Single phase blower vs 3phase? (project now finished)

[BandsawWarrior]

I bought a big old blower (16" inlet and outlet) to suck chips out of planer moulder we're setting up.  It came with an old 20HP European motor.  I'd like to put a 10hp single phase on it so that I don't tap out my rotary phase converter that is also running the moulder.  I know that it won't move the same amount of chips but I'm hoping it will get the job done.

My question is....is a 10Hp single phase motor going to move the same amount of chips as a 10Hp 3 phase?  Am I right in thinking that the 3 phase motor will just do it more efficiently "cheaper"...

thanks,
Tyler

[red oaks lumber]

if the blower came with 20hp it was designed that way, you want to cut the hp in half? it might work marginal. you won't have the same cfm with smaller motor, leaving planer shaving floating around in the moulder will give you finish issues .

[SPIKER]

Having worked with Blower design I can say no if it was designed to run on a 20 HP 3 phase motor then putting a 10HP unit on it will more than likely overload the motor and also not move the air as well as the design was meant for.   as far as single vs 3 phase a 10 HP is generally 10HP but you will use a greater amp draw on the 10HPsingle phase vs the 3 phase & as part of it there will be issues with how they run that will be bad.  the start up load of the single phase will also be much harder starting the blower than the 3 phase unit.

mark

[BandsawWarrior]

Thanks for the responses.  You guys are confirming kind of what I thought.  My theory was that if the blower was designed to pull 8000 or 9000 cfm and I just need to pull 4500 cfm I could get away with the smaller motor.  I'm trying to dodge having to buy another phase converter lol...

thanks,
Tyler 

[sparky]

A 10 HP single-phase motor will match the performance of a 3-phase motor with slightly less efficiency, since 3-phase motors are inherently more efficient. There is a law of physics with fans that states that at twice the fan speed, the HP required is 2 cubed, or 8 times, the HP required at the original speed. If you have determined that you need significantly lower cfm from the fan, the fan speed can be reduced and the HP will be reduced significantly. MY background is electrical engineering, not mechanical, so I can't tell you what HP is needed at the reduced cfm.

Since you have a phase converter, you may be able to do an experiment with the existing 20 HP fan motor. You could install the fan on your planer exhaust, reduce the fan speed by replacing one of the pulleys, and attempt to determine if the lower fan speed might give enough air flow to clear the chips from your planer. You will need to be able to measure the current of the 20 HP motor to know what HP it is producing. The efficiency motors is fairly constant down to 50 % of their HP rating. If the airflow appears adequate at about half the nameplate current of the 20 HP motor, you may be able to get by with a 10 HP motor. It becomes a judgement call at this point. Obviously, you won't be able to run both the planer and the fan on your converter for a proper test.   

This is a rather complex issue with no easy method to arrive at an exact answer.

Sparky

[slohand]

Bandsaw...
You can get by with less hp at the same RPM  if you have restriction on the inlet air flow.
What I would do is test run the motor on your blower and check the amp useage.  With inlet full open(briefly) see what the amp load is on the motor and how that compares to the rated amps on the plate.  The motor should run around 2/3 of rated amp load. If it greatly exceeds it, then  use a piece of plywood to restrict the inlet opening size until the motor comes down to it's normal rated amp loading (or a little less). Then figure out how many square inches of opening allows the motor to operate normally. Then size your inlet ducting based on that.

If you can't get adequate CPM then you have to go up in HP.

[r.man]

Bandsaw, how do you know your converter won't handle the extra load? 10 hp is 10 hp no matter the phase but a 10 hp three phase is probably cheap enough, especially used, to warrant the converter upgrade. It has been my experience, and I don't mean guess, that many things are oversized and if you are willing to try something that the people in the know say won't work, it might. I once had two fluid people tell me that I needed at least a 3 hp pump and would be safer putting in a 5 hp. Turned out the customer owned a 1 hp so we installed that, risked a bit of labour loss, and it worked fine. If it is a cheap experiment and you can stand the time involved try what you want. Maybe you are a design genius and don't know it.

[Larry]

You might be able to add a second idler to your existing rotary phase converter.  Depends on the control circuity in your existing converter and you will need some electrical knowledge.

There is also a pretty nifty DonP blower calculator in the tool box.  It will tell ya how many hp required for the speed of your blower.  From actual use I can tell you it works great.

[D._Frederick]

You don't say if the blower is direct drive or belt driven, if it is belt driven just increase the size of the blower pulley to reduce its rpm and the hp required. 

[BandsawWarrior]

It's direct drive.  The motor that is on there now is a European 50Hz 380v motor so it has to come off anyways.  The inlet is removed in the photo so we can get the fan off the motor shaft. 



I think I'm going to switch to a pulley since the motor will be off anyways.  That way like you guys mentioned I can slow down the speed until the motor is pulling the correct amount of amps. 

If it still doesn't pull enough with a 10hp single phase I have two worst case scenarios.  1.  I have a free 20hp 3phase 480v motor I can put on and buy another phase converter.  But I would also have to upgrade my 240v to 480v transformer to run everything off the same system :( 
2.  Or add a second single phase blower and split the 4 heads up between the two blowers.  This way I can save buying a phase converter and transformer which would be around $4k plus installation and materials.   

  thanks for the posts everyone!

I'll update with pics as we make progress.  Just incase it might help someone else. 

[Brucer]

A few ideas for you, Tyler.

- Flowrate (CFM) varies in proportion to the RPM.
- Pressure varies in proportion to the square of the RPM.
- HP varies in proportion to the cube of the RPM (as Sparky mentioned).
- Do not, under any circumstances, run the fan at a higher speed than it was rated for. Running a fan too fast will usually cause it to self-destruct. With the kind of HP you're looking at, you'll get shrapnel flying through the casing.

You can reduce the horsepower that a fan draws by adding some resistance to the system (as slohand mentioned). There is a limit to how far you can go with this. Keep in mind as well that fans like this are selected for a particular system. Whatever system you build may already have more resistance than the what the fan was designed for, so the fan may not draw as much horsepower to start with.

Converting it to belt drive gives you the flexibility to change the speed to whatever you need. Shaft design is critical, though. Make sure the bearings are no further apart than the bearings on the motor, and make sure the shaft is at least as big as the motor shaft.

[trim4u2nv]

I just finished upgrading a 20hp cyclone and blower 220V 3 phase.  It draws about 60 amps with no ductwork on the 16 inch intake (overloaded from 50 A nameplate rating.)  It draws 42 amps with 4 - 6inch ductwork pipes hooked onto the moulder dust manifolds.  This is running below full nameplate rating of 45-48A.  The trunk line is 15 inches big end and 8 inches small end.   I haven't tested amps with the main line closed.  Afraid of collapsing the duct.

We experimented with a 20hp motor with a reducer to a 12 inch trunk line and got lower amp readings in the 30s.  But the fan has design curves and if you restrict the flow too much you put the fan into a stall condition.  Kind of like driving up hill and upshifting into too high of a gear.   It will vibrate and shudder instead of running smooth (short bearing life.)  Your impeller looks like a curved airfoil here is a link to some fan data on this type of fan running at 3600rpm (solid curve.) Or running at 1800 rpm (dashed curve) called the hummer model (lower noise.)

http://www.belfab.net/en/products/lw_dw_nbm_nbm-op_sbm/lw.html

We had a 380v blower at one time which could be tapped 220/380 volt with 6 leads.  Not the standard 9 leads in american motors.  It had a wye delta starter for low amp startups.  How it worked was 220v line voltage was applied to the 380v winding (motor windings wye)  only drawing 33% amps and torque.  When about 3 seconds elapsed the motor starter changed the windings to delta configuration. After starting, 220v (motor windings delta) was kept applied as the running voltage.   Therefore you could run this motor at 220v if it was wired delta.  If you run it at 220v too long though, in wye configuration it will overload because it was intended to run 380v.   Check the nameplate or number of leads on top of the motor.  This setup only ran at 220v at startup or continuous running even though it was rated 380v.  Also a 50hz motor run at 60hz may not likely overheat but will run 20% faster.   Usually they are designed to run well at 220v/380v but would overheat at 480v.   

http://www.usmotors.com/products/ProFacts/1-120-7.htm

[Brucer]

....  But the fan has design curves and if you restrict the flow too much you put the fan into a stall condition.  Kind of like driving up hill and upshifting into too high of a gear...

Technically it's called surge. There's a few fan designs where it can't happen but on most of them it will.

The shifting analogy is a good one. To carry it one step further -- your engine is reving too high so you upshift. Then the engine can't produce enough torque and the vehicle slows down, so you downshift. Once again the vehicle picks up speed and the engine over-revs. Etc.

Typically you'll get a slow pressure pulse -- about 2 seconds per cycle. You can hear it and feel the vibration anywhere you touch the fan or ductwork. It can be very destructive over a long period of time. On a single-inlet fan it can hammer the bearings to shreds and wreck the impeller.

If this happens the fix is to remove some restrictions -- open dampers, install larger ducts, etc. If your fan is surging it won't help a bit to change the speed.

[bandmiller2]

Tyler,my knowledge on this matter pales compared to the gentlemen above,but it seems the blower is way oversized for your application.Blowers are handy but use alot of power to move a small amount of material.I would look for a smaller blower that would save you in the long run. Frank C.

[BandsawWarrior]

I just wanted to update this topic and let everyone know how we made out with the blower.  Maybe it will help future blower designers  :D 

Our task - (a 20hp 3phase blower converted to 10hp single phase)

Why you might ask?  I couldn't run the blower off the same system as the planer due to power and transformer limitations.

We put on the 10hp single phase motor.  There were two things that were very costly about going this route...a single phase motor that size is very expensive and the starter is very expensive as well.  I managed to find used components for the starter so that worked out okay.  Also, the low voltage single phase motor required a large expensive wire.

I reduced the fan speed with our pulleys by 200rpm.  It doesn't seem like much but that's what I went with it.  I had a custom intake hood made with four matching inlets for the planer, a 8", 7" and two 6". 

Our motor was rated at 40 full load amps.  When we first turned it on without any blower pipe connected it was pulling 58amps...I was a little worried at this point to say the least.  Then we hooked up all the pipe and flex tube and flipped the switch...39amps.  Awesome!  We pulled it off with a combination of lower fan speed the smaller inlet.

We've had time to run some larger 5000bf orders through the planer and it worked great.  It's quite the sight to see it shoot shavings 50' out the back of our building   ;D





A little video action. 
http://youtu.be/tj44EVBcsy0