Pentek PID30 VFD Questions

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by Arlen Angell, Apr 13, 2019 at 9:51 PM.

  1. Arlen Angell

    Arlen Angell New Member

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    I recently put in a new 3Hp 3 phase pump and a Pentek PID30.
    The pump is set at about 380 feet, well is bored and cased down to 560 feet.
    The static water level is 320 ish feet.
    Drop pipe is 1.25 schedule 40 steel
    Pressure tank is 60 gallon charged to 47psi
    Pump is a Webtrol WT1030-L
    The well contractor installed everything but the VFD. Drives and automation are my field of expertise, and the contractor told me it would work good with the defaults. It does for the most part.
    I have a few questions/observation that I’m hoping some of you can help me out with.

    1) The service factor amps for the motor is 10.1, however the pump running at 60hz will move about 15gpm at a pressure of about 20 psi at the surface. This seems to fit with the pump curves. Problem is the motor will run at 12 amps! The contractor told me I would get 14-15 GPM, but I assumed that I wouldn’t have to over amp the motor to get it:D
    I have set the max freq in the drive to 55 hz. This gets me about 12 gpm, and puts the amps at about 9.5
    Question: Is that the best way to handle it? Should a different pump have been selected?

    2) What is the proper way to determine the proper minimum freq? Default is 30hz, but the pump doesn’t seem to move water at 45hz and below (it doesn’t build pressure with no water flowing)

    3) The pumped seemed to react a little too quick (maybe because of the large pressure tank), so I lowered the prop band to 1000 in the pid setup. It seems to run better.
    Question: Any advice on setting the integration and derivative ?

    4) When I have a faucet running...maybe 1 or 2 gpm, the drive will slow down to 47 hz and hold 60psi perfectly. I would expect that it would run like this forever. However after awhile, I suppose when the wake delay expires, the drive will go into the pressure boost mode, then go to sleep. Then it drops down to the 55 psi mark, and the whole process starts again. That seems to diminish the value of having a drive. The pump actually probably cycles more with the VFD than with the single speed system.
    Question: Is this a necessary evil, or can that behavior be adjusted out?

    That should be enough to get a conversation going:)
     
    Last edited: Apr 14, 2019 at 4:26 AM
  2. Reach4

    Reach4 Well-Known Member

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  4. Arlen Angell

    Arlen Angell New Member

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  5. valveman

    valveman Cary Austin Staff Member

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    Sorry you are having problems, but this is pretty funny. Drives and automation are your field of expertise, yet you are having problems with a PID? The PID is supposed to be a simple plug and play drive? All you should have to do is enter the horsepower of the pump and the desired set pressure? That is their main sales hype. I hear Drillers installing Aquavar brand drives for the same reason, they also should be plug and play. The more complicated drives like the Yaskawa have many adjustments, which can be confusing. However, as you have discovered, every pump system is different and a drive with many adjustments is usually required to make it work properly.

    The minimum speed or frequency to maintain the minimum flow rate required is important. There are probably not three people in this country who know how to figure the minimum speed. However, with your 320' static water level, a pump that builds 880' of head, and a 7 GPM minimum flow required to cool a 3HP motor in 5" casing, your minimum speed will be 2,857 RPM or 45Hz. It is unusual for the default of 45HZ to actually be what you need, but in this case it is. If you have 4" casing, the minimum cooling flow is 1.2 GPM, which would be a minimum frequency of 43Hz.

    With 5" casing and a minimum cooling flow of 7 GPM, the VFD is not really very useful. The pump will need to cycle on and off when using less than 7 GPM, which is most of the time for household use. Only when using between 7 GPM and 15 GPM, as it is only a 10 GPM pump, will the VFD be able to keep the pump running steady and still give adequate cooling to the motor.

    With a minimum speed of 45HZ, anytime you are using less than 7 GPM, the pump will cycle repeatedly. With a 10 PSI on/of bandwidth a 60 gallon size tank only holds 7 gallons of water. So your pump will probably cycle on for 2 minutes and off for 2 minutes anytime you are using the normal 3 GPM water in the house. So yes it will probably cycle more with the PID VFD system than if it had a normal pressure switch with a 20 PSI bandwidth.

    Also the service factor amps on a 3HP, 230V, 3 Phase motor is 10.9 amps. However, the PID30 is only good to 10.1 amps, and your pump wants to draw more than that. Harmonics, voltage spikes, reflective waves, and other things the VFD causes is probably why the motor is drawing high amps. You will need to set the max frequency no higher than 56Hz so the amps do not increase above 10.1, which will limit your max flow to 12-13 GPM.

    I don't know how they expect a regular pump man or homeowner to know how to properly set a VFD system, as even people who do drives for a living do not understand how the pump they are controlling works. Drives are great on conveyor belt systems, elevators, even piston type pumps. But the Laws of Affinity causing a pump with a regular centrifugal impeller to lose head by the square of the pump speed, greatly reduces any benefit of varying the pump speed.

    But now you are stuck with a three phase motor and small wire down the well, so you have no choice but to make this work. Usually about the third time people have to replace that expensive drive they realize something needs to change. Then they will pull the pump, replace the three phase motor with a normal single phase motor and purchase the larger wire needed. Then they will have a normal long lasting dependable pressure tank/pressure switch controlled pump system again.
     
  6. Boycedrilling

    Boycedrilling In the Trades

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    Why did your pump installer not install and program the PID30? I hope they explained to you, that by doing it yourself, you voided the warranty. The 3 year warranty on the PID30 is void if not installed by a Pentair Pro Dealer.

    1st question, max amps and max flow. The motor will run at whatever hertz is required to meet the flow. It will not run at 60 hz, unless you are trying to pump more that 12 gpm. Can’t answer you over amperage question. SF amps for a Pentek 3 hp motor is 10.1. However you said you have a WEBTROL brand pump. What brand motor is on that pump? we roll manufactures their own motors. It might not have the same SF amps as a Pentek. Pentek, Franklin, and Grundfos motors don’t necessarily have the same amps for the same horsepower motor.

    2nd question. Yes default min hz is 30 hz. Most installers don’t adjust this. But the proper way to set min hz is to determine the min hz required to produce 30 psi at no flow.

    3rd question. Don’t mess with PID settings. 99.9% of the time they are correct at default settings. I think I’ve changed these settings TWICE, after consultation with Pentair tech support.

    4th question. Yes this can be adjusted. Again your installer should have done this.
     
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  7. Arlen Angell

    Arlen Angell New Member

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    Valveman,
    Thank you for your reply. I think you misinterpretted a couple things that I said.
    The default values actually work pretty good, but I like to make things work a little better.

    The default minimum speed is 30 hz. I noted that the pump doesn’t seem to move much water below 45 hz as it doesn’t build pressure when no water is being drawn when running below that frequency.
    I have a 4 inch casing, so maybe I should set the minimum speed at 43 -46 hz. Given my observation on how it performs and your calculation, it sounds reasonable.
    As I noted, the service factor amps on my particular motor is 10.1 . The max that the drive can be programmed for is an 11.5 amp SF(not 10.1 as you said)
    I definitely disagree whole heartedly with the notion that harmonics and reflected waves are causing the pump to over amp. The reason that I can say that with confidence, is that the 3hp single phase motor with an identical pump over amped by the same percentage (19amps)
    That was one of my questions. I’m wondering if the pump is just so far over on the curve, and moving 15 gpm takes more hp than the service factor power of 3.45hp.
    I’m happy I went with the drive this time as there was nothing I could do with the single phase motor to lower its volume to get it’s amps down.
    That pump and motor only lasted 3 years running in that condition (19 amps).
    Before that, Life was good with the 2hp Aermotor. That lasted 17 years, then developed a hole in the drop pipe. I figured it would be nice to get a little more flow so I opted for a 3hp Webtrol. I’m wondering if the contractor should have selected a different pump.
    But, as I said, I limited the frequency to 55 hz and it works giving me a good strong 12 gpm (not much more ,if any ,than the 2 hp aermotor with a 1.25 SF)

    All in all, I like the drive. I really like the soft starting, and of course the speed limiting.

    Point #4 from my original post, is what I don’t like. After thinking about it, they are almost forced to shut the pump off after a period of time of frequency stability. The drive has no way of knowing whether the pump is actually moving water. Like I said, it doesn’t increase pressure at 45hz and below. So the drive would settle out at a speed and pressure and sit there running and may not be moving any water for cooling the motor.
    It would seem like having some flow feedback along with the pressure transducer would make for a better system. Seems like the way it operates is safe, but irritating.
    I emailed the Pentair guy...we’ll se what he says.

    BTW, I have #6 wire going down to the pump.

    Thanks for the conversation...keep it coming if you have time.
     
  8. Arlen Angell

    Arlen Angell New Member

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    The contractor was working on the pump while I installed the drive. We agreed this was the best, since I’m a master Electrician with 1000’s of hours of VFD experience.
    It is a Pentair Motor on a Webtrol pump. The motor has a SF amps of 10.1.
    When I water cows with a 1 inch hydrant, the pump will run at max freq, and it pumps 15 gpm. I‘m thinking that’s why it over amps...operating that far over on the curve.
    I limited it to 55 hz so it draws 9.5 amps at about 12 gpm

    I will give that method of setting the min freq a try thanks! Would my tank precharge of 42 psi interfere with that?

    I like the way my pid settings made it behave. I have allot of experience with PID loops...just
    not on well pumps!

    Regarding number 4, I would love to hear your thoughts! There is a boost delay, but that just delays the inevitable. It appears that when the frequency stabilizes—no matter where it is, after the boost delay expires, the drive goes to sleep. It seems like it relies on instability in the control loop to stay running! It makes sense the more I think about it. ...if the pressure is at setpoint, the drive has no way of knowing if you are actually moving water. It could get into a condition of running at say 45 hertz after the faucet is closed.
    Still don’t like it, it would seem that by me making the pid control the pressure perfect, it may make it worse since the frequency isn’t hunting around!
     
    Last edited: Apr 14, 2019 at 12:23 PM
  9. Boycedrilling

    Boycedrilling In the Trades

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    Of the VFD’s on the market for the domestic market, I think the Pentek Intellidrive is the best VFD on the market at this time. It is a Danfoss that has been customized for Pentair for use on centrifugal and submersible pumps. It has 40 plus parameters that can be edited, not counting parameters on the “secret” menu.

    When I need a VFD that is 3 phase in/out or 5 hp and above, I use Yaskawa Drives. I have also used ABB, Hitachi, and Mishubishi drives. Dating myself I’ve also used Unicorn and back in the 80’s and 90’s we used Robicon drives.
     
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  10. Arlen Angell

    Arlen Angell New Member

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    Yes, I think it is a quality drive, and easy to setup. The only thing I don’t like is how it goes into sleep mode. I edited my last post, and added some information. I would really appreciate your insight if you don’t mind.
    What is the “secret” menu that you speak of?
    By the way, 42hz builds about 33psi with no flow, so I set it there.
     
  11. Boycedrilling

    Boycedrilling In the Trades

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    I sent you a link to the electronic manual.

    The only time I’ve needed the secret menu was to edit the parameter for ground fault amperage.
     
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  12. Boycedrilling

    Boycedrilling In the Trades

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    The way sleep mode works is this.

    When the pressure has reached set pressure. Default is 60. I normally change this parameter to 50 psi. Pump slows down to minimum hertz. After a preset amount of time, parameter is adjustable. If pressure hasn’t dropped, pump goes to optional pressure boost. I use pressure boost, but change parameter to +5 psi from default +3 psi. This is where you sometimes have problems in adjusting s time to sleep and pressure boost. 80% works fine out of the box. 20% of the time takes some tweaking. Then the pump shuts off, going into sleep mode. The pressure differential for the pump to start is adjustable. Preset is -10, I change that to -15. This ends up giving you the full 20 psi of drawdown from the pressure tank.

    I did have to narrow this drawdown a couple of weeks ago for a customer that has old calciumed up galvanized plumbing. Also increased set pressure for them up to 65 psi. With the flow restrictions in their pipes, they didn’t have any pressure in the bathroom shower.
     
  13. Boycedrilling

    Boycedrilling In the Trades

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    Use the pump out button if you want to run the pump at a set hz to check flow and pressure. The hz parameter is preset to 45, but can be edited,
     
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  14. Arlen Angell

    Arlen Angell New Member

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    The sleep mode doesn’t behave like that on mine. Maybe something changed with firmware revisions?
    It doesn’t go down to min frequency before is goes into pressure boost then sleep.
    It appears that when the freq stabilizes and doesn’t change for the boost delay time, it goes into the boost mode, then sleeps.
    For instance, the shower was running, and the freq was at 47hz. Pressure was holding right at setpoint of 60. It would go into pressure boost after 1 minute, then sleep. I have duplicated this several times. I can change the boost delay, and it takes longer, but the end result is still the same. It was never anywhere near the min freq of 30 hz.
    If the control loop is a little unstable and the freq jumps around, it won’t do it, but after a couple of minutes the hz will eventually stabilize, and the same thing will happen.
     
  15. Arlen Angell

    Arlen Angell New Member

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    Yes earlier today that’s how I figured out the min freq needed to build 30psi
     
  16. valveman

    valveman Cary Austin Staff Member

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    See this is what most people do not understand about pumps. The amps will drop by restricting the pump with a simple valve. Especially if you pick the right pump, the amps will drop just as much as if you used a complicated, computerized variable frequency drive to reduce the RPM. I like VFD's and use them on my positive displacement hydraulic pumps (plastic machines). But when you have a centrifugal pump that will naturally drop from 3.4HP to 1.6HP without every varying the speed, a VFD is just adding expense and complications to what could be a simple long lasting pump system.

    10S30 curve with HP.jpg
     
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  17. valveman

    valveman Cary Austin Staff Member

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    Having said all that this pump is deeper and builds more pressure than we like to do with a CSV. But it is only a 10 GPM pump, so varying the flow rate with a VFD or a CSV doesn't help much. A regular 80 gallon tank with 20 gallons draw would have given two minutes of run time because this is only a 10 GPM pump, and the pump would always be working at the best efficiency point or it would be off.

    When varying the speed or reducing the flow with a CSV a 3HP pump will use a lot more energy. Even though the horsepower drops from 3.4HP at 11 GPM to 1.6HP at 1 GPM it is actually using over 500% more energy to pump the water. At 11 GPM the pump is producing 3.2 GPM per HP, while at 1 GPM the pump is only producing .62 GPM per HP.

    There maybe some benefits for using a VFD, but saving energy is not one of them. People falsely claiming a VFD saves energy to help sell the most expensive and shortest lasting pump system is what I don't like.
     
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  18. Arlen Angell

    Arlen Angell New Member

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    That may not be understood in the well drilling industry, but it is well understood in the process pumping/HVAC world. Circuit Setters, or Triple Duty Valves are routinely placed on the discharge of the pumps to throttle them. Usually though, VFD's are still the preferred method of volume control for centrifugal pumps and fans.
    I did not know that the well industry had a version of the "circuit setter" until I started reading here about the cycle stop valve.
    I would have definitely tried one if the well contractor had pitched one to me!
    I think you said that a CSV might not be a good solution because of the pressures of my deep well.
    I guess I will have to put up with the goofy sleep mode behavior!
    If the Pentek fails, I will just get an off the shelf ABB and use a PLC and write my own logic. I think that would still be cheaper than a Pentek.
    I have been in contact with the Pentek area technical guy. We'll see if he has any ideas. It is more of an annoyance than a problem, just because I think they could do better.

    If I wouldn't have went with a VFD, then should the contractor have selected a different pump? Looking at the pump curve, given the head that is required for my well, it seems obvious that the Webtrol pump would try to move 15 GPM. Which is a problem for a 3HP motor.
    I would think Webtrol would somehow deal with this in their charts. On industrial fan and pump curves you commonly see points on the curve called out with the HP required.
    It seems funny that a contractor would tell you your pump is going to pump 14-15 gpm, then overamp the motor to get it!
    I'm talking about a contractor that has been in business for many decades and several generations!
    I should start a new thread on the pump selection, as I would like to understand that process.
     
  19. valveman

    valveman Cary Austin Staff Member

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    I don't think the natural amp drop is well understood in any industry. I get in a lot of heated arguments about it all the time. Most people think restricting a pump with a valve makes it work harder, and I have a hard time convincing them otherwise, even when I post a pump curve.

    I believe the "preferred method for volume control" is VFD, because very few know how pumps and fans work naturally. They think they can just add a VFD to any pump or fan and make it do what they want. If they want it to be efficient, they should be sizing the pump or fan to do what they want, not wasting energy with a VFD.

    They do load up submersibles, but they should still be within the service factor. A 3HP drawing 19 amps in single phase is a problem, as the service factor is only 17 amps. It would need a 5HP motor to survive at 19 amps for very long.

    With a pump that builds 880' of head and a static level of 320', the back pressure on a CSV would be 242 PSI. This is about twice as much pressure as we want across a CSV, so we would use two of them. The first CSV would take the 242 PSI down the the CSV set point of say 140 PSI. Then the second CSV would see the 140 PSI and take it down to the 60 PSI needed. The CSV's would need a 3 GPM bypass, as I wouldn't run a 3HP motor at less than 3 GPM for cooling purposes.

    A 16 GPM pump would have been better for that well. The 16S30 would have been less expensive, had better horsepower drop, and would have worked with only one CSV1A, as it would have only had 173 PSI back pressure. But hey, why would anyone want to go to the trouble of picking the perfect pump for that well? VFD manufacturers say "you don't have to know anything about pumps. Just use one of our VFD's and any pump will do any job and save energy in the process". LOL!
     
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  20. valveman

    valveman Cary Austin Staff Member

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    OK guys, talking to Arlen has finally helped me understand why nobody worries about figuring the minimum speed with these VFD's. They apparently have the PID drives set up to go into sleep mode when the hertz stabilizes anywhere for a certain length of time. How can this work? Anytime you are running water steady for any length of time the pump will cycle on/off when it should run continuously. Is there anyway to make these things run continuously until they see a preset minimum frequency for a certain period of time? That would solve Arlen's problem.
     
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  21. Boycedrilling

    Boycedrilling In the Trades

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    Yes Cary, that IS how the sleep mode is supposed to work. And it does 80% of the time right out of the box. Demand is satisfied, pump runs a preset amount of time at minimum speed with no drop in pressure. That indicates a no flow situation and the pump shuts off. 20% of the time there’s some adjustment of the parameters needed. To get the sleep mode to run correctly. That’s where the skills and experience of the installer come into play.
     
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