Re: [CAD_CAM_EDM_DRO] VFD drive problems with older 3-phase motors (correction)

Ted Inoue wrote:

>(correction to my previous post)
>I've heard that there may be problems using VFD drives with older
>motors, and I am indeed having problems with mine. But I'd like to get
>input from others on their experiences.
>
>The motor I'm trying to run is a big 3HP 240v 3-phase, 2-speed mounted
>on a Logan Lathe. It was run by the guy who sold it to me using a
>rotary converer, which I haven't tried yet, but will to see if I can
>get it going that way.
>
>For testing, I bypassed all the controls, contactors, etc. and hooked
>the VFD directly to the motor. The motor has 6 wires which I've tested
>with an ohm-meter and concluded that it's wired in a delta format with
>1-2-3 being one set of connections and 4-5-6 being another. At least,
>that's what I'm guessing based on the measured resistances.
>
>Originally, I tried the VFD outputs to the 1-2-3 motor inputs, and
>could get the motor to respond slighly in both directions, but with
>absolutely no power. Enough to rotate about 1/2 rev.
>
>

Can you find out how much current it is drawing while this is happening?
Does the VFD trip out with an overload or something?
What is the voltage and frequency setting of the VFD when this
happens?
Can you run some other 240 V 3-Phase motor with the same VFD?

You are concentrating on the motor, when the setup of the VFD may be
the problem. Do you have the programmer unit (keypad and display) and
programming book for the VFD? What is the rating of this VFD?

>Is there something obvious I could be overlooking? I scoped the
>outputs and I am getting high voltage, periodic (i.e. pwm pseudo-sine)
>outputs (with the motor connected).
>
>

The high-voltage pulses from a VFD are very hard to interpret, as to the
equivalent sine voltage and current that it is supposed to synthesize.

Jon