Don't forget that unless you have another source of cooling for the motor, you may want to limit the low speed. Otherwise I agree with cow. Fun.
IMO anything thats going to run less than 1/2 base speed, gets external cooling. In this application its not as serious as it would be in a constant torque application. This is a variable torque load. So do not buy a VFD at nameplate motor rating. Reduction in VFD size is allowed here.
I assumed the VFD was the speed control and the start/stop commands were initiated at the VFD itself not unlike a motor control with start/stop buttons. Remote switching could be an option but not a necessity here. Please steer me in the right direction if I'm going astray.
You are right on both statements. You can run from the control or remotely. Your customers choice.
In the case of centrifugal fans there is no usable flow below ~30% of the full scale speed and heat becomes the problem with centrifugal loads only at the very low ~2-5% end, but with some motors, not even there. So limiting fans, agitators and pumps at 30% speed is quite common.
Once again the motor manufacturer should be consulted.
Start, stop, and speed adjustments can be done with the VFD alone, assuming it is accessible. You can program in min and max speeds as well as lockout reverse to help make sure nobody accidentally screws up. Remote control is pretty simple as they typically operate at low voltage DC (provided by the VFD).
Well reported.
Most FVD's are designed to run one motor. RTFM carefully if you need multiple loads.
The average VFD has 3-4 ways to control the speed. One might be a pot. You could use two fixed resistors in series, with a toggle switch shorting out one as needed.
Also, unless the fans are rated "inverter duty" you may want a load reactor. The FVD creates faux sine waves full of sharp transitions; the reactor helps reduce those.
True, but multiple motor applications abound. Most VFD's will accept speed references from potentiometer (0-10 VDC) and 4-20 ma. They also will accept a multitude of sensors including temperature.
You might want to download the manual for the drive you're thinking about using and give it a read.
Correct. Better to know whats coming in, before it comes in.
One caution is some motors are not compatible with VFDs. The high voltage wave it creates can damage motor windings, so we typically see inverter duty spike resistant windings.
And as mentioned, fan motors depend on air flow to cool the motor. Motors have a turndown ratio, IE range of low to high speed. You may not be able to go below 30 hz with out overheating the motor. There are motors designed for low speeds
Determine how the speed will be set? Keypad or? Automatic based on air temp?
The biggest advantage of VFDs is the energy savings. Running at 50% speed is 1/8 of the power as 100%, due to the affinity laws
All three phase motors are compatible. Some just more compatible than others...LOL
Inverter duty magnet wire is the correct term. When using the term "Spike Resistant" we should give Baldor Electric the nod. It's their patent.
Basically its just a coating applied to the wire that changes the voltage rating to 1600 volts.
Turn Down Ratio! You must be in this field or you read alot. Good selection of terms. However, I do not like to put a value on minimum speeds. I like to let the motor manufacturer tell me how slow I can go. If they cannot, I use 1/2 of base speed.
Another point for the OP. You do not want to suddenly shed the load; the open circuit output may spike enough to cook the VFD.
When you turn the fan on/off, do it with VFD control inputs.
An open circuit output has no physical connection to the motor. But your point is well taken.
Never use VFD power to start and stop motors. It must be done with the on board or remote I/O from the control.
In todays markets of VFD Look at the Allen Bradley PowerFlex 70 or 700 series. The come complete ready to hook up with a LCD HIM (human interface module) where you can program all the motors data values. And as said before a simple two wire start stop circuit. As for speed of the fan this is controlled with a simple 10k pot. wired directly to the drive, by adjusting the pot. you are adjusting the output hz. I have installed many of VFD and the 70 and 700 are tops. They do make a smaller unit for blower and fans check into it. ( no i am not a Dealer)
The only time I would ever install an AB drive is if it was in the specs and I could not convince the customer/designer how big a mistake they are making by choosing AB.
The guys at my electronic repair shop cannot stand to see an AB come in the door. Every PA I know hates AB too. Just to much money for what you get.
There are to many controls just as good or better out there. But there will always be AB guys and you will never change their mind.
AB costs twice as much as a reasonable drive should and does.
Yep. They think highly of their equipment. Train a guy on AB and its the best drive on the market. Take the same guy and train him on Yaskawa and he realizes there is life after AB. I do like there PLC's. Thats about it though.
