So I'm creating a power supply for my personal use. Dual polarity 15V using a 24-0-24 V transformer. I was using a two pin plug to connect the transformer to the mains. However I was told that I need to 'ground the chassis' to avoid getting a shock. How do I go about this? Should I use a 3 pin plug? Transformer is centre tapped.

P.S. My country has a 230 V 50 Hz supply

 

The ground connection is a safety feature that only becomes active during a fault. As a beginner, I think you should use it. Only a highly skilled person has a good chance of no faults, and even then, a safety feature is always a good bet.

ps, a 24-0-24 volt secondary is good for about a dual 30 volt supply. I think you have the wrong transformer.

 

Connect the ground wire from the cord to one of the screws holding your transformer to the chassis of the supply.

 

The transformer gives you galvanic isolation so there is no real need to ground the common of the supply secondary, unless you desire to, but as already stated you should ground the transformer case and frame.
And as per @#12 , a 12-0-12vac secondary should give you sufficient to regulate to 15vdc when rectified and smoothed.
Max.

 

I would tend to use about 15-0-15 v secondary to leave room for rectifier loss, capacitor ripple, regulator head room, and power line sag.
(15 DC + 1.4 on the rectifiers + 1.7 for the regulator + 2 for the ripple voltage)/ sqrt2 = 14.2VAC

 

Ok guys a status update here. I rigged up my connections as per this circuit I've attached. I started the power and found that the positive half works well but the negative half gives me a constant voltage. So I shut down the circuit and re examined the circuit. Found no faults ( maybe I screwed up in looking for screw ups). Turned the power on again. This time I found that my transformer was bubbling some sort of liquid and emitting smoke. What am I doing wrong? I'd prefer not to burn down my house.

 

What is the voltage rating of the capacitors?
What package is the LM337 - TO220?
Carefully check the pin connections against the datasheet.

 

You have a bad or misconnected transformer, a miswire in your circuit, or a faulty component, take your pick.
What constant voltage is the negative output?
Check the capacitor polarities.
Unfortunately you may have zapped the transformer.
It's always a good policy to monitor the input current when first turning on a new circuit.

 

LM317/377 to the same heat sink??
Common mis-connected?
Max.

 

Don't forget that the LM317 and LM337 have different pinouts.

Also, R1 should have the un-connected end wired to its wiper. The same applies to R4 -- unused end to its wiper.

This is important. If the wiper ever bounces or gets dirty the pot will go open circuit. This puts the maximum voltage on the load.

 

You have a bad or misconnected transformer, a miswire in your circuit, or a faulty component, take your pick.
What constant voltage is the negative output?
Check the capacitor polarities.
Unfortunately you may have zapped the transformer.
It's always a good policy to monitor the input current when first turning on a new circuit.

I haven't miswired the circuit. Checked a hundred times. Faulty component? Maybe. It's hard to get quality components over here.
Constant voltage was 35 volts. Capacitor polarities are fine. Monitor input current at??

 

Don't forget that the LM317 and LM337 have different pinouts.

Also, R1 should have the un-connected end wired to its wiper. The same applies to R4 -- unused end to its wiper.

This is important. If the wiper ever bounces or gets dirty the pot will go open circuit. This puts the maximum voltage on the load.

What is the liquid though? I thought transformer oil is only for bigger transformers. What can cause this reaction?

 

What is the liquid though? I thought transformer oil is only for bigger transformers. What can cause this reaction?

The "liquid" was probably the varnish on the wires in the transformer. A common result when the secondary of a step down transformer is wired to the mains instead of the primary.

 

The "liquid" was probably the varnish on the wires in the transformer. A common result when the secondary of a step down transformer is wired to the mains instead of the primary.

Although he said he had 35V on the negative side at the regulator, which would seem to imply that the transformer orientation was correct.