# Auto start a VFD by floats



## tlewis01 (Sep 17, 2010)

Need help reading the schematics i have for this auto start application


My question is how does the floats wire to the relay and then the relay to the VFD?


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## oldtimer (Jun 10, 2010)

tlewis01 said:


> Need help reading the schematics i have for this auto start application
> 
> 
> My question is how does the floats wire to the relay and then the relay to the VFD?


 Hire an electrician to do the job.


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## varmit (Apr 19, 2009)

The text on your drawing is a little tough to read, but this drive, as almost all VFDs, use a drive internal power supply to power the drive I/O. This is usually 24 VDC. The drive inputs would wire through the relays ON DRY CONTACTS. DO NOT CONNECT THE DRIVE CONTROL WIRING TO AN EXTERNAL 120 VAC POWER SOURCE. The level switches operate the relays.


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## Electric_Light (Apr 6, 2010)

It's like thermostat wiring, which is considered limited energy low voltage.


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## miller_elex (Jan 25, 2008)

WTF. Why would you want a drive on something that is discrete, e.g. on / off??

Drives used in this capacity WASTE power, because of the loss due to rectifying and inverting A/C.

If you wanted more efficient control then have a lead / lag with two or more pumps and four floats. The possibilities are endless. A drive is NOT the answer unless the height (head) is critical.

Of course, I don't know what your application is because I can't read that drawing.


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## Jlarson (Jun 28, 2009)

miller_elex said:


> WTF. Why would you want a drive on something that is discrete, e.g. on / off??
> 
> Drives used in this capacity WASTE power, because of the loss due to rectifying and inverting A/C.
> 
> ...


Yep, I had a customer the other day saying their bill went up 200 dollars after a VFD was installed by a well contractor. The thing is run by a single float switch. I was just shook my head.


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## sparky970 (Mar 19, 2008)

Why do you want to use a VFD with floats?


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## Introyble (Jul 10, 2010)

well it would of helped if you sent a legible copy of your print


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## John Valdes (May 17, 2007)

Edit. Duplicate.


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## John Valdes (May 17, 2007)

miller_elex said:


> WTF. Why would you want a drive on something that is discrete, e.g. on / off??
> 
> Drives used in this capacity WASTE power, because of the loss due to rectifying and inverting A/C.
> 
> ...


That's the key question. We have no idea what the application is. The addition of one pump could exceed the VFD cost and power consumption cost easily.



Jlarson said:


> Yep, I had a customer the other day saying their bill went up 200 dollars after a VFD was installed by a well contractor. The thing is run by a single float switch. I was just shook my head.


Sounds like your customer should have consulted you instead of the well contractor. What was the reason for the inclusion of the VFD? 
I have had customers report savings with VFD's if applied to the correct project. Cooling towers being one good example. 



sparky970 said:


> Why do you want to use a VFD with floats?


Floats are nothing more than switches and can be used in any combination with a VFD to accomplish a process or task. Think PID loop. Think pressure. Think volume.


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## Jlarson (Jun 28, 2009)

John Valdes said:


> Sounds like your customer should have consulted you instead of the well contractor. What was the reason for the inclusion of the VFD?
> I have had customers report savings with VFD's if applied to the correct project. Cooling towers being one good example.


Yeah well. The VFD an a transformer run in reverse is there to run a 480 3ph
well off of a 240 single phase service. VFDs do save money in some situations but that isn't one of them.


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## McClary’s Electrical (Feb 21, 2009)

Jlarson said:


> Yeah well. The VFD an a transformer run in reverse is there to run a 480 3ph
> well off of a 240 single phase service. VFDs do save money in some situations but that isn't one of them.


 

If a motor is going to be ran AT OR NEAR 60 htz, a VFD is a waste of money initially, and a waste of more money during operation due to losses.


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## Jlarson (Jun 28, 2009)

mcclary's electrical said:


> If a motor is going to be ran AT OR NEAR 60 htz, a VFD is a waste of money initially, and a waste of more money during operation due to losses.


Yeah, it runs at 60hz. I would have put in a roto phase with an input contactor to shut it off between pump runs, but what do I know I'm just an electrician.


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## Electric_Light (Apr 6, 2010)

The OP may have his reason for using it. We don't know the application, cycle rate or the size of this system. 

When you start a large motor across the line, it creates a voltage drop. Some utilities restrict the size of motor that maybe started across the line or number of starts per hour. You know how your lights dim in a room when you start a vacuum?

Large motors have high enough starting current that it will cause flickering to utility's other customers, so to ensure quality utilities often impose aforementioned restrictions.

Across the line starting is also tough on mechanical parts. It's similar to holding your engine at 3,600RPM, then dumping the clutch. The tires chirp, or if they don't, it puts a lot of stress on the transmission. 

VFDs allow efficient soft starting of large motors exceeding sizes or cycles per hour permitted by the utility with minimal adverse impact on other customers. The drive can basically be programmed like accelerating gently from a dead stop at a stop sign to 60mph. 

Agricultural processing and oil & gas industries utilize VFDs just for that. Across the line starting of medium voltage centrifuge had such a high starting current it had adverse impact on upstream 12kV transmission line. The answer? Increase the speed gradually with VSD rather than starting across the line and letting the motor slip until synchronous speed is reached.


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## McClary’s Electrical (Feb 21, 2009)

Electric_Light said:


> The OP may have his reason for using it. We don't know the application, cycle rate or the size of this system.
> 
> When you start a large motor across the line, it creates a voltage drop. Some utilities restrict the size of motor that maybe started across the line or number of starts per hour. You know how your lights dim in a room when you start a vacuum?
> 
> ...


 


Ummmmm,,,,,yes,,,,I'm sure we're all aware of that. 

If that was the op's concern, he could have used a soft start, not a VFD


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## MDShunk (Jan 7, 2007)

I have occasionally used VFD's where a soft start would have worked. Not sure why. Just feeling froggy thay day, maybe. 

VFD's work best on wells when you use a pressure transducer rather than a pressure switch, and pump the well with a PID loop. No noticible change in pressure to the user that way. Instead of cut in and cut out pressures, you have a constant pressure.


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## miller_elex (Jan 25, 2008)

John Valdes said:


> Floats are nothing more than switches and can be used in any combination with a VFD to accomplish a process or task. Think PID loop. Think pressure. Think volume.


In that case it would be an instrumentation job, and the floats serve as safeties in the 'oh sh1t' capacity. 

When someone says floats, my first reaction is SUMP PUMPS, like boiler condensate.


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## Jlarson (Jun 28, 2009)

MDShunk said:


> I have occasionally used VFD's where a soft start would have worked. Not sure why. Just feeling froggy thay day, maybe.
> 
> VFD's work best on wells when you use a pressure transducer rather than a pressure switch, and pump the well with a PID loop. No noticible change in pressure to the user that way. Instead of cut in and cut out pressures, you have a constant pressure.


That's one of my favorite ways to do it, the well contractors on the other hand are like PID, what's that, and you end up with a crappy SQD pressure switch.


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## miller_elex (Jan 25, 2008)

MDShunk said:


> VFD's work best on wells when you use a pressure transducer rather than a pressure switch, and pump the well with a PID loop. No noticible change in pressure to the user that way. Instead of cut in and cut out pressures, you have a constant pressure.


I like that, but wells fill a tank, and that would have floats.

A circ pump on a loop, with a wet diff pres at the end of the supply is a completely different story.

Maybe the OP's application is irrigation related.


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## MDShunk (Jan 7, 2007)

miller_elex said:


> I like that, but wells fill a tank, and that would have floats.
> 
> A circ pump on a loop, with a wet diff pres at the end of the supply is a completely different story.
> 
> Maybe the OP's application is irrigation related.


Fantastic. Constant pressure on the irrigation heads.


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## Jlarson (Jun 28, 2009)

miller_elex said:


> I like that, but wells fill a tank, and that would have floats.
> 
> A circ pump on a loop, with a wet diff pres at the end of the supply is a completely different story.
> 
> Maybe the OP's application is irrigation related.


A lot of small wells out here in AZ have no storage they pump right into there system on demand, I think the design sucks, plus it makes chlorine injection a royal PITA.


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## John Valdes (May 17, 2007)

Jlarson said:


> Yeah, it runs at 60hz. I would have put in a roto phase with an input contactor to shut it off between pump runs, but what do I know I'm just an electrician.


The VFD uses little to no current when not running the pump and VFD's are much less expensive than RPC's. I would use a VFD in your scenario over the RPC in every case.



Electric_Light said:


> The OP may have his reason for using it. We don't know the application, cycle rate or the size of this system.
> 
> When you start a large motor across the line, it creates a voltage drop. Some utilities restrict the size of motor that maybe started across the line or number of starts per hour. You know how your lights dim in a room when you start a vacuum?
> 
> ...


Very good educated post. Thanks.



mcclary's electrical said:


> Ummmmm,,,,,yes,,,,I'm sure we're all aware of that.
> 
> If that was the op's concern, he could have used a soft start, not a VFD


I doubt most here are aware of that. 
He could have used a soft start but most likely needed more control than a soft start would provide. We are guessing at what the OP has. He is gone anyway.



MDShunk said:


> I have occasionally used VFD's where a soft start would have worked. Not sure why. Just feeling froggy thay day, maybe.
> 
> VFD's work best on wells when you use a pressure transducer rather than a pressure switch, and pump the well with a PID loop. No noticible change in pressure to the user that way. Instead of cut in and cut out pressures, you have a constant pressure.


Great example of why a VFD could be incorporated into the system. :thumbsup:



miller_elex said:


> In that case it would be an instrumentation job, and the floats serve as safeties in the 'oh sh1t' capacity.
> 
> When someone says floats, my first reaction is SUMP PUMPS, like boiler condensate.


Float switches are used for all types of applications. And they are nothing more than switches. The diagram he provided did not give any hint as to the type of float switch. This very well could be a process control in a manufacturing facility. The drawing indicates it was engineered system. I am certain the OP has contacted the authors and already has his answers. He did leave after all.



MDShunk said:


> Fantastic. Constant pressure on the irrigation heads.


:thumbsup:


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## Jlarson (Jun 28, 2009)

John Valdes said:


> The VFD uses little to no current when not running the pump and VFD's are much less expensive than RPC's. I would use a VFD in your scenario over the RPC in every case.


My RPC plan would have been cheaper especially after all the service calls for patching the drive and controls up. The RPC would be a more bullet proof install, it's a bad place for a drive, direct sun, high ambient, bad power, voltage sags, end of the distribution line with like 2,000 feet of private feeder between the meter and drive. I put an input contactor on RPCs too so when the well isn't running the RPC shuts off.


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## John Valdes (May 17, 2007)

Jlarson said:


> My RPC plan would have been cheaper especially after all the service calls for patching the drive and controls up. The RPC would be a more bullet proof install, it's a bad place for a drive, direct sun, high ambient, bad power, voltage sags, end of the distribution line with like 2,000 feet of private feeder between the meter and drive. I put an input contactor on RPCs too so when the well isn't running the RPC shuts off.


I did not realize this was an outdoor application. I would have to do a cost to cost analysis in this case. :thumbsup:


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## Electric_Light (Apr 6, 2010)

Jlarson said:


> My RPC plan would have been cheaper especially after all the service calls for patching the drive and controls up. The RPC would be a more bullet proof install, it's a bad place for a drive, direct sun, high ambient, bad power, voltage sags, end of the distribution line with like 2,000 feet of private feeder between the meter and drive. I put an input contactor on RPCs too so when the well isn't running the RPC shuts off.


Before the advent of VFDs, controlling AC motors was difficult. It was common in elevators installed prior to 1980s to use DC motor. Rarely the DC power was provided by the utility (like Con Edison of NYC). Some are retrofitted to static converter, but many still operate get DC from 208/230 or 480 3ph to DC 230V or so using a motor generator. 

In some situations, static converter isn't usable, like if the emergency generator isn't able to handle the 0 to 100% load change seen by elevator motors.

New elevator machines don't use mazes of relay panels anymore. You'll see a panel about the size of a bookshelf with VFD(12 x 12 x 8" or so maybe for 50hp motor), disconnect, communication board (for intercom) and dispatch management(if its ganged setup).


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## Jlarson (Jun 28, 2009)

John Valdes said:


> I did not realize this was an outdoor application. I would have to do a cost to cost analysis in this case. :thumbsup:


Very much outdoor. All the stuff is right at the edge of its temp range too.


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## John Valdes (May 17, 2007)

Electric_Light said:


> Before the advent of VFDs, controlling AC motors was difficult. It was common in elevators installed prior to 1980s to use DC motor. *Rarely the DC power was provided by the utility (like Con Edison of NYC)*. Some are retrofitted to static converter, but many still operate get DC from 208/230 or 480 3ph to DC 230V or so using a motor generator.


DC motors are operated from DC drives using AC input. I am not sure what you mean. I have never heard of any utility providing DC power to customers. I think that was resolved when Tesla blew up Edison's DC technology.


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## Electric_Light (Apr 6, 2010)

John Valdes said:


> DC motors are operated from DC drives using AC input. I am not sure what you mean. I have never heard of any utility providing DC power to customers. I think that was resolved when Tesla blew up Edison's DC technology.


Many traditional elevators are DC motor driven. Consolidated Edison of NYC provided DC power to grandfathered elevator users, but after 125 years of service, they discontinued such service in 2007. 

The so called "DC drive" that is solid state is referred to as "static drive" in elevator field. When the original install was motor-generator, static converter can save energy, but it can also cause problems. The line current responds directly to motor load and building electrical or backup generator may not be able to handle it, especially launching fully loaded elevator cab.

Motor-generator (basically three phase motor driving a DC generator) had a significant amount of rotational inertia that functioned as a massive flywheel to cushion and cut down dI/dt substantially. 

See this article:
http://www.mceinc.com/DMS/Article%5CTom%5Cstatic_drives.pdf

DC motors were easier to control then since they can control the output by varying the field current using resistors.

VFD AC driven elevators use advanced software programming for quickest leveling and maximum creature comfort with controlled rate of acceleration. During braking, some systems dump kinetic energy into multi-kilowatt resistor box in machine room or more advanced drives have the ability to pump it back into the grid.


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## John (Jan 22, 2007)

Here is what I think it is with limited prints and information. I think it’s a sewage pumping lift station control and not a complicated motor start/stop circuit. There are two level switches with both of them being a pendent type float mounted at a low level and the other one mounted at a higher level in the lift station pit. The lower level switch would be for most of the time and be used for energy efficiency. During times of high inflow the upper pendent switch would activate the VFD to drive the pump at a higher speed to keep the pit from flooding. Basically two pumps for one. 

Makes Sense…No?:no:


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## John Valdes (May 17, 2007)

Electric_Light said:


> Many traditional elevators are DC motor driven. Consolidated Edison of NYC provided DC power to grandfathered elevator users, but after 125 years of service, they discontinued such service in 2007.
> 
> The so called "DC drive" that is solid state is referred to as "static drive" in elevator field. When the original install was motor-generator, static converter can save energy, but it can also cause problems. The line current responds directly to motor load and building electrical or backup generator may not be able to handle it, especially launching fully loaded elevator cab.
> 
> ...


That was an excellent lesson. I learn something every day. Thank You.



John said:


> Here is what I think it is with limited prints and information. I think it’s a sewage pumping lift station control and not a complicated motor start/stop circuit. There are two level switches with both of them being a pendent type float mounted at a low level and the other one mounted at a higher level in the lift station pit. The lower level switch would be for most of the time and be used for energy efficiency. During times of high inflow the upper pendent switch would activate the VFD to drive the pump at a higher speed to keep the pit from flooding. Basically two pumps for one.
> 
> Makes Sense…No?:no:


John, I have no idea. I hate when someone asks a question and leaves. We must read between the lines in this instance. I will consider this case closed unless the OP has more information.


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## John (Jan 22, 2007)

John Valdes said:


> That was an excellent lesson. I learn something every day. Thank You.
> 
> 
> 
> John, I have no idea. I hate when someone asks a question and leaves. We must read between the lines in this instance. I will consider this case closed unless the OP has more information.


What do mean "Read between the Lines" It was so bad of a pdf conversion the lines were just barely visible, #[email protected]$$#@

No print is better than a FU'd print 

Frickin fly by posting.

AHHHHH!! feel better now:jester:


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## Electric_Light (Apr 6, 2010)

Maybe someone screwed up and the basement machine room computer he was posting from flooded and no longer able to post response?


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## John (Jan 22, 2007)

John Valdes said:


> That was an excellent lesson. I learn something every day. Thank You.
> 
> 
> 
> John, I have no idea. I hate when someone asks a question and leaves. We must read between the lines in this instance. I will consider this case closed unless the OP has more information.


http://www.pumped101.com/vfd pump selection level control.pdf

Check it out. :whistling2:


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