[chbot] VFD with Chocolate fish

Marshland Engineering marshland at marshland.co.nz
Fri Jul 2 10:58:18 BST 2021

I think problem solved.

My thinking.

I originally bought a 220 v single in 380 volt 3 phase out VFD. I got a 220v
in and out. I asked the supplier to correct the mistake and they sent me
complete new board. 

In the meantime I bought a another complete 220 to 380 v drive. That is the
reason I have 2 identical boards.  

The 220 in and 220 v out has a bridge rectifier directly connected to mains
and then to the HV caps. 

The 220 to 380 only has one mains lead connected to 2 of the 3 phase rectifier
pins. I think they have use a 3 phase 380v in and out to bastardized into a
220v in and  380 out. But they got it wrong. What was confusing as the PCB
mount relay on the board with one pin connected to one of the mains input
terminals. The other pin missing. Well not quite. They bent the second pin 90
deg and soldered it to a pad on the top of the PCB. There is a large 300 ohm
resistor connected to this mains input terminal.  What I think happens is, the
caps are charged through this resistor until it reaches a suitable voltage,
then the relay comes in and connects the mains to the caps. Ie to stop the
inrush correct. So effectively the caps are charged with a 1/2 wave rectifier.
If I had to describe the VFD, I would call it a 380 v in and 220 out. At low
powers, the DC volts would be quite high but as power increased, the rms of
the caps would be drop to be around 220 v out.


Cheers Wallace. 

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