Battery System Monitor

Find out how to monitor your renewable energy system battery bank

Once you get beyond the simplest renewable energy system, it is necessary to include some battery bank monitoring equipment. Batteries are one of the most expensive and fragile components of a renewable energy system, and so it is essential that their status is carefully monitored. It is also very useful to track the charge coming in from the various sources in a combined system - usually photovoltaic solar panels and wind turbine generators - in order to see from where you are getting power.

Probably the best known battery system monitor is the Bogart Engineering Tri-Metric 2020 Battery System Monitor. This device displays battery voltage, amps, amp-hours, battery percent full, and five other data functions, and works with systems from 12V to 48V for around £100. Great value as it costs the same as one decent battery and should increase the lifetime of your batteries:

Bogart Engineering have now introduced the new PentaMetric Battery Monitor which offers even more capability than the TriMetric.

Another alternative if you are on a limited budget is a simple digital multimeter. Available from just £5, a digital multimeter can be used to measure the voltage of your battery bank, and the current (amps) being put into or drawn from the batteries when being charged or under load.

http://www.reuk.co.uk/Fuel-Cells.htm

Germanium Diodes

Learn about the advantages of Germanium Diodes

Diodes are a very important component of most alternative energy generating systems - for example in PV solar panels they are used to stop energy being radiated back out into the night sky from the batteries, and in wind turbine generators they are used to rectify AC into DC electricity.

Typical diodes are made of silicon because of its ease of processing and stability however they have one disadvantage: a silicon diode has a forward voltage drop of around 0.7 volts. Therefore in a Bridge Rectifier where the current passes through two diodes, the total forward voltage drop is 1.4 volts. This is very significant in low voltage systems. A Germanium Diode typically will have a forward voltage drop of 0.3 volts which means they are much more efficient. Older germanium diodes had a larger leakage of current at a reverse voltage, but now American Microsemiconductor supply a range of improved low leakage current germanium diodes. Diodes such as the most common 1N34A cost around 5 pence each.

An interesting article about the practical use of Germanium Diodes in a crystal radio set is here, and discusses the forward voltage drop of a selection of germanium diodes in real world testing. The OA47 came out tops with a forward voltage drop of under 250mV.

http://www.reuk.co.uk/Germanium-Diodes.htm

Shunt Regulator

Find out about the uses of shunt regulators with alternative energy

A Shunt Regulator is a small electronic component that clamps a power supply voltage at a fixed level. Hundreds of times per second it checks the power supply voltage, and if the voltage is over the limit (set by adding a couple of resistors to the regulator in a small circuit) then the extra voltage is bled off through a resistor. If the voltage is below the fixed maximum, then no current passes through the resistor.

How can shunt regulators be useful to alternative energy generators. Well, for example a solar panel rated at 12V will actually generate up to 20V. If this panel is to be connected directly to equipment requiring an input of 12V, that equipment could be damaged if the voltage is too high. 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 the excess power into a resistor and losing it in the form of dissipated heat, it is possible to put it to better use, for example to heat or pump water.

A common shunt regulator used in solar applications is the LM431. This is a 3-terminal adjustable shunt regulator which can have its output voltage set to any value between 2.5 and 36V by the correct selection of two resistors. LM431's are available for example from eBay at just $4.50 for 25.

http://www.reuk.co.uk/Shunt-Regulator.htm

Fuse And Solar Panels

Using a fuse to prevent a short when connecting solar panel to battery

It is essential to fuse the wiring between a solar panel set up and the battery bank for safety. If the current flowing in the circuit is higher than it can safely handle overheating occurs. An overload is most commonly caused by a short circuit. An appropriate fuse will cut the current flow if a short occurs in the wiring between the solar panel and the battery. The size of the fuse should be just a little over the maximum current provided by the solar panels - for example, if the highest current from a solar panel is 3A then a 4 or 5A fuse should be used. If a short occurs the fuse will burn out and the short circuit be over within hundredths of a second before serious damage can occur. A short circuit is extremely dangerous, and if not prevented will often lead to fire breaking out when dealing with 12V lead acid batteries. The fuse should be positioned on the positive side of the circuit as close to the battery as possible. Each battery should have its own fuse.

Automotive blade type fuses and fuse holders (pictured below) are excellent for this purpose as the fuses are easily accessible if they need changing, and it is clear if a fuse has blown. Blade fuses are available in many different sizes, each being a different colour.

http://www.reuk.co.uk/Fuse-and-Solar-Panels.htm