Thread: External DC - finding best of bad options

Well, I have looked into the Felder AF22. This is a 3 HP dust extractor, and Felder provide performance curves for it. Attached.

Bottom line is that it too, will not provide the 800 to 1000 cfm airflow at 4000 fpm as required if we go by Bill Pentz's recommendations.

With no ducting attached, this unit will achieve 868 cfm at 20m/s (4000 fpm) airsteam velocity if the inlet is 160mm. Once ducting is attached, that will decrease further. How much I have not calculated, but you can look at curves A and C (both for 120mm inlet), and see the way that pressure and to a lesser extent flow are pulled down by the addition of 4 metre of flexible hose. That's without elbows, junctions, gates and a realistic run of ducting.

Granted, the filter bag area is 1.8m2 (about 20ft2), and the Chinese 2-bag 3HP units have about twice the filter bag area. This will help them perform a bit better than the Felder AF-22. But it is not likely to give any miraculous jump in their performance. So it looks like 3HP dusties are all useless for dust collection too, at least by Pentz's criteria.

So, suburban woodies, the story is this: give up woodworking. You cannot get a DC system that will work unless you get one of those 5HP cyclones. That will sound like a jet engine taking off, have to run pretty much the full day you're working and I don't know what you're paying for power. Put it outside and the neighbours are within their rights to complain at the bloody racket all day every day. Or keep it inside and forget about a reasonably quiet pastime - you'll feel like you're working in a steel factory.

Me too. I can see that if I live where I am living now (medium-density suburban Canberra), I have a choice to either give up woodworking and preserve my health, or continue woodworking and risk my health. That does seem to be the conclusion here.

That'd be right - in the attachment to the previous post, in the table there, I got the values for airflow in the wrong order. So use this attachment here.

Originally Posted by Gunnaduit

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Interesting Felder NSW advised me not to enclose the full unit as that would put the motor in with concentrated fine wood dust. Nothing to do with hazard for Felder motors in particular but as a general precautionary principle with regard to electrical devices and potentially explosive combustible aerosols. Seems it could be sensible advice to me, although of course 3-phase induction motors are fully electromagnetic, no commutators, starting capacitors or centrifugally switched starter windings. But if I go with that advice, then instead of full unit enclosure in a cupboard, I would make a full polycarbonate cowl around the upper filter bag, sealed off at the bottom of the bag and educting to the roof vent. Motor remains outside this enclosure. Any thoughts or comments?

Just to add a little here, I have my cyclone/fan housing/motor totally enclosed in cool room insulation and no dramas so far, in principle the motor is isolated from any dust stream so should not fail from dust or suffer an explosion as a result of dust, a greater concern is how hot it might get in summer but no probs yet, if it went 8 hrs a day I would determine how hot is does get.
A DC system within a fully enclosed enclosure may present more of a concern but I have seen plenty of 3ph induction motors in all sorts of dust filled environments and they don't fail all that often. A few forumites here have done the full enclose on their systems, no reports of dramas with motors that I have seen. On dust explosions/fires in DC systems there have been a few threads on the subject, seems to be not so easy to get a system to explode, I myself had huge potential for an explosion but nope.


Pete

Originally Posted by Gunnaduit

But it is not likely to give any miraculous jump in their performance. So it looks like 3HP dusties are all useless for dust collection too, at least by Pentz's criteria.

So, suburban woodies, the story is this: give up woodworking. You cannot get a DC system that will work unless you get one of those 5HP cyclones. That will sound like a jet engine taking off, have to run pretty much the full day you're working and I don't know what you're paying for power. Put it outside and the neighbours are within their rights to complain at the bloody racket all day every day. Or keep it inside and forget about a reasonably quiet pastime - you'll feel like you're working in a steel factory.

Me too. I can see that if I live where I am living now (medium-density suburban Canberra), I have a choice to either give up woodworking and preserve my health, or continue woodworking and risk my health. That does seem to be the conclusion here.

That is a very fatalistic view of things with no reality. It is possible to quieten down a 5hp cyclone effectively and my neighbours certainly do not complain. As I keep saying, everyone makes their own choice in this life and in the end we have to live by those choices for better or worse. The noise issue is one I tell those making inquiries up front so they can make their choice. I have had some come back and tell me after they got it going that to them it was not an issue so it can't be too bad and no one has come back to me saying it was an insurmountable problem.

guys please this is important,,,,,,,,,,,,,,,,


i need the dimensions of a deep groove ball bearing to fit a 12mm shaft

Originally Posted by Gunnaduit

Anyhow, Felder don't have any of the AF14 for almost 3 months.
Go for a bigger machine than that, I might as welll consider the Pentz cyclone. Looks relatively simple. But you can't just get the rotor on its own then go out get a 3-phase Weg motor from the industrial supplier?

I pretty much did that, I made my own rotor but something suitable should be available off the shelf, Howden for e.g. I had all the metal bent/folded at the sheeties as per BP design and then welded it all up, bought a 3kw (4hp) 3ph WEG and plonked on top, not too certain on actual flows/pressures but seems to work well, I'll get organized to test it one day, it all lives outside (in suburbia) I have a muffler on the exhaust for noise suppression plus noise suppression inside the fan housing plus the cool room insulation, it's not completely silent but I struggle to hear it if I walk around the corner of the house or inside the house or 20m down the backyard within direct line of sight

A few pics...
Attachment 211436fan housing.jpgoverall view of DC.jpg
3kw motor.JPG

This a smaller fan wheel 9 or 10"
small fan wheel.JPGbackward curving blades.JPGfan wheel hub.JPG
The blade on the right shows size progression for the 12" which I currently have in the DC
blades.JPG



Pete

Ok, Mini, fair enough. I get grumpy when things don't turn out right. Anyway, it's a new day now. Noise is a big issue for woodworking in the new 'burbs where the old 1/4 acre block is a thing of the ancient past.

On the need for a 5HP cyclone as opposed to a 3HP sigle-stage DC, I don't really understand the discrepancy between performance on the 3HP Felder (18" radial paddle-wheel impeller) with its draw of 868 cfm through a 6.3" impeller inlet with no ducting (its performance is not sufficient), and BobL finding his 3HP Carbatec dusty getting 1250cfm with 6" ducting attached (which would be fine). That's a 30% difference in performance, and would open up wider if the Felder had ducting attached.

But caution suggests that unless it can be shown for sure that the Carbatec dusties absolutely cream the Felder dusties, and there's no engineering 'accounting errors' going on here, the working assuption from the only curves available (the Felder curves), does make it look like the single-stage dusties up to 3HP are not suited to fine dust extraction. Or am I being over pessimistic again -- distinctly possible!

Maybe this ought to all go off to Choice magazine who could test these things. After all, the health of, what, maybe 20 or 30,000 woodworkers across the country is at stake here, plus there's some press-release worthy scandal about bogus advertising claims, plus the next hidden respiratory disease scare to hit the country -- families at risk from woodworking dads. Hey, but as far as we know, it's actually true.

Pete, thanks a heap for the pics - what a monster! But I could do the same - I know a tame sheetmetal fella in the local industrial suburb. Your impeller is interesting to me as it is a standard shrouded airfoil-type centrifugal impeller rather than an open paddle-wheel type. Much more efficient. Presumably usable because the big solids have already separated out by the cyclone, so clogging is not an issue. How tall is your unit? Is it louder than one of those ordinary split-cycle air-conditioners you see on residential houses?

Ian

Originally Posted by Gunnaduit

Ok, Mini, fair enough. I get grumpy when things don't turn out right. Anyway, it's a new day now. Noise is a big issue for woodworking in the new 'burbs where the old 1/4 acre block is a thing of the ancient past

Noise certainly is an issue at all times, no doubt about that but we as woodworkers who use machinery generate more noise with a saw or thicknesser etc than any cyclone will ever do. The comment is often heard that with ear defenders on and the machine going that the cyclone cannot be heard by the operator. That does not take away the need to reduce it though. Most owners seem to achieve this quite well and to everyone's satisfaction so it is not too hard.

Originally Posted by Gunnaduit

On the need for a 5HP cyclone as opposed to a 3HP sigle-stage DC, I don't really understand the discrepancy between performance on the 3HP Felder (18" radial paddle-wheel impeller) with its draw of 868 cfm through a 6.3" impeller inlet with no ducting (its performance is not sufficient), and BobL finding his 3HP Carbatec dusty getting 1250cfm with 6" ducting attached (which would be fine). That's a 30% difference in performance, and would open up wider if the Felder had ducting attached.

Bob is the physicist here so I will leave that to him. All I can say is that both use a different style impeller and I might advance the notion that the Felder is designed with the view to making less noise but having sufficient performance in their eyes to do the job. Beyond that I can make no comment and would certainly not denigrate the product.

[quote=Gunnaduit;1501986]But caution suggests that unless it can be shown for sure that the Carbatec dusties absolutely cream the Felder dusties, and there's no engineering 'accounting errors' going on here, the working assuption from the only curves available (the Felder curves), does make it look like the single-stage dusties up to 3HP are not suited to fine dust extraction. Or am I being over pessimistic again -- distinctly possible![quote]

All may not be what it seems. There are two sources for numbers, America and the rest. In America the motor runs at 3450 rpm and I bet that those are the figures quoted in any literature here as the manufacturing source would be the same. The Europeans quote numbers at 2800 rpm so the airflow if quoted on the same machine would be lower, which it isn't of course. What Felder might have done is traded off noise against air flow but that is only an assumption on my part.

[quote=Gunnaduit;1501986]Some of the performance difference could be in the source of those figures. One source could be American and the Felder source is definitely European. The Americans run their motors at 600rpm faster so would see a performance advantage in that. The Australian retailer goes along to the manufacturer and asks for figures so they trot out the Yank numbers and he publishes them here. I am not saying that is what happens just offer it as a possible explanation. Never let a good story get in the way of the truth....[quote]

The big problem with any test is there are no defined standards to test against as far as machine performance goes and little more in the way of required standards. If you walk into a cabinet making workshop in Oz it quickly becomes apparent that any OH&S dust issues either are ignored or there are none. The dust control industry is only interested in the big industrial scenario and all in all the small end of town is left to its own devices. I would suggest that unless someone jumps up and down and does some intensive lobbying for many years that situation will not change. If the government was to get involved in the specification of dust collection in the home workshop it would be a disaster and I bet there would be far less hobbyist woodworking done.

Originally Posted by Gunnaduit

Maybe this ought to all go off to Choice magazine who could test these things. After all, the health of, what, maybe 20 or 30,000 woodworkers across the country is at stake here, plus there's some press-release worthy scandal about bogus advertising claims, plus the next hidden respiratory disease scare to hit the country -- families at risk from woodworking dads. Hey, but as far as we know, it's actually true.

The biggest problem as I see it is at the manufacturer/design end of the industry. Somehow they need education on what what is required in a machine for it to be effective when hooked up to the DE, get that right and half the problems would disappear overnight.

Let's assume that we find a test and Choice conducts the test and everyone says great I know what to buy now and go out and do it. Then they hook it up to the machine and are P'd off because it does not work so Choice gets a serve for not knowing what they were doing. The real problem is the machine has not been designed with DE in mind, the manufacturer put a DE port somewhere on it and started selling them giving no care about what happens later. This is a big issue and one they do not want to address. I have had that conversation and all I got was a shrug of the shoulder or similar. I myself have come up with strategies to modify machines but a lot of owners understandably do not want take an angle grinder to a machine that cost them a lot of money! To me it is a device that doesn't work so needs fixing and modifying it doesn't worry me but I can understand why others might not want to do that.

Thanks for listening and sorry for the formatting errors but this was my third attempt at formatting and I quit!

I've been crook with gastro for the last couple of days so haven't been able to keep up with this thread.

OK, with the extra information under the fan curves I can see these curves are not just impeller curves but includes the info about inlet diam and some other info, and what Gunnaduit said earlier about extrapolating to zero does apply.

In this case the AF22 with the 160 mm inlet is easily going to be able to pull >1000 cfm since it will pull that at about the 5" pressure point and the remaining 4+" should be enough to cope with the ducting and a few bends etc.

What the curves also clearly show is what a dog the 120 mm openings are. It also shows that 4m of flex loses ~2.8" of pressure and 37 m3 per hour.

BTW we have not mentioned ports on machines which are still bottlenecks on most systems.

Mini, listening with open ears (reading with open eyes?), keep talking! On the other hand I should probably leave off, but I'm genuinely concerned and lacking an all-round good solution here.

The problem personally is that now, unless I find a good solution I'm never going to really enjoy woodwork any more, if I know every saw cut just gets me that little bit wheezier. Yes I might not, but then I might. Its not a great thing to have at the back of your mind, that you might not be acting in your own best interests.

Noise is such a concern, not because I can't put on earmuffs (I wear them now anyway) but "what will the neighbours think". If the dusty could go on only when the saw (or whatever) is actually spinning, then off again when the cut (sand, rout, whatever) is done, that might be ok. But that's not how it works -- or maybe it is?

Type of impeller should make some difference for noise. The possibility with a cyclone is that it might be possible to use properly shaped fan blades (CFD designed if necessary, for lowest noise generation), as long as all that fancy work doesn't just end up clogging. The single stage dusties - Felder one and my old 1HP Carbatec chip collector - have a paddle wheel rotor, just square radial blades. You couldn't do worse for making noise in a fan (the turbulence loss must chew about half the available energy) but it is as clog-proof as you can get, necessary because all the chips, sticks, rusty nails, everything, fly through the impeller (no cyclone to drop them out). So maybe the cyclone should (or could) theoretically make less noise than a single stage dusty. But I don't know - it needs one of those dB meters.

The Felder data I got was all from the Operation Manual (i.e. the user guide) issued in Austria and printed multi-European languages + English. The curves, the motor rpm and voltage, units of measurement and so on all seemed to relate to Europe. So as far as it goes, that is a consistent set of data for the AF-22 in that attachment I mounted in this thread last night. The one thing I got wrong in my post this morning was adding the AF-22 rotor diameter - 18" was off an equipment review, but going by the diagrams in the Felder manual it is probably 400mm (about 15.75").

I did actually send off an email to Choice in case they were interested in this issue of bad equipment on the market, dodgy performance figures in the advertising, and the underlying health risk, but as I perhaps shouldn't have commented in my email to them, I didn't expect much to come of it. Still, you never know.

The uni engineering faculties have fluid dynamics labs, where it is not a hard thing to set up and measure flow, pressure and so on. Nobody's got money, but students do have to do a short research project. Two different dusties and all these issues = one good short research project.

Originally Posted by Gunnaduit

BTW we have not mentioned ports on machines which are still bottlenecks on most systems.

My rant about machine manufacturers while not specifically mentioning ports was meant to include them.

Hi Bob, hope the gastro's over. Bad news, that.

In this case the AF22 with the 160 mm inlet is easily going to be able to pull >1000 cfm since it will pull that at about the 5" pressure point and the remaining 4+" should be enough to cope with the ducting and a few bends etc.

What I was thinking when I looked at these curves, but stand to be corrected, is that the point on the curve that matters is where the aistream velocity is at least 20m/s = 4000fpm. On the 160mm curve, that point is back at 868 cfm. Then flow will drop with ducting and elbows etc., also with the tool hoods as you say.

So how does it work? How are you seing the curves when velocity is taken into account?

Or put it this way: do you think that from these curves it would be possible to estimate the operating point in terms of power, cfm, velocity and pressure, in a scenario of a typical double-garage-size ducting system?

For performance figures using different type impellers etc have a look at this, it seems to be the standard referral site for any questions about impellers etc.

Cincinnati Fan - Industrial Fans and Blowers

Yes I downloaded the "Cincinatti Fan Engineering Data Catalog Eng-409" yesterday, from that link, it is certainly a useful little book.

And here's the real eye-opener diagram, that indicates how the whole system balances at a certain point depending on your fan curve, fan power, and the ducting system resistance, assuming a certain rpm.

The beaut thing to do would be to aim for a calculation of this in a practical instance. Gets back to the AF-22, because the fan curves are there. Pity there's no power curve, but maybe that can be estimated by assuming an impeller efficiency factor and using the pressure/flow data. And then assuming a typical duct system. Would be ballpark maybe, but great to see both the logic and the outcome.