Thread: 2hp DE Build

Today I made the top and bottom plates for the blower. 18mm MDF. 3mm router bit with template guide on the router. I'll cut the hole in the bottom plate when I have the 150mm hose adaptor.

For the side wall of the blower I have a few options:
*2.5 or 3mm polycarbonate. Will be expensive to buy a long thin strip I think.
*0.8mm galvanised steel sheet. I haven't priced this yet, but I suspect I'm going be charged for a full sheet. Bunnings have small sheets but I have no way to cut it cleanly and it will need at least one join.
*2.5mm aluminium sheet. I have a 1800x300 length of this. I can cut it with my track saw. However it's very stiff and I'm not sure I will be able to bend it to the required radius. Perhaps I can anneal it?

Appreciate suggestions for material for the sides and where to get it without being gouged.

I'd try a sheet metal fabricator. Like gutters, flashing etc.
Probably get an off cut, even colourbond. A strip 100-150 wide? They might even cut it for you... Or Aviation snips would do it easily. Especially if you have offset type. Dewalt 254mm Left Cut Offset Aviation Snip DWHT14677 | Total Tools

*2.5 or 3mm polycarbonate. Will be expensive to buy a long thin strip I think.

That would be pretty exxy as its usually sold in large sheets. If the DC was always used in a closed enclosure where it is unlikely to be knocked I would even consider using 1mm PC. From memory a 1.2 x 2.4m sheet costs about $90. Bunnings has even larger sheets of 0.8 mm for $140. I have bought several of these sheets and found endless uses for it in my workshop. Its brilliant for guards and covers and I lined the top of my electronics bench with a large piece of it

*0.8mm galvanised steel sheet. I haven't priced this yet, but I suspect I'm going be charged for a full sheet. Bunnings have small sheets but I have no way to cut it cleanly and it will need at least one join.

Joins are OK provided they are streamlined.
On my forge blower where flow was not critical I used some galv pieces from the back of an appliance and used a simple lap joint and pop rivets.
New Blower for gas powered forge
If flow was critical, a grooved flat lock seam could be used.

*2.5mm aluminium sheet. I have a 1800x300 length of this. I can cut it with my track saw. However it's very stiff and I'm not sure I will be able to bend it to the required radius. Perhaps I can anneal it? .

To anneal the Al, it will need to ALL be heated to just visible red heat and held it there for some time. This is near impossible to do with a single small flame as the Al conducts the heat away too quickly. I have done small pieces in my mains gas furnace and on a BBQ burner covered all over with firebricks. BTW it is really easy to overheat and melt the Al

For my next blower I would consider using the SS from a clothes dryer drum. It usually has some rounded bends in it but they can be hammered out. They won't be perfect but they will be good enough for a blower.

FWIW:
One way an improvement in impeller performance could be ascertained would be to measure the static pressure pulled by both blowers so maybe reassembling the original impeller and measure that first.
However, even if an improvement is obtained I wonder if there will be much or any advantage over the original blower once a cyclone is attached.
The BP blower is designed to suit the BP cyclone so the likelihood of it working efficiently on a third party cyclone would be debatable.
My real concern is that using any cyclone on a 2HP/12" blower is likely to significantly restrict air flow. This is why BP uses a 15/16" impeller and 4HP motor on his cyclone and bear in mind that the BP cyclone is extremely efficient.

Any sheet metal or air conditioning ducting workshop will cut it for you, cost would be negligible and exact size just fit it on and continue.

Thanks all for the replies.

I think Colourbond is only 0.55mm? Might be a bit too thin for this job.
I figured annealing the Al might be a problem. I won't even attempt it.
Will call a few sheetmetal fabricators for a quote. Would be a nice surprise if cost was negligible, but my limited experience with these sorts of places is they see walk-ins as a cash cow. Will also check out the Bunnings PC sheets. I agree it's very handy stuff.

I'm not expecting a huge improvement in blower performance. There will definitely be some improvement, because the original blower housing isn't spiral shaped. They just offset the fan inside a round housing to create a pseudo spiral- a method Bill Pentz says results in poor performance. I had to make a new blower anyway, as the original steel housing could not be modified to suit my DE design.

I believe the Oneida cyclones are very efficient. There will be a pressure loss of course, but the filter will not get clogged as badly/quickly, so I will have a win there with the pressure loss.

Another question for the brains trust:

BP's blower design has 1½" of clearance between the ends of the fan blades and the bottom plate of the blower housing. He says this is to allow large chunks of timber to pass safely through the blower. I can't see how a chunk that large could ever pass through a cyclone. I'd like to reduce that gap to something like 10mm. Is this likely to improve performance or reduce it?

Originally Posted by jack620

Another question for the brains trust:
BP's blower design has 1½" of clearance between the ends of the fan blades and the bottom plate of the blower housing. He says this is to allow large chunks of timber to pass safely through the blower. I can't see how a chunk that large could ever pass through a cyclone.

if the bin over fills or there is some sort of (usually major) pressure failure of the bin the the sawdust and any bits of timber will not settle out and come straight through the cyclone to the impeller.

Small gaps need to be treated with care on impellers as this can turn them into screaming banshees.

Ahh yes, I'd forgotten about the noise issue. I think I'll set the gap at 25mm. Seems a reasonable compromise.

Some progress today. I ended getting a strip of 1mm zincalume from a roofing supplier for $21. They even folded it for me. The new blower is complete.

I used a power meter to measure the old and new blowers with no restrictions on the inlets or outlets. I was surprised to see they were nearly identical. Although it's possible the new blower is more efficient and moving more air for the same power consumption.

My meter measures true power (i.e. it allows for power factor) and as you can see, neither blower is demanding the rated power from the 2 HP motor. That's good to know.

The pics show the setup for each measurement.

Originally Posted by jack620

Some progress today. I ended getting a strip of 1mm zincalume from a roofing supplier for $21. They even folded it for me. The new blower is complete.

I used a power meter to measure the old and new blowers with no restrictions on the inlets or outlets. I was surprised to see they were nearly identical. My meter measures true power (i.e. it allows for power factor) and as you can see, neither blower is demanding the rated power from the 2 HP motor. I guess that's a good thing. .

Good news withe Zincalume

Your power reading is pretty consistent with what I was measured for the modified 2HP DC motor ie ~1100W (including power factor correction). Your unmodified DC must be better than mine because that was only ~1000 W.

I found this to still be a little bit disappointing as it means the impeller is simply not moving quite as as much air as the motor is capable of moving - it means the impeller is slightly too small for the motor.

Mine had a motor on it rated at 240V @7.7A or 1850W with power factor correction bringing it back to a nominal 1480 W. I even tested the motor on my mini-dyno and it easily developed 2 real HP although I'm not sure I would like to run the motor for too long under these power levels as it did get quite hot. Probably a 12.5" impeller would be a better fit to a 2HP motor as 13" really requires a 3HP motor. I know some folks that run a 14" impeller on a 3HP motor but the impeller itself is high restricted so the motor never develops more than 3HP continuous.

One reason for the poor performance of the 2HP impeller/motor combo is that it was really designed to be run at 60Hz. 60Hz meansthe naked impeller should pulls ~20% more air but it will also consume a lot more power and get really hot. To counteract this these DCs are built in a restricted state (eg 4" inlets) and once the filter bags and ducting is added end up running under a very safe regime. Bill Pentz mentions often how modifying impellers used with 60Hz motors can lead to motor burn out as these operate much closer to the edge of performance

When I upgraded my 3HP DC with a single phase motor to a 3P motor and VFD the intention was to use the motor at a higher speed to draw more air. This does indeed work wonderfully well but it does draw a lot more current. If I did that with just a 3H 3P motor it could have over heated the motor so I went to a 4HP motor. BTW having the DC in an enclosure with shirt loads of air running past does help keep it cooler than usual.

Have you measured it static pressure as that will be another useful indicator.

Originally Posted by BobL

...it means the impeller is slightly too small for the motor.

Probably a 12.5" impeller would be a better fit to a 2HP motor as 13" really requires a 3HP motor.

I think so too.

Originally Posted by BobL

Have you measured it static pressure as that will be another useful indicator.

Not yet. Do you mean static pressure of old vs new blowers?

Originally Posted by jack620

I think so too.
Not yet. Do you mean static pressure of old vs new blowers?

yep!

OK, I'll try to do that before I dispose of the carcass of the old DE.

I've been looking for cartridge filters at reasonable prices. Someone posted a link a couple of weeks ago to Pneuvay Engineering. I rang them today. They don't sell cartridges that capture dust on the inside as your typical hobbyist DE uses. All their filters flow outside to inside, which is a PITA. However, they are much cheaper than anything available through the usual suspects.

They have a generic brand 99.999% 0.5 micron filter for $115. I've made a Sketchup drawing of it to give you an idea of its size. Given the dollar saving over the inside-to-outside filters, I reckon it would be worth making an enclosure to accept this type of filter. Has anyone on the forum done this? Are there any obvious problems I'm missing?