motor load control
motor load control
(OP)
Gentlemen,
I have a vfd that I'd like to use on a machine that requires a certain range of power to move material.
Hopefully, this vfd will replace several components. (A reversing contactor, soft starter, and a non-functioning load detector.)
Variable speed is not a primary requirement, but can I get a control signal from the drive that will allow me to externally adjust for load on the motor within certain limits, ie. 20-40% of nameplate KW. (2HP)
As I understand it, sensing power used by the motor should reflect the true load, regardless of varying levels of voltage or amps.
Any simple ideas for how I can get contact closures at the minumum and maximum power settings would be appreciated.
Regards,
Ralph Marotta
I have a vfd that I'd like to use on a machine that requires a certain range of power to move material.
Hopefully, this vfd will replace several components. (A reversing contactor, soft starter, and a non-functioning load detector.)
Variable speed is not a primary requirement, but can I get a control signal from the drive that will allow me to externally adjust for load on the motor within certain limits, ie. 20-40% of nameplate KW. (2HP)
As I understand it, sensing power used by the motor should reflect the true load, regardless of varying levels of voltage or amps.
Any simple ideas for how I can get contact closures at the minumum and maximum power settings would be appreciated.
Regards,
Ralph Marotta





RE: motor load control
RE: motor load control
I have two drives actually. Both are Allen Bradley Cat.160 series. One is a preset model and the other is analog signal follower.
The only useful output configuration I see listed for either is one that signals when the motor is running above a preset current.
Won't the current change with varying voltage, even though the load has not changed?
Regards,
Ralph Marotta
RE: motor load control
Larger drives and more expensive small drives typically have more configuration options.
RE: motor load control
Despite all that, I am curious as to what type of material handling application you have that could take advantage of that feature without reducing speed. On constant torque applications, AC motors will only use as much power as the load demands of them, with or without a VFD. So even with kW sensing in a VFD, you have 2 choices of action;
1) Program kW limits at which the VFD will shut down, or use output relays to control something else that is controlling the load:
2) Automatically have the VFD change speed based on the loading. When you change speed, you are changing power. So if you want to maintain a power level setpoint, you can do that IF changing speed is a possibility. To do so you will also need the ability to do PI control at the very least. Some VFDs have that ability, some do not. If not, you will need an external PI or PID controller.
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: motor load control
The motor is used to drive a suspended rake/conveyor, which spreads crushed ice inside a storage bin.
The load detector monitors power used by the rake to determine the proper amount of ice that is being moved during the leveling and bin loading/unloading process. The rake is raised and lowered above the ice as needed, using a hydraulic lift, in response to the load detector contacts. Too much power here could damage the rake or it's drive chain components, so speed change won't help.
Since there have been past problems with these controls, and I already had the drive, I thought I might simplify the circuit by installing it to replace the other discrete components.
The replacement load detector will probably cost at least as much as a new drive, so it looks like I need to find a different drive.....
I just thought there might be a simple way to set up the one I already have.
Thanks for the help guys.
Regards,
Ralph Marotta
RE: motor load control
Emotron EL-FI M20 load monitor
[link http://www.loadcontrols.com/products/products.html[Load Controls Inc.[/link]
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376