Introduction: AC to DC - Half-wave Rectification of AC

Picture of AC to DC - Half-wave Rectification of AC

Ever need a constant DC output to test things, but batteries run out too quickly?
Or maybe a battery needs charging?

Changing AC to DC is as simple as two words - transformer, diode. Let's go.

Step 1: Why?

Picture of Why?

DC outputs can be extremely helpful. If you need to test any DC motor but you dont want to have to go find batteries, just flick this on! Or perhaps you need to charge a battery? Yep! This handy little device will aid any project testing, because guess what? It won't run out of battery! Even something AC that requires low voltage can be powered from this. As you can see, it's very versatile.

Step 2: I Can Explain

Picture of I Can Explain

Have you ever tried to power something DC using AC? Don't. A DC motor, for example, will go a random direction every time you turn it on. Or it just won't move.

I know most of you know the following already, but I'll explain the difference.

DC - Direct Current, the simpler type of current. This current travels one way, negative to positive. Usually low voltages that can't shock you.

AC - Alternating Current. This current comes from generators and power stations and is constantly changing direction. This speed of direction changing is called frequency measured in hertz. 1 hertz is one change of direction per second. The frequency of home electricity in Europe is 50 hertz. This electricity is usually very high voltage.

You CAN power AC motors on DC, but these motors are usually large and you would need a high DC output, i.e a good few high-voltage batteries, to make it run well.

Step 3: What You'll Need and Where You Can Get It

Picture of What You'll Need and Where You Can Get It

Necessary items:

Step-down transformer - you can get these out of any AC powered appliance that obviously uses low voltage.

Diode that matches the output of the transformer - get these out of ANY electronic thing.


Not necessary, but highly recommended items:

Capacitor that matches the transformer output - get these out of nearly any appliance, AC or DC.

Soldering iron - if you don't have one and you don't know anyone that does, don't bother.

Cooling fan/heat sink - get both of these out of old computers.

Potentiometer - anything that has volume control or similar will have one.

On/Off switch - also will be found in any appliance

If you can't find the stuff you need like the transformer or diode, don't worry. They go very cheaply wherever they're sold.

Step 4: What Each Part Will Do

Picture of What Each Part Will Do

Transformer - This will lower the AC voltage, because you will never need a 230 volts DC output. Ever.

Diode - This is the bit that actually converts the current. Seeing as diodes only allow current to travel one way (see pic no.2), they don't let alternating current, well, alternate. So if the current only goes one way, that means it's DC! Woohoo! (You can also use LEDs for this). This process is called rectification. This circuit will only half-wave rectify the current. I will publish another Instructable on how to full-wave rectify a current.

Pic no.3 will let you know which side of a diode is which. The arrow should point from positive from negative. In this circuit, it won't matter which way you put the diode, but it will switch around the positive and negative output terminals.

Capacitor - even though the current is only going one way, it's still trying to alternate. So the current dips, then rises, dips, then rises (see pic no.5). This is unsuitable for things like radios and TVs.

And what a capacitor does is store charge (rather like a battery). It then releases this energy and recharges. This continues the entire time the appliance is switched on and is why some lights don't switch straight off on appliances, they fade off.

What this will do on our circuit is charge and release charge quickly and lowers the depth of the dip in current(see last pic). This is not necessary, but helpful. This process is called smoothing.

!BE CAREFUL! Large capacitors can give you a large shock when charged, and some can kill you! Always give large capacitors a few days to discharge after using them before you touch them.

The soldering iron is handy for connecting wires to components, but you could get away with twisting wires around stuff.

The cooling fan or heat sink is obvious, this circuit (like all others) might get a bit hot after being used for a while.

The potentiometer is very handy, with it you can vary the DC voltage output, which you might need for testing different motors, lamps etc.

Step 5: Put It All Together

Picture of Put It All Together

Now, simply wire the components up as shown in the schematic.
Note - the rectangle with the T on it is the transformer,
the middle symbol is the diode
and the symbol on the right is the capacitor.
You can easily add in switches,potentiometers, fans and heat sinks anywhere in the circuit.
Note - switching the direction of the diode will switch the polarity of the DC output.

Step 6: That's It!

Picture of That's It!

Well, I hope you enjoyed reading this as much as I did making it!
Please comment if you have a problem, I'd be more than happy to help.
Follow if you want to see more interesting electronics!


russ_hensel (author)2015-04-14

Your cap should be in parallel, not series, please recheck.

1300rpm (author)russ_hensel2015-04-15

Sorry, but you are incorrect. My circuit will work exactly the way I designed it.

russ_hensel (author)1300rpm2015-04-15

It will work exactly the way you designed it, they all do. But if you want it to work like a power supply you need to move the cap.

Take a look at:

1300rpm (author)russ_hensel2015-04-15

I'll check that out, thanks for pointing it out

About This Instructable




Bio: 'Why buy it, when you can build it?' Got confused in one of my Instructables? Just email me and I'll explain it all to ... More »
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