DO NOT USE THIS DANGEROUS ADJUSTABLE ADAPTER!

[Athosworld]

This adjustable 3vDC to 12vDc power supply is outputting 4 TIMES MORE THAN THE SET VOLTAGE
, transformer is very warm after 30 seconds of use.

I think this is caused by the bare copper transformer outputs that combine and make a higher voltage.

 

[Nigel Goodwin]

Sorry, but you are almost certainly completely wrong:

1) The wires aren't bare, they are varnished, same as almost every small transformer out there.

2) It's unregulated, so the voltage will be MUCH higher than expected without full load.

3) It's a small mains transformer it WILL run very hot, this is perfectly normal - basically the transformer, the less efficient they are. Large transformers (power stations etc.) are pretty well the most efficient machines that are made.

4) If the wires had somehow rubbed through the varnish and were touching, that would cause a shorted turn - and you'd know it was getting HOT then

 

[picbits]

What mains voltage are you running ? That looks like a 110V PSU and if you're putting it on 240V you'll get a much higher output and it will get hot very quickly.

 

[Athosworld]

What mains voltage are you running ? That looks like a 110V PSU and if you're putting it on 240V you'll get a much higher output and it will get hot very quickly.

Running at a 127 vAC 60hz

 

[Athosworld]

Sorry, but you are almost certainly completely wrong:

1) The wires aren't bare, they are varnished, same as almost every small transformer out there.

2) It's unregulated, so the voltage will be MUCH higher than expected without full load.

3) It's a small mains transformer it WILL run very hot, this is perfectly normal - basically the transformer, the less efficient they are. Large transformers (power stations etc.) are pretty well the most efficient machines that are made.

4) If the wires had somehow rubbed through the varnish and were touching, that would cause a shorted turn - and you'd know it was getting HOT then

I checked them and they are indeed bare, they spark if they touch.

Also, the big transformer is almost the only thing in the circuit

 

[For The Popcorn]

Also, the big transformer is almost the only thing in the circuit

This supply is an old-school "battery eliminator". The output voltage is not regulated – it depends on the current drawn by the load.

The simplest AC – DC converter consists of a transformer, single rectifier diode and a filter capacitor.

Better than a half-wave supply is a full-wave supply. This type of design can use a center-tapped transformer and two rectifier diodes

or a bridge rectifier (four diodes, either separate or pre-connected in a single package).

These simple supplies are unregulated and depend on the resistance of the transformer coil and the load current to achieve the "rated" voltage. If the load current is lower than the power supply design load, the voltage will be higher than "rated". If the load current is higher than the design current, the voltage will be lower than "rated".

Different voltages of this type of "battery eliminator" are provided by changing taps on the transformer output. Since the purpose of this type of supply is to replace batteries, the current is expected to be within a limited range. And battery-operated devices can handle a range of voltages.

I must have been around 14 when I cut one of these supplies apart and learned all this.

 

[Nigel Goodwin]

I checked them and they are indeed bare, they spark if they touch.

Unusual, and unlikely - but don't do it - if they were touching on there own the transformer would self destruct, and wouldn't have high output.

Also, the big transformer is almost the only thing in the circuit

I know, because it's just a crude unregulated PSU, and it's tiny transformer, not a big one

It's exactly the same as the circuit you've just been given in your other thread.