Pressure switch activated countdown timer for submersible pump driver

wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
So here is my dilemma. I am about to install a new well pump. The pump is a traditional 230V, 1/2hp, but I am going to incorporate a Franklin Monodrive, a constant pressure driver. The Monodrive should all but eliminate startup surge and play well with my off-grid system. The only downside I see is the 35 watt idle power for the driver. I hate to run that 24 hours-a-day, and I don't really see an need to. I could certainly connect the driver to a standard countdown timer and manually turn it on when I want to use the pump, but I think I can come up with something a little more sophisticated.

The constant pressure driver is designed to maintain a constant pressure, say 50psi. Basically, it monitors pressure using an electronic pressure sensor. As soon as the pressure drops below 50 psi, it turns the pump on and ramps it up just enough to maintain 50psi. What I would like to do is cut power to the pump driver most of the time and use the pressure tank to maintain pressure in the system until the pressure gets down to about 25psi. Once the pressure tank reaches 25psi, I would like to use a traditional mechanical pressure switch to trigger a countdown timer that will run the pump driver for a set period of time (~1 hour). I talked with Franklin and they didn't see any problems with running the driver in this fashion, but they didn't have any suggestion for a countdown timer that I could use.

Anyone know of a timer that could work for this application? I could certainly program something myself using an arduino controller and a relay, but it seems like I should be able to come up with an off the shelf solution.

Thanks in advance,
Bill

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    :confused:That sounds as though you want to take a constant pressure system and turn it in to one that cycles on @ 25 psi and off at 50 psi.

    Couldn't you just have a timer turn off the pump during the night so it would not run at all? When morning came and the system reactivated it would have to pull power and run up to 50 psi again, then stay there until the timer shut down. That would be a conventional 24 hour timer.

    Not sure I see any advantage here over setting it for 35 psi constant. Could be an interesting experiment to measure the actual power consumed under the two operating states though.
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    The main advantage of the constant pressure driver is two-fold. First, the pump will be soft-start and will be much less likely to cause problems when I'm running my shop tools. Second, the pump won't work any harder than it has to to maintain pressure once it gets to pressure.

    You're right about me wanting to have both a constant pressure system and a more traditional pressure tank system. Basically, I would like it to function as a constant pressure system during high use periods and as a traditional system during low use periods. Although a 24-hour timer could achieve this, my wife does shift work in the ER, so our high use periods are very hard to predict. Not to mention she won't be a happy camper if she gets home at 2am and jumps into a non-functional shower ;)
  • BB.BB. Super Moderators, Administrators Posts: 29,517 admin
    Re: Pressure switch activated countdown timer for submersible pump driver

    Run a timer and have a 2 hour twist timer at the front door to override... But would have to think that they must support a pressure tank some way.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    Have the pressure switch bypass the timer: IF in 'OFF' hours AND pressure <25 psi THEN 'ON'

    Possible?
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    The standard pump motor is designed to be run at full speed. I don't think that running it at variable speed will improve pump life. The triac used to vary the speed of the pump creates abrupt changes in voltage compared to smooth sine-wave. IMHO, if anything, it should be damaging to the pump, the same way as cheap MSW inverter is.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    NorthGuy wrote: »
    The standard pump motor is designed to be run at full speed. I don't think that running it at variable speed will improve pump life. The triac used to vary the speed of the pump creates abrupt changes in voltage compared to smooth sine-wave. IMHO, if anything, it should be damaging to the pump, the same way as cheap MSW inverter is.

    The unit in question is a Franklin VFD designed to work with their pumps. It's output would not be the choppy waveform of an MSW inverter and should not have a significant effect on the motor's longevity. I wouldn't try it with just any pump motor though; it seems to be meant for 3-wire set-up.
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    They advertise that it will work with any 3 wire pump and that it should not lower longevity. Only time will tell I guess. For what's it's worth, I will be using a Franklin 3-wire pump. I have pretty good energy usage numbers from my previous Lorentz solar pump, so I will do a side-by-side once I have the Franklin in place.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    The unit in question is a Franklin VFD designed to work with their pumps. It's output would not be the choppy waveform of an MSW inverter and should not have a significant effect on the motor's longevity. I wouldn't try it with just any pump motor though; it seems to be meant for 3-wire set-up.

    I see. That explains why it consumes so much power. Looks like it converts AC into DC and then back to AC of different voltage and frequency. All these conversions have losses.

    When you switch it on when it's 25 psi in the tank, it probably will run the pump at full speed (as it would run without driver) until the tank reaches 50 psi, then it keeps working the pump until you switch it off. The only benefit I see is keeping the constant 50 psi pressure instead of varying it.

    I use a simple mechanical switch set to 45(on)-60(off) psi. I don't feel any difference in pressure during the operation. When we bouht the house, the switch was set to 20-40 psi. When the tank was getting empty at 20 psi while you're taking shower it was extremely frustrating. So, I put in a new switch, set it to 45-60, and pumped up some extra air into the pressure tank to adjust it to the new level. It feels real good since then.
  • BB.BB. Super Moderators, Administrators Posts: 29,517 admin
    Re: Pressure switch activated countdown timer for submersible pump driver

    Look at the power usage numbers numbers closely... If the Lorenz was a permanent magnet pump and the Franklin is a induction motor--You will lose a fair amount of efficiency with the induction motors (upwards of 20%???) as the induction motor has to also generate it own magnetic field in the armature.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    BB. wrote: »
    Look at the power usage numbers numbers closely... If the Lorenz was a permanent magnet pump and the Franklin is a induction motor--You will lose a fair amount of efficiency with the induction motors (upwards of 20%???) as the induction motor has to also generate it own magnetic field in the armature.

    The comparison will be unscientific and mostly anecdotal as I will definitely be comparing apples to oranges. The lorentz was smaller and ran directly off the batteries (with the use of 24-48v converter). The new one runs off the my inverter (and an autotransformer), so I suspect there will be some significant losses. Most of the year, my water demands are pretty low. When they are high -- in summer when watering the garden, animals and wind break -- I have plenty of energy to spare. Considering this, I opted for sacrificing efficiency for the convenience of getting a system that's stocked, understood and trusted by a local supplier.
  • Texas WellmanTexas Wellman Solar Expert Posts: 153 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    I really think you should re-think your strategy.

    First off-why are you using the Monodrive? I don't mess with a ton of VFD but my understanding is that the monodrive is used for a 1-phase 3wire or 2wire motor. You lose soft start with the 2-wire motor FWIW. Mono-drive is limited to 30-60 HZ in the VFD. Mono-drive is typically used where there is already a well pump installed that somebody wants to convert to VFD (constant pressure).

    If you're going to swap the entire pump and all why not go with the sub-drive? The sub drive uses a 3-phase motor (.75-1.5 HP) and ranges from 30-80 HZ. The expense is in the VFD, not the motor. I haven't looked at the numbers recently but the subdrive SHOULD be more energy efficient.

    One more thing to consider-Franklin now has their own solar line. Basically it's a subdrive that is DC-ready fed into a std. 3-phase system. Subdrive for solar. I haven't read much on their specs and from what I remember it is geared toward larger pumps.

    I really think you should just bite the bullet and put in a grundfos SQF. It will run on either AC/DC straight out of the box from 30-300VDC or 90-230 VAC. They also have the soft start function and it will operate exactly like a normal well pump when coupled with a pressure switch. No extra timers, switches, etc. And if you're looking at the mono-drive then you're already in the ball park.

    The SQF does like the higher voltages (60-90V) but it will run on lower volts (minimum of 30V).

    Good luck.
  • Texas WellmanTexas Wellman Solar Expert Posts: 153 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver

    OK I did a little digging. The Franklin solar only goes 1.5 and 3 HP pumps and it's set-up for high flows and it is NOT very energy efficient. You're basically going to do the same thing it does but you will need the extra equipment (DC to AC and then back to AC). It seems like you're going to be losing a lot of energy in the conversion process.

    How large is your pressure tank? I would definitely get the biggest I could if you're going to set your system up like that. A large galv. tank (220 gallons or more) can have a 50+ gallon drawdown if it's set up right. The trick is to always keep the big tank full when you've got the energy.
  • wrdaiglewrdaigle Solar Expert Posts: 65 ✭✭✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    I would definitely get the biggest I could if you're going to set your system up like that. A large galv. tank (220 gallons or more) can have a 50+ gallon drawdown if it's set up right. The trick is to always keep the big tank full when you've got the energy.
    I'm not sure I understand your logic behind incorporating a giant pressure tank into a system with VFD, but that may be irrelevant as you're previous response is in fact convincing me to rethink my strategy.

    Although I like the idea of the SQF, I'm not sure I am ready to go that way. I think I am unlikely to ever run it directly off solar panels. I just don't pump enough water to justify the number of panels that I would need to dedicate to it. I am likely to get more panels in the near future, but I would rather tie those into my battery to help me get through short winter days. Seeing the panels sitting at the well (largely unused) in the middle of the winter while I'm running the generator would really get to me. Is it possible to divert the energy to a battery bank when the pump isn't running. Now that would be tempting.

    Instead, I think I'm just going with a regular single phase pump -- sans Monodrive. I'm still a bit concerned about the startup surge while I'm running shop tools, but dedicating my kohler generator to my shop will take care of that problem (I have been meaning to do that someday anyway). In order to minimize the number of startups, I will likely look into add a second pressure tank. If I add another 40 gallon tank, that will give me about 22 gallons of draw down to work with. In the summer, when irrigating my biggest zone, this will set me up for about 7-8 startups per hour for a period of about 4 hours. In winter, I will be looking at fewer than 4 startups/day. Any thoughts on this plan? It would certainly be cheaper.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    wrdaigle wrote: »
    If I add another 40 gallon tank, that will give me about 22 gallons of draw down to work with. In the summer, when irrigating my biggest zone, this will set me up for about 7-8 startups per hour for a period of about 4 hours. In winter, I will be looking at fewer than 4 startups/day. Any thoughts on this plan? It would certainly be cheaper.

    I have a very small tank - 4-5 gallons of draw, pretty much one toilet flush. Nothing else would fit where it is now and I don't want to move things. So, it gives me 20-30 starts a day. I always was afraid that this is very bad for the pump, but it did work fine for 12 years that we have lived in the house, and who knows how many years before then. May need to change the pump soon ...

    For big things, I try to match the outflow to pump production. This way I can use lots of water in one start. For example, filling my bathtub takes 60 gallons in one start.

    Xantrex inverter takes the surges very well. It has no problems starting both pump and table saw at the same time. Either of my generators don't have any problems starting the pump.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Pressure switch activated countdown timer for submersible pump driver
    wrdaigle wrote: »
    I just don't pump enough water to justify the number of panels that I would need to dedicate to it. I am likely to get more panels in the near future, but I would rather tie those into my battery to help me get through short winter days. Seeing the panels sitting at the well (largely unused) in the middle of the winter while I'm running the generator would really get to me. Is it possible to divert the energy to a battery bank when the pump isn't running. Now that would be tempting.

    Nothing wrong with your logic here, but here is another consideration: lightning. If your well pump is connected electrically to your main power system there is an increased chance of lightning damage to the pump. What happens is that the pump case is grounded to the well, but the wiring inside the pump is referenced to your main ground rod at the house. When lightning strikes, the house ground and the well ground may be 1000's of volts apart and this may cause arcing between the wires in the pump and its case.

    By having a well/pump power system that only sees ground potential at the well you limit the chances for lightning damage.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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