What Happens if Uncharged VFD is Connected to Charged DC Bus

[bodoo23]

if the dc fuse of the uncharged drive is closed when the dc bus of other drives is charged , what happens ? Is there any risk of damaga capacitor ? As I know, capacitor can stand to very high currents thanks to its nature. I know the fuse might clear but if the fuse is oversized, is there any risk for capacitor ?

 

[rdrast]

In general, connecting a discharged VFD directly to a full voltage source is a very bad idea. If there are fuses in line, they will probably instantly clear, even if drastically oversized, and yes, there is the potential to damage/destroy the capacitors, as most drives don't incorporate a precharge circuit directly on the DC bus.

 

[bodoo23]

In general, connecting a discharged VFD directly to a full voltage source is a very bad idea. If there are fuses in line, they will probably instantly clear, even if drastically oversized, and yes, there is the potential to damage/destroy the capacitors, as most drives don't incorporate a precharge circuit directly on the DC bus.

Thanks for your clear respond. I was thinking that the inrush limiter/precharge circuit is just for protecting the front end of vfd but as I understand from your respond, it also protects capacitor from damage right ?

 

[rdrast]

When AC Powered, the charging circuit if most VFD's, especially larger ones, automatically reduce the inrush charging current to the rectifier/capacitor bank.



When powered directly from a DC Bus, unless the drive was designed with an inrush limiter, there generally is not one, as the DC Bus terminals are connected directly to the DC bus in the drive.