inverter and motor
inverter and motor
(OP)
I wish to replace motor gearbox combination that is driven via a dc drive, with an ac motor and new gearbox fed from an inverter.
the system is designed to run at two speeds at its output low speed is 8rpm high speed 45rpm
the current gearbox output is rated at 50nm.
I am aware of the difference in starting charichteristics of ac and dc motors and aware that inverter technology limits the torque of a motor at low speeds
how do i go about sizing the inverter motor and gearbox for this application, i am tempeted to look at the KW rating of the existing motor and just oversize everything and trim it in with the inverter and ircomp facility but really i would like a more informed approch can anyone provide me with some guidance, formulae or poibt me in the right direction
the system is designed to run at two speeds at its output low speed is 8rpm high speed 45rpm
the current gearbox output is rated at 50nm.
I am aware of the difference in starting charichteristics of ac and dc motors and aware that inverter technology limits the torque of a motor at low speeds
how do i go about sizing the inverter motor and gearbox for this application, i am tempeted to look at the KW rating of the existing motor and just oversize everything and trim it in with the inverter and ircomp facility but really i would like a more informed approch can anyone provide me with some guidance, formulae or poibt me in the right direction





RE: inverter and motor
Inverter technology is better stated as a "Variable Frequency Drive" or VFD. This is because an inverter can be many different things. A VFD is an inverter but it is much, much, more being variable and outputting complex waveforms not generally ascribed to an "inverter". A more classic inverter would be the ones in your computer's UPS (Uninterruptible Power Supply) which takes DC and inverts it into a fixed non-complex AC waveform to closely simulate your local AC power.
Next; a VFD can provide the motor's normal full torque right down to a fraction of an RPM. This will impact favorably, the solution you are seeking.
Also keep in mind that a 3ph motor is much more efficient than your existing DC motor so I am not seeing a need to 'up' your power requirements.
I will get off now and let others who live this particular subject to give you the other details you seek.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: inverter and motor
Select a drive with sensorless vector capability and also encoder feedback capability as a safety net if you end up needing it. Do not buy an encoder for the motor unless sensorless vector proves inadequate.
You will find, if properly commissioned and tuned, that the AC system will match the DC performance usually without the encoder option being used. If you, for example, have to develop full motor torque at zero speed and hold the shaft perfectly still while doing it, you may need to add the encoder. Otherwise, probably not.
The days of oversizing everything when switching from DC to AC are over.
Good luck.
RE: inverter and motor
FAQ237-1062 (click on this to be redirected)
JRaef.com
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RE: inverter and motor
Since you only need 50nm at 45 RPM, the output power is less than 1/4 kw. The gear’s input power requirement should be stated by the manufacturer or the gear should come mounted to an adequate motor. The required motor may be 1/2 kw or more, but you may still find a limited VFD offering at such a low power rating. The VFD should be a sensorless vector type rated for constant torque duty.
If the existing DC drive is a simple design without a tachometer, it is unlikely that the VFD will need encoder feedback.