Technical Note — Electric Pump Control

Peter Edmonds

Created: ; updated: .


The Observant C3 Platform can remotely start and stop an electric motor by activating the contactor that supplies power to the motor. Electric pumps interface with the platform using one or two DC coil relays depending on configuration. In most implementations one or two normally open DC coil relays are used to control an appropriately rated high voltage contactor which can establish or interrupt the power supply to the pump motor. 



The digital outputs of the C3 can be used to control contactors associated with the running of electric pumps:  

  • DC Motor Pump controlled with relay closure.*
  • AC Induction Motor Pump controlled with relay closure.*



* On-site installation including starter (if applicable), drive (if applicable), contactor, emergency stop and appropriate fail-safe circuits not provided by Observant. Observant C3 will interface with 12 VDC relay coil for on-off control. 

Safety Disclaimer
Pump must be installed by a qualified electrician and/or mechanic. The connection of a C3 to an electric motor should only be performed by an experienced electrician. Fail-safe circuits must be included that are appropriate for remote operation. Remote monitoring and/or control through the Observant platform does not constitute or replace hard-wired safety shutoffs. An Emergency Stop button and appropriate power disconnects should always be in place at the same location as the motor.


Choosing a Control Circuit

Electrical motor contactors are typically controlled by high-voltage AC supplies. These need to be controlled by the nominal 12 VDC outputs of the C3 by using 12 VDC coil, mains-rated, contact relays.

There are two possible configurations for the control circuit :

  • Latching Start/Stop Control
  • RUN-OFF-AUTO with Non-Latching Relay Control Circuit

For the RUN-OFF-AUTO non-latching relay control circuit, the C3 uses one output to continuously energize a 12 VDC non-latching relay when the motor is running. As a result, this configuration should not be used if the pump needs to run for longer periods of time. This is because it will draw power whenever the pump is active and can, therefore, significantly drain a Field Unit's battery unless it is powered from mains power.

In a latching Start/Stop control circuit, the C3 uses two outputs to control two 12 VDC coil relays. Both relays can be pulsed by the C3 to emulate momentary switches. Since this configuration requires only short pulses from the C3 to operate, it should be used if a pump needs to be on for greater than 3 hours a day and the Field Unit is powered via a solar panel. 

However, if the pump is on for less than 3 hours a day OR the Field Unit is to be powered from mains power (ie. not reliant on solar), then a non-latching relay control circuit can be used. This provides greater safety since a non-latching relay will switch to the default 'Off' state if it fails, whereas a latching relay circuit will be unable to switch to the 'Off' state if it fails while it's On.


Supported Devices & Installation 

For relay specifications and installation instructions, refer to the Tech Note of your chosen control circuit configuration :


Monitoring Pump Status

You can combine the electric pump control solution with a complementary monitoring solution that will provide feedback about the pump's operation. The following sections describe the various monitoring solution. If you're unsure about which solution best suits your needs, contact our Support Team   

Monitoring On/Off Status

Flow switches and/or pressure switches can be connected to the C3's Dual-Purpose Digital/Analog Inputs to monitor pump intake and output. For installation details and specifications refer to :

Continuous Flow/Pressure Monitoring 

Alternatively, complementing the Pump Control solution with the Flow and Line Pressure Monitoring solution will give you the added capability of monitoring the flow and/or pressure values to get a complete picture of your system. For further details refer to :

Manuals, Links and Downloads

Related Solutions

The Technical Note, Electric Pump Control is available for printing or downloading in either letter (OBS-USR-TN004-R1-LTR) or A4 (OBS-USR-TN004-R1-A4) format.

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