Do I need a dv/dt output filters?

Well, the current (pardon the pun) concern is precisely because of the change to IGBT's where the switching is so fast, rather than the old Darlington pair.

But I'd agree that this should not be a problem. I've done some power analysis on several hundred HP VFD's, and observed the reflected wave, but I can't see the additive effect amounting to enough to exceed the safety of any industrial motor insulation, and unless it was continuous, and perfectly phased wrong so as to present a short, there almost can't be an issue. I'm no EE, but I'm not ignorant of the subject either.
 
The Darlington Pair... Weren't they from the Beverly Hillbillies or was it Andy of Mayberry?

... Nah, it's not a problem and if something does rear-up, there are other factors at-play. About the only filter someone might consider is a line choke on the supply lines to the VFD. These are just the plastic encased pieces of ferrous ring that you often see on laptop power supplies (aka. wall warts). VFD can produce some conducted emission back into the house wiring and screw-up your TV reception etc... If that happens, try tweaking the VFD frequency and if that still doesn't work, make a 1" diameter ring of soft iron and loop all three supply conductors once through the ring. Most of the stray signal will be induced into the ring and dissipated as a tiny amount of heat only measurable by theoretical calculation and not detectable with any common form of thermometer. Oh, before you make any kind of inductor ring, check the house grounding first. That's the most probably root cause.

Ray



Tony Wells said:
Well, the current (pardon the pun) concern is precisely because of the change to IGBT's where the switching is so fast, rather than the old Darlington pair.

But I'd agree that this should not be a problem. I've done some power analysis on several hundred HP VFD's, and observed the reflected wave, but I can't see the additive effect amounting to enough to exceed the safety of any industrial motor insulation, and unless it was continuous, and perfectly phased wrong so as to present a short, there almost can't be an issue. I'm no EE, but I'm not ignorant of the subject either.
Click to expand...
 
Ahh, Briscoe Darling. It was the Andy Griffith Show. Actually, that "band" was The Dillards, and they still perform. I think only one of them has passed away. Briscoe, played by actor Denver Pyle was not part of the real band. Neither was Charlene, if I remember right. She was played by Maggie Peterson.
 
This thread has been most useful to me, answering all of my questions. Your answers have been easy to understand, directly to the point. Thank you all, I greatly appreciate your effort in answering this post.
 
That's what we're here for, rogee. Glad you found some answers.
 
Those guys were great. I used to love those episodes!

Have you ever listened to the soundtrack from the movie "Oh Brother, Where Art Thou"? Lot's of great music there too. I have bluegrass on one of my Pandora music stations. Great stuff!


-Far enough off-topic.

Nite y'all.


Ray

Tony Wells said:
Ahh, Briscoe Darling. It was the Andy Griffith Show. Actually, that "band" was The Dillards, and they still perform. I think only one of them has passed away. Briscoe, played by actor Denver Pyle was not part of the real band. Neither was Charlene, if I remember right. She was played by Maggie Peterson.
Click to expand...
 
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