Battery mAh Capactity Tester

low voltage disconnect with stopwatch for battery testingPictured above is a device we made recently to help estimate the capacity of 12V and 24V batteries. It is based loosely around our 12V Low Voltage Disconnect with Display, but with some major changes and functionality additions.

The customer for this device has a Farnell Electronic load which is capable of discharging batteries at up to 1.5kW (e.g. 12V @ 125A). He wanted to be able to use this to discharge batteries under test, to time accurately the discharge duration, and to automatically turn off the electronic load when the battery voltage falls below a user set level (for example 9.5V for a 12V battery).

This electronic load can be controlled externally by terminals on the back of the unit (Load Enable/Disable). If 5 VDC is connected across those terminals, the electronic load is enabled (turned on), otherwise it is disabled (turned off).

We therefore designed a device which the user can set with their choice of low voltage threshold. Then, when they press the Start Button, a regulated 5V is put across the terminals on the back of the electronic load which starts discharging the battery under test. At the same time, a stopwatch (created in software on the Arduino Pro Mini around which this controller is built) starts to display the number of days, hours, minutes, and seconds that have elapsed since the battery discharge began.

When the battery voltage is measured to have fallen below the low voltage threshold, the stopwatch stops, and the 5V signal to the electronic load is disconnected preventing the battery being discharged any further and potentially being permanently damaged.

The time on the stopwatch is saved in memory on our device and is displayed on the LCD until the user presses the reset button. It is saved in this way just in case after a multi-hour/day test has been completed, someone accidentally disconnects the battery from the timing device before noting the displayed timing results.

If you need any kind of voltage measuring device, low voltage disconnect, and/or timer, please email with details of your exact requirements.

Low Voltage Disconnect used as Charge Controller

Pictured below is our 12V Programmable Low Voltage Disconnect with Display as sold in the REUK Shop. The product is designed to prevent batteries from being overly discharged and damaged by automatically turning the load devices on or off depending on the measured battery voltage.

reuk programmable low voltage disconnect used as a battery charge controllerWe recently made a few modifications to this design of this LVD for a customer to enable this device to be used as a charge controller; turning it into a high voltage disconnect.

There is a battery bank and a generator which is used to charge it. We replaced the standard 12V output on the low voltage disconnect board with a relay so that it could switch the generator on and off automatically. We then changed the code on the Arduino microcontroller so that the relay would open (turning off the generator) if the battery bank voltage exceeded a user set value, and would then close the relay again (turning on the generator) when the battery voltage fell below a second user set value. By doing this the batteries are well cared for – never being overcharged, and never becoming overly depleted.

If you require a low voltage disconnect or a modification made to one of our LVD products such as this charge controller, please email with details of your requirements.

Programmable Low Voltage Automatic Battery Charger

Our Mini Programmable 12V Low Voltage Disconnect (LVD) is designed to disconnect loads from batteries when the battery voltage falls below  a user set value, and then reconnect the loads when the battery voltage gets back above a second (higher) user set value.

low voltage connect from REUK low voltage disconnectWith a few modifications to the code on the microcontroller of this device it can also be reconfigured as a low voltage connect – a device which will (typically) be used to connect a charger to the battery when its voltage gets low, and then disconnect it when the battery voltage gets higher after charging.

Today we made such a low voltage connect for a customer with a semi off grid garden office, a PV solar charged battery bank, and a selection of lights, 5V chargers, and other low voltage DC loads to be powered. He has a mains powered 5A bench power supply which he wanted to automatically connect to the battery bank via a solid state relay (SSR) when the battery bank voltage fell due to a period of poor solar generation (English weather) or from using a lot of battery power.

With our low voltage connect controlling the SSR, the battery bank will never be able to get overly-depleted and battery power will always be available to power the garden office.

If you need any kind of low voltage disconnect, low voltage connect, or high voltage disconnect etc, please email with details of your requirements.

Poultry Lighting Controller with LVD and Display

We have been selling a selection of poultry lighting controllers for many years now – devices designed to stimulate egg production in the winter months using artificial light at dusk and/or before dawn to trick the birds.

Pictured below is a bespoke lighting controller we recently made for a more advanced poultry lighting controller including a double voltage regulator so that more LED bulbs can be used in a large poultry house, an automatic low voltage disconnect, and an LCD display to show system status and for use in setting up the system.

Poultry lighting controller with low voltage disconnect and display

This device will automatically detect dusk and turn on the lights in the poultry house for a user-programmable number of hours (including zero). The lights then turn off (if they had been on) and remain off for 9 hours to give the birds a 9 hour sleep and a 15 hour day for maximum egg production. The lights then turn on in the early morning and remain on until dawn when natural light is bright enough to take over.

display for poultry lighting controller with lvd

Dawn and dusk are detected using a light dependent resistor, and the user can calibrate the exact light level which they consider to be at the threshold between day and dusk, and between night and dawn.

To protect the battery from being run too low of charge and being damaged, the user can programme into the device three trigger voltages: a voltage below which the on board red LED will turn on as an early warning, a voltage below which the output (to the lights if on) will be turned off, and a voltage above which the low voltage disconnect will be cancelled restoring the outputs automatically when the battery is recharged.

manual override active on poultry lighting controller

There is also a manual override option which enables the lights to be turned on manually at any time (low voltage disconnect permitting) when the poultry house needs to be cleaned or the eggs to be collected etc.

At all times the backlit LCD display shows the status of the system including the currently measured battery voltage, whether the LVD is engaged, whether the outputs are on or off, the current position in the cycle DAY, DUSK, SLEEP, PREDAWN, DAWN (or MANUAL when the override is active), and the currently measured light level relative to the user set threshold.

If you need any kind of poultry lighting solution, please email with details of your exact requirements and we should be able to put something suitable together for you.

Poultry Lighting Controller with Low Voltage Warning

We have been selling poultry lighting controllers for the last eight years designed to increase egg production during the long nights of winter. See here for details: Poultry Lighting Controllers.

Pictured below is a modified version of our standard Mark 3 lighting controller (sold here: REUK Super Poultry Lighting Controller) to which we have added a low battery voltage warning LED.

poultry lighting controller with built in low voltage warningThis modified version is designed primarily for use in lighting set ups where a solar panel is not used, and so the battery has to be charged by the user. When the battery voltage powering the controller and connected lighting falls below 12.0V, the red LED turns on to show the user that they need to recharge the battery as soon as possible to ensure reliable operation and battery longevity.

Contact if you need any kind of poultry lighting controller with details of your exact requirements.

Low Voltage Disconnect with LCD Display

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

REUK low voltage disconnect with LCD displayAs 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.

LCD display on REUK low voltage disconnect (LVD)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 with details of your requirements.

Arduino Datalogger Testing

We recently built and tested a very simple SD card datalogger based around an Arduino Pro Mini – the smallest and cheapest Arduino board commonly commercially available. We have previously described datalogging to an SD card with an Arduino in our blog post Arduino SD Card Datalogging (to log temperatures). In this example we are instead logging the voltage of a solar charged battery used to power the lights in a shed.

REUK Arduino Battery Voltage Datalogger

The Arduino Pro Mini (£3) was programmed from a PC via an FTDI breakout board (£5), and connected to an Arduino micro SD module (£1) fitted with a 1GB micro SD card (£3).  Note that the unlabelled components in the image above are not required for this datalogger – we just built the controller so that it can later also be used as a low voltage disconnect.

We programmed the Arduino to read in the voltage of a 5Ah 12V SLA (via a 47K-10K voltage divider) and write it to a log file on the SD card once every second. The battery is connected to an 80 Watt PV solar panel via a solar charge controller. The battery is also connected to  three 1W LED spotlight bulbs which were left permanently on so that the battery would drain over night and be recharged during the day.

The datalogger was left connected to the battery from around 10:30am one day to around noon the following day in mid-April with blue skies both days.

USB memory card reader

In order to view the data collected on the micro SD card we just needed a USB all-in-one memory card reader (£1). Plug the micro SD card into the reader, plug the reader into a PC via USB, and download the collected data.

The collected data file (which was simply a list of voltages measured to 2 decimal places) was 97070 lines long with a file size of 680 kB. Therefore our 1GB card could have logged the battery voltage once a second for 3-4 years.

Looking through the datalog in a text editor it was obvious that the battery voltage did not change very fast at all. Therefore logging the voltage every second was unnecessary for this application – every 30 seconds or every 60 seconds would have been adequate.

Knowing from experience that plotting 100,000+ data points with Excel is usually an unhappy experience, I first copied the log file over to my Raspberry Pi, and ran the following sed script to create a new smaller file containing just every 60th record from the log file. (This is equivalent to having set up the datalogger to log the voltage once per minute in the first place.)

sed -n '0~60p' logfile.txt > 60slogfile.txt

This command took just 0.24 seconds on the Raspberry Pi (thanks to the raw speed of sed) and I then dropped the new smaller (1617 records) log file into Excel and made the following plot of the results.

Datalogger data collected from solar powered shed lighting

The vertical axis shows the measured voltage, and the horizontal axis shows time with the far left being 10:30am on day1 and the far right being noon on day2.

The plot shows how the solar charge controller carries out a bulk charge phase to rapidly charge the battery (peaking at 14.6V) and then maintains a float charge (around 13.6V) during the day while the solar generation far exceeded the charge used by the spotlights. At night the voltage of the battery drops rapidly down hitting a low of 11.95V before the sun rose high enough to start to charge the battery again.

If you need a voltage datalogger like this, a voltage datalogger with a built in low voltage disconnect to protect the battery from being too deeply discharged, or any other kind of single or multi-channel datalogger, please email with details of your exact requirements.

Automatic Low Voltage UPS Shutdown

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.

Low voltage detecting automatic shut down for Uninterruptible Power SupplyThe 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.

Mains Backup for Solar Charged Battery Bank

Pictured below is a controller designed to automate backup mains charging of a battery bank which is charged by an array of photovoltaic solar panels.

Main charger back up for solar pv charged battery bankThis controller is based around our low voltage disconnect products. It constantly monitors the voltage of the battery bank. When the voltage falls below a user set low voltage (e.g. 12.0V), the on board relay closes which connects a mains powered battery charger to the battery bank.

When the battery voltage then gets up to a user set high voltage (e.g. 13.6V), the on board relay opens which disconnects the battery charger.

This controller is fitted with manual overrides so that the user can ‘override’ the controller and force the mains powered battery charger to come on when off, or turn off when on.

This is very useful for a solar powered system since the battery bank voltage may be getting low and the weather forecast may also be bad for the coming day. In that scenario, it is worth charging up the battery bank fully immediately to prevent the battery bank from hanging around at a low voltage for an extended period of time (which is bad for battery longevity).

Similarly, if the mains charger is on because the battery bank was low on charge, but the weather forecast is for non-stop sunshine, the override enables the charger to be turned off to leave the solar panels to do the rest of the work.

If you need a controller like this, email with details of your exact requirements.


Playhouse Lighting Controller with LVD

Pictured below is the connection diagram for a controller we have built to be used in a child’s playhouse. The playhouse will have a solar charged battery which will be used to supply power to three LED spotlights with a light switch, a small fan to circulate air and prevent the playhouse getting damp or too hot, and a dual cigar lighter socket with USB sockets which will be used to charge battery powered gadgets.

Connections for low voltage disconnect with twin outputs - regulated for LED lighting and to power a fan for ventilationAs the playhouse will be used by children, safeguards have been fitted to prevent the battery from becoming excessively depleted and permanently damaged.

In order to prevent the lights being left on and forgotten, when the light switch is turned on, a timer starts and if after one hour the light switch has not been turned off, the lights turn off automatically and will not turn back on until the light switch is toggled.

The output from the controller to the LED lighting is regulated to 12.0V so that excessive voltage (particularly when the batteries are being charged) does not damage the voltage sensitive bulbs.

To reduce power consumption, the fan which is used to ventilate the playhouse is turned on for just one hour every six hours automatically by the controller. The output to the fan is not regulated as the fan is rated for use with up to 18V, and if the battery voltage is high it is because there is or has been a lot of sunshine. Therefore the faster fan speed will prevent the playhouse getting too hot and stuffy.

In order to prevent the battery from running too low on charge, an automatic low voltage disconnect is incorporated. When the battery voltage falls below 11.9V, the outputs to the fan and lighting turn off, and only turn back on again when the measured battery voltage exceeds 12.4V.

The cigar lighter / USB socket is connected directly to the battery as the gadgets being charged by it will not draw much current for long if left connected since their batteries will get full and charging will stop automatically.

If you need a controller such as this, or with any of the features it has, email with details of your exact requirements.