VFD (Solving DC bus issue)

pguerra75

Member
Location
US
Maybe the OP would have the good grace to confirm that......
So I just posted a new thread and realized that I left this one open ended, my apologies. The issue has been solved. The issue was primarily caused by the load. A High pressure reciprocating pump. The load was actually driving power back to the VFD on its return cycle. There were two options for a fix. Getting a MUCH bigger VFD, or add braking resistors to dump the extra energy. We opted for the later. System has been working well for almost three years now.
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
So I just posted a new thread and realized that I left this one open ended, my apologies. The issue has been solved. The issue was primarily caused by the load. A High pressure reciprocating pump. The load was actually driving power back to the VFD on its return cycle. There were two options for a fix. Getting a MUCH bigger VFD, or add braking resistors to dump the extra energy. We opted for the later. System has been working well for almost three years now.
Well, thank you!
 

garbo

Senior Member
So I just posted a new thread and realized that I left this one open ended, my apologies. The issue has been solved. The issue was primarily caused by the load. A High pressure reciprocating pump. The load was actually driving power back to the VFD on its return cycle. There were two options for a fix. Getting a MUCH bigger VFD, or add braking resistors to dump the extra energy. We opted for the later. System has been working well for almost three years now.
We had the same trouble on 50 to 100 HP return fans. I contacted Danfoss about installing brake resistors and they told me that it had to be ordered while purchading a drive. So we had to place the two 100 to 150 supply fans on hand and turn speed down to 20% to get the return fan from running too fast in reverse for drive to restart.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
We had the same trouble on 50 to 100 HP return fans. I contacted Danfoss about installing brake resistors and they told me that it had to be ordered while purchading a drive. So we had to place the two 100 to 150 supply fans on hand and turn speed down to 20% to get the return fan from running too fast in reverse for drive to restart.
Yeah, typically drive mfrs include the “brake chopper” 7th transistor on smaller drives only, because they are part of a module that comes with it. But on larger drives they use discrete transistors for the brake chopper, so it has to be added in the original build of the drive, meaning it has to be ordered with it. For future reference, there are several sources of external brake choppers though that can be field retrofitted to most drives. Bonitron is one of the better known ones out there. I’ve had to use them several times.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
We had the same trouble on 50 to 100 HP return fans. I contacted Danfoss about installing brake resistors and they told me that it had to be ordered while purchading a drive. So we had to place the two 100 to 150 supply fans on hand and turn speed down to 20% to get the return fan from running too fast in reverse for drive to restart.
they make brakes that can be put on the fans to keep them from spinning backwards. :)
 
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