Increasing torque with high power 380V spindle on a low power 220V VFD ?
I'm seeking getting higher torque than from a typical 24000 RPM 2.2kW spindle + VFD setup but don't need higher than 6000 RPM. Chinese spindles don't advertise torque so going back to first principles torque is related to power and rotational speed.
Torque (Nm) = power (W) / ( 2 * 3.1416 * RPM / 60 )
List of common available spindles @ voltage, phase current, and ideal torque:
[220V round spindles]
Spindle 1500W 24000rpm 0.59Nm 220V 3.9A
Spindle 2200W 24000rpm 0.87Nm 220V 5.8A
[380V square spindles]
Spindle 1500W 18000rpm 0.80Nm 380V 2.3A
Spindle 2200W 18000rpm 1.16Nm 380V 3.3A
Spindle 3500W 18000rpm 1.80Nm 380V 5.3A
Spindle 4500W 18000rpm 2.39Nm 380V 6.8A
I'm thinking why I cannot just use a Square 3.5kW 380V, 5.3A/phase spindle on a single phase input 2.2kW, 6A/phase, 220V VFD and take advantage of double the torque 1.80 Nm vs 0.87 Nm. I only need 6000 RPM so the drive voltage wont stop me here.
Has anyone else followed this path ?
Adam
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Re: Increasing torque with high power 380V spindle on a low power 220V VFD ?
Originally Posted by int1
Just buy a 4 Pole spindle 220/240v if that is what your voltage is
The 240v VFD won't be able to have enough bus voltage for the 380v 300Hz spindle
380V will have a very poor performance running on 220v
The 2.2Kw is not 5.8A for them to be 2.2Kw they have to be in the range of 8.5A to 10A rated this depends on the power factor being used and the manufacture
Mactec54
Re: Increasing torque with high power 380V spindle on a low power 220V VFD ?
you can do that, but i would buy the 4.5KW spindle if you need to get 1.8nm of torque continuously.
you will need to program the vfd correctly so as to get the most torque for the least amount of amps.
because of the dc resistance of the windings, you need more volts than the linear volts/hertz relationship gives you. so for instance, at 6000 rpm that would nominally be 126 volts at 133 hz. you may find that is enough volts, but at 1.8nm of torque on that 3.5kw spindle you may find that the motor draws more than 5.3 amps. so you'll need to increase the applied voltage to the motor until the amps reach a minimum.
same at lower speeds. many vfds are programed for 20% "boost" volts (or they call this something else) what that means is the vfd delivers 20% of its maximum voltage (48 vac for a 240vac drive) at zero hertz. as the frequency increases, the linear volts per hz is added on to the initial starting voltage. this voltage is needed to overcome the dc resistance of the windings. because you're using a miss matched motor (380vac) on a 220vac drive, that percentage will almost certainly need to change to something other than the default value.
obviously, if the spindle is air cooled via a fan on the motor shaft, you will need to replace the fan with a separate blower.
edit: you will need that 4.5Kw spindle to get 1.8nm of torque continuously because you didn't include the motor efficiency in your calculations.
for your 3500 watt motor.. 3500 watts is 1.73*5.8a*380v
this is further evidence that all of these motors are rated by the input volt amps.. not the shaft output watts.
you will likely find these motors to be 80% power factor and 80% efficient, which means the motor shaft torque will only be 64% of your calculated value.
Re: Increasing torque with high power 380V spindle on a low power 220V VFD ?
@int1 did you try that experiment? What are the results?
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