The problem of static electricity

chenbingjy

The problem of static electricity [Copy link]

 

I designed a circuit board to be powered from a power adapter.

The power adapter is 220 to 24V.

A sensor is connected to the board.

When we went to other companies to debug their machines, we found that the casing of our sensor was different from that of other companies’ machines.

There was static electricity on the outer shell, about 90V, which shocked a girl.

Later, I connected the ground wire of the three-phase electricity to the sensor housing, and everything was fine.

Now my boss asked me to redesign the board so that there can be no static electricity.

I'm a newbie and don't know how to do this. Can an expert help me? Thanks!

btty038

You just share the land.

maychang

That is not static electricity, but the distributed capacitance between the AC mains side of your "power adapter" and the 24V DC output terminal, which causes an AC potential difference between the 24V DC output terminal and the ground or "other people's machines".

Since "just connect the ground wire of the three-phase electricity to the sensor housing, it will be fine", I think you already know what to do.

chenbingjy

btty038 posted on 2019-6-26 15:18 You just need to share the land

Thank you! How do we share the land?

Is it true that the ground wire of the three-phase electricity is connected to the sensor shielding wire?

maychang

chenbingjy posted on 2019-6-26 15:26 Thank you! How to share the ground? Is the ground wire of the three-phase power connected to the sensor shield wire?

"How do we share the same ground? Is the ground wire of the three-phase power connected to the sensor shield wire?"

It is connected to the earth (or protective ground wire), and is definitely not connected to the neutral wire of three-phase electricity.

chenbingjy

Master maychang, I am a rookie.

Our boss said it was unprofessional to do so.

Can you tell me the professional wiring method? I am too new to it.

chenbingjy

maychang posted on 2019-6-26 15:29 "How do we share the same ground? Is the ground wire of the three-phase power connected to the sensor shielding wire?" It is connected to the earth (or protective ground wire), absolutely...

The word "earth" is too abstract and I don't understand it at all.

maychang

chenbingjy posted on 2019-6-26 15:35 The word earth is too abstract, I don’t understand it at all.

The Earth knows, right?

To connect to the earth is to connect the wire to the earth. You can use a bare wire to throw into the water of a deep well (this is how the earliest ground wire was made), you can drive an iron rod into the soil and connect the wire to the iron rod, or you can connect it to the water pipe (if it is an iron pipe).

However, the power department has already prepared it for you. The power department has already connected the hole in the middle of the socket on the wall of your office or residence to the ground. You just need to connect the PE terminal or shell of your "power adapter" to this hole.

Take a look at the power cord of the desktop computer you are using. It has three legs, and the longest leg is the one that is plugged into the middle hole of the wall socket, so you just need to connect the place that needs to be grounded to the longest leg of the power cord.

captzs

The first post said, "Later, I connected the ground wire of the three-phase electricity to the sensor housing, and everything was fine." Since we have already done it, why not just follow this?

chenbingjy

Thank you.

If we use this three-pin power adapter and connect the longest ground wire to the ground wire of someone else's factory, will it be OK? Please give me some advice.

chenbingjy

captzs posted on 2019-6-26 16:03 The first post said "Later, the ground wire of the three-phase electricity was connected to the sensor housing, and it was fine." Since it has been done, it will be OK if it is handled in this way!

Our boss said that was unprofessional.

chenbingjy

captzs posted on 2019-6-26 16:03 The first post said "Later, the ground wire of the three-phase electricity was connected to the sensor housing, and it was fine." Since it has been done, it will be OK if it is handled in this way!

Our boss said that was unprofessional.

chenbingjy

captzs posted on 2019-6-26 16:03 The first post said "Later, the ground wire of the three-phase electricity was connected to the sensor housing, and it was fine." Since it has been done, it will be OK if it is handled in this way!

Our boss said that was unprofessional.

maychang

chenbingjy posted on 2019-6-26 16:05 Thank you. If we use this three-head power adapter and connect the longest ground wire to the ground wire of someone else's factory, will it be OK? Hope...

"We can use this three-pin power adapter and connect the longest ground wire to the ground wire of other people's factories, right?"

It is to connect your sensor housing (you mentioned the sensor shield wire before, maybe it is the shield wire) to the longest pin of the power adapter socket.

maychang

chenbingjy posted on 2019-6-26 16:05 Thank you. If we use this three-head power adapter and connect the longest ground wire to the ground wire of someone else's factory, will it be OK? Hope...

In fact, it is better to connect the metal shell of your circuit board to the longest leg of the power adapter socket, and connect your sensor housing, etc. to the metal shell of your circuit board. This is how desktop computers are done. You use the resistance range of a multimeter to measure the connection between the desktop computer housing and the long leg of the power cord.

chenbingjy

maychang posted on 2019-6-26 16:22 "We use this three-head power adapter, and then connect the longest ground wire to the ground wire of other people's factories, right?" ...

Thank you! I understand.

chunyang

What you encountered is not static electricity. Generally, there are two reasons: 1. The switching power supply has a Y capacitor, and you did not reliably connect the system ground to the ground according to the specification. 2. As maychang said above, it is caused by coupling through distributed parameters or similar reasons in other people's equipment, which is caused by connecting to your system. But for your system, the latter 2 is unlikely.

Solution: Connect the power supply according to the specification. The power supply must be a single-phase 3-wire system, which is a 3-pin plug/socket used by computers and home appliances. The distribution board must have a ground connection point according to regulations. Note that it is not the neutral line. Do not make a mistake, otherwise it may lead to fatal consequences! If the site is not standardized and there is no ground wire, then remove the Y capacitor in the switching power supply you are using, or choose a power supply without a Y capacitor.

chunyang

chenbingjy posted on 2019-6-26 16:05 Thank you. If we use this three-head power adapter and connect the longest ground wire to the ground wire of someone else's factory, will it be OK? Hope...

It is not suitable to use the power adapters used for such consumer electronic products in industrial sites. Look at industrial power supplies instead. Don't be greedy to save a little money but bring huge after-sales troubles. In the end, you will spend more.

topwon

This is not static electricity, it is probably leakage from the power adapter.

Logically, since this adapter uses a 3-pin AC input terminal, the 24V output ground should be short-circuited with the AC input ground pin, right? In this way, the downstream equipment does not need to add a ground wire. This is a temporary solution.

To solve the root cause, we need to find out why the leakage occurs. Generally, the value of the Y capacitor between the primary and secondary of the adapter is too large. First confirm that without installing the post-stage equipment, is the voltage difference between the output ground of this 24V adapter itself and the ground of other machines also 90V?

chenbingjy

Thank you everyone, we originally used a 2PIN AC input terminal.