Shunt Regulator

Find out about the uses of shunt regulators and dump load controllers in renewable energy applications

A Shunt Regulator is a small electronic component that clamps a power supply voltage at a fixed level. Hundreds of times per second the shunt regulator checks the voltage, and if the voltage is over the limit then any extra voltage is dissipated as heat through a resistor (1) or other dump load. If the supplied voltage is below the set maximum, then no current passes through the resistor.

Using Shunt Regulators

How can shunt regulators be useful to alternative energy generators. Well, for example, a PV solar panel (2) rated at 12V will actually generate up to 20V in full sunshine. If this panel is to be connected directly to equipment requiring an input of 12V, that equipment could be damaged - particularly if it draws only a small current and if it contains sensitive electronics. Therefore, by passing the solar panel's generated current through a shunt regulator circuit, the voltage reaching the equipment can be clamped at 12V* very accurately.

Rather than dumping any excess generated power into a resistor and losing it in the form of dissipated heat, it is possible to put it to better use, for example diverting it to heat or pump water. In such a situation the shunt regulator may also be called a dump controller since the circuit decides when incoming power (from a wind turbine (3) or solar panel) should be dumped - for example into an immersion heater element (4).

Shunt regulators are an essential part of any Solar Charge Controller (5)

* An alternative way to obtain a fixed 12.0V from a solar panel is to use a 12 Volt Regulator (6).

Shunt Regulator Components

A common shunt regulator used in many solar and other applications is the LM431 (7) (aka TL431). This is a 3-terminal adjustable shunt regulator which can have its output voltage clamped to any value between 2.5 and 36V by the correct selection of two resistors. This component is available for sale in the REUK Shop (8): buy LM431 (9).

TL431 programmable shunt regulator used in a shunt regulator circuit

Click here to view the TL431 programmable shunt regulator datasheet (10) (PDF).

Build a Complete Dump Controller Circuit

The following link to Hurd Solar (11) takes you to a comprehensive circuit diagram for a dump / shunt controller which will protect a battery (12) from being overcharged (and therefore damaged). Unassembled controller kits are available for sale ($12) or you can purchase the components and put one together following the detailed assembly instructions and parts lists on that website.
For people in the UK, all required components are available for sale at Rapid (13), and Maplin (14).

Web Link References

(1) http://www.reuk.co.uk/Resistor-Colour-Codes.htm
(2) http://www.reuk.co.uk/How-Do-PV-Solar-Panels-Work.htm
(3) http://www.reuk.co.uk/wind.htm
(4) http://www.reuk.co.uk/200W-12V-Immersion-Heater.htm
(5) http://www.reuk.co.uk/Solar-Charge-Controller.htm
(6) http://www.reuk.co.uk/LM2940-12V-1A-Low-Dropout-Regulator.htm
(7) http://www.reuk.co.uk/TL431-Battery-Voltage-Monitor.htm
(8) http://www.reuk.co.uk/REUK-Products-For-Sale.htm
(9) http://www.reuk.co.uk/buy-TL431.htm
(10) http://www.fairchildsemi.com/ds/TL/TL431A.pdf
(11) http://ghurd.info/
(12) http://www.reuk.co.uk/Lead-Acid-Batteries.htm
(13) http://www.awin1.com/cread.php?awinmid=1799&awinaffid=80045&clickref=&p=http%3A%2F%2Fwww.rapidonline.com
(14) http://www.maplin.co.uk/?C=41578