Re: [CAD_CAM_EDM_DRO] RF problem with VFD help

stan mcdonald wrote:

> Hello list.
> I have an inverter 220 single phase 40 amps draw at full load, it
> generates alot of RF noise on the AM radios.
>
> To eliminate this noise problem seems to be more of a challange then I
> had hoped for but I have to eliminate this. I have installed a 1" pipe
> in the ground about four feet down and then removed a screw from the
> condute inspection cover from the hydro meter and ran a wire from the
> meter cover down to this grounding rod. This helps some. I also grounded
> the machine to the breaker box since it is about 20 feet from the box I
> took the liberty of using alot heavier wire then is required. I also
> installed the inverter in a steel NEMA box. I have two options that I
> know of left. Build a filter or use an isolation transformer.
>
> The transformer is expensive so I looked through some electronics books
> and found a low pass filter which is suposed to pass 60 HZ
>
> 220 single phase in __________L1_____I___________ SINGLE PHASE OUT
> I
> I
> C1
> I
> I
> 220 single phase in __________L2______I____________SINGLE PHASE OUT
>
> C1=0.01 UF
> L1 & L2 1MH
>
> The capacitor is no problem but where can I get a coil that will pass
> the 40 amps?
> Is there a better way to eliminate this RF?

You can make your own inductors. You may not need a lot of inductance.
If you can find some ferrite material, just winding insulated wire around
it makes an inductor. Even without the ferrite core, just winding wire into
a coil provides inductance, just not as much. Also, what you want is to
put the capacitors (need to be rated for line to ground service) from line
to ground. .01 uF is pretty small. You may need as much as .1 uF of
capacitance, and may need to use 4 of them, 2 before the inductors, and
2 after.

I had the same problem (drove my computer controlled air compressor
wild, and also put fuzz on the video monitor on my CNC machine) but I
was only running 1 Hp on the mill, so I used a modest commercial line filter
unit. I have seen some of these in larger sizes in such catalogs as
C&H, Herbach&Rademan, Surplus Center, etc.

Jon