Water Pump Relay Controller Circuit Schematic

Water reservoir automatic level control, Simple circuitry - 12V supply

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By means of a Relay, employed to drive a water pump, this circuit provides automatic level control of a water reservoir or well. The shorter steel rod is the "water high" sensor, whereas the longer is the "water low" sensor. When the water level is below both sensors, IC1C output (pin #10) is low; if the water becomes in contact with the longer sensor the output remains low until the shorter sensor is reached. At this point IC1C output goes high, Q1 conducts, the Relay is energized and the pump starts operating.

Now, the water level begins to decrease and the shorter sensor will be no longer in contact with the water, but IC1C output will be hold high by the signal return to pin #5 of IC1B, so the pump will continue its operation. But when the water level falls below the longer sensor, IC1C output goes low and the pump will stop. SW1 is optional and was added to provide reverse operation. Switching SW1 in order to connect R3 to pin #11 of IC1D, the pump will operate when the reservoir is nearly empty and will stop when the reservoir is full. In this case, the pump will be used to fill the reservoir and not to empty it as in the default operating mode.

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Circuit diagram:

Water Pump Relay Control Circuit Diagram

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Parts:

R1 = 15K - 1/4W Resistors
R2 = 15K - 1/4W Resistors
R3 = 10K - 1/4W Resistor
R4 = 1K - 1/4W Resistor
D1 = LED - any type and color
D2 = 1N4148 - 75V 150mA Diode
Q1 = BC337 - 45V 800mA NPN Transistor
IC1 = 4001 Quad 2 Input NOR Gate CMos IC
SW = SPDT Toggle or Slide Switch (Optional)
RL1 = Relay with SPDT 2A @ 230V switch
Coil Voltage 12V - Coil resistance 200-300 Ohm
Two steel rods of appropriate length

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Notes:

• The two steel rods must be supported by a small insulated (wooden or plastic) board.
• The circuit can be used also with non-metal tanks, provided a third steel rod having about the same height of the tank will be added and connected to the circuit's negative ground.

Momentary Switch Teamed With Latching Relay circuit and explanation

This circuit allows an SPST momentary pushbutton to act as a push-on push-off switch, using a DPDT latching (bi-stable) relay. It was originally intended to allow a single pushbutton switch on the dash of a vintage car to provide a latched function. The relay only draws current when it is being switched. At other times, the only current drain on the 12V supply is the leakage current of one 22µF capacitor, which is very low. It works as follows.

Assume that initially the latching relay is in the reset state, with pins 4 and 6 connected together. In this state, C2 charges up to +12V via 2.2kO resistor R2 while capacitor C1 remains discharged as it is not connected to the 12V supply. If S1 is pressed, C2 discharges via the relay’s “set” coil, diode D2 and S1. This switches the relay into its set position, connecting pins 4 and 8. C1 then begins to charge via R1. While S1 is being held down, the relay does not return to the reset position because the current supplied via R1 is insufficient for the coil to latch the armature. As soon as S1 is released, current no longer flows though the coil so C1 can finish charging, ready for the next button press.

Circuit diagram:

Momentary Switch Circuit Diagram Teamed With Latching Relay

Once the relay has switched and C1 has finished charging, pressing S1 again causes the relay to switch back to the reset state via the same process. The unused set of relay contacts can be used as an SPST or SPDT switch. The circuit as shown has been tested with the Jaycar SY4060 relay. It will work with other DPDT twin-coil latching relays but the resistor and capacitor values may need to be adjusted to suit. Relays with lower resistance coils will need larger value capacitors and smaller value resistors.
Author: Merv Thomas - Copyright: Silicon Chip Electronics Magazine

Energy Saver Relay Coil circuit and explanation

Some relays will become warm if they remain energized for some time. The circuit shown here will actuate the relay as before but then reduce the ‘hold’ current through the relay coil current by about 50%, thus considerably reducing the amount of heat dissipation and wasted power. The circuit is only suitable for relays that remain on for long periods. The following equations will enable the circuit to be dimensioned for the relay on hand: R3 = 0.7 / I Charge time = 0.5 × R2 × C1 Where I is the relay coil current. After the relay has been switched off, a short delay should be allowed for the relay current to return to maximum so the relay can be energized again at full power. To make the delay as short as possible, keep C1 as small as possible. In practice, a minimum delay of about 5 seconds should be allowed but this is open to experimentation.

Circuit diagram:

Relay Coil Energy Saver Circuit Diagram

The action of C2 causes the full supply voltage to appear briefly across the relay coil, which helps to activate the relay as fast as possible. Via T2, a delay network consisting of C1 and R2 controls the relay coil current flowing through T1 and R3, effectively reducing it to half the ‘pull in’ current. Diode D2 discharges C1 when the control voltage is Low. Around one second will be needed to completely discharge C1. T2 shunts the bias current of T1 when the delay has elapsed. Diode D1 helps to discharge C1 as quickly as possible. The relay shown in the circuit was specified at 12 V / 400 ohms. All component values for guidance only.

Author: Myo Min - Copyright: Elektor July-August 2004

Handy Time Delay With Relay Output circuit and explanation

This circuit is designed to provide delayed relay switching action at power on. The delay is a function of the time constant produced by the combination of R1 and C1. At power on, C1 charges slowly via R1 and the coil of the relay. When the voltage across C1 exceeds both the base-emitter voltage of Q1 and the gate trigger voltage of the SCR, gate current flows. This fires the SCR and switches on the relay. At power off, diode D1 rapidly discharges C1 through the 100O resistor, so ensuring that every time the circuit is restarted, as in a temporary outage, the delay time is maintained.

Circuit diagram:

Time Delay Circuit Diagram With Relay Output

Just about any NPN transistor can be used for Q1, since after SCR1 fires, it is effectively out of the circuit. In fact, the only part that’s still active after SCR1 turns on is the relay. You can’t get much simpler than that! This circuit can be used to delay speaker turn-on, so avoiding the "thump" that occurs in some stereo systems at power on. A 5-second delay is enough for this application, requiring approximately 560kO for R1 and 10µF for C1. Another application might be as a motor protector in a short power outage.

Author: R. Besana - Copyright: Silicon Chip Electronics

Relay Selector Pushbutton circuit and explanation

This circuit was designed for use in a hifi showroom, where a choice of speakers could be connected to a stereo amplifier for comparative purposes. It could be used for other similar applications where just one of an array of devices needs to be selected at any one time. A bank of mechanically interlocked DPDT pushbutton switches is the simplest way to perform this kind of selection but these switches aren’t readily available nowadays and are quite expensive. This simple circuit performs exactly the same job. It can be configured with any number of outputs between two and nine, simply by adding pushbutton switches and relay driver circuits to the currently unused outputs of IC2 (O5-O9).

Gate IC1a is connected as a relax-ation oscillator which runs at about 20kHz. Pulses from the oscillator are fed to IC1b, where they are gated with a control signal from IC1c. The result is inverted by IC1d and fed into the clock input (CP0) of IC2. Initially, we assume that the reset switch (S1) has been pressed, which forces a logic high at the O0 output (pin 3) of IC2 and logic lows at all other outputs (O1-O9). As the relay driver transistors (Q1-Q4) are switched by these outputs, none of the relays will be energised after a reset and none of the load devices (speakers, etc) will be selected. Now consider what happens if you press one of the selector switches (S2-S5, etc). For example, pressing S5 connects the O4 output (pin 10) of IC2 to the input (pin 9) of IC1c, pulling it low.

Circuit diagram:

Pushbutton Relay Selector Circuit Diagram

This causes the output (pin 10) to go high, which in turn pulls the input of IC1b (pin 5) high and allows clock pulses to pass through to decade counter IC2. The 4017B counts up until a high level appears at its O4 output. This high signal is fed via S5 to pin 9 of NAND gate IC1c, which causes its output (pin 10) to go low. This low signal also appears on pin 5 of IC1b, which is then inhibited from passing further clock pulses on its other input (pin 6) through to its output (pin 4), thus halting the counter. So, the counter runs just long enough to make the output connected to the switch that is pressed go high. This sequence repeats regardless of which selector switch you press, so the circuit functions as an electronic interlock system.

Each relay driver circuit is a 2N7000 FET switch with its gate driven from one output of IC2 via a 100W resistor. The relay coil is connected from the drain to the +12V supply rail, with a reverse diode spike suppressor across each coil. If you want visual indication of the selected output, an optional indicator LED and series resistor can be connected across each relay coil, as shown. For selecting pairs of stereo speakers, we’d suggest the use of relays like the Jaycar SY-4052. These operate from 12V and have DPDT contacts rated for 5A. Note that although four selector switches are shown in the circuit, only two relay drivers are shown because of limited space. For a 4-way selector, identical relay drivers would be driven from the O2 and O3 outputs of IC2.

Author: Jim Rowe - Copyright: Silicon Chip Electronics

Output Relay Delay Audio Amplifier circuit and explanation

This is a simple circuit which I built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier. The idea of the circuit is wait around 5 seconds ofter the power up until the speakers are switched to the amplifier output to avoid annoying "thump" sound from the speakers. Another feature of this circuit is that is disconnects the speaker immediately when the power in the amplifier is cut off, so avoiding sometimes nasty sounds when you turn the equipments off.

Circuit diagram:

Audio Amplifier Output Relay Delay Circuit Diagram

Component list
C1 = 100 uF 40V electrolytic
C2 = 100 uF 40V electrolytic
D1 = 1N4007
D2 = 1N4148
Q1 = BC547
R1 = 33 kohm 0.25W
R2 = 2.2 kohm 0.25W
RELAY 24V DC relay, coil resistance >300 ohm

Circuit operation:

Then power is applied to the power input of the circuit, the positive phase of AC voltage charges C1. Then C2 starts to charge slowly through R1. When the voltage in C2 rises, the emitter output voltage of Q1 rises together with voltage on C2. When the output voltage of Q2 is high enough (typically around 16..20V) the relay goes to on state and the relay witches connect the speakers to the amplifier output. It takes typically around 5 seconds after power up until the relay starts to conduct (at absolute time depends on the size of C2, relay voltage and circuit input voltage). When the power is switched off, C1 will loose it's energy quite quickly. Also C2 will be charged quite quickly through R2. In less than 0.5 seconds the speakers are disconnected from the amplifier output.

Notes on the circuit:
This circuit is not the most accurate and elegant design, but it has worked nicely in my small home-built PA amplifier. This circuit can be also used in many other applications where a turn on delay of few seconds is needed. The delay time can be increased by using bigger C2 and decreased by using a smaller C2 value. Note that the delay is not very accurate because of simplicity of this circuit and large tolerance of typical electrolytic capacitors (can be -20%..+50% in some capacitors).

Author: Tomi Engdahl

How To Reduce Relay Power Consumption circuit diagram and explanation

Relays are often used as electrically controlled switches. Unlike transistors, their switch contacts are electrically isolated from the control input. On the other hand, the power dissipation in a relay coil may be unattractive for battery-operated applications. Adding an analogue switch lowers the dissipation, allowing the relay to operate at a lower voltage. The circuit diagram shows the principle. Power consumed by the relay coil equals V2/RCOIL. The circuit lowers this dissipation (after actuation) by applying less than the normal operating voltage of 5 V. Note that the voltage required to turn a relay on (pickup voltage)is usually greater than that to keep it on (dropout voltage).


In this respect the relay shown has specifications of 3.5 and 1.5 V respectively, yet the circuit allows it to operate from an intermediate supply voltage of 2.5 V. Table 1 compares the relay’s power dissipation with fixed operating voltages across it, and with the circuit shown here in place. The power savings are significant. When SW1 is closed, current flows through the relay coil, and C1 and C2 begin to charge. The relay remains inactive because the supply voltage is less than its pickup voltage. The RC time constants are such that C1 charges almost completely before the voltage across C2 reaches the logic threshold of the analogue switch inside the MAX4624 IC.


When C2 reaches that threshold, the on-chip switch connects C1 in series with the 2.5 V supply and the relay coil. This action causes the relay to be turned on because its coil voltage is then raised to 5 V, i.e., twice the supply voltage. As C1 discharges through the coil, the coil voltage drops back to 2.5 V minus the drop across D1. However, the relay remains on because the resultant voltage is still above the dropout level (1.5 V). Component values for this circuit depend on the relay characteristics and the supply voltage. The value of R1, which protects the analogue switch from the initial current surge through C1, should be sufficiently small to allow C1 to charge rapidly, but large enough to prevent the surge current from exceeding the specified peak current for the analogue switch.

The switch’s peak current (U1) is 400 mA, and the peak surge current is IPEAK = (VIN – VD1) / R1 + RON) where RON is the on-resistance of the analogue switch (typically 1.2 Ω). The value of C1 will depend on the relay characteristics and on the difference between VIN and the pickup voltage. Relays that need more turn-on time requires larger values for C1. The values for R2 and C2 are selected to allow C1 to charge almost completely before C2’s voltage reaches the logic threshold of the analogue switch. In this case, the time constant R2C2 is about seven times C1(R1 + RON). Larger time constants increase the delay between switch closure and relay activation. The switches in the MAX4624 are described as ‘guaranteed break before make’. The opposite function, ‘make-before break’ is available from the MAX4625. The full datasheets of these interesting ICs may be found at http://pdfserv.maxim-ic.com/arpdf/MAX4624-MAX4625.pdf

Solar Relay circuit diagram and explanation

With extended periods of bright sunshine and warm weather, even relatively large storage batteries in solar-power systems can become rather warm. Consequently, a circuit is usually connected in parallel with the storage battery to either connect a high-power shunt (in order to dissipate the excess solar power in the form of heat) or switch on a ventilation fan via a power FET, whenever the voltage rises above approximately 14.4 V. However, the latter option tends to oscillate, since switching on a powerful 12-V fan motor causes the voltage to drop below 14.4 V, causing the fan to be switched off.

In the absence of an external load, the battery voltage recovers quickly, the terminal voltage rises above 14.4 V again and the switching process starts once again, despite the built-in hysteresis. A solution to this problem is provided by the circuit shown here, which switches on the fan in response to the sweltering heat produced by the solar irradiation instead of an excessively high voltage at the battery terminals. Based on experience, the risk of battery overheating is only present in the summer between 2 and 6 pm. The intensity of the sunlight falling within the viewing angle of a suitably configured ‘sun probe’ is especially high precisely during this interval.

This is the operating principle of the solar relay. The trick to this apparently rather simple circuit consists of using a suitable combination of components. Instead of a power FET, it employs a special 12-V relay that can handle a large load in spite of its small size. This relay must have a coil resistance of at least 600 Ω, rather than the usual value of 100-200 Ω. This requirement can be met by several Schrack Components relays (available from, among others, Conrad Electronics). Here we have used the least expensive model, a type RYII 8-A printed circuit board relay. The light probe is connected in series with the relay. It consists of two BPW40 phototransistors wired in parallel.

Solar Relay Circuit Diagram

The type number refers to the 40-degree acceptance angle for incident light. In bright sunlight, the combined current generated by the two phototransistors is sufficient to cause the relay to engage, in this case without twitching. Every relay has a large hysteresis, so the fan connected via the a/b contacts will run for many minutes, or even until the probe no longer receives sufficient light. The NTC thermistor connected in series performs two functions. First, it compensates for changes in the resistance of the copper wire in the coil, which increases by approximately 4 percent for every 10 ºC increase in temperature, and second, it causes the relay to drop out earlier than it otherwise would (the relay only drops out at a coil voltage of 4 V).

Depending on the intended use, the 220-Ω resistance of the thermistor can be modified by connecting a 100-Ω resistor in series or a 470-Ω resistor in parallel. If the phototransistors are fastened with the axes of their incident-angle cones in parallel, the 40-degree incident angle corresponds to 2 pm with suitable solar orientation. If they are bent at a slight angle to each other, their incident angles overlap to cover a wider angle, such as 70 degrees. With the tested prototype circuit, the axes were oriented nearly parallel, and this fully met our demands. The automatic switch-off occurs quite abruptly, just like the switch-on, with no contact jitter.

This behaviour is also promoted by the NTC thermistor, since its temperature coefficient is opposite to that of the ‘PTC’ relay coil and approximately five times as large. This yields exactly the desired effect for energising and de-energising the relay: a large relay current for engagement and a small relay current for disengagement. Building the circuit is actually straightforward, but you must pay attention to one thing. The phototransistors resemble colourless LEDs, so there is a tendency to think that their ‘pinning’ is the same as that of LEDs, with the long lead being positive and the short lead negative. However, with the BPW40 the situation is exactly the opposite; the short lead is the collector lead. Naturally, the back-emf diode for the relay must also be connected with the right polarity. The residual current on cloudy days and at night is negligibly small.