Solar Charge Controller

A Solar Charge Controller (or Regulator) is a device which protects the batteries in a solar electric system from being overcharged or being over-discharged.

Overcharged batteries have a much shorter life time than well cared for batteries since the electolyte is boiled off as gas and lost. Overly discharged (i.e. flat) lead acid batteries become permanently damaged, so a solar charge controller is used to disconnect any load when the battery is discharged down to a safe cut off voltage.

LEDs and (in the more expensive regulators) LCD displays are used to show the current state of the charge of the battery, the state of the current entering the batteries from the solar panel(s), and the current being drawn from the battery by loads.

Do You Need a Solar Charge Controller?

A charge controller is not always required if the maximum current going into the battery is more than 10% of the batteries Ah capacity (C/10) - i.e. if the battery is 60Ah then a charge controller is certainly required if the current from the solar panel is likely to exceed 6 Amps - as long as you make sure you don't over-discharge the battery.
Some suggest a charge controller is required if the maximum current from the solar panel is just 1% of the Ah capacity (C/100) of the battery bank.

PWM - Pulse Width Modulated Battery Charging

Good quality solar charge controllers are up to 30% more efficient than basic 'on-off' regulators as they have provide pulse width modulated (PWM) battery charging. When the voltage of the battery bank reaches the regulation voltage (14.1V), instead of stopping charging altogether, the patented PWM algorithm reduces the charging current and continues charging slow enough to prevent the battery overheating or gassing.

PWM helps to get the batteries charged up to well over 90% capacity, extends the life of the battery, and means that more of the power generated by the solar panels is stored. Since the batteries store more energy on average, a smaller battery (or less batteries in a battery bank) can be used reducing overall system costs.

Solar Charge Controller Manufacturers

Well known manufacturers of solar charge controllers include: MorningStar, BZ Products, Iota, Outback, RV Power Products, ProStar, Solar Converters, Statpower/Xantrex,Trace/Xantrex.

Buy a Solar Charge Controller in the UK

Prices range from around £15 to many hundreds of pounds depending on the size of the solar power system to be regulated and the quality and features of the controller.

With solar charge controllers you really get what you pay for. It is well worth spending a few pounds extra to buy a good quality PWM controller from the start since it will pay for itself by getting more energy into your batteries and by protecting the batteries properly.

We have a range of high quality pulse width modulated solar charge controllers in the REUK Shop including the 4.5A SunGuard Solar Controller (pictured above), and 10A SunSaver Solar Controller (pictured at the top of this article) - both manufactured by MorningStar Corporation and sold with a 5 year warranty.


http://www.reuk.co.uk/Solar-Charge-Controller.htm

Use Thermostat As 12 Volt Timer

As we have previously discussed in our article 12 Volt Programmable Timer Switch, it is not possible near impossible to purchase a programmable timer which can be powered directly from a battery bank used to switch on and off connected devices.

Programmable Thermostat

Most domestic central heating systems come complete with a thermostat - a device used to switch on the heating when the temperature in a room is below a particular value. During the last 20 years, these devices have become more intelligent - enabling the user to program the times of the day the heating system is to be active. Domestic thermostats have also become less power hungry, and are now often powered by a couple of AA batteries.

It is therefore very simple to use such a programmable thermostat (pictured above) to switch items other than central heating on and off at different times of the day - for example, security lighting, irrigation pumps, and so on.

Using a Thermostat as a Programmable Timer

Within the thermostat is a relay which is only triggered when the ambient air temperature is below the target temperature programmed into it. Therefore, if the thermostat is programmed with a target temperature of say 30 degrees Celcius (here in the UK), the relay will be remain closed (i.e. ON) since we almost never get to 30 degrees here. We can then use the programmable timer to set the times through the day at which the device to be controlled should be on or off.

Note that many modern thermostats can also be switched to a cooling mode with the relay triggered only when the temperature is above a target value. Such thermostats can therefore also be used in refrigeration and air-conditioning systems to switch on cooling devices. A typical thermostat has a programmable range from 5 to 30 degrees Celcius, therefore if you live somewhere where temperatures of 30 degrees are likely, the cooling mode should instead be used with a target of 5 degrees Celcius. Therefore the relay will remain triggered as long as the temperature remains above 5 degrees.

Once that is set up, all that remains is to follow the instructions provided with the thermostat to set the on/off times. Some thermostats repeat the same programme every day, others can have each of the seven days of the week programmed differently giving the user more control.

Connecting to the Thermostat

At the back of most thermostats is a piece of terminal strip into which wires from the device to be turned on are connected.

The image above shows the rear of a typical programmable thermostat with three connections: NO (normally open), COM (common), and NC (normally closed). One wire of the external circuit is always connected to the common terminal. The second wire must either be connected to the normally closed or the normally open terminal. Normally open is used if the external circuit is to be ON unless the thermostat relay is triggered. Normally closed is used if the external circuit is ON only if the thermostat relay is triggered. Usually the normally closed terminal is used so that when the thermostat 'turns on' the relay, it turns on the external device.

Buying a Suitable Programmable Thermostat

When choosing a programmable thermostat is must be battery powered (so that it does not need to be connected to a mains supply). If it uses 2 AA batteries as is common, it is possible to use a couple of rechargeable AA batteries or use a voltage regulator to connect it directly to a renewable system battery bank.

One key thing to look out for is the maximum current for the relay. Values from 3 to 10 Amps are typical in cheap domestic thermostats, which means that 36 to 120 Watt 12 Volt devices can be switched on/off using them.

On ebay.co.uk there are many suitable new and used thermostats going for as little as £7 plus £3 for delivery. It is usually better to go for a second-hand good quality unit, rather than a cheap Chinese import as you will get more for your money (and it's always good to recycle and reuse when possible).


http://www.reuk.co.uk/Use-Thermostat-as-12-Volt-Timer.htm

12 Volt Programmable Timer Switch

Automatic 24 hour timer switches for 240 Volt mains electricity are very easy to find and are very cheap - prices start at just 99 pence! With such a timer (see image below) it is possible to set the times a plugged in device (typically a lamp - but also fans, pumps, irrigation systems, and other appliances) will switch on and off through a 12- or 24-hour period.

Unfortunately equivalent programmable timers for 12 Volt applications are not so easy to come by, and those that are available tend to be very expensive since they are not so mass produced. In this article we will introduce a couple of the better 12 Volt Timers available as well as looking into how you can make your own timer.

Flexcharge 8-Event Programmable 12 Volt Timer

Pictured above is a digital 12 Volt programmable timer manufactured in the USA by Flexcharge. Costing around US$85, this is a 7-day timer which can be programmed with up to 8 on (and 8 off) events per 12 hour period. An internal battery is included which will stored programming data for up to 3 months without external power.

DT-01 Digital 12 Volt Timer

Pictured above is the DT-01 Digital 12 Volt Programmable Timer - available in USA for around US$65. Typically used in automatic fish feeders (see super-feed.com for details), this timer provides up to 8 on and off cycles per day individually settable for the seven days of the week.

The internal lithium battery will retain programmed timings for up to five years when disconnected from the main 12 Volt battery, and the incorporated relay is rated at up to 16 Amps meaning this timer can be used to switch on and off up to 200 Watts of devices.

90-124uA are drawn by the timer when it is switched off (i.e. just 90 one-millionths of an Amp), and 33-49mA (i.e. 33 one-thousands of an Amp) when the relay is energized.

Click here for the DT-01 Specification Sheet.

Use a Programmable Thermostat as a Timer

An affordable alternative to the dedicated 12 Volt timer discussed above is a programmable thermostat. These battery-powered devices can easily be converted to run from solar power, or from the battery bank of a renewable system (via a voltage regulator).

These thermostats contain a built-in relay which can be used to switch 12V DC and 240V AC devices on/off according to the times programmed in by the user. Used good quality units are available for as little as £10.00, and new Chinese imports start at around the same price.

Click here to read our Use Thermostat as 12 Volt Timer article.

Make a 12 Volt 24 Hour Timer Circuit

Since commercial 12-Volt powered timers are so expensive, it is worth investigating putting one together yourself using easy to obtain electronic components.

Click here to view Two Simple 24-Hour Timer Circuit Schematics. These simple timers use a CMOS 4060 integrated circuit as a counter providing reliable 24 hour operation. See image below:

http://www.reuk.co.uk/12-Volt-Programmable-Timer-Switch.htm

PIR Sensors

A Passive Infra-Red (PIR) sensor is an electronic device commonly used in security lighting, and burglar alarm systems. A PIR sensor is a motion detector which detects the heat (infrared) emitted naturally by humans and animals. When a person in the field of vision of the sensor moves, the sensor detects a sudden change in infrared energy and the sensor is triggered (activated).

Passive Infrared Detectors

At the front of a PIR sensor unit is a fresnel lens (pictured above). This special kind of lens is used to gather light from a very wide field of view and focus it directly onto a passive infrared sensor (as shown below).

Some electronics inside the PIR sensor unit then decide whether the infrared light detected is from a warm moving body, and if so, triggers a switch.

Uses for PIR Sensors

The commonest use for a PIR sensor is automatic security lighting. Whenever a suitably large (and therefore probably human) warm body moves in the field of view of the sensor, a floodlight is switched on automatically and left on for a fixed period of time - typically 30-90 seconds *. This can be used to deter burglars as well as providing lighting when you arrive home at night.
* The duration the light is left on for can usually be set by the user.

Such PIR security lighting systems are available from a wide range of sources from as little as £10.00 up in the UK.

PIR Sensors and Renewable Energy

The vast majority of commercial PIR sensor products are built to run on 240 VAC mains electricity. This makes them unsuitable for most renewable energy powered systems such as motion activated CCTV systems in remote locations. Although a power inverter can be connected to the RE system battery bank to obtain the necessary voltage, using it for 24 hours per day for such as small load would be a huge waste of energy.

Fortunately 12 Volt DC powered PIR sensor units are available. These (such as this 12V PIR sensor available in our REUK Shop and pictured above) can be connected directly to a 12V battery or battery bank, and used to trigger a Relay when motion is detected. The relay will switch on/off a light or any other 12VDC or even 240VAC device if required.

If a power inverter is necessary to power a 240 Volt device switched on by the PIR sensor, then the inverter can also be turned on as and when required rather than needing to leave it on 24 hours per day. This saves a considerable amount of energy.

This PIR sensor will run off 10-14 Volts DC electricity and draws a current of under 10mA.

PIR Sensor Timer Circuit

12 Volt PIR Sensors do not usually include a built-in timer. Therefore, it is necessary to put together a very simple circuit so that whatever device is connected to the PIR sensor will stay switched on for the desired length of time.

The circuit shown above will turn on a floodlight or other device for a time in seconds approximated by the value of the capacitor C (meaured in microFarads) multiplied by the resistor R (measured in megaOhms) multiplied by 0.75.

For example, if R = 1M and C = 22uF, the floodlight would remain lit for around 16 seconds after the PIR sensor switched off.

Weaknesses of PIR sensors

In order for a PIR sensor to work well most of the time, they are designed with certain limitations. A PIR sensor cannot detect a stationary or very slowly moving body - if the sensor was set to the required sensitivity, it would be activated by the cooling of a nearby wall in the evening, or by very small animals. Similarly, if someone walks straight towards a PIR sensor, it will not detect them until they are very close by.

PIR sensors are temperature sensitive - they work optimally at ambient air temperatures of around 15-20 degrees Celcius. If the temperature is over 30 degrees, the field of view narrows and the sensor will be less sensitive. Alternatively, if the temperature is below 15 degrees, the field of view widens and smaller or more distant objects will activate the sensor.


http://www.reuk.co.uk/PIR-Sensors.htm

Solar Tracker

Most photovoltaic (PV) solar panels are fitted in a fixed location - for example on the sloping roof of a house, or on framework fixed to the ground. Since the sun moves across the sky through the day, this is far from an ideal solution.

Solar panels are usually set up to be in full direct sunshine at the middle of the day facing South in the Northern Hemisphere, or North in the Southern Hemisphere. Therefore morning and evening sunlight hits the panels at an acute angle reducing the total amount of electricity which can be generated each day.

During the day the sun appears to move across the sky from left to right and up and down above the horizon from sunrise to noon to sunset. This is shown in the schematic above of the Sun's apparent motion as s
een from the Northern Hemisphere.

Solar Trackers

A solar tracker is a device onto which solar panels are fitted which tracks the motion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. When compared to the price of the PV solar panels themselves, the cost of a solar tracker is relatively low.

In terms of cost per Watt of the completed solar system, it is usually cheaper (for all but the smallest solar installations) to use a solar tracker and less solar panels where space and planning laws permit.

A good solar tracker can typically lead to an increase in electricity generation capacity of 30-50%.

How to Solar Trackers Work

There are many different types of solar tracker which can be grouped into single axis and double axis models.

Single axis solar trackers can either have a horizontal or a vertical axle. The horizontal type is used in tropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in high latitudes (such as here in the UK) where the sun does not get very high, but summer days can be very long.

Double axis solar trackers have both a horizontal and a vertical axle and so can track the Sun's apparent motion exactly anywhere in the World. This type of system is used to control astronomical telescopes, and so there is plenty of software available to automatically predict and track the motion of the sun across the sky.

Tracking the Sun

Above is a simplified schematic diagram of a vertical-axis solar tracker fitted to a solar panel located in the UK (high latitude Northern Hemisphere). A pair of sensors (typically a type of cadmium sulphide photoresistors are used) point to the East and West of the location of the Sun.

The light detected by the Eastward-facing sensor is at a lower intensity to that detected by the Westward-facing sensor. Therefore, the solar panel must be turned westwards (by the motor controlled by the solar tracker circuit) until the levels of light detected by both the East and the West sensors are equal. At that point the solar panel will be directly facing the sun and generated electricity optimally.

Obviously real world solar trackers (such as the one pictured above) are not so simple. A solar tracker must be able to reset itself at sunset so it is ready for sunrise, it must cope with heavy cloud, and it must work reliably 365 days a year. In addition a mount for the solar panel must be constructed which can cope with strong winds, and a suitable motor found.

Buy a Solar Tracker

A wide range of commercial solar trackers are available - typically in Australia, USA, and Germany. There are also great plans available free of charge online for building your own DIY solar tracker from easy to find components. Read on for some useful online commercial and DIY solar tracker resources.


http://www.reuk.co.uk/Solar-Tracker.htm