Is it normal for small 6VA 15v transformer to vibrate like this?

Not normal, sound like excessive current somewhere?
Either a winding, or something on the load, it is possible the bridge has shorted?
Disconnect every thing from the secondary and see if it persists.
If earthing the secondary, make sure the DC side is not grounded also.
Max.

 

Not normal, sound like excessive current somewhere?
Either a winding, or something on the load, it is possible the bridge has shorted?
Disconnect every thing from the secondary and see if it persists.
If earthing the secondary, make sure the DC side is not grounded also.
Max.

That's the first thing I tried, but it kept on vibrating without any load. I also checked the amperage coming out of the secondary to the circuit and it is well within the 6VA limit (I think it was only 50 or 60mA).

 

It could be loose lamination's which is rare.
A obvious sign it is high current if the transformer heats up after a short period off load.
Max.

 

It got pretty hot when I made the mistake and short it for a while. But now it doesn't get hot any more, just vibrates and hums.

Before that incident, which also was before I solder the wires to the terminals, it never got hot or vibrated; and as I remember I tested it with the load.

 

I also don't understand why the designer chose that 15v transformer, when the purpose is getting 12v DC. I mean, out of the secondary I'm really getting around 21v after the filtering capacitors, to bring it down to just 12v after the regulator.

Wouldn't a 12v transformer do; or even a 9v?

 

You would only need a 9vac maximum for a 12vdc supply, but depends on whether a regulated supply was needed.
Max.

 

I think I found out where those 13.5v between the Neutral and Earth come from. I noticed that each cable that I connect to a socket (a cable with 3 wires, which is supposed to have the Earth disconnected) leaks between 0.1v and 0.9v to the Earth cable. I also found that some devices leak much more; like the computer, which for some reason leaks up to 7v to the Earth wire.

Now, since I have a lot of cables and devices connected to the same extension, which is connected to just one socket, I guess that the voltages from the leakages are adding up and reaching those 13.5v.

Is this a reasonable assumption?

First, are you absolutely certain that the ground terminal on your electrical outlets is not connected? It sounds like it is connected, if you can measure a voltage between it and the neutral terminal. How did you measure the neutral-ground voltage difference? On the receptacle while a device is plugged into it? On another receptacle on the same circuit?

The voltage you measure between neutral and ground is due to the V=IR voltage, from current flow in the neutral conductor between your distribution panel and the outlet. Any other devices drawing current on the same circuit will increase the voltage on the neutral conductor. Since the wire from the outlet to the distribution panel (or wherever neutral is referenced to ground in your case) has a nonzero resistance this length of wire will have a voltage across it whenever current is flowing through it.

The fact that the voltage between neutral and ground is not always zero is the most important key in all the complicated earthing/grounding issues. If there were no voltage difference, then they could use the same conductor. But neutral is a current-carrying conductor and so it will have a voltage rise above earth ground.

 

First, are you absolutely certain that the ground terminal on your electrical outlets is not connected? It sounds like it is connected, if you can measure a voltage between it and the neutral terminal. How did you measure the neutral-ground voltage difference? On the receptacle while a device is plugged into it? On another receptacle on the same circuit?

The voltage you measure between neutral and ground is due to the V=IR voltage, from current flow in the neutral conductor between your distribution panel and the outlet. Any other devices drawing current on the same circuit will increase the voltage on the neutral conductor. Since the wire from the outlet to the distribution panel (or wherever neutral is referenced to ground in your case) has a nonzero resistance this length of wire will have a voltage across it whenever current is flowing through it.

The fact that the voltage between neutral and ground is not always zero is the most important key in all the complicated earthing/grounding issues. If there were no voltage difference, then they could use the same conductor. But neutral is a current-carrying conductor and so it will have a voltage rise above earth ground.

I'm absolutely sure it's not connected because I changed a lot of wall sockets at home, and I'm absolutely sure there are only 2 wires: load and neutral; there's nowhere to connect the earth. I also checked the main panel yesterday and there seem to be only 4 wires: 2 for load and neutral coming in the house, and the 2 load and neutral for the internal installation.

I measured the voltage between the (dummy) Earth and the other 2 (real) wires by plugging in a cable or an extension with 3 wires. Then plugged in a multimeter to measure the voltages between the 3 wires. I recon that less than 1v might be an erroneous reading from my cheap multimeter, but once you connect other devices (e.g. the computer), the voltage builds up. The computer alone adds 7VAC between the Earth and the other 2.

 

If the right size conductors are used in your home then I would expect no more than a very low voltage between any live conductor and GND <=1.5v.
Do you have a system there where the local earth ground conductor is connected to the neutral at the panel?
And what is the type of earth ground, water supply pipe or ground rod?
Max.

 

I am still confused.

You state categorically that you have no earth to connect to.

Yet you show in your first circuit that you have connected a transformer core to mains earth?

Either of your two circuits could be correct and valid within UK regs in appropriate circumstances.

However neither are sensible electrically as they stand, since you are only using half of the secondary/rectifier circuitry.

Do you understand how transformer/rectifier circuits work?

All this about voltages between this and that.

Can you post some sketches or better some photos?

With all due respect you have got your details mixed up several times here now.

 

If the right size conductors are used in your home then I would expect no more than a very low voltage between any live conductor and GND <=1.5v.
Do you have a system there where the local earth ground conductor is connected to the neutral at the panel?
And what is the type of earth ground, water supply pipe or ground rod?
Max.

Then it's fine, because once I separate all the devices from the extension, I get less than 1v.

I don't have an earth anywhere in the house; only 2 wires enter the house, and only 2 wires go to each socket. There's no earth in the installation.

I am still confused.

You state categorically that you have no earth to connect to.

Yet you show in your first circuit that you have connected a transformer core to mains earth?

Either of your two circuits could be correct and valid within UK regs in appropriate circumstances.

However neither are sensible electrically as they stand, since you are only using half of the secondary/rectifier circuitry.

Do you understand how transformer/rectifier circuits work?

All this about voltages between this and that.

Can you post some sketches or better some photos?

With all due respect you have got your details mixed up several times here now.

The earth connection is not available on the wall sockets or the electrical installation, that's an optional 3 wire that comes with the new type of cables and extensions I'm using (e.g. the computer cable).

The diagram shows an earth connection, and I do have a mains cable for the device with the 3 wires -earth included-, but that doesn't connect anywhere in the wall socket.

This is the problem as I figured out so far: I have an extension to which I connect a lot of devices, the extension has an earth, and all the devices have an earth, but the wall socket doesn't have an earth. Now, when I have all those devices connected to the same extension, and I measure the voltage between the earth (which is disconnected in the main socket) I get up to 13.5 VAC.

I guess that each device/cable leaks some voltage to the earth connection; especially the computer with 7 VAC.

 

I can't see where the confusion is...

Wall socket without earth:

Extension sockets with the optional earth -top and bottom pins- (which in this case doesn't connect anywhere in the wall socket, because there is no earth connection):

Cable I'm using for my devices (computer, etc.) with the optional earth (which again, doesn't connect anywhere in the wall socket; since there is nowhere to connect it).

What details exactly have I mixed several times?

 

Then it's fine, because once I separate all the devices from the extension, I get less than 1v.

I don't have an earth anywhere in the house; only 2 wires enter the house, and only 2 wires go to each socket. There's no earth in the installation.

So where are you obtaining a earth ground? If at all?
Is your service supply referenced to ground at all?, anywhere?
Max.

 

So where are you obtaining a earth ground? If at all?

From the devices that have an optional earth connection; for example, the ones using this type of cable, like the computer:

Now, imagine 5 of those cables connected to the same extension -also with an optional earth-... that's how I got the 13.5 VAC from the earth to the other 2 wires.

Is your service supply referenced to ground at all?, anywhere?
Max.

I don't think it is; at least I can't see an earth connection anywhere in the house -it's not in the panel, and there are none in the wall sockets-.

 

Adam, please take note I am not getting at you, I really am trying to help.

But we have 34 posts and you still have not clearly stated your setup without contradicting yourself.

I'm sure that the difficulties can be cleared up if we can determine the correct information between us.

So thanks for the pics, that's the outside of the sockets. What about the inside and the house distribution board?

Max is really straining at the leash here to kill all the problems.

My reply to your first post was to try to clear up a mixing up of earth and neutral. My last post was to point out that you have connected your transformer to an apparantly non existent earth, and Max the bloudhound has now picked up that scent.

 

But I said from the beginning there is no earth in the wall sockets (either inside or outside); just load and neutral.

This is what was always used in Spain: no earth, just load and neutral.

If you tell me where you think I got confused, maybe I can clear it out.

 

This is more or less what the inside of my wall sockets look like:

I was thinking: could the casing be acting as an earth? I noticed that in my house the holes in the walls where the sockets fit are surrounded by a sort of metallic round plate.

If it is: how can I test it? How do I test an earth connection?

 

But I said from the beginning there is no earth in the wall sockets (either inside or outside); just load and neutral.

If you tell me where you think I got confused, maybe I can clear it out.

Well apparently you did not say this from the beginning.

so I kept both sides of the transformer isolated; only connecting the core of the transformer to the MAINS EARTH and to the chassis of the device,

No wonder we have been tilting at windmills, (you may have heard of that guy!).
Max.

 

Well apparently you did not say this from the beginning.

No wonder we have been tilting at windmills, (you may have heard of that guy!).
Max.

With that I meant the earth of the cable that goes to the mains. In the same post I said the earth is disconnected in the wall socket, so there's no other earth but on the mains cable (which doesn't connect anywhere once it reaches the wall socket).

 

I was thinking: could the casing be acting as an earth? I noticed that in my house the holes in the walls where the sockets fit are surrounded by a sort of metallic round plate.

Yippee Progress

That's a very good question.

The plug you showed in post#34 has a sprung metal earth connection, which engages the earth strap shown in post#37.
The plug ditto post#36 does not.

Yes it is entirely possible that conduit has been used as an earth continuity connector.
I do not know if this is accepted practice in Spain or not, it is not used in the UK because corrosion at the joints (or simply the builder's failure to join) can destroy the earth continuity.

I think that link I posted for you from a Spanish based electrician suggests such practice is disallowed in modern Spain.