VFD assistance needed

[PetrosA]

A machinist buddy of mine asked for some help that's challenging me to learn some

He has a 3-phase milling machine currently working off a phase converter. Speed control is via belts and pulleys on the machine. He would like to look at VFD options if it would allow him to control speed on-the-fly.

It seems to me that this is possible based on some videos I've seen on youtube where it looks like guys have used a VFD to go from single to three phase and use them to control speed as well.

What do I need to get to make this work?

Thanks

 

[BobRossi]

You need a VFD capable of being fed with single phase. The available power will be reduced by 1/3. There are low cost VFD's on the market that are capable of running on 220v/1ph. Invertek is one.

 

[Rampage_Rick]

I've got a 10HP 230V pump running on an A-B 1336 Plus VFD. Bought the drive on eBay for $800. Assuming the drive supports single-phase input, the rule of thumb is you have to double the size of the drive (i.e. a 10HP motor requires a 20HP drive)

 

[zbang]

Depending on the age and insulation condition of the motor, it may not take kindly to the VFD output.

 

[GoldDigger]

Although a VFD will offer speed control, it cannot do torque multiplication in the same way that gearing or belt ratio changes can.
As long as the motor can supply sufficient torque at low speed without the added multiplier from the drive ratio, it is worth considering a VFD.
But it will be hard to get that information.
A large diameter tool running at low RPM to get the same linear speed at the contact point with the work will require a lot more tool-shaft torque than a small diameter tool running at high RPM.

It may be feasible to use the VFD speed control to reduce the number of belt changes you need to make (i.e. switching back and forth between adjacent ratios) but not to handle the full speed range from lowest ratio to highest.

If the motor is grossly oversized, then there may not be an issue.

 

[mike_kilroy]

Using a VFD does NOT reduce the power by 1/3: you will get the full motor rating from it.

Some really really really old motors will not like the spikes from vfd; 99% of all 230v ones will be fine. some real antiques may benefit from an output inductor. but don't kill the project based on this! list your motor nameplate if you want opinions from some of us who do this every day - you are likely fine.

 

[petersonra]

Using a VFD does NOT reduce the power by 1/3: you will get the full motor rating from it.

I think he meant if you feed a three phase drive with single phase power you can do this, but can only get 1/3 of the power the drive is rated at because you are only using 1/3 of the semiconductors on the input side.

 

[Jraef]

Using a VFD does NOT reduce the power by 1/3: you will get the full motor rating from it.

I think what he was referring to was the usual need to de-rate the VFD, not that the MOTOR loses power.

PetrosA, here's how this works.

Presumably, since he has an existing single phase motor, the shop has 230V. So you would replace the motor with an equivalent 3 phase 230V version, then feed a VFD with single phase, it will produce 3 phase for the motor. All VFDs are inherently capable of this, because what a VFD does is convert the incoming AC to DC, then INVERT the DC back to AC for the motor. The incoming AC then is just a raw material for making DC power, so the VFD can use 1 phase or 3 phase for that. But there are a couple of catches that you need to be wary of;

1. The current DRAWN from the single phase source will be higher than the current going to the motor, by a factor or the sq. rt. of 3 because of the difference between 3 phase and single phase. So that means the components in the VFD conversion section will see more current, by a factor of 1.732x, than they might otherwise be rated for. In addition, the rectification process always involved creating ripple on the DC bus, and rectifying single phase creates SIGNIFICANTLY more ripple than 3 phase. Capacitors are what smooths out that ripple, so using single phase means needing MORE capacitance. So the generally accepted factor for de-rating a VFD is 50% minimum, then if the environment is hot (above 25C), many smaller drives require 65% de-rate. You must ask the question and get an answer in writing or something published, there is a lot of misinformation and guesswork out there about this issue.
2. If your motor is 3HP and under, many many of the small VFDs on the market are capable of, or have versions capable of, doing this phase conversion trick WITHOUT de-rating the drive. That's because at that small of a size, the larger components cost the same anyway. But over 3HP, you will need to at least double the size of the drive vs the motor FLC.
3. There are a few brands out there which have input phase loss protection on the drive, and that feature cannot be defeated, which renders them unable to perform this task. You often cannot tell unless you read the manual, so be aware of that.
4. The torque multiplication issue mentioned above is an important one. Belt / gear ratio changes for changing speed also MULTIPLIES torque inversely. When you use a VFD, torque remains flat. Sometimes that makes a difference on machine tools, sometimes not. It's application specific.
5. Use a Sensorless Vector Control (SVC) capable VFD on a machine tool, not the cheap surplus versions "V/Hz" versions often available on Fleabay. SVC allows the drive to provide steady torque at very low speeds, usually down to around 1Hz, whereas the cheaper V/Hz drives get squirrely at around 15Hz or so. If you are never going to go below 15Hz, then don't worry about it.
6. Be aware there are some very cheap and VERY bad drives on the internet auction sites from China, often with no brand name mentioned. That's because they are absolute junk and have a terrible reputation, so to keep selling them to unsuspecting people, they have removed all mention of the manufacturer, Huanyang. STEER CLEAR!
7. There are potential issues with motor winding insulation on old motors, and/or bearing currents causing "fluting" of the bearing races. But these are more often associated with voltages that you would not typically use in a single phase source system like this. They can be mitigated, but I often don't recommend it up front on 230V drives unless / until there is a proven risk. What I usually say is that if you have NOT yet bought the motor, but one that says it is "inverter duty". If you have the motor already, and it is not, use it anyway and if it dies, replace it then with a better one.

 

[Fulthrotl]

A machinist buddy of mine asked for some help that's challenging me to learn some

He has a 3-phase milling machine currently working off a phase converter. Speed control is via belts and pulleys on the machine. He would like to look at VFD options if it would allow him to control speed on-the-fly.

It seems to me that this is possible based on some videos I've seen on youtube where it looks like guys have used a VFD to go from single to three phase and use them to control speed as well.

What do I need to get to make this work?

Thanks

i've got a 1 hp one sitting in the garage for when i put the pool back into service....
takes single phase, and runs a three phase motor off it, with full controls... i think
i paid about $175 or so for it.. din rail mounted.

 

[PetrosA]

Wow! Thanks for all this info. It's a Leroy-Somer LS90L2 motor. Here's a pic:

 

[PetrosA]

Most of you are referring to HP ratings, which I don't see on this nameplate. Should I use the standard 745W and assume I'm dealing with a 2 HP motor? Since that's under the 3HP rating that Jraef mentioned, do I not need to worry about derating the drive?

Is there a benefit to choosing a 240V Delta output vs. a 380-440V output VFD since the motor is dual rated? I believe it's running on 240V from the phase converter at present. I understand that the input would remain the same regardless.

For calculating my branch circuit, do I use the kW rating (1500W/240V=6.25A) or take whichever amperage (220V (6.65A) or 320-440V (3.95A-3.32A) and use that? Either way, I'm guessing I'm good with a 20A circuit?

 

[Jraef]

Most of you are referring to HP ratings, which I don't see on this nameplate. Should I use the standard 745W and assume I'm dealing with a 2 HP motor?

Yes

Since that's under the 3HP rating that Jraef mentioned, do I not need to worry about derating the drive?

Depends on the drive in question. Like I said, MANY drives, but not all, 3HP 230V and below will not need de-rating. Read the information carefully, and again, if there is no brand name or you see Huanyang, they lie about their ratings anyway, so don't believe them.

Is there a benefit to choosing a 240V Delta output vs. a 380-440V output VFD since the motor is dual rated? I believe it's running on 240V from the phase converter at present. I understand that the input would remain the same regardless.

Drives cannot create voltage. For you to use 440V from a typical 240V single phase source, you would need to buy a transformer to step up the voltage. Absolutely no point in that whatsoever. If you have 240V available, stick to the 220V connections (Delta).

For calculating my branch circuit, do I use the kW rating (1500W/240V=6.25A) or take whichever amperage (220V (6.65A) or 320-440V (3.95A-3.32A) and use that? Either way, I'm guessing I'm good with a 20A circuit?

For calculating your branch circuit, FIRST you must find a VFD you want to use. That's because there is a special rule in NEC Article 430.122 stating that your branch circuit conductors going TO the VFD must be 125% of the max amp rating of the VFD, not the motor. So you can't make assumptions yet, you need to read what the max amp rating (input amps) of your VFD is before sizing your conductors. The VFD will also have a published list of acceptable circuit protective devices, fuses in all cases, some also include circuit breakers. But some of the cheaper ones are NOT listed to be used behind CBs, unless there is ALSO a fuse, which makes it kind of pointless. So again, pick your VFD first, then follow the manufacturers instructions on sizing the circuit and devices ahead of it. FROM the drive to the motor, it's normal; 125% of the motor nameplate FLC.

 

[kwired]

Wow! Thanks for all this info. It's a Leroy-Somer LS90L2 motor. Here's a pic:

Correct that you need to assume 746 watts per horsepower - motors not specifically designed for North America are typically rated in kW instead of Hp. Your drive may or may not have both kW and Hp ratings.

Other information I get from that name plate:

The motor is not quite the same method of changing voltage as typical NEMA dual voltage motors - those you are typically placing low voltage across two coils (per phase) in parallel to one another, or in series if operating at high voltage and the low voltage is half the high voltage rating.

This motor you connect the windings in delta configuration for low voltage but the high voltage you connect them in a wye configuration. This makes the high voltage rating 1.73 times higher then the low voltage rating.

So this motor is rated 220 volts or 380 volts @ 50 Hz but also is rated for 60 Hz 440 volts. Speed will be 1745 @ 60 Hz but only 1440 @ 50Hz. Technically does not mention any 60 HZ rating @ ~220 volts, though unless the motor is marginally sized for the application it probably will work fine if you set the V/F ratio correctly - though it will be at absolute upper end or even a little above your supply voltage if you are running from a nominal 240 volt system. I come up with needing about 255 volts @ 60 Hz to have same V/F ratio. Some drives possibly can still do this - especially if input RMS voltage is up close to 250, but likely will need to be a drive with a higher three phase input rating then what the driven load is.

Don't know some of the terminology I am searching for here but the peak voltage will be higher then the RMS input voltage (I believe 1.414 times higher) but only for part of each half cycle - so that limits actual power you have in the DC bus at the higher voltage and kind of ultimately brings the capacity down to about what input RMS is anyway - but an oversized drive may be able to store enough in the bus to still make it work? Jraef can probably explain it better, but I think I am on the right path here.

 

[Jraef]

...
Don't know some of the terminology I am searching for here but the peak voltage will be higher then the RMS input voltage (I believe 1.414 times higher) but only for part of each half cycle - so that limits actual power you have in the DC bus at the higher voltage and kind of ultimately brings the capacity down to about what input RMS is anyway - but an oversized drive may be able to store enough in the bus to still make it work? Jraef can probably explain it better, but I think I am on the right path here.

You are right about the peak voltage, the rectifier draws current at the peaks, so that's the limit, and the inverter still creates RMS voltage, so the net maximum output AC voltage is still the same as the input voltage. But over sizing the drive doesn't help with voltage, only current.

 

[JRW 70]

I believe kwired is right with the capacitors as a
store/release device. On VFD's, they are apparanty
considered a consumable item, after not too long
ago replacing them for a pump. Then all was work-
ing quite well.

JR

 

[Tony S]

The motor is:
1.5KW (2HP)
50/60Hz (1440/1745RPM)
220V Delta
6.65A

Leroy Somer motors are good as are their VSD?s. Just going by the name plate, that motor isn?t all that old.

Get in touch with Emerson Industrial with the frame size and serial number if you want full information.

 

[kwired]

You are right about the peak voltage, the rectifier draws current at the peaks, so that's the limit, and the inverter still creates RMS voltage, so the net maximum output AC voltage is still the same as the input voltage. But over sizing the drive doesn't help with voltage, only current.

I kind of thought maybe the larger capacitor(s) in an oversized drive may be able to hold enough charge to ride through the process in a situation like described, but maybe not.