Thread: New dust extractor reccomendations and build log

Looks identical to the Gregory machinery version.
Which was more like $600 delivered. You could compare the specs.
I think the Gregory had a larger impeller than the others I looked at.

Virtually all of these DC-7 machines have a 12" (305mm) impeller. When companies quote larger impeller sizes than this it makes me wonder if they're talking about the housing and not the impeller, although there are almost certainly some that have bigger impellers. The other thing that separates the ordinary DC-7 from the better ones is the size of the ducting at the point indicated in the attached pic. The cheaper ones are a bit strangled here.

In the case of the Gregory Machinery DC that russ57 has linked to a 355mm (14") impeller is right at the upper limit of a 3hp motor to drive, it could be correct though. You won't believe the difference between your current machine and even an 'ordinary' DC-7. If you upgrade the ducting and machine ports to 150mm and install blast gates you'll have the basis of a very good system. It would be better if you can build an enclosure for the DC. Do you have enough head height in your proposed position to accommodate a DC-7?

Originally Posted by aldav

In the case of the Gregory Machinery DC that russ57 has linked to a 355mm (14") impeller is right at the upper limit of a 3hp motor to drive, it could be correct though.

The reason that it's possible to use a 3HP to drive a 14" impeller on that DC is probably because it's effectively operating as a semi-choked system (ie small inlets and outlets, bags etc) and the motor is only operating at 50Hz. For those that are not aware lower frequency mains supply and a choked a DC moves less air and hence less current is drawn by the motor.

If any restrictions to air flow were to be removed or opened up, or higher mains frequency used, the motor will draw more current and in the long could risk overheating. Bill Pentz warns about this on his website.

This is also why it is important to measure motor currents when opening up DCs inlets and outlets etc. It's especially the case if 3Phase motors are used to drive impellers at higher frequencies where the currents can increase rapidly.

When I modified the generic 2HP DC I systematically measured motor currents as I opened up the inlets and outlets etc.

My DC only has a 13" impeller but when I added a 3phase motor so I could spin it faster with a VFD, I used a 4HP motor because at 60Hz the motor draws a total of 13.5A which in the long run is too much for a 3HP motor but is OK for a 4HP motor.

Originally Posted by aldav

. Do you have enough head height in your proposed position to accommodate a DC-7?

This is definetly something I would have to double check. Boxing it in might be a bit hard as well just due to the location and stuff I have stored around it.

I'll double check the measurements tonight and may pull the trigger on the bayer one

So will driving a 14” impellor with a 3hp 240v motor connected to a 15A mains power point (no VFD) and a 6” system be O/K?

Yep. As BobL has warned though if you went to 8" ducting and inlet and the DE had the equivalent volume of the 8" ducting at the previously discussed choke point you'd be getting up towards your 15 amps and be at risk of cooking the motor.

Will the speed of an AC motor change between free spinning ( no choke points) and with choke points?

Originally Posted by Lappa

Will the speed of an AC motor change between free spinning ( no choke points) and with choke points?

Short answer is yes but the change in speed is usually small, and the direction of the speed change is counter intuitive.

A motor/impeller with large unrestricted entry and exit ports will turn slightly slower than if the entry and exit ports are smaller and/or more restricted.
However the motor/impeller with the larger unrestricted entry and exit ports moves more air so is doing more work and hence will be drawing more current.
Likewise a restricted I/O port DC will reduce motor current draw.

So will driving a 14” impellor with a 3hp 240v motor connected to a 15A mains power point (no VFD) and a 6” system be O/K?

The 15A GPO/circuits on some DCs are used because of the high start up currents.
A 3HP motor on 240V normally runs at about 9A, constantly operating above say 10A is problematic.
I would strongly recommend measuring the currents involved. If its continuously more than ~10A then I would be concerned. It might be fine in its fully rigged up (constricted) state but for example if a filter bag was to blow off the current might shoot up and eventually overheat the motor. I would make sure there was a thermal cut out switch on the motor.

When I switched over from 3HP SP to 4HP 3P I also added a temp sensor to monitor what happens when the DC is run for long periods at 60Hz. Turns out the Temp does go up over time but its not too bad especially on cold days.

Won't your circuit breaker take out the fan before thermal due to the current draw?

That is another question, is it worth putting in a separate circuit for the dust extractor. Currently i would have the table saw and the exactor plus what ever else I would be running at the time (maybe a pedestal fan battery chargers etc)

Wouldn't want to see the saw bog down during a cut and take everything out due to power draw.

Would be very surprised if the Bayer DC does not require a 15 amp outlet. This mandates a dedicated circuit and breaker.

Originally Posted by havabeer69

Won't your circuit breaker take out the fan before thermal due to the current draw?

Sure, but breakers should not be routinely used to protect appliances.

10A GPOs are usually run on circuits with 16A breakers and some 15A GPOs might even run on 20A circuits.
Breakers are not designed to protect appliances but the wiring so they don't activate instantly when they reach the breakers rating and depending on the current being drawn may still work for many seconds at a higher current rating before activating.

Appliances are supposed to protect themselves so most motors have some form of thermal protection or on 3P Machines a current limit. The motor I have tested extensively is the single phase 3HP motor on my table saw which runs on a 15A GPO with a 20A breaker and this motor's internal thermal protection activates at 17A in about 10 seconds. These motor protections are designed for occasional use so if they are repeated triggered they may still damage the motor.

That is another question, is it worth putting in a separate circuit for the dust extractor. Currently i would have the table saw and the exactor plus what ever else I would be running at the time (maybe a pedestal fan battery chargers etc).

Yes it is but it depends on the power rating and types of machines.
An unchoked 2HP (1.5kW or ~6A at 240V) DC will draw close to 6A continuously.
However a 2HP TS does not continuously draw its full rated power (6A).
At free running speed it might only draw 2A, and then the current drawn will depend on load. Cutting 25 mm pine it might only draw 4A, but 50 mm hardwood might draw 7A (yes more than its rating).
6A used by the DC plus 7A by the TS (=13A) by the TS, which is more than 10A but a 10A circuit on a 16A breaker can provide 13A indefinitely especially as the 7A used by the TS is not continuous but happens in pulses.

A 3HP DC and a 3HP will be pushing it but the main issue for these larger machines is the start up currents which can be over 50A for a second or two. Some 16A breakers can cope with this and some cannot.

An unchoked 3HP DC might start from a 10A/16A GPO/breaker but then it draws 9A continuously. Now starting up a 3HP TS on the same circuit is very likely to trigger breakers.
The safest mode of operation is to have a 3HP machinery on their own 15A circuits.

I have 6, 15A circuits for my 3HP+ machines (DC, BeltS, BandS, Welder, TS and a spare) in my shed so I don't have to constantly switch machine plugs in and out of sockets.

FWIW VFDs can be programmed for something called a "slow start" which basically eliminates high start up currents. Of course this only applies to 3 Phase Machinery.

Originally Posted by aldav

Virtually all of these DC-7 machines have a 12" (305mm) impeller.

they all look like they're churned out of the same factory. the only difference i can see is that the carbatec one asked for an extention piece on the outlet of the fan to accomodate larger bags, other then that (and slightly different claimed specs) the ones sold from the common wood work places all look exactly the same other then a different company sticker on the front. so i assume its the same factory somewhere churning these out.

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the only one i found to give the fan size is the last one which is the renegade brand which states its a 12" fan but pretty much the exact same claimed specs as a couple of the others

• Renegade Dust Collector
• 2200 Watt (3 HP) Motor
• Air Movement 2300CFM
• Fan Diameter 305mm
• Inlet Diameter 150mm
• 3x 100mm Intake Hoses
• Bag Diameter 500mm
• Bag Height 850mm
• Shipping Weight 64kg

so after all that i can't really see any benefit of choosing a more expensive one for what is the exact same machine.

I don’t have direct knowledge of any of these, but be wary of assuming they’re the same. It’s common practice in China for factories to work off the same design, but they all set their own specs and quality control etc. So two machines may look the same, but one might be made of 1mm coke can tin with a cheap motor, and the other may be decent construction, a good motor, and some bloke with a head torch checking it all over at the end.

Additionally, locals here may have specified the build price and quality, with the factories then building to spec.

I've examined dozens of small (5HP or less) DCs mainly for leaks, and can't recall any significant differences in motors, or metal thickness used. The only obvious material differences I've identified have been in the materials used for the plastic collection and the filter bags. As well as different materials the bags can vary in thickness with thicker bags less likely to develop leaks. Thicker filters also condition quicker than thinner bags.

The most common source of DC leaks are ill-fitting plastic bags and filters which can usually be remedied with a bit of care.
Next comes holes in the plastic bags, more common in thinner bags and usually caused by repeated use of the same bag and larger wood chips splinters inside the bags continuously swirling around and puncturing holes in the plastic and the plastic flapping/rubbing/abrading against the DC frame or something else.
Then comes holes in the filters and gaps in the metal structures between impeller and filter/collection bag housing. The causes of these two are almost always in DCs that are moved/towed around inside sheds.

The easiest solution to all these problems is to locate the DC outside the shed, or in an air tight enclosure inside a shed and vented outside the shed.