Smoothing Capacitors
Smoothing Capacitors
Find out more about the uses of smoothing capacitors in renewable energy circuits
electric circuit | educationA
capacitor is a device which stores
electrical charge. In the most simple terms it can be thought of as being similar to a rechargeable battery in that it stores power to be used at a later time.
Charging a capacitor is simply a matter or putting voltage across its legs until current stops flowing.
Capacitors are an essential component in the majority of electronic circuits.
There are many uses of
capacitors in
renewable energy generation, however one of the most important is in smoothing the output of a
bridge rectifier after it has converted AC electricity (typically generated by
wind turbine generators etc) into DC (used to charge batteries and power many low voltage devices).
Bridge Rectifier
Alternating current (AC) electricity
alternates - i.e. the voltage cycles from a positive maximum to a negative maximum and back again repeatedly. When this is
rectified by a
bridge rectifier all negative voltages are
rectified into positive voltage as shown below:
If this direct current (DC) voltage is used to light an LED for example, then it would flash on and off repeatedly. This is usually not considered to be desirable and there are many cases where a fixed voltage is required. In these cases a
smoothing capacitor is used.
The smoothing capacitor circuit shown above requires just one
capacitor placed across the output from the rectifier. As the output voltage increases, the capacitor is charged, and as the output voltage falls back to zero, the capacitor releases its charge (stored energy). The resulting voltage across the capacitor looks like this:
Capacitor Ratings
Capacitors are rated according to their
voltage and
storage capacity. The larger the capacity of a capacitor, the more charge it can store and the longer it will take to discharge. However, a very large capacitor will take a long time to charge initially and so it will take a while before a constant voltage is output. If the current drawn from the circuit is large, then the capacitor will discharge quickly and the amount of
ripple in the voltage will increase.
If the voltage in the circuit is above the rated voltage of the chosen
capacitor, the capacitor will be damaged and may even
explode. Therefore it is essential to choose a capacitor with a voltage in excess of the maximum output voltage from the bridge rectifiers.
Choosing a Capacitor
Typically in
renewable energy applications a
1000 micro Farad (1000uF) capacity smoothing capacitor is chosen. These are available with a range of voltage ratings including 10V (pictured above), 16V, 25V, 35V, 63V with higher voltage capacitors costing more than those with lower voltage ratings. If the amount of
ripple in the voltage is more than 10% then a capacitor with a higher value - e.g. 2,200 micro Farads - should be used.
NEW 1000uF 16V capacitors are now available at the
REUK Shop.
Example Smoothing Capacitor Circuit
At the top of this page is pictured a very simple circuit using a
smoothing capacitor. Two AC inputs from a small
stepper motor wind turbine are rectified by a
W005 1.5A bridge recifier into DC voltage to light an LED. Without a
smoothing capacitor the LED would flash on and off, so a
1000uF capacitor is used to supply a constant voltage to the
LED.
The output from a
Sturmey Archer Dynohub wind turbine once rectified should also be passed through a
capacitor if it is to be used for anything other than battery charging.
Article Last Modified: 11:47, 4th Apr 2007Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
Recommended Related Articles
People who read this article also enjoyed the following articles:
Stepper Motor BasicsLearn more about stepper motors and their use in RE electricity generation
Article Last Modified: 09:54, 4th Apr 2007wind | educationRelays and Renewable EnergyFind out more about relays and their uses in renewable energy applications
Article Last Modified: 13:33, 14th Aug 2010electric circuit | electronics | generalRepeat Timer CircuitMake a repeat timer circuit with large intervals between ON times
Article Last Modified: 09:58, 15th Aug 2009electric circuit | electronics | generalElectricity with Stepper MotorsFind out the basics of generating electricity with stepper motors
Article Last Modified: 17:07, 10th Jun 2008windStepper Motor Voltage Doubler CircuitDouble the voltage from a stepper motor using two bridge rectifiers
Article Last Modified: 10:45, 9th May 2007general | electric circuit | educationMaking Voltage Doublers and MultipliersFind out how to construct an AC voltage doubler circuit. Extend it to a tripler circuit and more.
Article Last Modified: 14:29, 26th Apr 2007electric circuit | educationBridge RectifierFind out more about bridge rectifiers.
Article Last Modified: 15:33, 2nd Feb 2007electronics | wind | waveLM317 Voltage CalculatorA handy online output voltage calculator for the LM317, LM338, and other linear voltage regulators
Article Last Modified: 12:29, 17th Aug 2010electric circuit | electronics | generalLM317 High Current Voltage RegulatorFind out how to build an LM317T based high current voltage regulator
Article Last Modified: 12:29, 17th Aug 2010electric circuit | electronics | general | educationLight Dependent ResistorFind out more about LDRs and their use in renewable energy projects
Article Last Modified: 09:26, 24th Oct 2007electric circuit | solar
|
|
|
