[SOLVED] Electronic Low Level Trip, Aquarium Sump Pump

Firstly, I'm not well versed in the electronics world.

The goal of my home project is to provide an electronic shutoff for my aquarium sump pump when the level gets too low.

I'm looking at using a float switch to trigger a 9V power source (battery), the 9V signal will then trigger a normally closed relay hooked up to my 120VAC pump.

This would work well if there were not water in the discharge piping of the sump pump..

as soon as the low level switch is activated the pump would stop and the water in the line would flow back into the sump and the level switch would reset turning back on the pump.. this leads to the pump being cycled on and off every few seconds (not good)

A solution I've been investigating is to somehow delay the activation of the NC relay.

If the NC relay was not activated until about 3 seconds after the level switch was triggered then the level would get low enough so as not to reset the level switch.

TLDR:

Looking for some way to delay a 9V signal from starting once connected for about 3 seconds, then the circuit should remain energized until the 9V source is disconnected.

hi akuno,
Its possible to add a 3Sec delay before switching Off the pump, but have you considered a mechanical solution.?
A small non return valve at the lower end of the pipe.
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I have considered that, and it may work well at first.

The issue is the aquarium service i'm operating in. The check valve may not have a 100% seal after a few months in the aquarium water has produced biological fouling. The valve would slow down the interval of pump restarts, but may not prevent them completely.

Also, the introduction of the check valve will increase the total developed head required to deliver the water back to the return tank and reduce the maximum flow rate attainable.

I would prefer an electronic solution. I'm also attaching an annunciator in parallel with the trip mechanism to inform of level/pump trip status.

I will continue to look into a mechanical solution as well though.

Thanks for the reply

Hi,
You could use the 9v signal to control a MOS FET transistor Gate via diode into a 3 sec Res/Cap time out, the relay would be in the Drain of the MOSFET. [say a 2N7000]

Do you follow that OK.?
E

EDIT:
This is one option, the LTSpice sim shows the level switch Opening but the relay remains energised for ~1 second, to increase the On time increase the 1uF to say 3.3uF

The 400R represents the relay coil.

I'm not sure what i'm looking at.

so, i can see what V2 and Relay 400 are in the diagram.

I'm confused at what is happening in the lower left side of the diagram with V1 and line sw1. it looks like it's representing the level switch

I was just assuming the level switch acted a lot like a standard toggle switch isolating or connecting the source from the circuit.
( https://www.zoro.com/i/G2923024/ )

I'm looking at a relay like ( https://www.newark.com/te-connectiv...12/power-relay-dpdt-12vdc-15a-plug/dp/17M0327 )

Also, from the graphs of the circuit response i'm guessing the switch is activated at T=0sec.
It looks like there is an initial current spike through the relay (will this trigger the relay momentarily?)
then the current goes full scale at T=1sec energizing the relay and shutting off the pump.
Then at T=3+sec the current dies off going to the relay (i want the current to continue to flow until the float switch is open again)

hi,
As I understood the operation you were asking for is:
You manually operate a sump switch, which turns on the emptying pump, when the water level falls to the required level the sump switch turns Off the emptying pump motor.
The problem you have is that the water remaining in the discharge pipe runs back and raises the water level, so the level switch operates the pump and so on ...

The lower left is the Sim of the level switch.
[no momentary triggering of relay]

If you could confirm the action required I am sure we can come up with a simple solution.

As I read the d/s for the Zoro level switch its got NO and NC switch action.

E

All you really need is a float switch with more hysteresis or "backlash" or some float level signal with electronic hysteresis like a Schmidt trigger.

esp,

Oh, sorry for not being very clear.

For an aquarium sump you have water being pumped out continuously to the main aquarium, the aquarium then over flows and drains back into the sump. So for normal operation the sump pump is continuously pumping and the water level is constant.

the low level trip is to protect against a blocked drain scenario. if the drain from the main tank into the sump is plugged then level will build in the main tank until it over flows onto the ground (bad). I want to set the low level switch in the sump return at such a level that the main tank will only get really full but not over flow when the drain plugs.

That being said, the relay should remain unenergized and NC for the majority of it's life allowing the pump to run. However, when the level in the sump is low (meaning the level in the main tank is raising) i want the pump to stop and stay stopped until i come unplug the drain and restore the level.

@sunnyskyguy - I already have the level switches, i would not mind getting a different one if that will solve my problem. could you point me in a direction to find a float switch that would have a larger deadband and work in a salt water aquarium? (corrosive environment, and drinking water safe)

Thank you all for your kind help with this project. From my research so far I know I can get a system that will solve the problem, but circuits and electrical engineering are not my background. I'm a chemical engineer by trade.

hi ak,
Does this diagram represent the required operation.?

If the overflow pipe becomes partially blocked, there maybe sufficient 'seepage' past the blockage to lift the float, so as I understand it, when Off after 3 secs, the pump remains Off until manually reset.
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yes esp1.

I was just thinking about the same issue last night. And if the pump remains off until manual reset the 3 second delay is not really required.

I think the more ideal solution would be to have the float switch trip the pump off instantly, then the pump stay off until some manual action was taken. Maybe a momentary push button, or a switch.

but if this is the case i would also like to have an audible alarm be energized while the pump is in the tripped state. So i guess i would just place the alarm in parallel with the relay. If the pump is off for too long my fish run out of oxygen, so i would like to have a warning.

Thanks for helping me think through this.

Is this type of circuit easier to build? or maybe something inexpensive is already readily available?

hi,
The 'zoro' float switch does have NC and NO contacts [ according to the d/s].
I am assuming they mean , a change over set of contacts.?
So in normal operation, 'float' above minimum level, relay coil connected to 'Opened' contact [ +12V to relay wiper].

When the float switch contact 'closes',due to the sump being below the min level, the 12V is connected to the Relay coil, which energises and Stops the motor.

To get a 'latching' action, you could use a low power relay coil across the motor relay coil, so that would operate at the same time.
Use the contacts on the small relay to give 12V back to itself and the motor relay, they will then remain energised.

You will need a manual 'Run Pump' switch, connected in series to the +12V on the relay coils, pressing the Set sw will open an so the relays will be de-energised and the pump will run.

Do you follow that OK, if not I could post a circuit.

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- - - Updated - - -

hi ak,
I see that your relay is a double pole double throw, so we could use that second pair of contacts to give self latch action.
No need for a second relay.
E

I think I still need to see the diagram.

However, I think I understand the idea.

12V+ attached to the level switch, a NO 12v relay, and a NC 12v relay, then back to the source in series.
the NO 12v relay will have 12v power on the load side that will supply the coil when the relay is energized and closed.
The NC 12v relay will have the 120v pump attached and will be opened when either the level switch is closed or the NO 12v relay is closed.

This seems like a pretty simple design to achieve.

can you recommend a relay for either the NO 12v low power relay, or for the NC 12v relay for the motor?

Thank you so much for the help on this. I think this system will work beautifully.

- - - Updated - - -

I just saw your update. That is convienent.

Also, i would just put the run dump switch on the lead comming from the load side of the NO 12v relay correct?

Hi,
A quick question are you using both sets of changeover contacts on the motor relay.? if not I will do a sketch using the spare set for latching.


EDIT:
This option uses the spare set of change over contacts on the Pump relay.
If there is not a spare contact pair, use a low cost 12V change over relay for the latching operation, connected in parallel with the pump relay coil.

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Gold plated relay contacts are found in all <2A rated Telecom syle signal relays .

I Would think the plating is thick enough (10u") to be less corrosive to act as a fluid sensor gap switch for any CMOS biased with 1M. The gap would need to be large enough for water surface tension to not bridge with a drop and will provide some hysteresis when pump has stopped and fluid level risen.


.... but surface salt resistance may required experimemtation of the pullup resistor value... E.g. 10k to 1M with ground sensing on the contact..

This could be wired with enameled magnet wire >= AWG30 and filtered with a Cap to supress stray noise... a standard Schmitt trigger gate is best suited for this.

To latch the event two gates crossed over like Set/Reset inputs or any Flip Flip edge triggered on ground sense, inverTed to rising edge into FF Clk with output disabling the pump driver (logic level mosFEt and driving an LED with 5mA direct with series current limit e.g. (5-2Vred)/5mA= -~620 Ohm.. others can draw a schematic for you.

esp1 - Thank you for all of your help with this project. That schematic looks beautiful.

I will also put some kind of audible annunciator in parallel with the LED and the relay coil, but i can definitely build that with my limited skills

I won't put it together for a couple more weeks because I’m waiting on some other parts to come in to put the aquarium set-up together, but I’ll come back and post my results when it's finished.

Esp1, I have decided to add an air pump to the equation which will come on when the sump pump is off.

I'm wondering if i can just use the NO side of the same side of the relay that the sump pump is on.

Is there any problem hooking up more than one +120vac to the same common pole of the relay? I understand i would want to be sure not to put a +120V with a 0V on the same common.

The diagram would look like:

hi.
The mains wiring is normally referred to as Line [HOT, 120Vac ] and Neutral, not 0V.

A single 120Vac LINE connection to the relay contact common wiper is all you need, refer diagram.

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hi,
I am assuming that the incoming 120Vac to the relay wiper is already fuse protected.? If NOT, I would recommend that you add a suitable fuse in that connection.
E

Thanks esp1,

Yes the line is protected from over amp. I'll also be using a GFCI device since water is in the area.

I think i'm going to use a couple of extension cords so i do not modify the cording on the sump and air pumps.

I'll have a male end plug into the GFCI outlet that will supply the 120V to the common pole, take neutral from both the air pump and the sump pump, and run ground from the sump pump (air pump is not grounded). Then, I'll have 2 female ends that receive 120V air pump plug to receive from the NO pole and sump pump to receive from the NC pole, and give neutral to back to the GFCI outlet (spliced together on the male plug neutral line).

Do you see any obvious flaws with this arrangement?

Here is a diagram of the arrangement (sorry it's kind of odd).



- - - Updated - - -

Sorry, it's a bit late here.

The correct/complete diagram is:

hi,
Your second lower drawing is OK.

If you need a state indication for showing if the Pump Or Air is ON, consider buying two 120V Neon mains indicator lights.
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