Project of the Day – Well Pump Float Switch Fail Safe Controller

Today we put together a fail safe protection system for a well pump used to fill a header tank for a domestic water supply. This fail safe is designed to be connected in series with the existing pump controlling Stuart Turner float switch to cut the power to the pump if the header tank is about to overflow. If the primary float switch sticks or otherwise fails and does not turn off the pump when it should, the fail safe system will override it and turn off the pump.

The heavy duty MONO pump in this particular system is rated at 1hp (0.73kW) and pumps water up from from a well 15 metres below the header tank at a rate of 10 gallons per minute. Therefore a float switch failure and the subsequent flood of water overflowing the header tank and going through the house could be extremely serious and costly.

fail safe protection for well pumpPictured above is the solution we came up with. A secondary float switch is fitted into the header tank just above the existing float switch. In normal operation, this secondary float switch is closed which keeps a relay on our controller closed through which the mains live passes on its way to the existing primary float switch.

If the level of the water in the header tank reaches the secondary float switch, the float rises up which opens the switch. This causes the relay on our controller to open cutting the live connection to the primary float switch and therefore to the pump keeping it turned off.

button with integrated LED

We have added a button (pictured above) which under normal operation can be used to test the fail safe for peace of mind – pressing the button causes the relay to open and the LED in the button to light up for a few seconds.

If the fail safe is triggered by high water then the pump turns off and the LED in the button turns on to give a visual warning that something has gone wrong. The home owner must then check the header tank, remove any obstruction from the primary float switch, confirm that float switch is working reliably, and then press the button to manually reset the fail safe. There is no automatic reset of the fail safe as this would be far too risky – flood damage was averted and now manual intervention is a must.

12V Regulator with Low Voltage Disconnect (LVD)

Pictured below is our new 12V regulator with integrated Low Voltage Disconnect (LVD) battery protection for LED lighting applications.

12v low voltage disconnect (LVD) with 12V low dropout regulator outputThis device will supply power to up to 10 Watts of LED lighting at a safe voltage when connected to a 12V battery while at the same time protecting the battery from being excessively discharged and therefore having its lifespan reduced. It is a combination of our established 12V regulator and low voltage disconnect technologies.

Connections for 12V regulator with low voltage disconnect - REUK

We currently only have this item for sale here: 12V regulator with LVD, but we will be adding it to the REUK Shop soon.

Solar Water Heating Pump Controller with Solid State Relay

A few days ago (link to the article) we described our new solar water heating pump controller based around our standard 2013 controller, but fitted with waterproof digital temperature sensors for use in pools, hot-tubs, and so on.

solar water heating controller for pool with solid state relay

Pictured above is a second version which we subsequently made for a special order which is designed to control an solid state relay (SSR) instead of the usual on board mechanical relay since this was to be used with a large mains powered pump which pushes water from a swimming pool in France around 12 solar water heating panels.

The type of relay pictured has four screw-on terminals. To close the relay you supply <20mA of 3-32VDC to two of the terminals, and that effectively shorts out the other two terminals (though in reality it does not ‘short out’, it just allows AC voltage of 24-380 VAC to pass internally through it into one terminal and out of the other).

As they are not mechanical, solid state relays tend to last longer, switch faster, and use less power. They do however generate/release some heat, they are more expensive, and this type of external relay needs to be housed in a suitable enclosure as it switches mains electricity.

Click here find out more or buy a solid state relay now. Prices start from around £5 each.

Project of the Day – Thermostat Controller for Innovative AC Cooler

Today we have worked on a thermostatic controller which is used to open a solenoid valve when the temperature measured by a sensor exceeds a user set level.

programmable thermostat to control a 12V DC solenoid valve

This controller is for a telecoms company which have servers in a data centre which are cooled by air conditioning (AC). The AC units are located outside an office in an area from which heat cannot escape, and so it builds up eventually causing the AC units to fail.

Four years ago when we first heard from this company, they had set up a Hozelock irrigation system on a timer to spray water mist around the AC units from 8am to 7pm on workdays, but they wanted something thermostatically controlled so that water would only be used to cool the AC units when it was actually necessary.

12 volt dc solenoid valveWe provided them with a complete solution including enclosure, 12VDC solenoid valve, controller, and a waterproof temperature sensor (an LM335 we sealed with epoxy into stainless steel tubing – the method for its manufacture is explained here: Make a Waterproof Temperature Probe). This has worked very well ever since reducing the peak temperature of the data centre by 6 degrees Celcius. However, after 4 years in all weathers the temperature sensor has started to become unreliable, and the company also wanted some modifications to the programming of the controller so that the water mist can be triggered at lower temperatures.

The new controller which was pictured above now uses a commercial waterproof DS18B20 digital temperature sensor and we also substituted a MOSFET for the relay which was on the original unit so that the whole controller is now solid state. This controller should help to keep the AC units cool for a good few years to come.

The use simply uses the button on the controller to set the threshold temperature above which the misting is to be turned on (settable in 1 degree steps from 25 degrees Celcius). After 10 seconds of the temperature being measured over this threshold the misting will start, and it will run until the temperature falls by a couple of degrees.

New Solar Water Heating Pump Controller with Waterproof Sensors

Pictured below is our new solar water heating pump controller with waterproof sensors. It is heavily based around our standard 2013 Solar Water Heating Pump Controller, but modified to use waterproof DS18B20 digital temperature sensors in place of the LM335 analog temperature sensors we normally use.

Solar water heating pump controller with waterproof temperature sensorsAs it can take up to 0.75 seconds for the controller to get a reading from a DS18B20 sensor, and since sometimes digital sensors output spurious data, there have been some modifications made to the logic which decides when the circulation pump should be turned on and off, but all the original functionality of the 2013 controller has been retained.

This controller is ideally suited for use with swimming pool and hot tub solar water heating systems as well as many other applications where having waterproof temperature sensors is essential.

We will shortly be adding this new product to the REUK Shop, but in the meantime, if you are interested in purchasing this controller or something similar to meet your exact requirements, email neil@reuk.co.uk.