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Transformer help.

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marclurr

New Member
Hey there,

I've just started getting into electronics and before I go crazy on anything 'useful' I want to gain more understanding about the different parts, in particular, transformers.

I pulled apart an old clock radio and it had an AC transformer between the main circuit board and the mains plug. I salvaged it from the radio to experiment with it.

What's confused me is that is has 3 output wires. On the corresponding connections on the circuit board, two of the connections said "AC ~" and one said "AC 0".

The first thing I want to do it see what voltage it outputs, but I'm not sure how to wire it up.

If someone could point me in the right direction with the connections and if possible, explain where I would connect my multimeter probes to test the voltage.

By the way, if it helps, I'm in the UK, so my mains voltage is 240v @ 50Hz .


Cheers
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hey there,

I've just started getting into electronics and before I go crazy on anything 'useful' I want to gain more understanding about the different parts, in particular, transformers.

I pulled apart an old clock radio and it had an AC transformer between the main circuit board and the mains plug. I salvaged it from the radio to experiment with it.

What's confused me is that is has 3 output wires. On the corresponding connections on the circuit board, two of the connections said "AC ~" and one said "AC 0".

The first thing I want to do it see what voltage it outputs, but I'm not sure how to wire it up.
The secondary probably has a centre tap, so it will be somthing like 6-0-6.

If someone could point me in the right direction with the connections and if possible, explain where I would connect my multimeter probes to test the voltage.
Measure the secondary between all possible connections, you should have the same voltage (6V in my example above) between two combinations, and double that (12V in my example) in the third.

You must have your meter set to AC volts.

By the way, if it helps, I'm in the UK, so my mains voltage is 240v @ 50Hz .
Actually, it's been 'officially' 230V in the UK (and all the EU) for many years now.
 

marclurr

New Member
Actually, it's been 'officially' 230V in the UK (and all the EU) for many years now.
Ahh right. I thought I'd heard that somewhere before. Thanks for clearing it up ;)


Okay I did the tests you mentioned and your were right, said 8.4v so I'm guessing it was trying to be 9 :) The only thing I have to ask now is how would I wire this up to do something useful?

If you could just explain a simple circuit, perhaps powering a single LED?

Thanks for your quick response btw ;)
 

marclurr

New Member
Yeah I've been looking at bridge rectifiers. Just two more questions if you would be so kind :)

1. Would I need any specially rated diodes, or would any do?

2. How would I wire it up? I've seen the circuit diagrams for the bridge rectifier but they only show two connections to the diode bridge.

Cheers
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The diagram I posted the link to shows four connections to the bridge.

You just need 1N4001 rectifiers or similar, it's not at all crticial - you need four of them to build a bridge, or buy a ready made bridge.
 

RODALCO

Well-Known Member
For a LED you also need a series resistor. to keep the current below 20 mA, otherwise the LED will burn out.
Start with 680 ohms for a 8.4 volts supply.
 

marclurr

New Member
he diagram I posted the link to shows four connections to the bridge.
Yeah I felt embarrassed after that post as I looked on the wiki page and there it was staring me in the face lol. I used the version with 2 diodes and used it to power an led with a 330ohm resister in front of it. Worked perfectly. Just need to do a bit more research into it now thanks for the initial help :)

Mark
 

grim

New Member
Ahh right. I thought I'd heard that somewhere before. Thanks for clearing it up ;)


Okay I did the tests you mentioned and your were right, said 8.4v so I'm guessing it was trying to be 9 :) The only thing I have to ask now is how would I wire this up to do something useful?

If you could just explain a simple circuit, perhaps powering a single LED?

Thanks for your quick response btw ;)
I'd go with Nigel's inspired guess of 6-0-6:D off load it will give about 8.4-0-8.4
 
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