9:58 AM

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Make A Bridge Rectifier From Diodes

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.
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9:32 AM

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Interconnecting Batteries For Battery Bank

CjAngel

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Find out how best to connect batteries together into a battery bank

For any off grid renewable energy system the battery bank is probably the most important component. It doesn't matter how much power you generate - if it is not stored safely and efficiently then you will have no electricity when you need it. Batteries are also one of the most expensive parts of wind, solar, and hydro power generation systems so they need to be well cared for.

Unless you have a very small system you will need more than one battery - therefore you will need to connect the batteries to one another to form a battery bank. Left is an illustration from SmartGuage Electronics showing how this is often done:

The Problem
Because of the small amount of resistance in the cable used to interconnect the batteries, and from the connection between the cable and the battery posts, the battery closest to the installation is charged the most, discharged the most, and worked harder, whereas the battery furthest from the installation is charged the least, discharged the least, and worked the least.

The Reason
The power from the bottom battery has to pass through the main connection leads whereas the power from the top battery has to pass through the main connection leads and another four sets of interconnecting leads. Although the resistances are tiny - it is the fact that they are so small that makes them have such a big effect on the current flowing to each battery.

SmartGuage Electronics used a computer simulation in 1990 to calculate the following assuming a battery internal resistance of 0.02 Ohms, interconnecting lead resistance of 0.0015 Ohms per link, and a total load on the batteries of 100 amps:
  • The bottom battery provides 35.9 amps.
  • The next battery up provides 26.2 amps.
  • The next battery up provides 20.4 amps.
  • The top battery provides 17.8 amps.

...which means the battery closest to the installation is worked twice as hard as the battery at the top of the battery bank! These surprising findings have since been reproduced in real world situations.

Connecting Batteries in a Battery Bank
So it the example given above shows you how NOT to connect batteries to make a battery bank, how should you do it? It is actually very simple - instead of taking the negative AND positive feeds from the same battery (in the example above it was from the bottom battery) , you should take one feed from each end of the interconnected battery bank - e.g. +ve from the top battery and -ve from the bottom battery. See the image from SmartGuage Electronics..

With the same example load of 100 amps presented above the new loads on each battery are as follows:
  • The bottom battery provides 26.7 amps.
  • The next battery up provides 23.2 amps.
  • The next battery up provides 23.2 amps.
  • The top battery provides 26.7 amps.

To get the batteries perfectly balanced requires a different scheme involving a little more work and expense (more cables and connections required), but is only really necessary if you have very expensive batteries or a more than 6 or so batteries in your bank.

Warning: Be Safe When Handling Lead Acid Batteries
When handling lead acid batteries, great care must be taken. You should always wear gloves and safety goggles because if acid sprays or spills from a battery onto your skin or eyes you could sustain a serious and permanent injury. Invest in a bottle of surgical eye wash and leave it next to your battery bank at all times so you can flush your eyes immediately if you get acid in your eye.
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9:03 PM

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What Is A Shunt

CjAngel

,

Find out what is a shunt resistor and how it is used in RE applications

A shunt (aka a current shunt resistor or an ammeter shunt) is a high precision resistor which can be used to measure the current flowing through a circuit. Using Ohm's Law we know that the voltage dropped across a resistor divided by the resistance of that resistor is equal to the current, therefore if we measure the voltage across a shunt resistor in a circuit, we can easily calculate the current.


For example, pictured above is a typical 100 Amp Shunt Resistor. This can be used to measure currents of up to 100 Amps - although to prevent overheating it should really only be used to measure continuous currents of no more than 60-70 Amps.

* If a shunt resistor overheats it can permanently change the resistance of the shunt.

This shunt is calibrated such that the voltage drop across it is 100mV when the current flowing through it is 100 Amps. Therefore we can calculate the resistance of this shunt to be voltage divided by current = 0.1 / 100 = 0.001 Ohms (typically to within ± 0.25% accuracy). Therefore if a voltage drop of 28mV is measured (using a standard multimeter or 0-100mV range voltmeter), we know that the current flowing is 0.028/0.001 = 28 Amps.

(The power wasted by the shunt resistor is given by multiplying the voltage by the current = 0.028 * 28 = 0.78 Watts in this example.)

To save making this calculation manually each time it is possible to re-label a 0-100mV moving coil voltmeter so it instead reads 0-100 Amps. This would be achieved simply by sticking the word "Amps" over "mV" on the face of the meter which would now be an ammeter rather than a voltmeter.

Using a Shunt Resistor in a Renewable Energy System
It is very important to know how much current is flowing in and out of the battery bank in a renewable energy system. When charging the current flowing into the batteries should never be more than 10% of the battery capacity - e.g. a 100Ah battery should not be charged with more than a 10 Amp current or it may be damaged and/or overheat.

It is also very useful to know how much current is being generated by a wind turbine or solar panel, because that information helps you to calculate how much power is being generated. For example a 12 Volt 15 Watt PV Solar Panel may produce a voltage of 18 Volts when it is very cloudy and 21 Volts when it is very sunny.

When it is cloudy you may measure a current of just 0.1 Amps and when it is sunny a current of 0.8 Amps. Power is equal to voltage multiplied by current, so the solar panel is generating just 2 Watts when it is cloudy and almost 17 Watts when it is sunny.
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8:37 PM

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Bridge Rectifier

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.
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2:57 PM

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Ways To Save Electricity

Every year electricity gets more and more expensive. Read on to find out how you can save electricity and money with this handy selection of energy saving tips.

Saving Electricity Tips
The biggest electricity users in the home tend to be heating and/or air conditioning, water heating, washing machines, tumble dryers, dishwashers, lighting, and the refrigerator. When looking to save electricity, spend the most time focussing on these big energy hogs to get the biggest effect for your efforts.

Here are a selection of tips to help you to reduce your electricity consumption:

1. Turn off your television, video, hifi, playstation, and other entertainment devices when they are not being used.

2. Do not leave your television etc in standby mode. Devices can use up to 90% as much power in standby mode as when they are on, so it is a serious waste of energy when a device is left constantly on standby. If you keep forgetting, consider purchasing a PowerSafer - a device which automatically cuts power to appliances when they go into standby mode.

3. Replace all of your inefficient incandescent light bulbs with energy efficient CFL bulbs. Replace halogen spotlights with much more efficient and longer lasting LED Spotlights.

4. Hang your clothes out to dry rather than using an electric tumble dryer. Ideally use a spin dryer before using the tumble dryer.

5. Cook many items at the same time when your electric oven is hot.

6. Use a microwave to reheat food or to cook small portions. Although a microwave uses a lot of power, it does so over a very short time and so saves energy overall.

7. Turn down your heating system thermostat. For every degree you lower your heat between 60° and 70° F you can reduce your heating bill by up to 5%. Wear an extra layer of clothing in the house so that you stay warm. Turn down individual radiators - for example, 16°-18° is warm enough for bedrooms whereas 20°-22°C is more comfortable in bathrooms. Rooms that are rarely used can have their heating turned all the way down or off.

8. Purchase energy efficient white goods (washing machines, tumble driers, fridges etc). Although they usually cost a little more initially, the cost savings in electricity will cover that many times over. As an added benefit, efficient items are usually better made and last longer than inefficient models.

9. Vacuum clean the condenser coils at the back or underneath your fridge freezer. Accumulated dust reduces their efficiency by up to 25% adding that cost to your electricity bill.

10. Keep your fridge full, but not so full that air cannot circulate properly.

11. Fold clothes straight out of the tumble drier while they are still warm to save on ironing.

12. Cool cooked food before you put it into the fridge.

13. Do not put uncovered liquids into the fridge. Their evaporation will make the fridge have to work harder.

14. Heat only as much water as you require for drinks and cooking. If you keep forgetting, purchase an energy efficient eco kettle.

15. Use a convection oven. A small fan inside circulates hot air throughout the oven cutting cooking times by up to 30%.

16. Don't preheat the oven for roasting.

17. Don't keep opening the oven door. Every time you do so, your oven loses 20°C of heat.

18. Put lamps in the corner of a room so that the light is reflected off two walls.

19. Turn down the temperature on your washing machine. Heating the water uses the majority of the electricity, so by doing a warm wash instead of a hot wash, big savings are possible. See Wash Most Clothes at 30 Degrees.

20. Defrost frozen food in the fridge since this helps to cool the fridge.

21. Running a full load in an efficient dishwasher will use less hot water than washing up by hand in the sink! Save money, save time, and save electricity.

22. Boil water in a kettle rather than on a hob to save 50-70% of the energy and to get your water boiled faster.

23. In the summer use ceiling fans on a fast setting instead of air conditioning to keep cool. In the winter, running the fans slowly will push warm air collected at ceiling height down to where you want it. (If the slowest setting on your fan is too strong, reverse the direction of the fan in the winter so that the accumulated warm air is blown up against the ceiling and bounces more gently down around the walls and into the living space.
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2:49 PM

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Resistor Colour Codes

Learn how to identify different resistors with their colour code


The humble resistor is a key component of many renewable energy systems. They are designed to resist electricity and can therefore be used to supply the correct voltage to the various components in an electric circuit.

Because resistors are so small - too small to print numerical resistance values on - they are instead marked with four, five, or (less commonly) six coloured bands. Each colour represents a different number and so the value (in Ohms) of the resistor can easily be calculated.

The last coloured band is usually used to indicate the tolerance - a measure of how accurate the stated resistance is, i.e. 1%, 2%, 5%, or 10%. In the case of six band resistors, is used to show the temperature coefficient - a measure of how much the resistance of a resistor is changed by changes in temperature.

Remembering the Resistor Colour Code Values
There are many mnemonic phrases to help you to remember the order of the colours:
Black Brown Red Orange Yellow Green Blue Violet Gray White
...which correspond to the values 0-9. For example:
Bad Beer Rots Our Young Guts But Vodka Goes Well.
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