Low Voltage Disconnect with LCD Display

Posted on May 20, 2014 by neil

Pictured below is our latest low voltage disconnect circuit with LCD display.

As with our standard programmable low voltage disconnect (LVD), this device is designed to protect batteries from being discharged too deeply and permanently damaged. The user can set the low voltage at which the output loads will automatically be switched off, and also the higher cancellation voltage above which the output loads will be switched back on again.

This particular LVD has a backlit LCD on which system information is constantly displayed. It is also used when setting the low and high voltage thresholds which makes things a lot clearer and simpler than using LEDs or a rotary switch to programme those in.

As shown above the display shows the measured battery voltage updated multiple times per second and given to 2 decimal places of resolution (and calibrated to be accurate to within +/- 0.02 Volts across the range 10-16V).

The system status is usually ON or OFF, but can also be LOW or HIGH when the battery voltage is transitioning one of the thresholds about to change the state of the system. The high and low threshold voltages are also permanently displayed.

In order to avoid the output cycling on and off too often (particuarly as the battery voltages can spike or dip depending on the loads they are powering) there is a time delay during which the voltage must remain under/over the voltage threshold before the system will change from ON to OFF or OFF to ON respectively. During that time delay the backlight of the display flashes as a visual indicator that the threshold has been breached. We chose to flash the display itself rather than flashing an LED either on the board or on leads, since it is much easier to panel mount just the LCD than to mount both that and an LED indicator.

This particular client-tailored LVD has a MOSFET directly switching the output loads which can have a maximum total rating of 3 Amps. We can also make this with a relay fitted on board for direct switching, or a lower rated output which can be used to energise a high current (or high voltage) rated relay external to the board – e.g. an automotive relay or a solid state relay (SSR).

This low voltage voltage disconnect with LCD is now available direct from the REUK Shop. Click here to find out more or to purchase now: buy REUK Low Voltage Disconnect with LCD.

We will shortly be adding a very similar unit with the addition of datalogging functionality. Over the last couple of years we have sold many LVDs with built in dataloggers (see here for an example: Low Voltage Disconnect with Display and Datalogger), and we now have refined things to the point that the product is ready for general sale. In the meantime, if you have any requirement for a low voltage disconnect with or without a display and with or without datalogging, please email neil@reuk.co.uk with details of your requirements.

Low Voltage Disconnect with Early Warning Alarm

Posted on February 19, 2014 by neil

Pictured below is another of our low voltage disconnect (LVD) circuits designed to protect batteries from being overly discharged.

This particular LVD has a few added features. First of all, to reduce power consumption by the LVD itself, it has been designed to work with a latching relay. The chosen relay (click here to download the latching relay datasheet) has two coils – one coil to latch the relay closed (set coil), and the other to release the relay (reset coil).

This controller can be programmed as per our standard REUK Programmble Low Voltage Disconnect with the disconnect voltage and cancellation voltage. While the voltage is good, the relay will be left latched closed, and then when the voltage falls below the disconnect voltage, it will be latched open.

As an added feature, when the measured battery voltage is 0.2V or less more than the disconnect voltage, the external LED (which can be panel mounted somewhere easily visible) turns on, and an on board piezo buzzer sounds briefly every half a minute until either the user starts to charge the battery, or the disconnect engages due to even lower measured voltage.

If you need any kind of low voltage disconnect circuit, email neil@reuk.co.uk with details of your exact requirements.

Automatic Low Voltage UPS Shutdown

Posted on February 14, 2014 by neil

Pictured below is a special low voltage disconnect controller designed to switch off an uninterruptible power supply (UPS) when the battery bank to which it is connected is low on charge.

The system for which this controller was built is as follows. A 72V 2.3 kW solar PV array is connected to a 48V 50A MPPT solar charge controller. The charge controller charges a 48V battery bank (made up of an array of 12V batteries); and that feeds a 3.5 kW UPS which supplies electricity to the house.

The UPS does not have a low voltage disconnect feature and so from time to time the batteries were being discharged too far. Obviously the owner wanted to avoid this as the battery bank is a very expensive part of the system.

This particular UPS has a standard female USB port on it, and if its pin1 is shorted out with one of its other pins, the UPS switches off.

Therefore our controller is a slightly modified version of our standard programmable low voltage disconnect. One of the 12V batteries in the battery bank is constantly monitored. If the voltage measured stays below a user set low voltage threshold (e.g. 12.0V) for 10 seconds, the on board relay closes for 2 seconds which shorts two of pins in the USB socket and forces the UPS to switch off immediately. Therefore the battery bank is protected from being run down excessively.

Offer of the Day – 88Ah Deep Cycle Battery £56.95

Posted on June 18, 2013 by neil

Our recommended offer of the day is this 12V 88Ah deep cycle battery offered in the UK at just £56.95 including delivery (to mainland UK locations south of Glasgow/Edinburgh). As the image above shows, order this battery before 4pm to have it delivered next day, and it comes with a 4 year warranty.

This battery has dimensions of 257 x 172 x 220mm and is suitable for solar charging as well as for general leisure and marine usage.

Click here for more information or to buy this 88Ah 12V battery now at this low price.

Compressed Air for Storage of Renewable Energy

Posted on May 22, 2013 by neil

The wind tends to blow more strongly at night when demand for the electricity wind turbine generators can make is at its lowest. Therefore, finding ways to store energy so that it can be used at times of high demand is essential.

The Pacific Northwest National Laboratory has been studying how compressed air could be the solution to this energy storage problem.

When electricity generation exceeds demand, a large air compressor (powered by the generated electricity) forces air underground into natural porous rock reservoirs. When demand increases, this high pressure air is release back up the surface where it is heated and turns turbines to generate electricity. The overall cycle is up to 80% efficient.

The research looked into suitable locations for this type of compressed air energy storage – not easy since the location must be near to high voltage power lines, have very specific geology, and be near to either natural gas lines or a geothermal heat source for heating the compressed air.

One of the locations they studied had an air reservoir large enough that the energy stored could be used to generate electricity for 40 days – perfect for storing the surplus hydro electricity generated in the spring for example.

For more information see this press release.

Testing Car Battery Voltage Meter

Posted on April 19, 2013 by neil

Pictured 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.

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.

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.

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.

The 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.

Rust to Help Storage of Intermittent Renewable Energy

Posted on April 7, 2013 by neil

The main disadvantage of some renewable energy sources (particularly wind and solar) compared to fossil fuels is you cannot guarantee to have the power you need when and where you need it. Wind speeds are not stable, and it can be cloudy (certainly in the UK) and its always dark at night.

In order for a very high percentage of our power needs to ever be met by renewables, it is essential that new improved ways are found to store power so that it is available even when the sun is not shining and it is not windy. Otherwise we will need more fossil fuel power stations as fall backs to ensure that electricity demand can be reliably met at peak times.

One of the cleanest ways of storing power is to use surplus renewable electricity to break water down into its constituent parts – oxygen, and highly flammable hydrogen. The hydrogen stored at times of surplus is then burned to power a turbine to generate electricity at times when renewables cannot meet demand directly. Best of all, the waste product from burning hydrogen is…pure water.

Until now the catalysts (electrolysers) used to split water into hydrogen and oxygen have been expensive, exotic, and often toxic rare earth metals such as iridium oxide and ruthenium oxide. With such high production costs it had been thought that storing energy by splitting water would never be cost effective. But, recent research from University of Calgary in Canada has found that iron oxide (rust) combined with a few other inexpensive materials can be used as a catalyst at a cost of one thousandth that of existing commercial catalysts while working at 85-90% efficiency.

This ability to split water into hydrogen commercially using renewable energy will also greatly help the future of hydrogen fuel cell powered cars. It also has a great deal of potential for off grid renewable systems currently using batteries for storage, but which will soon hopefully generate their own hydrogen for a small hydrogen powered generator replacing their existing polluting and expensive to run diesel generator.

REUK.co.uk

The Renewable Energy Website

Category Archives: storage