On Mon, 21 Apr 2008, Kirk Wallace wrote:
> Date: Mon, 21 Apr 2008 08:08:37 -0700
> From: Kirk Wallace <[EMAIL PROTECTED]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] VFD Interference
>
> On Mon, 2008-04-21 at 05:52 -0700, [EMAIL PROTECTED] wrote:
>> Hi Kirk
>>
>> One needs to be just a bit careful about grounding these sorts of
>> shielding -- if that is what's going on. I recommend star or single
>> point grounding where only one end of the shielding is connected to
>> the frame. If you bond both ends of power wire shielding you'll see
>> ground loops through the metal of the machine as well as the radiated
>> power signals that you are trying to eliminate.
>>
>> Rayh
>
> I thought these might be for shielding because they were not connected
> at the motor end and had lugs at the controller end. I should have noted
> how they were connected before I started ripping everything apart
> (Dooh). Another thing, this is currently another one of my plywood
> specials, so electrically, everything is hanging in space. Once I get
> things mostly sorted out I will make a proper steel housing.
With a VFD (or AC servo) you really really need to ground the motor. This is
of course also a major safety issue for any line operated motor.
For VFD or AC servo motors, there are often 1000s of PF of capacitance from
the stator windings to the motor frame. The high speed switched outputs will
couple to the motor frame giving you huge noise problems, not to mention the
shock hazard...
Peter Wallace
Mesa Electronics
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