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Question about a transformer
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uk.casmith:
I have purchased a clock from a shop in the UK. Open it with the idea of stealing the transformer and some components. I have some questions about using the transformer. I'm pretty new at this stuff:

FYI: All UK plugs must have a ground (earth) wire and the voltage is 220 volts.

The transformer has three wires running out of the transformer towards the circuit board. I've tried measuring the voltage but because it's AC I cannot get an accurate reading. If I measure the voltage after the diode i'm getting around 5.42 volts.

My question is if I disconnect the three wires: Two of them are the AC and one is ground.

Where do I connect the ground wire?

And if someone can give me some safety advice that would be great!

Thanks,

Cameron.
Benta:
You don't connect the ground wire. Small things like your clock are designed to be "floating" and just need phase and neutral. Reinforced insulation from the mains keep them safe for the consumer.
A symbol depicting two squares within another somewhere on your clock should show this.
tpowell1830:

--- Quote from: uk.casmith on September 16, 2018, 09:25:09 pm ---I have purchased a clock from a shop in the UK. Open it with the idea of stealing the transformer and some components. I have some questions about using the transformer. I'm pretty new at this stuff:

FYI: All UK plugs must have a ground (earth) wire and the voltage is 220 volts.

The transformer has three wires running out of the transformer towards the circuit board. I've tried measuring the voltage but because it's AC I cannot get an accurate reading. If I measure the voltage after the diode i'm getting around 5.42 volts.

My question is if I disconnect the three wires: Two of them are the AC and one is ground.

Where do I connect the ground wire?

And if someone can give me some safety advice that would be great!

Thanks,

Cameron.

--- End quote ---

Hi Cameron, welcome to the forum. I can give you some advice regarding mains voltage and safety, however, based on your question and context, I advise you not to do anything more until you pick up a book and study some basic electric theory. The problem is that anyone giving you advice on this forum would probably put you in danger and will create a liability to you and the advisor.

With that said, PLEASE seek out a mentor that can directly guide you before you get hurt or killed. I encourage you to go further and learn more and try things, but under the guidance of a more experienced tutor.

I repeat, do not go any further until you have more knowledge and guidance.

Hope this helps...
Brumby:
Welcome to the forum Cameron.

We always welcome anybody who wishes to ask questions about mains related subjects ... especially when talking about transformers and "ground".  We get rather nervous sometimes ... mains is not very forgiving, which is why any "remote advice" given here may seem overcautious.

I am curious about this statement:

--- Quote from: uk.casmith on September 16, 2018, 09:25:09 pm ---I've tried measuring the voltage but because it's AC I cannot get an accurate reading.

--- End quote ---

AC is not (on its own) a valid reason for being unable to get an accurate reading - so I must wonder what it is about your measurement that makes you say this?

Also, when it comes to commenting about a transformer, it is always useful to provide a photo showing it and the connections on it.  In your case, a shot or two of the wiring from the mains cord to the transformer would also be helpful.

With photos - please make special effort to:
 1. Get the subject in sharp focus
 2. Have it well lit
 3. Get as close as you can so that the area you want to show us fills as much of the frame as possible.
drussell:
Welcome!

Firstly, a photo or two of what you're looking at would be very helpful.


--- Quote from: uk.casmith on September 16, 2018, 09:25:09 pm ---The transformer has three wires running out of the transformer towards the circuit board. I've tried measuring the voltage but because it's AC I cannot get an accurate reading. If I measure the voltage after the diode i'm getting around 5.42 volts.
--- End quote ---

You should be able to get a proper reading using a meter that is set to the correct range to measure AC voltages.  What kind of meter are you using?  Perhaps a photo of that, as well.

Also, there is usually more that one diode, often what is called a bridge rectifier (which is actually four diodes in one package) with four leads.


--- Quote ---My question is if I disconnect the three wires: Two of them are the AC and one is ground.
--- End quote ---

Typically when there are three wires on a secondary winding, it is a centre-tapped winding.  This means that there is a winding with two "halves", with the third wire being connected to the point between the two halves, where they join.  This is a very useful feature for many applications for various reasons and purposes.

There should not usually be an actual ground wire, though, since once you are om the secondary side of a transformer, you arbitrarily call some point of your circuit "ground" potential, even though it may not truly be earthed.  Photo, please.  :)


--- Quote ---And if someone can give me some safety advice that would be great!
--- End quote ---

Firstly, since you are a beginner and don't want to be anywhere near the mains power yet, if you must experiment with a mains connected device, even just a transformer, be absolutely sure that all connections that are at mains potential are fully insulated!  Starting by using battery powered circuits or a self-contained wall-wart type power supply may be more appropriate, however, as long as things are truly insulated completely, the potential danger can be made to be minimal.

Again, if you provide some photos, we can help to see if this clock is insulated well enough to be in there poking and prodding around when you're just starting out and learning. 
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