VFD Wiring Question

So I found this kW to Amps calculator.

If the 1 Kw motor at 220v has ...
• a PF of 0.85 it should draw about 3 amps
• a PF of 0.50 it should draw about 5.2 amps.
• a pathetic PF of 0.30 it should draw about 8.7 amps.

My VFD can handle an output of up to 9.6 amps.

But I don't think this helps answer the question ... what should I program into the VFD? :frown:
 
simspace said:
The manual says the motor is rated at 0.5/1 Kw @ 60Khz for spindle speeds 800/1700 rpm.
But have no idea what the current draw is.

The lathe is 1.1/1.4 Kw @ 60Khz for spindle speeds 1450/2820 rpm.
The current draw is 5.4/5.6 Amps.
Click to expand...

Given motors this different, the only safe way to have one VFD power both motors is to have 2 switches and follow the following procedure:
a) power down the live machine.
b) count to 10 enunciating each number out loud while both machines are powered down
c) power up the next machine.
 
Mitch Alsup said:
Given motors this different, the only safe way to have one VFD power both motors is to have 2 switches and follow the following procedure:
a) power down the live machine.
b) count to 10 enunciating each number out loud while both machines are powered down
c) power up the next machine.
Click to expand...

Yeah, it's too risky. I decided to buy a second VFD. I'll have it Monday.
 
mksj said:
Just connecting the spindle wires directly to the VFD is not recommended...”
Click to expand...

Mark, can you elaborate on what you mean here?
Are you saying that the wires from the motor have to be connected to some intermediate device which is connected to the VFD?
 
The wire from the motor are a direct connect to the VFD, there are a few exceptions in some systems that use a safety interlock such as a contactor connected through an E-Stop system in an industrial setting. Also the VFD is operating in a straight V/Hz as opposed to sensorless vector.

If you connect the low voltage control wires directly to the spindle switch, then if you leave the switch in a run position by accident the lathe would restart on power up or release of a safety switch. Sames goes if you press the E-Stop and then release it, and the spindle is not in the stop position. If the lathe has a manual foot brake that also has to be accounted for in the control system design. Lathe have a few more things to account for, and also when it comes to safety you want to make sure that is wired safely. There are some simple relay designs that can be used, it also depends on the VFD.
 
mksj said:
The wire from the motor are a direct connect to the VFD, there are a few exceptions in some systems that use a safety interlock such as a contactor connected through an E-Stop system in an industrial setting. Also the VFD is operating in a straight V/Hz as opposed to sensorless vector.

If you connect the low voltage control wires directly to the spindle switch, then if you leave the switch in a run position by accident the lathe would restart on power up or release of a safety switch. Sames goes if you press the E-Stop and then release it, and the spindle is not in the stop position. If the lathe has a manual foot brake that also has to be accounted for in the control system design. Lathe have a few more things to account for, and also when it comes to safety you want to make sure that is wired safely. There are some simple relay designs that can be used, it also depends on the VFD.
Click to expand...

Thanks Mark, I appreciate the clarification.
 
So on the VFD parameters, there are a few things that do not add up. In addition these are both dual speed motors which present some further issues with using them with a VFD. So lets go through each one. The manual is available on-line but is a very large file, at least the one I downloaded.

The VFD asks for several different motor parameters:
PB.02 = Motor rated power in kW
PB.03 = Motor rated frequency also called the base speed which much be matched to the motor
PB.04 = Motor rated speed at the base frequency
PB.05 = Motor rated voltage
PB.06 = Motor rated current (A)

So first off you are going to want to run each motor with only one set of wiring (poles/speed) and not use the machine 2 speed motor selector. This may require direct wiring to the motor or if you want to power through the switch that connects to the motor wiring it should not be used. You want to select the motor windings/poles that will optimize maximum motor performance, so in both cases this would be the high speed windings.

The next issue is what is called the motor base speed frequency, the mill you indicated is 800/1700 RPM so this figures out to be an 8 pole and 4 pole motor at 60 Hz base speed. This is pretty common, so in this case you would be best to use the 4P setting, There is some loss of torque, but probably will not be noticeable running in sensorless vector mode. As far as motor current I would figure about 3.5A, efficiency/PF of 3 phase motors in this size is in the 0.8-0.85 range which is much higher then single phase.
PB.02 = 1 : Motor rated power in kW
PB.03 = 60 Hz : Motor rated frequency also called the base speed which much be matched to the motor
PB.04 = 1700 RPM : Motor rated speed at the base frequency
PB.05 = 220V : Motor rated voltage (this should be on the motor plate, if Asian this is the typical voltage)
PB.06 = 3.5A : Motor rated current (A) this can be adjusted and one also needs to factor in the motor overload current parameter

On the lathe we are faced with the same issue of the 2 speed motor with a bit of a wrinkle. It would appear that this is a 4 pole and 2 pole motor with a base speed of 50 Hz not 60. That is the only way that the RPM would work out correctly to what you have indicated. I would go with the 1.4 kW connections to the motor.
PB.02 = 1.4kW ; Motor rated power in kW
PB.03 = 50 Hz based on the RPM data : Motor rated frequency also called the base speed which much be matched to the motor
PB.04 = 2820 RPM : Motor rated speed at the base frequency
PB.05 = 220V : Motor rated voltage or nameplate voltage
PB.06 = 5.6A ; Motor rated current (A)

You will need to run the motor auto tuning once everything is hooked up and programmed described on P31. This must be done unloaded, so drive belt should be removed or neutral in a gearbox.

I have tried to wire several dual speed lathe motors (4P/2P) and have had less than satisfactory results as far as the motor stuttering and overall performance. Three phase motors are inexpensive, at the end of the day you may be better off getting a 2 Hp 1750 RPM 3 phase VFD rated motor and running it to 2X its base speed (120Hz) on the VFD. This should give you much better overall performance if you can fit a new motor.

Mark
 
You can buy another VFD for 100 bucks. You'll probably spend most of that on switches and wire to run 2 motors off one VFD. You probably won't be happy with one set of parameters for two motors anyway. You'll likely be bying the other VFD within 6 months anyway so do it now.
 
mksj said:
On the lathe we are faced with the same issue of the 2 speed motor with a bit of a wrinkle. It would appear that this is a 4 pole and 2 pole motor with a base speed of 50 Hz not 60. That is the only way that the RPM would work out correctly to what you have indicated. I would go with the 1.4 kW connections to the motor.
Click to expand...

@mksj, first ... thanks for the awesome post with such great detail. Super helpful.
Regarding the lathe, the motor nameplate does say it's 60 Hz.
Here's a pic if it's helpful. Sorry for the weird angle, it was really hard to get too.

 
This thread is the reason I am going to stick with my SB9......
 
You must log in or register to reply here.
Back
Top