Thread: Hafco DC90

Originally Posted by Chris Parks

There was some discussion years ago on the Clearvue forum speculating that the 15" impeller @ 60hz is flow limited using 150mm/6" ducting and 7" would be better. In the US 7'' is obtainable but but not here unless specifically made to order AFAIK.

Bill Pentz always said that 7" would be better with the larger impellers, but even he found the 7" ducting too expensive there and compromised by going with 6" for himself....

I passed on the 8" or 7" mains when I found the fittings too expensive, so in my shop I use all 6" diameter duct for mains and downdrops. It consistently provides over 1200 CFM at all my tools with plenty of airspeed to keep all clear.

I am not sure Chris, it does seem to be restricted a bit with the 150mm intake, I ran through the current draw tests again this morning, either way, there appears to be more suction running at 50Hz compared to the DC-7 unit it is replacing, and there feels to be a huge difference running it at 60Hz




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I will try and compare mine but not having a clamp meter I have to rely on what the VFD tells me.

Originally Posted by NeilS

Bill Pentz always said that 7" would be better with the larger impellers, but even he found the 7" ducting too expensive there and compromised by going with 6" for himself....

Neil, Bill Pentz at the time was not well off financially but I do take your point and in the end 150mm does an adequate job. I wonder if a sheet steel 7" duct could be a DIY job using external frames to roll it into and hold it into shape. I have seen MDF ducting made by someone in the UK that was rectangular in shape but it was a very neat job and its longevity would be doubtful. MDF is also porous but with an open gate that problem largely goes away.

Dust Extraction (spikyfish.com)

Thanks for providing all this info for your DC.

FWIW Trying to make sense of the 3P currents from a VFD measured with a conventional current clamp can be fraught with problems. Many conventional current clamps cannot handle the different frequencies and non sinusoidal waveforms output by vfds.

The clamp meter needs to have a “VFD mode” or be be a true RMS meter and used in conjunction with a low pass filter. Some vfds have these built into their current sensors and display more reliable/ comparative currents. Even the single phase side can experience stray frequencies reflected back from the VFD that can lead to wired results.

despite this I would still be interested to know what the Vfds currents are.

The VFD currents with the filters one are

@50Hz

150mm inlet 3.2
200mm inlet 3.4

@60Hz

150mm inlet 4.9
200mm inlet 5.3


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Originally Posted by Chris Parks

I have seen MDF ducting made by someone in the UK that was rectangular in shape but it was a very neat job and its longevity would be doubtful.

Yes, Chris, I am familiar with that type of ducting.

And it is exactly what I went with following discussions with Bill Pentz .... MDF for the flat sides and 3-ply for the bendy sides.

The corners in square and rectangular ducting are not ideal as they create additional drag and turbulence, but it is easier to make than round ducting unless you have the right sheet metal rolling and seaming equipment. Round gives the optimum cross section, but sometimes needs must. I did have to increase the cross section to compensate for losses in the square/rectangular/hexagonal duct, which Bill advised me on.

Rectangular vs round ducting.jpg

I did paint the inside with a moisture resistant paint to minimise any issues with moisture that goes through the ducting when I'm green turning. Installed mine back in 2006 and it is all still going fine... if anything it will be the galvo in the cyclone that will rust out first!

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I did a quick and dirty test for current draw on my system and though it does not relate to Andrew's it gives some indication of a mostly 150mm ducted system's air flow capacity with a 15" impeller through a cyclone. The system is as follows with all gates open

1 x 125mm flex line into 150mm hard duct - Bandsaw

2 x 100mm, one hard duct, one flex both into 150mm hard duct - Table Saw

1 x 125mm flex into 150mm hard duct - Thicknesser

1 x 150mm - Mitre Saw

70hz - 7.2 amps

60hz - 4.68 amps

50hz - 3.5 amps

After months of too much work and other stuff, I finally moved the new dc90 out into the DE enclosure and wired it up, it seems to have a lot more suction compared to the dc7 it replaced



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