Cycle Sensor Question; use of current as a flow rate proxy

[DIYguy]

I'm wondering about using the Cycle Sensor to run my jet pump (which is refilling a tank) from my low yield well.

Might it be possible to set a somewhat higher threshold than the 'dry run' condition which I abhor due to loss of prime? ( 300 feet of 2" suction, 25 foot well, etc.) My purported 'rationale' follows:
 
At first, the well has recharged and the suction is less negative, the flow rate is higher and thus the current might be higher, (with more water being raised from -5psi to +60)
 
As i draw down the well volume, the suction pressure goes to a more negative value,
 (let's say with the pump discharging through a ~PRV or CSV  into an open tank),
(more work for the pump to raise from -10psi to +60, but the venturi is becoming less efficient faster, and the throughput decreases faster than linearly)

Perhaps the current will  then go down below my elevated 'dry run' threshold, and the CS would shutdown for a delayed restart maybe 15 minutes later, to have less than 100 cycles/day.
If this worked, it would be an adaptive way to cycle the pump which would  not exceed the well yield ,
if I wait long enough between cycles so that the startup flow surge doesn't overpump immediately , in the first 10 seconds.


I'm sold on the Cycle Sensor, but just wondering what to expect from it before I order.
Also, does the Dry Pump detection require current continuously below threshold  10 seconds?
Does the threshold have 'hysteresis', where the current must  first exceed the threshold prior to detecting subthreshold current?

Before I go spend half a day testing, how reflective of  GPM throughput is the jet pump current? I imagine the inefficiency of the jet relative to a submersible would make this approach harder to do with a jet pump.

I'm paying $0.35 for my kwh, so, the intermittent operation seems attractive vs continuous  24 hr operation of a 1 HP jet throttled to 0.75 gpm.
Also, speaking of $0.35/kwh, what is the power supply current consumed by Cycle Sensor unit?
Thanks,
John

[Cary Austin]

As the water level in the well gets deeper, the head on the pump increases and the amps will decrease.  So yes you can set the Cycle Sensor to shut off the pump at any amp draw you want.  You don't have to wait until the well is completely dry for the Cycle Sensor to shut it off.  Just set it to go off at whatever amps needed before you start sucking air and lose prime.

The Cycle Sensor will look at the low amp setting for 10 seconds before shutting off the pump.  So you may have to set the amps a little higher to account for that.  But it will work as you are thinking.

And the Cycle Sensor uses about 4 watts.  About the same as a night light.

[DIYguy]

Well, I wired up a pigtail so I could get my current probe around the black wire. (Amprobe DcG-1000)
RedLion RJC-100, jet control roughly two turns from closed.

Three observations;
 1. with the jet suction at -17.5 inHg and the pump output up at 60psi (very little flow), the pump was drawing maybe 7.48A . when I cracked open a bib on the output to get the pressure down to 55, higher flow, the pump drew 7.53 A.

2. At first, the 60psi current was maybe 7.73 amps. this seemed to decline uniformly over time, without regard to pumping. I assume this is the motor heating up and having higher ohmic resistance of the windings.

3. When I open up the bib to get the pressure down to 40, the  current does go up a lot.

After 1/2 day of testing, The jet pump current seems rather insensitive to the input suction pressure, when the flow is limited by the peak pressure. I may try again tomorrow with higher flow, but I'm leery of losing prime during these experiments.

I didn't have a very good way to modulate the depth in the well, but I am not optimistic at this point.
Maybe my technique was not flawless, but i didn't have a flow meter.
I have no idea about the effect of that discharge control, and Red Lion was coy at best about what it actually does.

Thanks for your ideas.
John

[Cary Austin]

Red Lion wasn't being coy.  They just have no one left who knows how pumps work.  This has become typical in almost every profession.  They have people who can program the hell out of a smart phone or a computer, but they have no idea how anything mechanical works.

That backpressure controller is to keep some pressure on the jet nozzle to make it work.  You can tune it to make the pump work at its maximum.

There won't be much difference between the amp draw at 1 GPM and when it is pumping air.  But there is a big difference between the amps when the pump is producing high flow and low or no flow.  So when it gets down to pumping low flow at 7.5 amps, you set the Cycle Sensor to shut it off before you start sucking air.

[DIYguy]

What resolution of  threshold current does the Cycle Sensor offer?
Thanks,
John

[Cary Austin]

The Cycle Sensor is infinitely adjustable within two decimal points.  If the pump is running fine at 7.5 amps, you can make the Cycle Sensor shut it off at 7.49 amps.

[DIYguy]

OK, very helpful.

I was running more tests today, and I managed to overpump the well...
The pump sure sounds different with air in the jet!

Good news, at that point the run current dropped to 7.31 A (and pressure dropped to zero), so I could certainly differentiate that from the run current which is 7.53 when I have flow and maybe 7.48 when i have very little flow.
So, at minimum,  the Cycle Sensor would release me from babysitting the pump whenever it is on.

I have one other idea, to raise up the jet pump off the ground by 8 feet, so that the pump output will stall before I can pull air and lose prime. (23 feet down to the top of the foot valve). The Red Lion literature had mentioned the use of a 30 foot 'drop pipe' below a suspended jet in a low yield well. Now I understand 'drop pipe'. Probably some leftover wisdom from the guys who knew stuff...

One other way to use the CycleSensor is essentially a motor temperature sensor, and thus a pseudo-runtime controller.  I live close enough to the ocean that we don't have big air temp excursions. As the motor warms up from cold, the current creeps down, roughly 5% over 15 minutes. The 10mA resolution of the CycleSensor should be plenty good, if it is relatively insensitive to ambient temperature. If necessary I can thermally isolate the CycleSensor from the heated air coming from the motor.
Thanks again,
John

[Cary Austin]

Actually pump installers consider drop pipe to be that which is in the well holding a submersible or the jet assembly.  We would call the pipe extending below a jet assembly as a tail pipe.  And I was going to mention using a longer tail pipe, but noticed your well was only 25' deep.  I didn't think about raising the pump 8' off the floor.

Raising the pump 8' off the floor sounds like a major pain to me.  I think the Cycle Sensor will eliminate having to raise the pump.

I also don't think the motor warming up has as much to do with decreasing amps as the decrease in water level as you pump for the first 15 minutes.

The change in temperature should have nothing to do with the reading on the Cycle Sensor.

[DIYguy]

I expect you are correct regarding current drain decrease with decrease of water height in the well. My vacuum gauge is over at the well, 100 yard dash to or from the pump and current probe. No way to assess correlation until I can re plumb the RJC to fit suction and discharge gauges. The ports are too close for my gauges to both fit. My pump house roof is 8 feet up, although putting the pump on the roof rather defeats the concept of protective housing...
Am travelling on a troubleshooting, no progress to report.
John