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Make your own single or multi phase bridge rectifier from diodes

The electricity generated by most wind turbine generators is alternating current (AC). To use this to charge batteries or power most lighting and devices directly, it must be rectified into direct current (DC).

The simplest bridge rectifier is made up of just four diodes (components which allow electricity to flow in just one direction).

Three Phase Bridge Rectifiers

Typically wind turbines do not generate single phase AC (displayed in the above example), but instead generate multi-phase AC - usually three-phase AC electricity.

Therefore, more diodes are required to rectify the three phases of electricity - in fact six are required and must be wired up as shown in the diagram below.


Why Make Your Own Bridge Rectifier?

It is possible to purchase complete bridge rectifiers cheaply with current ratings from below 1 Amp to as much as 35 or 50 Amps.

To make a three phase bridge rectifier is a simple case of wiring them together and then to each of the three phases of generated electricity.

Pictured above is an example of a 35A bridge rectifier. Bridge rectifiers rated above 35A or 50A suddenly become very expensive. Therefore if your wind turbine has a total maximum output current of more than 25-30 Amps, it is worthwhile making your own bridge rectifier with high power rated diodes wired as shown above but fitted to a suitably large heatsink.

Find out more about bridge rectifiers.

For most alternative energy applications, we require a direct current (DC) voltage to be generated - for example to charge a bank of batteries. However wind turbines and wave power generators create an alternating current (AC) voltage.

This is where the Bridge Rectifier comes in. The AC voltage generated is passed through a circuit of four diodes arranged as shown below and emerged converted into a more useful DC output.

Diodes allow electricity to flow in only one direction, but there is a small voltage lost across the a diode of 0.7V called the forward voltage drop.

If the diode is wired in the wrong direction then no current (actually a very tiny current) flows across the diode. However, if the voltage is too high and goes over the diode's maximum reverse voltage, the diode will breakdown and fail.

Make a simple solar charger for 4 AA rechargeable batteries

In this article you will find out how to make a very simple solar battery charger for 4 AA rechargeable batteries using a small 6 Volt solar panel. A labeled photograph of the completed charger is provided at the end of the article.

Here is the parts list:

• 1 of 4 x 2700mah AA Rechargeable Batteries.
• 1 of 6V 250ma Solar Panel.
• 2 of 2 AA Battery Holder with Flying Leads.
• 1 of Blocking Diode.
  

The Solar Battery Charger Specifications
The long life rechargeable batteries used have a capacity of 2,700mah - therefore a charging current of 10% of this (i.e. 270ma) is safe. The nominal voltage of each battery is 1.2V, so four in series is 4.8V with a fully charged voltage of around 5.2V being normal. Therefore our 6 Volt 250ma solar panel is perfectly rated to be used as a charger for these batteries.

In order to prevent stored power in the batteries being released through the solar panel during the night, a blocking diode is used. Placed in the postive line from the solar panel this only allows electricity to flow from the solar panel to the batteries and not from the batteries to the solar panel.

Up to 0.7 Volts from the solar panel are lost as heat in the diode as electricity flows from the panel to the battery leaving us with a perfect charging voltage of around 5.30 Volts for the batteries.

Putting the Solar Battery Charger Together
To keep things simple no soldering is required to built this solar battery charger. Instead terminal strip is used to make the connections - only a small flat head screwdriver is required to secure each wire/component in place.

First of all the four batteries are put into the two battery holders and then the holders are wired together in series. To do this the positive lead from one battery holder is connected to the negative from the other. The remaining free wires - one positive and one negative - are our charging inputs.

The ringed end of the blocking diode (pictured above) is then connected to the positive battery input (red), and the other end to the positive output from the solar panel (red). The negative output from the solar panel (blue) is connected directly to the negative battery input (black) .

Pictured above is the completed Solar Battery Charger. The voltage measured across the points labeled B and C is the voltage coming in from the solar panel.

The voltage measured across the points labeled B and A is the voltage of the batteries. (Note that during charging the battery voltage measured will be higher than the true voltage of the batteries. Cover the solar panel to measure the true battery voltage.)

A suitable multimeter is required to make these measurements.

A zener diode can be used to make a simple voltage regulation circuit as pictured above. The output voltage is fixed at the zener voltage of the zener diode used and so can be used to power devices requiring a fixed voltage.

NEW The above mentioned article on zener diode voltage regulators has now been updated and a handy calculator has been added to help you select the correct resistor and zener diode values and power ratings.

Zener Diodes in Series With Loads
If you have a regulated fixed voltage - say 12 Volts from a desktop PC power supply, and you want to power something requiring a lower voltage, it is possible to simply place a zener diode in series with the load device. You would choose a diode with a zener voltage equal to the supply voltage minus the voltage drop across the load.

For example, if you have a 1 Watt 6 Volt lightbulb to power from a 12 Watt regulated power supply, a 6.2V zener diode could be placed in series with the bulb giving the bulb 5.8V, or you could overpower the bulb a little using a 5.6V zener diode and dropping 6.4V across the bulb. Heat would be generated in the zener diode so it is essential to calculate the power lost in it so a suitably rated diode could be chosen.

Using a 5.6V zener diode, and knowing the bulb draws a current of around one-sixth of an Amp, we can calculate the power loss in the diode (with Ohm's Law) to be just under 1 Watt. Therefore a standard 1.3 Watt zener diode should be up to the job.

Circuits with Zener Diodes
Zener diodes are key components in the circuits presented in the following articles: Make a Simple Battery Status Monitor, LM741 Voltage Indicator, and High Capacity Alternative to 9V Battery.

Find out more about the Zener diode

Diodes are electronic components which will let current flow in just one direction. They are used for example in PV Solar Panel installations to ensure that current can flow into the battery bank when it is sunny, but not escape through the solar panel when it is very cloudy or at night.

A Zener Diode is a special kind of diode which permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage.

The Zener voltage of a standard diode is high, but if a reverse current above that value is allowed to pass through it, the diode is permanently damaged. Zener diodes are designed so that their zener voltage is much lower - for example just 2.4 Volts. When a reverse current above the Zener voltage passes through a Zener diode, there is a controlled breakdown which does not damage the diode. The voltage drop across the Zener diode is equal to the Zener voltage of that diode no matter how high the reverse bias voltage is above the Zener voltage.

The illustration above shows this phenomenon in a Current vs. Voltage graph. With a zener diode connected in the forward direction, it behaves exactly the same as a standard diode - i.e. a small voltage drop of 0.3 to 0.7V with current flowing through pretty much unrestricted. In the reverse direction however there is a very small leakage current between 0V and the Zener voltage - i.e. just a tiny amount of current is able to flow. Then, when the voltage reaches the breakdown voltage (Vz), suddenly current can flow freely through it.

Uses of Zener Diodes
Since the voltage dropped across a Zener Diode is a known and fixed value, Zener diodes are typically used to regulate the voltage in electric circuits. Using a resistor to ensure that the current passing through the Zener diode is at least 5mA (0.005 Amps), the circuit designer knows that the voltage drop across the diode is exactly equal to the Zener voltage of the diode.

Monitor battery status with this easy electric circuit project - no skill required!

It is essential that the battery bank in a renewable energy system is well looked after. This means that the voltage of the battery bank must be known. It can be easily measured with a multimeter or a voltmeter, however a fun and inexpensive project is to make a very simple battery status monitor.

In a typical 12V system the voltage of the battery bank can fluctuate from 10.6 Volts (below this the battery is very dead) when heavily depleted and under load, to as much as 15 Volts when being heavily charged. A healthy full 12V battery bank would usually have a voltage of around 12.6 Volts when not under a load and between 13-14 Volts when being charged correctly - i.e. not too quickly. Therefore it would be interesting to have an indication of the status of the battery bank using an LED to show if it is being charged.

For this example we will use the arbitrary figure of 12.6 Volts to indicate battery bank under charge however this could value could be set lower or higher according to your own needs and system configuration.

The Battery Status Monitor Introduction
The status monitor uses a Zener Diode, a Light Emitting Diode (LED), and a Resistor - components which can be bought for pennies each.

Each Zener Diode has a specified Zener voltage. If the voltage in the circuit is greater than the Zener voltage, then the voltage drop (ie. the voltage reading across the diode) is equal to this Zener voltage. However, if the voltage in the circuit is less than the Zener voltage then no current flows. Therefore, if you put a Zener diode in series with an LED in a circuit, the LED will light if the circuit voltage is greater than the Zener voltage plus the voltage drop across the LED.

Making the Battery Status Monitor
We want our LED to light when the voltage of the 12V battery bank is 12.6 Volts or higher to indicate the batteries are being charged by our renewable energy set-up. Let's use the following components:

1 x 8.2 Volt Zener diode.
1 x standard green LED (Specfications: maximum current 30mA, voltage drop 2.5 V).

In order to make the LED last as long as possible we will not use the maximum current - instead we will aim for around 15mA.

The total voltage drop across the Zener diode and LED will be 8.2+2.5=10.7 Volts. A resistor is therefore required to prevent too much current getting to the LED and destroying it. The difference between the battery bank target voltage of 12.6 Volts, and the voltage dropped by the Zener and LED of 10.7 Volts is 1.9 Volts. These 1.9 Volts must be dropped across a suitable resisitor with a current of no more than 15mA - therefore using Ohm's Law we find that resistance = 1.9 Volts / 0.015 Amps = 127 Ohms coincidently the exact value of a manufactured resistor. Normally you would select the resistor with the nearest value above the resistance value calculated with Ohm's Law.

Therefore add to the parts list for this project:
1 x 127 Ohm Resisitor.

Choosing Correctly Power Rated Components
We now need to check the power dissipated in the Zener diode and resistor at different voltages so we can select suitably rated components, and check that the current flowing through the LED when the battery bank is at its maximum voltage is below the manufacturer recommended maximum.

If the battery bank were to hit 15.5 Volts the voltage drop across the Zener diode would remain fixed at 8.2 Volts and the drop across the LED at 2.5 Volts, therefore the voltage drop across the resistor would increase to 15.5-8.2-2.5=4.8 Volts. Again using Ohm's Law we find that the current through the resistor (and therefore through the LED) will rise to 4.8 Volts / 127 Ohms = 38mA. This is a little over the manufacturer recommended maximum current however, if your 12 Volt battery bank is regularly at 15.5 Volts the expense of replacing your little LED a couple of years early will pale into insignificance compared to the cost of the damage to your battery bank!

At a current of 38mA the power dissipated by the Zener diode will be 8.2 Volts * 0.038 = 0.31 Watts, and the power dissipated in the resistor will be 4.8 Volts * 0.038 = 0.18 Watts. Therefore a 500mW rated 8.2V Zener diode and a 1/4 Watt 127 Ohm resistor will be perfect.

Putting the Battery Status Monitor Together
There is no need to worry about soldering this together - the legs of the LED, resistor, and Zener diode can simply be twisted together.

The last item you will need is:
1 x Length of One Amp bell wire (split along its length into two pieces of wire).
..which is very cheap - or you can cannibalise any other single-core insulated wire you have lying around. With a maximum current of 40mA flowing through it the wire does not need to be thick, but it is best to always use insulated wire to prevent accidently short-circuiting the battery bank.

The short leg on the LED (pictured above) is the cathode and is connected with the wire to the negative terminal of the battery.

The cathode of the Zener diode (pictured above) is marked with a stripe (silver in this example), however Zener diodes are placed into circuits in reverse, so next connect the positive anode (long leg) of the LED to the positive (no stripe) end of the Zener diode.
Finally the cathode of the Zener diode is connected to one leg of the resistor, and the other leg of the resisitor connected to the positive terminal of the battery bank with wire.

The green LED of the completed simple battery bank status monitor will now remain lit as long as the battery bank voltage stays above 12.6 Volts.

Developing the Battery Status Monitor Further
This battery status monitor could not be more basic - it just indicates when the batteries have 12.6 Volts or more. However it would be very simple to extend the monitor to include an over-charge warning indicator when the voltage reaches say 14 Volts, and a battery healthy indicator which is lit as long as the voltage is over say 11.8 volts.

Simply recalculate the values of resistor and Zener diode required for each additional monitor and join each string of components in parallel to the battery to be monitored. The whole thing can be soldered together and built into a suitable box with the LEDs labelled so that everything looks tidy and you have a project to be proud of!