Trouble with Franklin Subdrive Utility (Help)

[KG5649]

Hello All,

I have been having trouble with my Franklin Subdrive 2-Wire VFD recently. Whenever a inside fixture (faucet, sink, toilet flush) is used by itself I have noticed the pressure gauge shoots up to about 65-70PSI initially and then the flow sensor (2nd green light) turns off and pressure drops to 55PSI and then the pump kicks in and shoots the pressure back up past the set point on the pressure switch of 60PSI and will continue this until water is turned off.

On the contrary if I go outside and turn on the hose bib to a water hose the pump turns on and maintains the set pressure of 60PSI. If I leave the outside hose running I can use any fixture in the house perfectly and it maintains pressure no issue.

Items tried to resolve issue: Pressure Tank replaced and increased size to 20 gallons. Set pressure tank at 42PSI (70% of set pressure per manual). Replaced Pressure sensor and installed check valve right after pressure sensor to reduce any turbulence that may be caused (per manufacturer recommendation).

Any thoughts as to what may be causing this issue? Appreciate the help in advance.

 

[Valveman]

I am sorry but those VFD's systems are designed to give problems. It is probably gliching like any computer. I have been replacing every VFD made since 1993 with Cycle Stop Valves. Here is what I consider a VFD repair kit.

https://cyclestopvalves.com/pages/vfd-repair-kit

 

[Sponsor]

 

[Craigpump]

2 wire VFD, stop and think about that for a second. In order to maintain constant pressure, that VFD cycles the pump on & off rapidly. Today's 2 wire motors leave a lot to be desired when installed properly and pumping into a large tank. Imagine what that rapid cycling is doing? I know for a fact that a Grundfos 2 wire motor would be lucky to survive 2 months under those conditions.

 

[WY_WaterWellGuy]

I have installed a couple of these 2W Franklin VFD’s (not by choice) and noticed they all exhibited the exact behavior you are describing OP. I can only assume that they are designed to operate this way.

I came upon this tidbit while flipping through the manual, might be worth a shot. Obviously you must turn off power to the VFD and wait 5 minutes before making any dip switch adjustments and only do this if you feel 100% comfortable in your ability to perform the work safely.


”Bump Disable (DIP SW3 - Position 5)
In applications where the occasional pressure bump is not desirable, the bump feature of the drive may be disabled. To disable the bump feature, DIP SW3:5 must be in the BD (up) position. Disabling the bump feature will result in the system having more difficulty shutting down in low-flow situations.”

 

[Valveman]

One of the problems with VFD's that I discovered in about 1991, is you have to know the minimum speed each pump in each different application can run and still produce the lift and pressure required. Every application will have a different minimum speed. Same pump at the same pressure with a slightly different pumping level will need a different minimum speed programmed in. This can be a fairly complicated math problem. To keep installers from having to do the math and make VFD's more "user friendly" they put in a "bump feature". Anytime the pump runs at any continuous RPM for a certain length of time, the VFD "bumps" the pressure up a few pounds, and shuts off the pump. The pump may not go all the way off, but to 30hz idle speed, which isn't pumping any water. If the pressure drops back to the set point, the VFD starts or ramps up the pump again and waits the required time before the next "bump".

The result is far from constant pressure. The pressure continually goes up and down as the pump continually goes off and ramps back up over and over. A little larger tank is usually recommended, as these systems are basically working like a regular cycling pressure switch system. We are told not to worry, as the soft start VFD controlled pump can be cycled as many times as you want.

Although soft start may help, continuous cycling isn't a good thing, not to mention the pressure pulsing up and down all the time. You will find that the new "user friendly" VFD's are cycling the pump more than if it just had a regular pressure tank and pressure switch, and the pressure is not constant either.

Some of the more programmable VFD's have a way to set a minimum speed. This was the only way I was ever able to make a VFD work properly. But even then if the water level in the well fluctuates at all the minimum speed needed will change.

Learning how to figure the minimum speed was also where I learned about the Affinity Law and the loss of head by the square of the speed. Because of the second Affinity law most of the pumps I figured and/or installed could only be slowed by about 10% and still produce the lift and head needed. Then I realized if the pump can only be slowed by 10%, reducing the energy consumed by the cube of the speed as in the third Affinity Law really didn't mean much. Further investigation showed me even though reducing the pumps speed with a VFD reduced the amp draw, the actual amount of electricity used per gallon increased, not decreased as I was led to believe.

I don't hate VFD's because I sell a Valve that competes with VFD's as many people might think. I understand VFD's very well, which is why I believe using a valve like the CSV is a superior way to get constant pressure from most systems. If nothing else, the complicated nature of the VFD prevents most people from understanding the consequences. This is just one instance where the Siren's song of supposedly saving energy with ultra modern electronics is not as good as the old tried and true mechanical pump systems. Now how many VFD people did I make mad this
time?

 

[KG5649]

Some of the more programmable VFD's have a way to set a minimum speed. This was the only way I was ever able to make a VFD work properly. But even then if the water level in the well fluctuates at all the minimum speed needed will change.

Appreciate the input, Valveman. Obviously a lot of factors to consider, but I cant wrap my head around why when a sink at 1.2GPM is turned on the controller senses no water and lets the pressure drop 20psi then turns on, overshoots the pressure set point and cuts back off. Yet, it seems anything around 10GPM the pressure stays constant. Shouldn't the controller and sensor recognize the flow in either scenario and turn the pump on to maintain pressure? Possible causes?

You mentioned adjusting the minimum speed, but if its not recognizing even a sink running until the pressure drops significantly how could this help? Thanks in advance!

 

[Valveman]

I am guessing you have a 10 GPM pump? If so, you are using all the water the pump can produce at 10 GPM, and the pressure doesn't increase and make the VFD do the "bump thing". I think it is going to "bump" anytime you are using less than 10 GPM. That is the only way they can make it shut down when no water is being used, without knowing and setting a minimum speed to activate the sleep mode. They are trying to make a VFD that is plug and play, easy to set up, and that is not really possible if you want it to act like a variable speed instead of just a pressure switch.

I have fixed a lot of these kinds of VFD's by adding a Cycle Stop Valve to the system. The CSV is set lower than the set pressure of the VFD. The CSV keeps the pressure from increasing to the point that causes the bump mode as long as you are using more than 1 GPM. The pump will just run at full speed all the time and the CSV will deliver the constant pressure. When no water or less than 1 GPM is being used, the CSV will let the pressure increase and the bump mode will shut off the pump, which will then stay off because you are no longer using any water. When you open a faucet the pressure drops and the sequence starts again.

 

[Fitter30]

Since we don't know the exact model look at this in the manual it adjusts over shoot.

Steady Flow SelectionSubDrive75/100/150/300,SubDrive2W/MonoDrive/MonoDriveXT

https://www.google.com/url?sa=t&sou...FjABegQIAxAB&usg=AOvVaw0nPuocZojuApihfZmG73dt

 

[Valveman]

Since we don't know the exact model look at this in the manual it adjusts over shoot.

Steady Flow SelectionSubDrive75/100/150/300,SubDrive2W/MonoDrive/MonoDriveXT

https://www.google.com/url?sa=t&sou...FjABegQIAxAB&usg=AOvVaw0nPuocZojuApihfZmG73dt

However, to reduce the on-time of the controller/pump/ motor, a “Bump-Mode” procedure is installed. During low flow (or leaky) conditions, this feature periodically increases the speed of the pump several psi above the set point and shuts off the pump. This adds some time to bleed off before the system starts up again.

This is the only thing I can find in that manual about the pressure problem, and I don't see anyway to fix it. "During low flow or leaky conditions", which happens when using any flow less than the max pump flow, the controller bumps up the pressure and shuts off the pump. "Time to bleed off before the systems starts again" means you are waiting for the tank to drain and the low pressure to start the pump again. This is no different than a regular pressure switch turning the pump on and off while the pressure continually goes up and down. The only difference is the soft start feature which they say will let the pump start as many times as needed without hurting the pump. Even with soft start, starting that many times is still not good for the pump and the pressure will continually fluctuate up and down, which is not constant pressure. As a matter of fact soft start can be very bad for a submersible motor. The motor bearing doesn't get any cooling of lubrication until the pump is up to half speed. The more times the pump starts the more times it goes from zero to half speed and the sooner the motor bearing will wear out.

A real VFD that would produce real constant pressure and not "bump" off every few seconds is one that can be programmed for the correct minimum speed needed for the particular pump at the particular conditions for each system. Every pump system has a different water level, different pump, and working at different pressures. This requires a VFD to be set differently for every application. So, they make the bump mode as a dumb way to keep from having to know how the VFD really works. Plug and play type VFD's maybe easy to set up but will not give the constant pressure performance they advertise and you will notice the pressure pulsing.

A CSV does a better job and doesn't have all the bumping and pulsing. A CSV makes any regular pump able to deliver real constant pressure. Adding a CSV can even stop the bumping and pulsing from a subdrive or monodrive system.
Like this....
https://cyclestopvalves.com/pages/vfd-repair-kit



.

 

[RunningMan]

Understand that ValveMan is the guy who invented CSV valves and he sells them. He has a, shall we say, slanted point of view. Many disagree with his claims, though I believe there are cases where he is sometimes correct. The Franklin controllers have an adjustment for overshoot. Valveman somehow forgot to mention this. BTW - I'm not a fan of the Franklin product. I just wanted to offer the alternative advice.

 

[Valveman]

He has a, shall we say, slanted point of view. Many disagree with his claims, though I believe there are cases where he is sometimes correct. The Franklin controllers have an adjustment for overshoot. Valveman somehow forgot to mention this. BTW - I'm not a fan of the Franklin product. I just wanted to offer the alternative advice.

I didn't invent the CSV until after I had been making and selling VFD's for quite some time. The CSV was invented to solve the issues I was having with VFD's, which was mostly angry customers from all the problems. Of course there are all types of "adjustments for overshoot" and multiple Band Aids designed into VFD's to try and solve some of the inherent problems. There have been redesigns of VFD's every year for 30 years now trying to solve some of these problems. Yet the laws of physics or mother nature can not be changed, making many of the problems of VFD's not fixable.

I do not claim anything that is not written on the pump curve. Many people may "disagree", but "opinions" do not matter as opinions do not trump the facts. I get angry when people say things like restricting a pump makes it work harder, when the fact that the amps drop as much when restricting a pump as they do when varying the speed is fact and written in black an white on any pump curve. I also get angry when people say a VFD saves energy, when the facts show energy use increases with the longer run times which uses more Kw's per gallon produced.

If I was in this just for the money I too would be selling expensive and short lived VFD's. I know enough about VFD's to con people into thinking they are a good idea, which is how most VFD's get sold. Instead I sell an inexpensive little valve that saves people thousands of dollars and makes their pump systems last many times longer than normal. My point of view maybe "slanted", but it is based on facts, not opinions.