VFD ON MILL QUESTIONS

[iron bark]

Hi All,

I have an RF30 mill which currently has a 2HP 1.5kw 1450 RPM induction motor fitted. It is running off a 15 amp outlet.

I want to fit a VFD and 3 phase motor to gain easier speed control, because changing belt pulleys is a royal PITA.

I have no experience with these things, so my questions for those who may have already done this are;

Should I up the motor power and VFD capacity to say 2 kw to compensate for power loss?

Do these setups maintain reasonable torque throughout the speed range?

Will the 15 amp power outlet be sufficient?

Is there any particular spec. I should be looking for in choosing a motor>

If anybody has a suitable motor available I would be interested.

I will have the single phase motor up for grabs when the conversion is done, if anybody is interested(original motor that came with the Taiwanese RF30)

I was thinking of using one of these http://www.ebay.com.au/itm/PROFESSIONAL-1-5KW-7A-220-250V-2HP-VARIABLE-FREQUENCY-DRIVE-INVERTER-VFD-at-/221229448192?pt=AU_B_I_Electrical_Test_Equipment&hash=item33824d7c00&_uhb=1

I would appreciate any advice from anybody experienced with these devices.

Cheers

Ned

[BobL]

Hi All,
I have an RF30 mill which currently has a 2HP 1.5kw 1450 RPM induction motor fitted. It is running off a 15 amp outlet.
I want to fit a VFD and 3 phase motor to gain easier speed control, because changing belt pulleys is a royal PITA.

What speed range would you like to be able to use without changing belts
Depending on what you range you use, be prepared to still change belts sometimes.


Should I up the motor power and VFD capacity to say 2 kw to compensate for power loss?
Going from a single phase phase to a 3 phase motor the power should be smoother so in general there is no need to do this.
Upgrading the motor power is common but it depends on what speed range you want to run across without changing belts


Do these setups maintain reasonable torque throughout the speed range?
This depends on your VFD and the speed range you anticipate operating across.


Will the 15 amp power outlet be sufficient?
You shouldn't even need 15A - 10 A will suffice for a 2HP motors. Especially if slow/soft start is programmed into the VFD.


Is there any particular spec. I should be looking for in choosing a motor
Look for a motor that is easily configurable from star (Y) connect to Delta (∆) connection.
It should should look something like this on the motor name plate - mostly they will use the Y/∆ symbols.

http://www.woodworkforums.com/attachment.php?attachmentid=309703&stc=1

Most Y only connected motors can be converted but it takes some hair raising digging around inside the motor and this should only be done by someone competent to do so.

[iron bark]

Thanks BobL for a very comprehensive answer.

The spindle speeds I usually use range from 100 to 640, with occasional use of 1010 for aluminium.

The spindle speed belt combination I have available ranges from 100 to 2080 for a 1400 RPM motor speed.. If I chose say the 640 RPM belt combination, the ratio of 2.18 would require a motor speed range from 218 to 1093 for a spindle speed range from 100 to 500. That would suit me just fine, and if I needed a higher speed I could change the belt.

For info, the different belt combinations I have give me the following speeds, 100, 160,190, 235, 305, 365, 640, 865, 1010, 1205, 1500, 2080

Are these sorts of figures reasonable and or possible, or am I barking up the wrong tree?

BTW, the reason I am using a 15 amp outlet is because the mill came with a 15 amp plug and I have had a 15 amp circuit installed into the garage for a welder and compressor.

Cheers,

Ned

[BobL]

Thanks BobL for a very comprehensive answer.

The speeds I usually use range from about 90 up to 500, with occasional speeds up to 1000 max.

If I could get a range from 90 to 500 without changing belts that would be ideal, but don't know if that is possible. The reason I am running on a 15 amp outlet is that the mill came with a 15 amp plug on it.

I appreciate your advice, thanks.

EDIT The speeds I mention above are spindle speeds, not motor speeds. I will work out the motor speeds and re-post. Sorry 'bout that.

No need, its the RPM range that matters - not the absolute RPMs

90 :1000 is about a 1:11 speed/RPM range.

In terms of a 1450 RPM motor you can usually double the speed (and not worry about the bearings or cooling), this is done by doubling the frequency to 100 Hz
At the other end of the scale most motors can ran OK at half their original rpms but as the rpms are increasingly reduced (especially under load) you have to worry about cooling and loss of torque.
I reckon you can go down to about 20Hz reasonably safely and you may be able to go to 120 Hz at the top end so this gives you a 6:1 speed ratio.
And all this is why changing belts usually becomes necessary to get the sort of range you are referring to.

If you positively-definitely don't want to change belts a sideways solution to torque loss in to use a bigger motor and/or better VFD but that does not help out with motor overheating.
To do this requires adding independent cooling to the motor, e.g. add an extra fan

It's often not possible to tell what an individual motor can do without trying it.
Some operations like drill are relatively short term and most motors can handle brief periods at higher temps but this is not the best idea for something like a mill.
JoeH found talked about a motor the other day that ran at 150 Hz, some motors with the right VFD run fine at 15 Hz so this would give a 10:1 range but this range is not common.

[iron bark]

BobL,

I was editing when you replied, so the figures and ranges in my edited post might make more sense.

Thanks again,

Ned

[gallegos]

Motor torque is fairly constant across the speed range of a VFD so power drops linearly with a reduction in speed. Depends on how you plan on using it but you might have to change belts anyway if you want the full power. The VFD would be handy at lower loads though.