vfd switching for test

[thekman]

I am about to hook up a VFD to a 3HP motor and familiarize myself with the menus and whatnot on it. As a general practice, when I'm using 230v I usually throw some type of switch in between what I'm playing with and the incoming power to save me a trip across the shop to the switch on the wall. (which may be questionable by itself here)
I understand that VFD's are susceptible to noise caused by bounce and other occurrences introduced by mechanical switches...my question is HOW susceptible? I plan to use an overload with a START and a STOP button on it...seems to have a sort of sliding action when making, and a pretty rough sounding breaking action.
Would a 3 phase on/off switch be better? (similar to a lightswitch)
Any thoughts appreciated...

 

[DickDV]

Never, yes, I mean never, use a switching device in the input power leads to a VFD as on/off or run/stop control. The drive has control input terminals for that purpose.

Powering up a drive is probably the most stressful event in a drive's life. They run best and longest if powered up and left that way using the control terminals for all control features.

Also, the drive software will have the capability of doing thermal overload protection for the motor. You do not need an external overload device except for unusual applications like multiple motors on the same VFD.

 

[jraef]

"How susceptible" is not a matter of degrees of likelihood of damage, the likelihood is always pretty high. But the damage is incremental and you don't know when it will get to the point of critical failure. So the best thing is to avoid it whenever possible. Can you put your isolation device on the line side? As Dick said, no need for an external OL.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[Skogsgurra]

Being too careful without knowing why is often the first step towards failure.

I have seen 'overcautious' guys doing incredible damage to simple gear. It is good that you asked here. That will help you a lot.

BTW, switching a VFD on is usually not very critical, don't let that frighten you. But lots of switching on/off shall definitely be avoided. And, please, do not open the output while running. That is bad practice and very seldom needed.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[thekman]

Oh, the OL is ONLY for applying power initially. Once on, it will remain on during my testing. I'm only using an OL for the on/off switching, it is purely for convenience, and not an active part of the circuit.
Incidentally, will applying power to the VFD without a motor do any harm....just to go through the parameters....I figure as long as it's not trying to turn the motor it would be ok...?

 

[jraef]

No, in fact the VFD may not even really care if a motor is even attached when you tell it to run, unless it is a Vector drive that is looking for feedback from the motor.

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ozmosis]

thekman
if it is just for parameter familiarization, why not check if the VFD has the ability to power the control section (including keypad)from an external 24vdc power supply. I know our drive can do this (with an option card) and I know of a couple others that can also. It means you are not having to connect 230+ voltages to the power section that, as already explained, have the potential to damage the VFD if not applied correctly.
You would not be able to run the output of the drive or connect/run a motor but it sounds like you don't really want to do this anyway.

 

[thekman]

Ozmosis, I'd love to do that, but don't really see any 'controls only' power connections....it's a leeson drive...pretty much just 3 phase in and control wiring, I figured it pulled off a couple of legs coming in to power the guts. I think I'd still need at least 208 single phase to try that....

 

[MAGTiger]

I tend to agree that the power on event is one of the most stressful time. But, it isn't that stressful. We do lots of testing in our lab and have multiple drives that for which we reconfigure inputs and output peripherals, so we are all the time switching on and off, multiple times a day using the breaker and in about 12 years have never had a drive failure during that event.
Now we have blown up a drive once while moving a connected filter and a bare braded ground strap touched an output terminal...oops. Bad practice moving live parts.

Neil

 

[thekman]

Thanks for all the replies...I'm having a terrible time getting information from my VFD mfr...I've read just about everything I can find here, in the "manual" and various other web searches concerning the DCIB functionality of my VFD and am still a little unsure of whether I need a brake resistor. I measure the DC bus voltage of 300VDC once power is removed and even after 20 minutes. Shouldn't the caps inside discharge through something other than an external resistor? Whey wouldn't they just put a resistor that is switched in/out in there on all models all the time? Is this just a function of the quality and price? I have no idea what the tolerance of the circuit inside is concerning DC overvoltage. I'm going to be driving a very heavy gate with the transmission, which can vary in size between installations, so the load will not always be the same. I'm not sure whether I need to put a braking resistor on it, or a DB module or neither.