Huanyang vfd puts out 175v instead of 220v

Transformers are design for specific operating frequency, more or less less sine waves, the sharp on/off pulse of a VFD is more like hitting a brick wall and the primary current goes vertical as Jim mentioned. VFD is probably toasted. Electronics, switch gear, contactors/coils, capacitors... also do not play nice being fed with the output of a VFD. There are types of transformers used on the output of VFDs which are specifically for that application and operated at a fixed frequency. There is mention of this for larger motors for wells, offshore submersible applications, etc. where the higher voltage = smaller cables/wires. Very expensive. I am a doctor not an engineer, so I just know what I read and have been installing/working with VFDs for the past 10 years.

What is typically done is to use a step-up transformer before the VFD, and then use the VFD to drive the 3 phase motor. The additional problems you would encounter, would be if feeding this with single phase then the VFD size would need to be ~doubled (5 Hp) to operate in a derated mode and it may not operate at all because of phase loss. Additional problem is the VFD voltage spikes on an older motor cause much more rapid degradation of the insulation and motor bearings (i.e., don't do it on an old 600V motor). Easiest approach is a 230V RPC to your current step-up transformer for 600V 3 phase to the machine. If you want VFD speed control, replace the motor with a 230VAC 3 phase motor.
 
The saw has an infinitetly variable vbelt drive so no need for the variable speed feature. I think I will go with a rpc. Thanks for the education. I am $130 poorer but better informed than I was this morning. Live and learn.
 
The failure was most likely because you connected the load while the VFD was running. But even so, it would have been an inefficient setup.
An expensive lesson for sure
M
 
So should I have bypassed the contactor on the saw and run it direct from the vfd? In that contactor there are phases split out for the blade welder, coolant pump and hydraulic pump So that would have required rewiring it all. But perhaps those were single phase. Anyway, I am more peeved at the waste of precious spare time than the 100 bucks And I learned something. Better I smoke this than something high dollar.

thank you to everyone here who shared their knowledge. Note to self: in the future ask here BEFORE you go out and buy stuff.
 
If you study how the saw works, it is likely simpler to use the switch that controls the contactor, to directly control a VFD, bypassing the contactor. You want the VFD to be wired directly to the motor it is controlling. I found, if you have 3 3 phase motors, I would run 3 VFD's. Except for lights, switches do not care how much voltage is going through them.
 
To sblack: ABSOLUTELY!
You should NEVER have contactors downstream of a VFD.
The main motor HAS to be connected directly to the VFD. Secondary smaller motors can be switched on and off AFTER the main load is running.
A blade welder will NOT run off a VFD, by the way.


Cheers
Joe
 
JimDawson said:
The VFD output waveform instantly saturates the the transformers iron core and the current spikes.
Click to expand...
Hi Jim.
Have you looked at the wave form of a VFD with a motor connected and running (with a scope)? Or for that matter with a transformer and motor connected and running?
Let me tell you you would be surprised....

Why do you think it would "instantly" saturate an iron core on a transformer and not on a motor? It certainly isn't a square wave or a saw-tooth wave form.
So I still don't understand why theoretically you can't use a transformer.

Someone else said a transformer is designed for a specific frequency. Yes, true. That only means it will be less efficient at another frequency.
50Hz transformers work OK on 60Hz - a 20% mismatch. So would a 60Hz transformer be OK at 72Hz? Maybe even at 100Hz?
I don't run any of my motors faster than 100Hz, because of bearings and ventilator fans.... and rarely slower than 20Hz because of lack of cooling (I mean of course under significant load).
So I don't buy that argument for this scenario, sorry.

In any case, I admit that I have 'ignorantly' connected a 3-phase transformer between a VFD and a motor and it worked fine. The transformer happened to be double the rating of the VFD and the motor was about half the rating of the VFD.
When I needed a bigger motor on that machine, I used a single phase transformer and a bigger 415V VFD, so I haven't got the old installation running any more.

Cheers
Joe
 
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