vfd before starter--OK?

I have a drill press which came with a single ph motor. I installed a 3 phase with a vfd, with the vfd output wired directly to the motor. Works fine.
I recently helped a friend who bought a drill press with a 3 ph motor (and starter--or whatever that box is). Rather than disconnect and bypass the box, he elected to run the vfd output into the box (using the existing power cord). The motor runs well, but when we slow it down a lot (like 20 hz or less), the box makes a clicking sound, like it's disconnecting,
and the motor stops. I guess that's a magnetic starter, but I don't know what I'm talking about. Also, it won't start when the vfd is set on low hz. Is this damaging anything? Should he bypass the starter & go directly to the motor?

Thanks.

Generally a VFD goes direct to the motor its controlling. Because the VFD cannot run up without the start (or equivalent) button being pressed it is an effective substitue for a Direct-on-Line (DoL) starter or No-Volt-Release (NVR) switch whose primary purpose is to ensure that a machine cannot automatically start up when power returns after a power loss. Whether accidental or by throwing a supply side breaker.

If the VFD has sufficient built in "safe-overload" capacity it is possible to use safely use one box preset to run at utility mains frequency to drive more than one machine provided the motors are sufficiently de-rated relative to the VFD nominal output. Typically no motor can more than 1/3rd nominal VFD output to ensure that the starting surge can be handled but simultaneous running of more than one motor up to nominal is OK. In such cases you must run via the machine contactor controls as the VFD does not provide individual protection. The VFD must also be set at, or close, to nominal mains frequency or the magnetic contractors will not operate properly. As you have found.

Clive

What Clive said.

Goods news is you have several 'easy' choices:

1) VFD (OR DC Drive,FWIW) that HAS the ability to function - and reliably so - AS a " Direct-on-Line (DoL) starter or No-Volt-Release (NVR) switch ".. make use of that feature, per its manual, and recycle the electro-mechanical starter elsewhere.

2) VFD (OR DC Drive) that incorporates a relay or buffered control to DRIVE a relay/contactor to the same effect? Make use of that - per the manual. (SSD 514C has BOTH, FWIW)

3) VFD (OR DC Drive) that has 'none of the above'?.
Put the existing starter ahead of or 'upline' of the VFD. Or go thee and GET a suitable "starter" to protect yeself.

A VFD (OR DC Drive) that automagically powers itself back ON after a power-outage (RUN optioned ON) is not wanted on most machine tools. There needs to be at least a 'look-see' by something with a brain (typically human) to ensure it is OK to resume the march after power has returned. Or not.

Otherwise, personal injury, damaged work, or damaged equipment can ensue.

Damage to the abused / mis-applied starter (post #3) is NOT the major concern.

Bill

As stated by several members above, assuming a one to one relationship between the VFD and the motor, there should not be anything between the output of the VFD and the input terminals of the motor. Once you push the run button on the VFD, it will send voltage (i.e..current) to the motor. Bad things can happen if there is an open circuit between the VFD and the motor. As stated, the contactor will not operate properly if the frequency is not high enough to engage the contacts. and therefore may look like an open circuit to the VFD ouotput.

I had a conversation with a person who used a TECO/Westinghouse L510 VFD for his lathe. He did not follow the manufacture's directions and wired the output of the drive to the input of the lathe, NOT the motor. He was using it as a 3-phase power supply and not as a 3-phase motor speed controller. While under the run condition, the operator turned off the lathe using the controls on the lathe and not by hitting the stop button on the VFD. Since the VFD was in the run command and sending current to the lathe, the current saw an open circuit, reversed and went back into the wrong end of the VFD. He told me this story when he needed to purchase another L510 since he had to pick up a fire extinguisher since he didn't pop the VFD or smoke it, he flamed it!

So, can bad things happen or do damage if you don't follow industry standards or the manufacturer's recommendations? YES!

Unless you have sized the drive appropriately to run multiple motors and have thermal protection on the 2nd and more motors, then there should NOT be anything between the output of the drive and the motor.

The drive will eventually blow up if you operate it this way.

Get rid of the starter in the circuit and connect the drive directly to the motor as instructed in the manual.

Thanks---I guess I know what I need to do.

Ron