Mysterious phenomenon From electric line

[nobtiba]

Dear All,

I am really confuse for one problem, attached here the schematic to better understand.

There are 3 electric plugs on the wall and i use them for system in the schematic. Don't know why when i turn Plug 1 ON, the vol meter on PSU show 32 V, since measure on input of Circuit board (which should be the same) is 7.8V. But if i turn Plug 1 off, then on PSU show 7.8 V (which seems to be true).

Another thing is, when turn Plug 1 ON, the camera keep sound "beep, beep,beep, ..." which show error. I guess there should be problem about power.

The system is on Lab of my university. I don't know wheather the cameras and other system draw out too much current ??? What equipment could help me avoiding these phonomenon ? Need your suggestion in urgent, please !

PS: ("the same" in red replace for the same connections in the un-continuous red dots)

 

[ericgibbs]

The system is on Lab of my university. I don't know wheather the cameras and other system draw out too much current ??? What equipment could help me avoiding these phonomenon ? Need your suggestion in urgent, please !

Hi Nobtiba,
As its a 'lab' power system I suspect that it will connected to the local mains suppy using an isolation transformer,
most likely you are exceeding the transformers rated current.?

Measure the 'ac' voltage of the bench power sockets while you reconduct the mains loading test.

 

[nobtiba]

It is measured : 239 V (ac). Is it wrong one ? ( we use 220 V in Singapore)

 

[ericgibbs]

It is measured : 239 V (ac). Is it wrong one ? ( we use 220 V in Singapore)

hi,
The higher than 'local' mains supply also suggests an isolation transformer.

Did the Vac measure 239Vac when you had ALL the equipment switched ON and the CCTV bleeping.?

Sounds like a strange question, when was the lab built.??

 

[nobtiba]

Yes, the Vac measure 239Vac when ALL the equipment switched ON and the cameras bleeping.

I dont know what is transformers rated current and what if i reached it ? How to avoid it ?

 

[nobtiba]

Why many groups in lab also use equipments and they also draw out the current, so why only me get meet the problem ? What is the different in my case? When i doing my experiment, will other people electric activity could effect me ?

If i lower the number of devices (for example: cameras) could help me avoiding that ?

 

[nobtiba]

I guess something wrong with my PSU, when i turn it off no sound, no " beep, beep, ..." any more. Howcome it still give good output, only wrong in the indicator display, and when turn off Plug 1, the display is right again.

However, i will change the PSU.

 

[ericgibbs]

I guess something wrong with my PSU, when i turn it off no sound, no " beep, beep, ..." any more. Howcome it still give good output, only wrong in the indicator display, and when turn off Plug 1, the display is right again.

However, i will change the PSU.

hi,
Let me know how it goes, if the fault clears, it would be a good idea to get the first PSU checked by an electrician.

 

[nobtiba]

Well, now, i turn off PSU but the sound still some where. Not very continuously but still have "beep, beep, beep..."

I forgot to mention in schematic that PC connect to electric board through parallel connection and the board connect to camera to control them.

If i disconnect parallel connection (as well as PSU), then no more sound, no more "beep, beep..." I don't know what computer could cause or harm the board to effect cameras through paralllel connection.

If disconnect PSU from the board, although all Plug is ON, the PSU seem to be right, i don't know how to check it.

 

[ericgibbs]

hi,
It could be an earth leakage problem or a ground loop problem.

Its difficult to say without seeing the installation.

Do you have a resident college electrical engineer who could checkout the mains system.?

 

[Pommie]

When you have interconnecting mains installations there is always the possibility that different equipment can end up on different phases. This seems unlikely to be your problem as most modern equipment is isolated. However, if you have connections between equipment that are connected to different socket and possibly different phases then this is still a possibility. Do you know if all equipment is isolated. You can verify this by removing any interconnection between equipment on different plugs.

Mike.

 

[nobtiba]

@ Eric: Sadly, i am that kind of "electric engineer". May need to ask for more experiences from yours...
@Pommie: So should i use same socket, plug for equipments that have interconnection ?

I try to remove some connection between them ( parallel connection and PSU connection mentioned on previous post) and didn't hear the sound any more.

Now i am not at lab to check plug them in the same plug.

 

[ecerfoglio]

I try to remove some connection between them ( parallel connection and PSU connection mentioned on previous post) and didn't hear the sound any more.

Now i am not at lab to check plug them in the same plug.

With those interconections removed, measure the voltage between the diferent equipment grounds (both chassis grounds and "cero volt references). Before measuring, put your voltmeter in a range that accepts 220 V , or better yet 380 V , as it is possible that your sockets and / or equipment are wired incorrectly (and even on different phases).

If there are more than a few volts between those grounds check the wiring of the sockets, and if there are any "strange" readings repair them (or get them repaired):

>> voltage between grounds in different sockets (should be CERO)
>> voltage between neutral in different sockets (should be CERO or near cero)
>> voltage between ground and neutral in the same socket (should be only a few volts) in every socket.
>> voltage between neutral and phase (=live) - This should be 220V in every socket.

 

[nobtiba]

I guess what Pommie said has something right. When i connect PSU in the same branch with my PC, then, connect PSU to the circuit board, the display on PSU show the right value, not "fake" value as above. So there may be smth with the phase although i don't know why is it.

Now, about the strange sound. It is still there. But i could narrow it down to connection between the circuit board with PC through parallel port. Only when i have this connection, then i hear strange sounds.

Must say that i am quite confident with the connection and wiring on circuit because my program to control it still work well. Maybe i just forgot to make some component to sucure the parallel connection to avoid it effect ( electro magnetic ?) to other component ? Just a guess