Pump Control Switch

Logic prevents two pumps from operating simultaneously.

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Off-grid, an inverter provides AC power for all devices in my cabin. When starting the inverter, it is sometimes necessary to shut-off the well pump in order to allow the septic pump to start and run. Mutual starting of the two pumps is not possible as the inverter will not start.

With several inductive loads, it becomes desirable to prevent concurrent switching that can stress components, and reduce life of the inverter.

A simple 2-load configuration does not require anything beyond the SPDT switch to prevent concurrent operation of two inductive loads, particularly at startup. Adding just another load however, adds complexity, presenting a problem worth solving with prioritization. I have had a priority multiplexer logic component determined for a few years without a serious application.
THIS may be the application for prioritization...

Living Off-Grid in Wales UK - (inverter overloading confirmed)

LAST UPDATE: 3-21-16 ATF1500A logic infusion. Resistor arrays? Open area is for DC supply components. Compare to the picture at the bottom.

Achieved WINCUPL compilations of three PAL devices. ATF1500T allows consolidation desired for concise design, reprogrammable, configurable, easily manufactured. Am now working to consolidate this effort to include the WINCUPL output for the ATF1500T, and other components, associated EAGLE components, and LTSpice simulations.

WINCUPL ATF1500T logic (below)

Improved logic integration resulted from attempt to design the board for testing the time base. I realized the logic gates can be added to the programmable logic array device. I need to port this part of the project out, but it makes the build much better for manufacture.

Result is a simpler-looking design. I decided the time base is not easily implemented using OTS parts. When seen this way (below) it looks pretty good.I'm looking for someone to program the logic.

BTW: A nice feature of the Inductive Load Center device is that it becomes practical to then disable the controlled devices, favoring use of power tools without interruption from a pump or other load. Just a flip of a switch can eliminate inconvenience, and resetting the inverter.

1-22-16 Progress at an implemtation of the retriggerable, free-running 2-phase monostable. (I could not get a 555 simulation to retrigger. I had to try.) Thus, I simplified my implementation, consolidating, using two LT1841 comparators. There can be modes: free-running retriggerable (VLFO), gated retriggering, synchronized mode, and single shot mode. I created a simulation using a short 10ms sync pulse with ten second duty pulse. For the model to work as intended, the incoming sync pulse must be debounced, and less than 10ms. This is not a bad building block, a variation of the 555, easy to use, and probably capable of doing a few things for which the 555 is not well suited.

BTB1S Drawing is of an implementable version. Propagation delay puts a trigger on inverting input, driving comparator to runaway. Output charges timing capacito. Not sure how it discharges... this can actually be implemented.

ILC PROTO SOURCE CODE I added a software implementation of the DUMMY CARD feature. This code compiles, and will allow me to create a tool for tinkering with user interface with simple LED's and buttons. It will be possible to implement a program mode to adjust delays. Am thinking to try thumb-wheel resistor setup... I will add some comments, and document the DUMMY implementation.

Am looking at software implementation of the DUMMY CARD for Arduino.

Briefly, it presents a user interface problem. Looks like a solution begs for an adjustable analog input value for each activated DUMMIED sensor. Is easy to call DCPRQ_update to update PRQ status if the delay is expired. This call would be in an if-else that determines if the DC option is in use. The function will require external values, and simply use them to return a result for each installed DC option. This is to determine downtime delay between PRQ requests. Example, it could be twenty minutes for the sensorless septic pump. The delay value could be adjusted with a voltage on one of the analog inputs.

In the function below, DC_ltime is read when a new DC_PRQ delay is begun. The time value is stored with the desired delay_PRQ value and are passed into the function to be used and compared with present time. Result is HIGH or LOW, and used to update the associated PRQ_State value.

int DCPRQ_update(unsigned long DC_ltime, long delay_PRQ ) {

	unsigned long ptime = 0;
	long Timer = 0;

	ptime = millis();   
	Timer = ptime - DC_ltime;

	if (Timer >= delay_PRQ){return HIGH;}
	return LOW;
Another possibility is to provide the hardware DC option based on a 555 timer implementation. I worried that it might be difficult to implement the retriggerable 1SHOT, but a 555 can be used, retriggerable after the... Read more »


FLOAT switches power to pump, but with LC is translated to logic PRQ signal. PUMP actuates via dedicated relay and line.

JPEG Image - 70.61 kB - 09/18/2017 at 02:16



AC to LOGIC conversion. Half-wave.

Portable Network Graphics (PNG) - 16.74 kB - 09/18/2017 at 02:03




JPEG Image - 43.97 kB - 09/17/2017 at 21:28



REVISED TO show missing inverted inputs to logic. PLD source is correct.

JPEG Image - 92.18 kB - 09/17/2017 at 15:04



S I M P L I F I E D Source includes chip diagram.

pld - 2.03 kB - 09/16/2017 at 23:23


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  • S I M P L I F I E D

    C. Prichard3 days ago 0 comments
  • Dual Purpose Circuit

    C. Prichard08/14/2015 at 17:34 0 comments

    UPDATE: 9-11-15

    Prioritized Production, or processing of any kind can possibly benefit by using a controller to automate which "jobs" are placed into sequence. In this application, the processing is limited, filling in low priority "jobs" even as higher priority "on demand job processing" is most profitable. The circuit for the Inductive Load Center can be applied to control automated gates to a conveyor system...

    Prioritized Zonal Heating seems a perfect second application for the circuit that prevents concurrent switching of inductive loads..

    Prioritization can restrict power to manage slab heat, circulating glycol where needed. Winter heating of the insulated garage can be minimal, low priority. A basement, and two other areas can be prioritized. Using one circulating pump, valves can be controlled to save energy.

    The Zonal Heating application application would use the same circuit, easily configured for different delays.

    An interesting possibility could be explored in programming, considering the temperature differential between the desired value, and actual. Controller response might vary with deviation from settings to put actual temperature back within tolerances. This would only be possible if adequate heat source is available. Software can expand on prioritization, to provide improvement. If this the Zonal Heating application can be improved with programming, it may be easier to find additional applications, approaching them similarly.

  • Schematic and Board

    C. Prichard06/23/2015 at 14:32 0 comments

    Pins 1, 2 are used to loop the ground connection from the 12V power input to pressure switch contacts, and back to the relay. When the pressure switch closes, and relay is energized, AC power switches from Pin 3 to PUMP 1 connected to X1 - 1.

    The device, approximately 1.5x1.5 inches can be encapsulated with pigtails, or made in such a way it can be mounted on/in an electrical enclosure commonly used in construction.

    A version with softstart may be useful, guaranteeing the relay cannot operate for a period of time, or until an input enable signal is received.

    I could call it an "EXCLUSIVITY POWER SWITCH" or "NON-CONCURRENCY SWITCH." The switch shown is rated for 16 amps.

  • Simplification

    C. Prichard06/22/2015 at 16:57 0 comments

    Wiring my cabin for state inspection, I realized AC neutral will be bonded at Earth potential. Design simplification will be to connect the AC neutral wires, and switch only the 120VAC power (black,) lines. The switch component can be an SPDT switch, the normally closed side connected to my septic pump. This will simplify the design, and installation.

    That AC neutral is bonded to Earth for safety anyway, precludes thinking there may be a "safety reason" to switch BOTH hot and neutral lines as in pump switches...

    I guess it is useful to look at connecting the deep well pressure switch directly to the SPDT relay. When triggered ON, the well pump operates. Otherwise, power is connected through the normally closed connection to the other (septic pump and sensor,) pump. This design uses no logic, or one-shot timing pulse and will mimic functionality of a grid-tied system that allows both pumps to operate simultaneously. One will hardly notice any difference.

    I'll try this first, as it is simple, and it may be in existence in some form. I'll draw the schematic in EAGLE and look at doing the board. An ample 12V wall wart supply could be used to provide power for the SPDT relay which will also be wired directly to the pressure switch.

    Right now, my new installation has each pump connected to its own 15-amp breaker in my main panel of six. Simplification, and use of my idea to wire the SPDT switch will allow use of a single breaker, and eliminate having to pay attention, keeping the water switched off to avoid startup conflicts.

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C. Prichard wrote 07/29/2015 at 16:08 point

7-29-15 If anyone wants to contribute to this topic, I think this project merits being divided into two projects. One, simply offers the SPDT exclusivity to prevent two loads from being switched concurrently. The spin-off project is the prioritizing, or Inductive Load Center with the patentable hardware design using the PMUX in a PAL, and the back-to-back re-triggerable monostable concoction, as simulated. Another part of this project is to present a programmable development piece of hardware which can function as the Inductive Load Center, as well as other programmed devices, controlling any type of device. 

Prioritization offers a way to allocate power to prevent overloading, The PMUX may be reprogrammed to provide other logic. Benefit of all this is that once understood, the device can be leveraged to work in combination with solar power, batteries, and inverters to provide adequate solutions to off-grid power systems that may include several inductive loads.

Option to implement the simple hardware solution, or to include processing and sensing of other input may interest a developer that sees potential to profit from production of a line of these devices, aimed initially at preventing concurrent switching, and overloading.

Once the spin-off project is created, it will receive more attention as it will include Arduino for the stated benefit to development of new applications...

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