Monthly Archives: April 2013

Project of the Day – Digital Photo Frame Low Voltage Disconnect

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Today we put together a special order low voltage disconnect (LVD) to be used with a product display case containing a digital photo frame.

To make the case portable, instead of using the standard 5VDC power supply, 8 series connected high capacity C sized rechargeable cells have been fitted to give a 9.6V power supply which goes through a dc-dc voltage converter to get the required 5VDC to the photo frame.

Low voltage disconnect for digital photo frame

Unfortunately when the voltage of the 8xC battery pack falls to 8.7V (when the battery pack is almost empty of charge), the photo frame software crashes and gets stuck in a constant reboot cycle due to not having enough power to restart.

The low voltage disconnect we designed measures the voltage of the battery pack and if is more than 8.80V it outputs power to the voltage converter and photo frame. If the measured voltage falls below 8.80V, then the output is turned off and only turns back on again when the measured voltage is found to be greater than 9.20V.

The display case is fitted with a standard off the shelf battery charger which takes a 12VDC input. An external 12VDC power supply can be plugged into the case to recharge the battery pack while at the same time powering the photo frame via the low voltage disconnect circuit causing the disconnect to be cancelled (since the measured voltage is now 12V) and the photo frame to restart.

When the 12VDC is supplied, the 8xC cells are automatically disconnected from their series circuit and connected individually in parallel to the battery charger for charging. When charging is complete, the 12VDC power supply can be disconnected, the battery pack voltage will be >9.20V, and so the frame will continue unaffected.

We sell our own automatic user programmable low voltage disconnect in the REUK Shop. If you have any special requirements which this product does not meet, let us know and we should be able to put something together for you.

Project of the Day – 12V PIR Alarm System

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Today we put together a 12V alarm system for a farm building located 100 metres from the farmer’s home. When motion is detected in the building by one or two standard , two relays close. The first causes a loud siren to sound, and the second turns on a bright strobe light visible from the farmer’s home.

PIR Alarm System with siren and strobeIf the controller is not reset by the farmer pressing an external panel mountable button then after 3 minutes the siren relay opens cutting the sound, but the strobe light is left turned on until the controller is manually reset to ensure that motion detection events are never missed.

If you need something along these lines then let us know. Click here for suitable low power consumption 12V strobe lights and/or low power high volume 12V sirens and sounders for your own projects.

12V Regulator for RC Planes, Helicopters, and Cars with Cameras

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With the price of high quality ruggedised mini video cameras and transmitting equipment falling rapidly, many people are now attaching FPV (first person view) cameras to their radio controlled planes, helicopters, and cars with very impressive results.

View from RC plane camera

One common problem though is interference. When radio transmitting equipment is powered by the same power source as motors, servos etc, interference (noise) can add lines and other unwanted effects to the transmitted images.

The camera and transmitter need a very stable fixed voltage – e.g. 12.0 Volts – as anything else will damage the sensitive electronics. Therefore a voltage regulator is required. For their high efficiency and small dimensions a switching type regulator would appear to be the obvious choice, but this type of regulator generates yet more interference. Therefore a lower efficiency linear regulator must be used.

In the second half of this excellent article The Tricopter V2.6HV David Windestål from Sweden explains in detail how he built a very stable interference suppressing linear regulator around the LM2940 low dropout voltage regulator.

Very stable 12V linear regulator for RC

This is almost identical to our standard REUK 12V regulator but the components L1 (1mH coil) and C1 (low equivalent series resistance ESR also known as low impedance 22uF capacitor) have been added working together to make an LC filter (Wikipedia: electronic filter) to strip out any noise from the ESC (electronic speed controller) and everything else connected to the same battery pack.

Regulator for RC helicopter camera transmitter

With a 16.8V LiPo battery pack fitted in his DIY tricopter and a transmitter drawing 300mA, the regulator only has to get rid of 1.5W of heat, so only a small heatsink was required resulting in the finished regulator ended up small and light which transmits video which is “crystal clear [without] a hint of interference”.

Renewable Energy Use up to 13% of Gross Final Energy Use Across EU

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Eurostat, the statistical office of the EU, has released its figures for renewable energy use across the EU27 – the 27 EU states – for the calendar year 2011. Of all energy use across the EU27, 13% came from renewable sources compared to just 7.9% in 2004 and 12.1% in 2010, well on its way to a target of 20% in 2020.

Looking at the countries individually, the top renewable energy users were Sweden (46.8%), Latvia (33.1%), Finland (31.8%) and Austria (30.9%), and the lowest were the tiny states of Malta (0.4%), Luxembourg (2.9%), followed by the United Kingdom (3.8%), Belgium (4.1%).

Between 2004 and 2011, the countries with the biggest gains in renewables usage were Sweden (38.3% to 46.8%), Denmark (14.9% to 23.1%), Austria (22.8% to 30.9%), and Germany (from 4.8% to 12.3%); while the UK went from 1.1% to 3.8% in the same time period. The EU target for the UK is 15% by 2020.

Click here for full details in the Eurostat 26th April 2013 press release: Share of Renewable Energy up to 13% of Energy Consumption in the EU27 in 2011.

Special Offer – Complete Evacuated Tube Solar Water Heating System

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Complete evacuated tube solar water heating system

Pictured above is a complete DIY 30 tube evacuated tube solar water heating system for sale here in the UK at £1,662 plus £45 for delivery.

While that obviously sounds like a lot of money (as it is) you get a lot for your money all from one place thereby making savings in postage and the time otherwise taken to spec and source everything.

Evacuated tube solar water heating systems (click link for more information from REUK site) are the most efficient on the market today. A 30 tube system such as this fitted with a 200 litre tank will meet the majority of a typical family household’s hot water needs for 3 seasons of the year, and make a good dent in water heating bills the rest of the time – even when it is freezing outside.

The kit comprises the 30 evacuated tubes, 200 litre insulated twin coil cylinder, roof fittings, solar contoller and pumping station, expansion vessel, pipework, and all the other fittings necessary to put together a complete solar water heating system together with detailed instructions.

Click here for more information or to buy now: 30 tube solar water heating kit. There are many other options – e.g. smaller or larger systems available from the same seller. Click here to view the range: DIY evacuated tube solar water heating.

Testing Car Battery Voltage Meter

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LED car battery voltmeterPictured above is a car battery voltage meter which is designed to be inserted into the cigarette lighter socket of a vehicle to test and display the battery voltage – purchased for £1.76 including delivery from Hong Kong.

It is relatively well made if a bit plasticky, but certainly as good as should be expected for a device at this sort of price. Inserting it into the car cigarette lighter socket it displayed the battery voltage accurately to well within 0.1V, and when tested with a variable power supply gave similarly reliable readings with an input voltage from 6V to 16V.

LED voltmeter for 12V car battery

The LED numerical display is bright – if anything too bright as the voltmeter draws 40mA when it is on which is too high to leave connected to a battery all the time (taking 1Ah of charge from the battery per day).

We purchased this to test and to take apart for a project. Breaking it open was very easy.

taking apart an LED voltmeter

The plastic end cap is threaded onto the positive end of the cigarette lighter plug, and can be unscrewed (with a bit of force). Inside is a 5A fuse which should really be a 100mA fuse to properly protect the device.

Then the two sections of black plastic can then be prised apart to expose the innards.

Components inside the LED voltmeter

There is a small circuit board with an IC on it, the LED display, a large resistor, some other common components, and a TL431 adjustable precision zener shunt regulator which is used as the voltage reference.

We wanted this to stick on top of a solar charged 12V lead acid battery to display the battery voltage so we chopped off all the unnecessary bits and pieces leaving just the two wires for connection to the + and – terminals of the battery.

mini LED voltmeter for 12V batteryThe blue plastic cover is pretty much vital as without it it is very difficult to read the voltage from the display.

Finally, to reduce power consumption, we wired a small push to make button to the white positive input cable and connected that and the black negative cable to the terminals of the battery. Now, whenever the button is pressed and held, the battery voltage is displayed. This mini LED battery voltmeter is only 3.5 x 2.5 x 1.0 centimetres in size and does the job perfectly.

If you are interested in buying one of these car cigarette lighter LED voltmeters click here.

Solar Cell Coating Could Improve Efficiency by 6%

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The journal Science had details today of research into a special coating for photovoltaic solar cells which could potentially increase the percentage of solar energy which is converted into electricity by 6%.

Solar panels do not convert all wavelengths of light into electricity – photons of light from the blue (higher energy) end of the spectrum are converted into heat if they are not reflected from the solar panel which a) means that that solar energy is wasted, and b) means that the solar panel gets hotter, which as our article (Effect of Temperature on Solar Panels) showed, reduces efficiency.

pantacene-solar-panels

Since the 1960’s it has been known that a material called pantacene (an organic semiconductor pictured above) has an interesting property. When a photon of light from the blue end of the spectrum hits pantacene, TWO electrons are generated. When a photon of light from the red end of the spectrum hits a normal solar cell, ONE electron is generated. Therefore by making a solar cell with a coating of pantacene, light from the whole visible spectrum can be exploited and the efficiency of the hybrid solar cell will be higher than the simple silicon solar panels currently available.

This is still very much in the prototype phase with many years of research still to come before it could become commercial. Pantacene though abundant, carbon-based, and organic, is currently expensive and technology has to be developed to enable the economical manufacture of hybrid solar panels.

Butanol – the Biofuel of the Future

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Ethanol from crop waste, corn, and sugar beet etc is currently added in small percentages to petrol to reduce fossil fuel use. It has lower energy density than petrol (lower mileage), is corrosive to engines (cannot be used in high concentrations), and it absorbs water from the atmosphere which can cause engine problems. 

Butanol is a heavier alcohol without any of these problems, but is more expensive to process (ferment and distill) from crops than ethanol. New research has led to new families of catalysts which will enable existing ethanol plants to output butanol by adding one reactive conversion step at the end of their processing.

This brings us one step closer to butanol (renewable fuel biobutanol) being commercially viable as the biofuel of the future to replace petrol.

Take a look here at our new article Butanol vs Ethanol Fuel of the Future for more information.

Portugal 70% of Power from Renewables in Q1

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The national grid operator in Portugal (Redes Energéticas Nacionais – REN) has announced that in the first quarter of 2013 70% of all power consumed was generated from renewables – a new record.

Surprisingly despite its sunny reputation and Southern European location, Portugal does not generate much electricity from solar PV – in fact just 0.7% of electricity generated in 2012 came from solar PV.

Castelo de Bode dam - Portugal hydro power plant

A huge 37% of Q1 2013 electricity generated in Portugal came from hydroelectric power – including from hydropower plants at Alqueva Dam (Europe’s largest dam) and Castelo de Bode Dam pictured above.

A further 27% of the power generated came from wind turbines, located primarily in the windy north east of Portugal.

Favourable weather conditions made a big contribution to this record, with hydro power generation up over 300% compared to the same period last year, and a 60% increase in wind power generation.

Portugal still have virtually no offshore wind turbines despite having a long windy stretch of Atlantic coastline to exploit, and very little solar PV despite being sun scorched. Therefore, with continued investment there is a great chance of seeing 100% of consumption being met by renewables soon in Portugal.