How to step up single phase motor speed for dust system?

[ondablade]

Hi guys. I have a Bill Pentz (Clear Vue Cyclones in the US) fan for my dust system which i sourced in the US, and i'm struggling to economically sort the issue of driving it at the 3,450 rpm it needs to perform really well.

It'd work in terms of chip collection, but my pressure drop will be around that where the fan curve shows the performance really starting to tail off and i don't want to risk it.

This is the difference in speed between a US spec 5hp single phase 2 pole motor at 60Hz, and the local 50Hz equivalent which gives 2,850 rpm.

I'd seen a Belgian guy post of buying a suitable inverter for the same drive for around €300 which would be fine (can't reach him as the post is several years old), but my quotes so far in the UK range from £650 - £1200 which is too much.

It's not rocket science, all it would need is a single stage 1.2:1 helical gearbox or maybe a toothed belt in a housing - capable of flange mounting to the motor and the flat fan casing at the other end.

Trouble is step-up gearboxes seem rare in industry (almost all are reducers), i've only been able to find stuff for driving hedge cutters etc off the back of tractors with less than ideal shaft configurations.

I've a few enquiries out which might yet yield something, but am i missing something?

ian

 

[9fingers]

Nearly all inverters for 5HP will need a 3 phase input. Do you have this available?
I would think that a toothed belt drive would be the way to go if you want the increased speed.
Two bearings, two pulleys a bit a shafting and a belt.
A flange mount motor would be ideal and need less metal work to mount the drive.

That said there are a lot of people who have built non Pentzian optimised cyclones and get adequate performance.

I have no complaints on my 14" 2850 rpm 3hp Burgess prototype. it works fine on 8 inlets and about 20 metres of 110mmducting
Search the archives here for Barry's design for more details.

Bob

 

[ondablade]

My supply is unfortunately single phase Bob, albeit i can go up to 43A and possibly if i'm to believe the markings on the board to 63A.

You're spot on about single phase input inverters. The biggest most do is around 2.2A. There are a couple that go up to 5HP (Siemens and another), but that's perhaps why they are so expensive. (less than half in the US mind you)

I've since found the link to the Belgian guy again, and yes, he had a three phase supply, and anyway it turns out he paid more than €300 i think. He psoted on the Clear Vue forum which i'd forgotten about, next step is to plough through that for ideas.

I guess a piece of heavy rectangular box section with a through shaft for the fan with flanged bearing units at one end should do the business. The other end could be set up to face frame mount the motor. It's not too hard to design up, but i'm just a bit cautious about the possibility of longer term reliability issues....

It does look too like i could get by on a 2,850 rpm motor, and for sure chip collection would still be very good. Trouble is the fan curve starts to fall fairly sharply just above the sort of pressure drop i'll have compared to the same fan at 3,450. It seems a pity having come this far to risk being a little sort of suck for effective fine dust collection if other things (e.g machine inlet ports) can't be at 100% optimum...

ian

 

[9fingers]

Cheapest I have found for 230v 4kw inverter is the omron v1000 series.

RS components 477-590 £363 plus taxes whatever your VAT is

Or buy second hand on Ebay if/when one comes up.

If you are ok with metal work than I'd do it mechanically to be honest

Good Luck

Bob

 

[Digit]

A step down gearbox, subject to construction, is a step up box if connected back to front!

Roy.

 

[ondablade]

I know you suggested going mechanical Bob, but the Omron V 1000 at that money makes it seem to me a very credible possibility too. I did lots of searching, but didn't find that one. (i've bad memories of RS prices from years ago, but they seem to have got a lot better)

I have quite a lot of experience on the machine design side of things, and can sort what should be a well engineered drive. I even picked up the Gates literature today so i can specify a toothed belt drive, and figure out how long lived it might be. It probably would be a bit cheaper, but on the other hand the inverter is plug and play more or less.

What's your thinking? Do you know if inverters are reliable in this sort of scene?

I guess a single stage helical box if i can find the ratio would be OK driven backwards Roy, and could definitely be used. Another for the list.

The issue on the inverter i'm not sure about is that of what amps it would draw compared to a single phase motor. It's been suggested to me (but maybe inaccurately) that they pull more as a result of inefficiencies in the way they create the output. I'll have to run that to earth as our ex state but still monopoly power supplier (who charges an arm and a leg for power - funny that) gets sweaty if you draw too many amps on a single phase supply.

Thank you very much guys, that's been a great help.

ian

 

[Digit]

A worm and pinion box can't be run backwards Ian and a 'cross cut' helical is probably not a good idea either. Personally I would stick to straight cut gears or a planetary type box.

Roy.

 

[9fingers]

I only advocated a mechanical solution as you seemed to think that inverters were too expensive.

I am a total convert to inverters. I have six in use in my workshops including one to drive my cyclone. I use another one on a demonstration rig to show others how versatile they are.

Inverters are very efficient indeed. The one on my cyclone claims 95 to 98% efficient.
The starting current drawn is much lower than for the same power single phase motor. I can run 3hp on a 13amp plug with no fuse blowing problems.

Obviously you need a 240/440v three phase motor to use with the inverter and these will be cheaper than the equivalent single phase motor.

As for reliability, I have been using inverters for nearly 10 years and have never had a failure.

Incidentally, the reason I have an inverter on my cyclone was to ensure that it did not suffer from any mechanical resonances. If there were any the inverter output can be programmed to avoid those frequencies.


One further important thing to check with your chosen inverter. Make sure that the switching frequency is programmable to a point above your hearing frequency. Some are fixed at 4kHz and so the motors whistle in use. programming it up to 12 or even 16kHz is much kinder on the ears.

Download the manual before you buy!!

HTH

Bob

 

[ondablade]

Thank you again Bob, that's another hurdle cleared. I thought you perhaps had a technical reason for disliking inverters. Very much not the case it seems!!

Thinking a bit more about efficiencies and reading the Omron manual even the quite large single phase model we're talking about relies on a heat sink for cooling which presumably suggests that it can't at least be wasting much energy...

I wasn't really prepared to cough up the £650 - £1,200 some are asking for an inverter, but the RS price is acceptable - i'm going to order one once it's all checked out.

On gears D. Thank you also. I know about worms, but am not 100% sure if a single stage parallel shaft helical box will allow reverse running - it's a long time (college) since i looked closely at helical gears. I doubt though that i would go the gear route in any form except via a ready made gearbox, as i don't know enough to set the tolerances tightly enough for either reliability or quietness...

ian

 

[PJ]

Surly it would be easier to reduce your pressure drop than increasing the speed of the motor? Are you at the minimum limit of air velocity to hold dust, for your given extraction quantity?


Philip

 

[ondablade]

I'm headed that direction too PJ, but there are a couple of factors i can't control.

The first is that my Hammer machines at 120mm have smaller ports than some would say is ideal to minimise the pressure drop/maximise the air flow/effectiveness of dust gathering at the machine, and the planer for example is not that easily modified.

I don't want to give away anything in this regard unless i have to.

The second possible issue is that (especially with a little restriction elsewhere) it could be (still to be checked out) that going with the 8 inch main duct prior to splitting to the machines that maximises airflow with this fan could just drop the air velocity lower than the 4500fpm it seems is needed for safe avoidance of deposition in the duct.

I am being pernickety - it probably would be OK at the lower rpm (it seems subject to a more precise working out of the exact duct runs and flow resistance that it would still shift lots more air than most commercially available systems), but it also seems a pity to do the work to get this far and then to compromise too easily...

ian

 

[PJ]

Ian,
Use 6" -5" Taper reducers to fit onto your machines. There is next to no loss in the reducer. Choose your 6" flex pipe with a clean wall if possible and as short as practical and you basically have a 6" run through. As you said with an 8" main you need to be careful to make sure the system always get enough air or dust may start to drop out, which may mean keeping another port cracked open other than the one your using.


Philip

 

[ondablade]

Ta PJ. I'll post some numbers in the next few days when i get a chance to sit down and carefully do the duct runs - another issue bothering me is that in order to avoid a duct across the floor in my main shop access way (i'll cut a channel if forced to) i may need to go to the opposite wall of my albeit smallish shop, and then some distance back out to the panel saw. i.e. i could end up with a bit more duct length than i originally thought.

Could be the numbers will suggest it'd be wiser to drop back to a 6 in main duct.

It's taken a few days with other things on to sort out a scale layout drawing and machine cutouts (i've upgraded from a Robland combo), so it's ready to draw the duct layout now.

Took about three days to figure a shop layout that covers the bases and still gives decent 8 - 10ft min machine infeed and outfeed spaces..

I got a pleasant surprise on the Omron V1000 inverter today - not only did i get excellent technical assistance from Omron UK, but also i can buy it locally at the UK/Euro price in Euros, get local support if needed, and avoid having to pay for shipping.

Local prices are usually a daft - 30 - 40% in excess of the UK, but Omron it seems have harmonised theirs. Here's hoping it's the start of a trend.

So it's on order.....

ian

ian