Have you ever been shocked by a capacitor?

soso

Have you ever been shocked by a capacitor? [Copy link]

 

Early in the morning, I saw the fireworks-like capacitors recorded by Xiaoxia ( https://en.eeworld.com/bbs/thread-1211473-1-1.html ), and I was shocked. I quickly went to interview the person involved with a gossipy mood.

He said: accidentally touching the capacitor on the power supply is quite stimulating, more than 300 volts, "refreshing". And most engineers will accidentally touch it.

Now the question is, have you ever touched a capacitor with residual power? How does it feel? How can you operate more safely in this situation?

仙猫

Take a 220V AC power supply and double the voltage to 622V DC to light up a broken fluorescent tube. At this time, the capacitor should be charged to 311V. When you touch the capacitor, you will be shocked by the residual electricity. What do you feel? Anyway, it is not a good feeling. If you are determined, you will know it by touching it.

When I was a kid, I was confused as to why I could get an electric shock even though the power was off. I thought it was an illusion caused by excessive nervousness, and I didn’t believe it until I got an electric shock again.

maychang

I have been shocked by an electrolytic capacitor after rectification of AC mains, but only once.

I once charged an 8uF paper capacitor to 1000V and then discharged it with a screwdriver, which knocked off about 1mm of the screwdriver head.

soso

Xianmao published on 2022-7-21 11:04 Take a 220V AC power supply and double the voltage to 622V DC to light up a broken fluorescent tube. At this time, the capacitor should be charged to 311V. When your hand touches the capacitor, it will be hit by the residual electricity...

Even we great engineers have our weak moments.

soso

maychang posted on 2022-7-21 11:14 I was shocked by an electrolytic capacitor after AC mains rectification, but only once. I once charged an 8uF paper capacitor to 1000V, then used a screwdriver to discharge it, and the screw...

This is the case even for alloy materials, so it would be unimaginable if it were human flesh.

maychang

soso posted on 2022-7-21 11:43 Even alloy materials are like this, it is unimaginable if it is human flesh.

At that time, there were no screwdrivers made of tool steel such as 8CrV, only ordinary high-carbon steel screwdrivers.

maychang

soso posted on 2022-7-21 11:43 Even alloy materials are like this, it is unimaginable if it is human flesh.

I was electrocuted by a charged electrolytic capacitor. My hand pressed on the electrolytic capacitor. The electrolytic capacitor was 8uF, charged to about 200V, and the two lead terminals were on the cylindrical end surface. After the electric shock, two yellow-black spots with a diameter of about 3mm were burned on the skin of my hand, and the skin at the spots became hard. It took almost a month to recover.

btty038

I wasn't electrocuted, I was just blown up.

littleshrimp

maychang posted on 2022-7-21 11:14 I have been shocked by an electrolytic capacitor after AC mains rectification, but only once. I once charged an 8uF paper capacitor to 1000V, and then used a screwdriver to discharge it. The screw...

My screwdriver was also broken.

okhxyyo

I got electrocuted and had a blister on my hand. . . .

秦天qintian0303

Fireworks are often seen in power applications. Most of the time, it is because the capacitor is not fully discharged.

soso

maychang posted on 2022-7-21 12:03 The electrolytic capacitor was charged and a hand pressed on the electrolytic capacitor. The electrolytic capacitor is 8uF, charged to about 200V, and the two lead terminals are in a cylindrical...

In this case, is it usually forgotten accidentally?

soso

Qintianqintian0303 posted on 2022-7-21 13:24 In power supply applications, fireworks are often seen. Most of the time, it is because the capacitor is not fully discharged

Is there a way to discharge the electricity first and then touch it?

soso

btty038 posted on 2022-7-21 12:25 I was not electrocuted, I was just blown up

Like in the Xiaoxia video? There is light.

wangerxian

No, I didn't touch the capacitor directly, but it's scary to think about it. I've used Farad capacitors in a competition before, and I saw someone use scissors to short-circuit the positive and negative terminals of the capacitor. The sparks were really scary.

秦天qintian0303

soso posted on 2022-7-21 13:32 Is there a way to discharge the electricity before touching it?

If you are not in a hurry, leave it for a few hours, or use a power resistor.

秦天qintian0303

soso posted on 2022-7-21 13:32 Just like in the shrimp video? There is light

If it explodes, there will be light and smoke.

chunyang

When I was in middle school, I DIYed a TV and was shocked by the electricity stored in the graphite coating on the back of a 12-inch CRT.

The inner and outer walls of the CRT are coated with a layer of graphite, and a high-voltage capacitor is formed with the CRT glass as the medium, which is used to filter the high voltage of the two-four anodes. According to the specification, the outer graphite layer of the CRT must be grounded, so that high-voltage filtering can be achieved. Netizens who have observed the inside of the finished CRT TV or display should have noticed that the CRT is "bound" by a braided wire similar to a shielded wire, and the braided wire is the grounding wire of the graphite layer high-voltage capacitor. I didn't have a braided wire at the time, and I was reluctant to use a shielded wire instead. The key is that I didn't know how to bind the CRT, so I didn't ground the graphite layer. When debugging the TV, I wanted to test whether the graphite layer was charged after turning it off, so I took a test pen to approach the graphite layer. The test pen consists of a megohm resistor and a neon bulb, and its own impedance is very high. But even with such impedance, before the test pen touched the graphite layer, the air was broken down, and an arc hit the test pen. I felt like my arm was hit hard and retracted violently. The test pen was thrown hard against the wall, leaving an obvious mark.

When the graphite layer of a CRT is not grounded, under normal operation, the outer wall will carry a voltage equivalent to the high voltage of the 24-anode. For a 12-inch black and white CRT, this voltage is 12,000 volts. If it is a later color large screen, this voltage will be even higher, reaching more than 20,000 or even 30,000 volts.

In view of the incident of electric shock caused by the stored electricity in the CRT capacitor, I thought of a solution. I made a grounding device using elastic copper sheets, which solved the hidden danger.

chunyang

I was blown up by a capacitor once. It was during a routine maintenance of the thermal control equipment of a generator set. I was blown up by a tantalum electrolytic capacitor. The tantalum electrolytic capacitor was metal-encapsulated and was made in China in the 1980s. It was much more powerful than the small aluminum electrolytic capacitor in the video. My hand was still on the tantalum electrolytic capacitor at the time, and it was numb for a long time.

soso

chunyang posted on 2022-7-21 14:57 When I was in junior high school, I DIYed a TV and was shocked by the graphite coating on the back of a 12-inch CRT. The inner and outer walls of the CRT are each coated with a layer of graphite, with the CRT glass as the...

Wow, this one is even more powerful, 12,000 volts.