On 08/15/2019 04:21 PM, Todd Zuercher wrote:
I am preparing to install a half dozen el cheapo Chinese VFDs on a machine.  
Any one have any idea if I need to or should be putting input line filters on 
them?  No mention of anything like this in the Chinglish manual.  If so how do 
you choose what size?  Could I use 1 big one, or will I need a separate one for 
each drive?
How about rectifiers on the output lines?  I'm assuming those are rated by kva.

RECTIFIERS on the VFD output? Or, did you mean reactors? If 50/60 Hz motors, it should not need reactors. Some high frequency motors may need reactors on the outputs to reduce circulating currents due to the very low inductance of those motors.
Is it possible to set the speed on all of these using a single analog command 
signal (they will all need to run at the same speed anyway.)

You might run into ground loop issues tying multiple VFDs to one speed control voltage. VFDs are pretty big noise sources. But, some of the better VFDs have a totally floating analog input section, and those should be fine. The really cheap VFDs do not isolate the analog input from the mains rectifier, and those would cause a fireworks show if you connect the inputs of several together. Better check with an Ohmmeter.

Jon


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