single phase VFD

[salmanAli1020]

We're testing a 110v single phase Variable Frequency Drive(VFD) connected to a single pump having randomly let's say: R= 10ohm, L= 50mH. and im putting these numbers to fiqure out the relationship between the output frequency from the VFD and the power consumption by the pump, so if u could make a curve or giving me the equations used in here i'll be thankfull.

Regards,
Salman

 

[waross]

I had not heard of a single phase VFD. What make and model are you using?
What type of motor are you using and what starting method is used?
What type of pump are you using. The power consumption characteristics of a centrifugal pump versus a positive displacement pump are quite different.
The power demanded by the pump depends on the pump speed and the dynamic head.
The power demanded by the motor is the power demanded by the pump plus the motor losses.
The effective impedance of the pump will change as the slip frequency changes.
Measure the power into the VFD with a Watt meter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[salmanAli1020]

Dear Carter,

OPTIDRIVE
AC Variable Frequency Drive

this is the type im using and it's connected to a single phase pump in a water and oil flow loop. Id like to make things theoretically (deponds on the power consuption, voltage and Impedance of the pump, .. not to the total head ft or flow rating) before taking measurements.

regards,
Salman

 

[jraef]

It's not related to the math inside of the VFd as much as you think, it's related to the load. You don't say what type of pump it is. If it is centrifugal, the power consumption by the PUMP will follow the Afinity Law stating that power varies by the cube of the speed change. So if the pump is running at 1/2 speed, it will require 1/8th the power it needed at full speed.

If it is a positive displacement pump, expect the power to vary directly with speed, so at 1/2 speed, it will require 1/2 power.

The only othe power consumption issue will be the conversion efficiency of the VFD and the motor efficiency, both of which will drop slightly with speed. Expect the VFD to be 97% eff at full speed, maybe 90% worst case below 50% speed (but remember, the power has dropped too, so it's a higher loss percentage of a lower value). The motor efficiency is all about the motor specs, but expect that to drop similarly.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[John2025]

Does a VFD work on a single phase motor? I thought not.

 

[xnuke]

VFDs can work on certain types of single phase motors like shaded-pole and permanent split capacitor machines, but since those types of motors tend to be small hp, there isn't a lot of use. Most people just use a throttling device on fans or pumps with these types of motors - since you aren't putting that much energy in, you aren't wasting that much by throttling.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[itsmoked]

That or they use a 1ph input 3ph output and use a 3ph motor which is considerably more reliable and the 3ph out VFDs are considerably less expensive.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[salmanAli1020]

yeh, you're right. Thanks guys i got half the answer I was looking for
we here are looking for curves, Powere vs frequency from the VFD, impedance of the pump vs frequency from the VFD. thanks you anyway and if some one could help me with this that's would be great.

Regards,
Salman

 

[salmanAli1020]

I dont need the curves for these nubmers, no I need just to understand the relationships. If similar experience has been done i need the results.
Hope you understand what I want.

Regards,
Salman

 

[itsmoked]

salmanAli1020; I'm sorry but I don't think we can help you with that. As jraef was explaining, you're asking for the power verse the frequency sent to the pump.. It doesn't work that way.

It's all about what the pump is pumping. If it was molasses you can see it would take more power than if it's water. Also, the speed of the pump while pumping whatever it is GREATLY affects the power required. The VFD has to supply whatever that power is - not the other way around. The VFD doesn't dictate the power.

So here we seem to be having you asking what the power will be based on the frequency.

To answer this you need the pump curve from the pump's specification. Then you need to understand the resistance presented by the plumbing of your piping system. You apply THAT to the pump's data sheet showing it's operating curve and from that you see what power the pump will be demanding from the motor at any particular speed. From that you can make your own chart showing the required power delivered by the VFD verses any particular speed you command.

Do you understand this? Did I make it clear enough?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[salmanAli1020]

itsmoked, thank you so much, that was 100% clear and understandable.

 

[waross]

I have never seen motors discussed in terms of impedance.
If you run a motor at a fixed frequency, the current will depend on:
The load.
The no-load losses.
The load losses.
The load may vary greatly, as Itsmoked points out, the load presented by a pump may vary greatly depending on the application.
You may work backwards from the current and the voltage to determine an impedance at one point in time, but that is more dependent on the load than on the motor characteristics.
For now, forget impedance.

Bill
--------------------
"Why not the best?"
Jimmy Carter