How does a power supply work.

[ynneb]

I have been asked to move this tutorial to this section so as to give it a kick start.

How does a power supply work?

This is a brief description of what happens when a power supply converts electricity from one form to another. Since I only understand in layman’s terms. That’s how I will explain it.

The relevance to having this tutorial in CNCzone is that most machines require such power supplies.

What is mains supply?

You will notice in the drawing below, the “mains supply”. This is most often what comes out of your power point. The mains supply is usually 110 volts or 240 volts depending on what country you are from. These are dangerous voltages and can kill if the path of electrocution goes across your heart.

What does alternating current mean?

The mains supply is an alternating current, also known as A.C. An alternating current means that the flow of electrons is moving back and forth very rapidly. You will see in the drawing that the positive and negative are constantly changing to reflect the alternating current. The speed that this alternating is happening is very fast, usually between 50 and 60 times per second. You may have seen on some power points with 60hertz written on them, this means that that the voltage that is been supplied is alternating 60 times a second.

Why do we need alternating current?
Why can't it just be stable and not changing?

With alternating current it is easy to change its voltages to higher or lower voltages without complicated circuits. All you need is a transformer. Many items need different voltages to work correctly.

How does a transformer work?

In the drawing you will see two coils of wire. The longest coil that is connected to the mains is called the primary coil. When this coil is energized it makes a magnet in the iron core. When the iron core is not energized it then demagnetizes and releases the energy into the other coil. The other coil is known as the secondary coil. Because the alternating current in the mains supply is alternating very rapidly it is making a magnet out of the iron core. So in other words it is magnetizing and demagnetizing at up to 60 times a second. This causes the secondary coil to receive all this energy. The process is know as induction

How does a transformer change voltage?

Let’s assume there are 100 loops of wire on the primary coil and 50 loops of wire on the secondary. Because there is half the amount of wire turns on the secondary this means in theory that the voltage that will be induced will be half. For example if 240 volts was on the primary there would be 120 volts on the secondary. If we wanted to make a smaller voltage the ratio of wire loops would be higher.

What is direct current?

Direct current also know as DC is different from alternating current in that it is not constantly changing from positive to negative. One wire will always be positive and one wire will always be negative.

What do diodes do?

Diodes will only let electricity flow in one direction. The arrangement of the diodes in the drawing is know as a bridge rectifier. It works like an automatic switch. When the alternating current is connected to the rectifier it constantly switches the circuit so that only the positive part of the current goes to one side and the negative part of the current goes to the other side. You can see this happening in the drawing.

Why do I need a capacitor in the circuit?

Even though we have now achieved direct current you will see that the voltage is still rippling. This means that the voltage is going up and down. It is not changing direction though. A capacitor will temporarily store a current and the release it when there is no current. Think of it like a battery. It charges up when there is power and gives out its charge when there is no power. Effectively when the rippling is at a low voltage the capacitor will make up the difference, and when the rippling is at high voltage it will also charge the capacitor. In theory this will ensure that there is no more rippling.
At the end of the circuit we will now have two wires. One wire will be the negative and the other wire will be the positive. They will also have stable voltages.

What next?

Most machines in this forum have stepper motors, and servo motors that require DC.
DC is good for driving these motors smoothly and with lots of torque.

[Eddymeister]

Great explanation ynneb...

Simple tutorials like this helps us newbies who aren't in an electrical profession understand things of this nature...
Better to understand whats going on rather than electrocuting yourselves...
Are there anymore tutorials like these around on this site..?