Project of the Day – High Voltage Connect

We have made hundreds of low voltage disconnects designed to protect batteries from being excessively discharged, but today we made a high voltage connect circuit. The requirement was for a device which will turn on a fridge when the battery voltage exceeds 12.2V and turn it off when the voltage falls below 11.8V, but with an LCD display and datalogging of the battery voltage.

In our blog post Low Voltage Disconnect with Display and Datalogger we gave details of how we put together an LVD with display and datalogger. In this case the powered device(s) are turned off when the voltage gets too low, and only turn back on when it gets above a certain level. A high voltage connect only differs in how it responds when initially powered.

high voltage connect modification of low voltage disconnect with datalogger and LVD displayOn start up, a high voltage connect circuit will only supply power to the output device(s) if the voltage is above the user set high voltage threshold; whereas a low voltage disconnect will only supply voltage to the output device(s) if the voltage is above the user set low voltage threshold. Other than that, both devices behave identically. A high voltage connect circuit is functionally identical to a dump load circuit.

low voltage disconnect with LCD and data logger

With this high voltage connect we incorporated an LCD display and datalogger. The datalogger stores the last 200 battery voltage readings – one every seven and a bit minutes so that the previous 24 hours of battery voltage are logged. The display shows the current battery voltage and state of the system together with the minimum, maximum, and average voltage measured over the previous 24 hours.

We will soon be adding programmable low voltage disconnect / high voltage connect circuits with displays and datalogging to the REUK Shop. In the meantime, if you need something similar to this email neil@reuk.co.uk with details of your exact requirements.

Project of the Day – Egg Incubator Day Countdown Timer

Pictured below is a project we completed for a day countdown timer for an egg incubator.
Egg incubator day countdown timer

It is important to keep track of the number of days that the eggs have been in the incubator waiting to hatch. When the user turns on the incubator and puts in the eggs, he uses the button on the timer to programme in the number of days that the eggs have until they are due to hatch. The timer then starts, and every day the day count display reduces by one until it eventually gets down to zero and the eggs hatch.

In order to build this we used a standalone Arduino set up. The external clock crystal gives pretty good time accuracy (used in conjunction with the Arduino millis() function). However, it is still essential to calibrate it to confirm it will be reliable over the 30 days or less that this incubator timer is likely to have to countdown.

In order to calibrate we temporarily programmed the timer to countdown hours (3,600,000 milliseconds) instead of days and left it running for 12 hours. Using an accurate stopwatch we timed how long it took the timer to run for its ’12 hours’ to compare it with the real 12 hours of the stopwatch. We then calculated by how much we needed to increase or decrease the number of milliseconds in the Arduino ‘hour’ so that its hour would match a real hour giving a very accurate timer. With this particular Arduino chip and clock crystal combination the Arduino lost less than a second in 12 hours even before the calibration.

Display on the egg incubator day countdown timer

To display the number of days until hatching we used two 7-segment LED displays which we multiplexed. Multiplexing takes advantage of persistence in the eye. If you light up one display quickly, then the other display, then the first again, and so on, the eye sees both displays on at the same time (as does a camera if the shutter speed is slower than the time taken to light up both displays – see above!). This technique makes it possible to control lots of LED displays without needing too many output pins on the microprocessor – just seven for the LED segments which are connected in parallel, and one for each display’s ground connection (if you use common cathode LED displays).

Temperature Sensors and USB Memory Sticks with Raspberry Pi

Over the last week we’ve added a few more Raspberry Pi related articles. For those of you interested in using the Raspberry Pi to make yourself a solar thermal controller or other monitoring or control system, then our article Connect Multiple Temperature Sensors with Raspberry Pi will help you to get readings from multiple DS18B20 digital temperature sensors via the GPIO on Raspberry Pi.

Connecting multiple digital temperature sensors to the Raspberry PiIf you are using your Raspberry Pi to play music and video through your television, then you will rapidly need a lot more media storage than you probably have on your operating system SD card. The cheapest and easiest way around this is to use USB flash drives. Our new article Mount USB Memory Stick on Raspberry Pi will take you through the steps required do this.

New Product – Rainwater Toilet Flush Pump Controller

This week we launched another new product – the REUK Rainwater Toilet Flush Pump Controller as pictured below.

REUK Rainwater Toilet Pump Flush Controller

We have been selling different rainwater toilet pump controllers now for seven years, so this new product pulls together all the experience and knowledge we have gained over all those years together with customer feedback from hundreds of users.

For simplicity, reliability, and cost, this device uses just one float switch mounted near the top of the header tank together with a mains powered pump with its own float switch protection.

Every thirty minutes the controller tests the status of the header tank float switch, and if the header tank is found to not be full then the pump is run until the header tank is full ready to gravity feed the toilet(s) in the home.

A button has been added to the controller to enable manual override of the thirty minute timer so that the pump can be force run until the header tank is full – particularly useful for system testing and topping up if required.

This device is not available yet in the REUK Shop. It is currently available for sale exclusively here for now: REUK Rainwater Toilet Pump Controller. We can also supply a suitable relay – ideally solid state, the float switch, and a 12V plug in power supply to complete full control system.

Contact neil@reuk.co.uk with details of your requirements for more information.

New Product – 12V PIR Motion Sensor Timer

This week we have launched a new product – a timer designed for use with the 12V PIR motion sensors typically found in burglar alarm systems.

REUK Programmable PIR motion detector timer

This device is based loosely on the PIR Relay Timer we have been selling since 2007 designed to keep an output such as lighting or an alarm on for a user programmable duration after motion has been detected by a PIR sensor.

This new device does not come with a relay; instead with an up to 3 Amp 12VDC output which can be used to directly power to up to 3A of lighting etc, or which can be connected across the coil of the user’s choice of relay – solid state or standard – to switch any current or voltage as required.

The user can programme how long the output will remain on after motion was last detected in steps of 10 seconds – 10, 20, 30, 40…etc seconds as per requirements.

This device is not currently available in the REUK Shop, but is available exclusively here: REUK PIR Timer for now.

Project of the Day – Special Programmable Timer

We had a special request for a modified version of our REUK Super Timer 2 for use setting dosing levels during plant development.

Our super timer can be programmed to close a relay for an interval from 1 second to 99 hours, and then open that relay for from 1 second to 99 hours repeating. It is a very useful and popular product, but in this particular application it was necessary to make the programming of the ON and OFF durations as simple as possible and to also display the current settings so that it was immediately obvious to anyone looking at it what those settings were.

simple relay timer with displayPictured above is our solution to this problem. The possible ON durations required were 1,2,3,4 or 5 seconds, and the OFF durations 1,2,3,4 or 5 minutes. Therefore there are two buttons – one to move through the ON options 1 to 2 to 3…etc seconds, and another button to move through the OFF options 1 to 2 to 3… etc minutes. The green LEDs show which ON option has been chosen, and the red LEDs show which OFF option has been chosen.

Because of the large number of inputs and outputs, 10 LEDs, two buttons, and a relay, we chose to use Arduino for this project, but as a standalone microcontroller as explained here: Standalone Arduino on a Breadboard so that everything could be put tidily on the one circuit board.

Project of the Day – Immersion Controller using Electricity Meter LED

Our standard Surplus PV Immersion Controller uses a light detector to estimate when the solar electricity generation from a domestic PV array is above a user-set threshold. It then turns on an immersion heating element to use the surplus electricity rather than exporting it to the grid.

REUK

This simple light detector approach works particularly well in homes where the householder is out all day since once the baseline electricity needs of the home are met, the surplus electricity can be used for free water heating instead of being exported (which would earn just a few pennies per kWh unit of electricity exported).

However, this system is not a true surplus electricity controller since if the home owner has a 4 kW solar array, and a 3kW immersion element, then if more than 1kW of electricity is being used in the home on other things – e.g. kettle, washing machine, or other heavy loads, electricity will be imported at a cost to cover any shortfall.

This week we have been working on the next level approach which is very useful for some households depending on how their electricity meter(s) are set up. In our article Flashing LED on Electricity Meter we looked at how modern electricity meters are fitted with a red LED which flashes at a rate proportional to the power passing through them. They are marked with something like 1000 Imp/Kwh which means that the LED will flash 1000 times per kWh unit of electricity passing through.

The meter for which we made this modified controller this week has such an LED which flashes while electricity is being exported and is off while importing. The flash rate is 1000 Imp/kWh and so if 1000 Watts of electricity is being exported, the LED will flash once every 3.6 seconds; if 2000 Watts of electricity is being exported, the LED will flash once every 1.8 seconds; if 100 Watts of electricity is being exported, the LED will flash once every 36 seconds, etc.

Using this information we modified the programming on our standard immersion controller so that instead of the light detector measuring the level of solar radiation and therefore estimating the power generated by the solar panel, it now measures the LED flash rate on the electricity meter so that it knows how much electricity is actually being exported net of any loads in the home.

half wave rectification of electricity to halve power use of immersion element

This controller is being used with a 1.5kW immersion heating element which is powered via a diode to give half-wave AC electricity cutting the power of the immersion element in half to 750 Watts. The solar array is rated at 4 kW.

We programmed this particular controller to turn on the immersion element when 1,100 Watts or more is being exported and then turn off the element when 200 Watts or less are being exported. If 1,100 Watts are being exported then when the immersion heating element turns on, the export will instantly fall down to 350 Watts, and there is an extra 150 Watts of hysteresis in place so that the immersion will not be turned off when the power taken by the devices using electricity in the home fluctuates a bit.

If you are interested in this type of modified immersion controller, please email neil@reuk.co.uk with details of your electricity meter(s), immersion power rating, and solar array power rating.

Surplus PV Solar Immersion Controller for Solid State Relay

Pictured below is a modified version of our standard Surplus Solar PV Immersion Controller a device designed to use electricity generated by photovoltaic solar panels to power a water heating immersion element rather than exporting the electricity to the grid.

REUK Immersion controller for Solid State Relay (SSR)

This version works identically to the standard unit, the only difference is that instead of having a mains switching relay on the circuit board itself, there is a 12VDC output when then solar generation is above the user-set threshold which can be used to control a solid state relay or other relay in situations where the 16A relay we usually supply would not be up to the job – e.g. for a very large immersion element.

25A solid state relayPictured above for example is a 25A rated SSR (solid state relay). The 12VDC output from our controller connects to the terminals labelled 3 (+) and 4 (-), and then the mains live cable is switched through terminals 1 and 2.

Click to buy Solid State Relays – prices start from around £3 delivered in the UK, and send an email to neil@reuk.co.uk if you are interested in this modified version of the immersion controller.

Project of the Day – Power Inverter Fan Thermostat

inverter fan themostat

Today we have been working on a small thermostat controller for the fan in a 24VDC power inverter. The existing fan was too noisy and on constantly, and was replaced with a quiet and more efficient fan to keep the power inverter internals cool with the above thermostat added so that the fan is only powered when necessary.

The temperature sensor used (not pictured) is an LM335.

The user can programme this thermostat to automatically turn on the fan at their choice of temperature, and the fan will then automatically turn off when the temperature has fallen by 5 or more degrees from that level.

New Mini 12 Volt Regulator with Fuse and Switch Terminals

mini 12v regulator with fuse and switch terminals

Pictured above is the new miniaturised version of our old (but still popular) 12 Volt Regulator with Fuse and Switch terminals designed to protect LED lighting and other sensitive electronics from damage when connected directly to a 12V battery which may give out up to 15 Volts when being charged (whether by solar, wind, or plug-in charger).

The new version is just 45mm x 45mm x 20mm in size – less than half the size of the original and also a bit cheaper too and still supplied with a couple of spare fuses. Click here for more details or to buy: Mini 12 Volt Regulator with Fuse and Switch Terminals.