 volt AC
而且远不像触摸120伏的交流电那样痛苦
and the lightbulb runs on it just fine
这个灯泡也运行正常
And it’s even a little brighter
甚至更亮一些
because it’s 170 volt continues
因为它是连续的170伏电压
Beside the lights the electric motors
除了电灯以外 家用电器中
were becoming more popular in home appliances
电动机也越来越受欢迎
like meat grinders or fans and such
像绞肉机 或风扇等
but even those could be made
但也可以用这些来制成
into brushless AC or brushed DC for example,
无刷交流电的或有刷直流电的——举例来说
of course a brushless AC motor like this one
当然 像是我从老微波炉里取下的
that I took from an old microwave oven
这样一个无刷交流电机
can last much longer than a brushed DC……
比有刷直流电机的寿命长得多……
Loose wires, avoid them,
小心避开松动的电线
anyways brushes in DC brushed motors wear out eventually
有刷直流电机中的碳刷最终都会磨损
And that’s why AC motors can last longer,
这就是为什么交流电机可以使用更久
but beside that fact there doesn’t seem
但除此之外
to be much preference between AC and DC
交流电和直流电似乎并没有太大的区别
But the real advantage of AC is not at home
但交流电的真正优势并不在家里
It’s before electricity even gets to home in transmission lines
而是在电还没通过传输线送到家里之前
And that’s why Edison’s DC power distribution system
这就是爱迪生的直流电配电系统
eventually died away,
最终消失的原因
Here, I made a transmission line using thin wires
在这里 我用细电线当作输电线
and using my supply I’ll try to place
并用我的电源供应器试着
10 volts across my 1 ohm load
将10伏特的电压连接到1欧姆的负载上
for 10 amps of current
得到10安培的电流
And I’m measuring the voltage across my load.
然后我要测量负载上的电压
Let’s try it
让我们来试一下
See the voltage is like seven and a half
看 电压是7.5
and you see my transmission line is starting to smoke and heat up
可以看到输电线开始冒烟并发热
and the voltage continues to drop
电压继续下降
see the line resistance is so much
可以看到线路电阻如此之大
that the voltage Across the load doesn’t even get to ten volts
负载的电压甚至还达不到10伏
It’s at seven volts for seven amps through the load
只有7伏7安培通过负载
and because of the high resistance.
而且由于高电阻
It’s heating up so much
它温度上升很快
Similarly because Edison was passing low voltage across the transmission lines
与此类似 由于爱迪在输电线上传输低压电
a ton of current was passing through the lines
所以有大量的电流通过线路
And there is a limitation to how thick you can make the wires
而且电线的粗度是有限制的
before they break under their own weight
否则 它们会被自身重量压断
or become too expensive
或者变得成本高昂
Huge currents through the resistance of the wire
巨大电流在长距离运输中受到线路电阻的影响
would result in large voltage drops over longer distances
其结果就是 电压大幅下降
And that’s why Edison’s system could only transmit power
这也就是为什么爱迪生的系统只能将电力
to around a mile or two from the power source
传输到距离供电电源一两英里远的地方
Otherwise the power loss would be so much over the lines
否则线路传输中的功率功耗就太大了
That would cause huge inefficiency,
那导致巨大的低效和浪费
Of course Edison was aware of his system
当然爱迪生也意识到了这个系统的问题
So he decided to let one of his genius employees
所以他决定让他的一个天才员工
to take care of the problem,
来解决这个问题
who was our beloved Nikola Tesla
这就是我们亲爱的尼古拉·特斯拉
He was working for Edison at the time.
他当时为爱迪生工作
According to Tesla
据特斯拉说
Edison promised him $ 50,000
爱迪生许诺他五万美元酬金
which was a lot of money back then,
那在当时是很一大笔钱
if Tesla was able to make great improvements to Edison’s DC system
只要他能极大地改进爱迪生的直流电系统
Which Tesla did in a few months
特斯拉在几个月后做到了
and when he went to Edison to ask for the money
当他去找爱迪生索要报酬时
He said”Haha. I was joking obviously
爱迪生却说 “哈哈 我那是跟你开玩笑呢
you’re not aware of our American humor,”
你可真不了解我们的美式幽默”
which Tesla said”…… I quit!”
特斯拉怒道：“……我不干了！”
Later Tesla came up with his genius system
之后 特斯拉想出了他那天才的电力系统
and developed it for Westinghouse company
并为西屋电气公司研发了出来
What he did was to transmit power much smarter.
也就是用更加巧妙的方式传输电力
He used AC
他使用的是交流电
so he could change the voltage level using transformers,
因此他可以利用变压器来改变电压
here I’ll use my auto transformer
在这里 我将用我的自耦变压器
to generate 10 volt AC
来产生10伏的交流电
which would result in 10 amp AC through my 1 ohm load
这可以让 1欧姆的负载产生10安培电流
But before I send it through the transmission line,
但在我通过输电线传输电流之前
first I’ll step the voltage up using my microwave transformer
我先用微波炉的变压器让电压升高
and then I would step the voltage down
接下来 如果我有一台变压器的话
after the line if I had a transformer,
我会在输电线另一端让电压下降
Well, guess I can borrow the one from our microwave.
好吧 我应该可以从微波炉里“借”一个出来
They’re using tamper proof screws to stop me
他们想用防护螺丝来阻挡我
What they don’t know is that nothing can stop me.
却不知道我是无可阻挡的
They are just postponing the inevitable
也就拖延我一小会
There we are.
搞定
I’ll just take a picture of the wiring before I pull it out.
拆出变压器之前 我先拍一张布线的照片
I don’t want to blow it up later.
我可不想等会儿把它给炸了
There we are.
拿到了
Ok, now we have both transformers connected.
现在两个变压器已经接好了
Let’s do some voltage measurements before I connect the load.
在连接负载之前 先测几处电压
At the input
在输入端
We have close to 10 volts
有将近10伏电压
so that’s good.
很好
On the transmission line
在输电线上
We get around 190-200 volts.
大约有190到200伏电压
And at the output
在输出端
Again we have close to 10 volts
也是接近10伏电压
so that’s pretty good.
非常好
Now let’s connect a load
现在让我们连上负载
Ok.
好的
And the voltage across this load is
然后 通过这个负载的电压
1.6 volts?
1.6伏？
That’s garbage.
垃圾
What happened?
发生了什么？
The transmission line voltage
输电线的电压
118 volts?
118伏？
Everything dropped
都降了
This is worse than the DC system.
这比直流电系统都差劲
What’s going on Tesla?
特斯拉 发生什么事了？
Let’s measure the transformer secondary winding resistance
测一下变压器二次绕组的电阻好了
Around hundred ohms.
大概100欧姆
No wonder
怪不得
There’s too much drop over the large resistance of the secondary,
二次绕组的电阻太大 导致电压降太多了
so these transformers are not made for this purpose
所以这些变压器不是用来干这个的
That was a bad example.
这是一次失败的示范
It doesn’t matter.
无所谓
I’m gonna transmit power no matter what.
管它呢 我要传输电力了
2 volts. 3 volts.
2伏 3伏
4. 5. 6. 7. 8. 9
4 5 6 7 8 9
And 10 volts across the load.
负载有10伏了
We did it
我们做到了
And our transmission line is not burning
输电线没有起火
so that’s always a plus
这是件好事儿
Nothing is exploding.
没有东西爆炸
What is the transmission line voltage now?
现在输电线的电压有多少？
820 volts!
820伏！
Well anyways, although this is a pretty bad example,
好吧 尽管这是个很糟糕的示范
you can see that I’m transmitting more power than the DC system
我用这种方式传输电力 比直流电系统要费电
But my transmission lines are not burning.
但输电线并没有起火
So, that’s sort of a success?
所以 这也算是一种成功喽？
See in this system
看看这个系统
I can transmit a lot of power in this case around hundred watts
我在没有把输电线加粗的情况下
without having to thicken the transmission line wires
传输了大概一百瓦的电力
And if the Transformers were better
如果变压器效率高一点
the efficiency would be higher, too
电力传输效率也会更高
In fact, in this system,
事实上 在这个系统中
the higher you convert the voltage to,
你把电压升得越高
the easier it is to transmit power over greater distances,
向更远的地方输电就越容易
with some limitations, of course.
当然还会有些限制
That’s why in real life,
这就是为什么现实当中
they convert it to 10 kilovolts or hundred kilovolts.
输电线里的电压有一万伏或十万伏
Why? Because in transformers,
为啥？因为在变压器上
the input and output power is ideally the same,
输入和输出功率在理想状态下是相同的
although not really,
虽然实际上并不是
because there’s always some power loss as you saw,
正如你所见 总是会有功率损耗
and power is voltage times current.
功率等于电压乘以电流
So for example,
所以举例来说
if I increase the voltage by 20 times,
如果提高二十倍电压
in order to have the same power,
为了保持同样的功率
the current has to drop by 20 times at the output of the transformer
变压器输出处和传输线中的电流
and over the transmission lines.
要降低到1/20
And because the power through a resistor
又因为电阻器的功率
is equal to resistance times current squared
等于电阻与电流平方的乘积
The power would be 400 times less wasted on wires
所以输电线上的功率损耗会降低400倍
And with high voltage comes great responsibility
高电压可不是闹着玩儿的
The transmission lines have to be placed far enough
输电线之间的距离一定要足够远
so no arcing happens
才不会有电弧产生
There is no easy way to do the same thing
并没有什么简单的方法可以处理
with Edison’s stupid DC system.
爱迪生那愚蠢的直流电系统
In order to change the voltage,
为了改变电压
you would have to convert DC to AC,
你就必须把直流电转为交流电
increase the voltage, and then convert the AC back to DC,
增加电压 然后再将交流电转为直流电
and lose a lot of power in the process
在转换的过程中损耗大量电力
Edison still couldn’t see this.
爱迪生仍然看不到这些
All he saw was that his company
他看到的只是他的公司
was losing the contract of his life to power the world
会丢掉为世界供电这个重要商机
So all he did was to grab the fact that
因此竭力抓住一点事实来攻击
Tesla’s system was running on super high voltage,
也就是特斯拉的系统在超高压下运行
like 10 kilovolt or 100 kilovolt,
像是一万伏或十万伏
and say that it’s super dangerous to people
并说它对人们极其危险
by electrocuting animals with 10 kilovolt in public
还当众以十万伏电压电死动物
Thomas Edison.
托马斯·爱迪生
He contributed a lot to science and technology
他在科学和技术领域贡献颇大
what he was also an…… businessman,
但他也是个卑鄙商人
and that bit him in the lower back area
这让他最终自食其果
the moral of the story, don’t be an……
这个故事告诉我们 别当烂人
GIVEAWAY TIME!!!
礼品放送时间
You know, CircuitSpecialists has been quite nice to me
说实话 “CircuitSpecialists”网站相当不错
providing all my basic tools and components and everything
提供给我所有基本工具 元件和其他要用的东西
And I really hope you find what you need In their website too.
真心希望你也在该网站上找到需要的东西
And I’m quite happy with the multimeter they sent me,
而且我很喜欢他们送我的万用表
which is an LCR meter. It measures inductance, capacitance resistance,
这是台LCR测量仪 可以测量电感 电容 电阻
voltage, current, and a bunch of more stuff.
电压 电流 还有很多东西
So thanks to CircuitSpecialists
所以感谢CircuitSpecialists
I’m gonna give away five of these
我要送出五台这种万用表
to my patrons at patreon.com
给“patreon.com”网站上我的赞助人
and you the viewers.
和在看视频的观众
Also, if you want to start electronics
如果你想开始学习电子学
you would need a lab power supply
你会需要一个实验室电源
And I’ll give away four of those too.
我会再送出四台实验室电源
As usual, my patrons are automatically in the draw.
跟往常一样 我的赞助者会自动获得抽签资格
For everyone else
对于其他人
please follow the link to the Google Form in video description
请点击视频简介里“谷歌在线表单”的链接
and let me know which one you need and I’ll draw your name
告诉我你要哪一款产品 我将从中抽出获奖者
and that’s it.
就是这样了
Unibrow out
一字眉主播跟你说再见