pulsing 24V motor with 240V

[Simon]

I'm tasked to design a hand drier that runs on 240V but we mostly use 24v stuff. Say i did 10% PWM on a 24V motor with 240 will this be a problem ? From what i understand providing the insulation can withstand the 240V I'm ok, Is that right ?

[daedalus]

why would you do that? mains driven motors will generally be cheaper, and you don't need speed control so the expense of a switching motor controller is somewhat unnecessary.

Regardless of insulation rating, its not a good design practice to operate motors outside of their spec. Nothing may happen, or you may have thousands of returns a year later after the motor bearings fail, or the whole thing may catch fire (if you have a short enough thermal time constant), even if it works you have a nasty failure mode should the switching element fail closed.

on another note, if you want to design a good hand dryer these days you really need to be looking at custom motors (like the dyson, cyclone etc use).

[Simon]

we deal mainly in 24V motors that is all. For 5 units a month a custom design is out. I am currently looking at supplies should anyone know of a good one for centrifugal (squirrel cage) fans running off 240V and about 700W in power

[daedalus]

ah, so its a small volume one-off kind of product, if it were me I would have a look on alibaba, or their express site. I'm sure there will be ac motor-fan modules available, you might even be able to find a complete unit to just rebadge / repackage at that quantity.

alibaba have a whole category of hand dryer parts listed.

[qno]

Usually the hairdryer motor is tapped from the heating element with a bridge rectifier.
It is often a 6 or 12 DC motor.

[mzzj]

we deal mainly in 24V motors that is all. For 5 units a month a custom design is out. I am currently looking at supplies should anyone know of a good one for centrifugal (squirrel cage) fans running off 240V and about 700W in power

700W motor in hairdryer  O0

Apparently you are trying to create something like this
So why not go to nearest hardware store and get yourself leaf blower 

[Simon]

Hair driers have very low power motors that make a draft. We are looking at no to little heating of the air but high air velocity/pressure. As we want the air to go through a small slot we need a fan/motor design that can supply a lot of pressure

[mzzj]

Hair driers have very low power motors that make a draft. We are looking at no to little heating of the air but high air velocity/pressure. As we want the air to go through a small slot we need a fan/motor design that can supply a lot of pressure

Vacuum cleaner motor?

[SeanB]

24V motor will for sure not withstand 240V, no matter how you pulse it. Do what the others do and take the heater winding and tap it at about 12-15% of the winding to get a low voltage rail to run the motor from. Simple, cheap and you needed the heat anyway. You will need to isolate the whole motor, frame, windings, shaft and fan ( if you are going to use a metal one) to pass mains safety creepage and clearance specs, along with conforming to the EU standard finger test for safety.

If you are looking for pressure you will be stuck with using a centrifugal blower, think of a standard workshop blower, a smaller cousin of the yard blower. A vacuum cleaner motor assembly will do there, they suck at the one end and blow out the other, though you will need a container for it, and a filter on input and output. They are common as universal vacuum cleaner replacement blowers, costs about 30GBP each as spares.

[Simon]

Hair driers have very low power motors that make a draft. We are looking at no to little heating of the air but high air velocity/pressure. As we want the air to go through a small slot we need a fan/motor design that can supply a lot of pressure

Vacuum cleaner motor?

yea sort of, we can't rip vacuum cleaners apart though, firstly my lot are not that creative and secondly we would need the warranty on the motors

[Simon]

24V motor will for sure not withstand 240V, no matter how you pulse it. Do what the others do and take the heater winding and tap it at about 12-15% of the winding to get a low voltage rail to run the motor from. Simple, cheap and you needed the heat anyway. You will need to isolate the whole motor, frame, windings, shaft and fan ( if you are going to use a metal one) to pass mains safety creepage and clearance specs, along with conforming to the EU standard finger test for safety.

If you are looking for pressure you will be stuck with using a centrifugal blower, think of a standard workshop blower, a smaller cousin of the yard blower. A vacuum cleaner motor assembly will do there, they suck at the one end and blow out the other, though you will need a container for it, and a filter on input and output. They are common as universal vacuum cleaner replacement blowers, costs about 30GBP each as spares.

They don't want heat

[David_AVD]

Why can't you use your 24V motor with a switchmode power supply?  How much current does the 24V motor draw?

[Simon]

nah just spoke to my boss, we are looking at about 1600W of motor so it has to be 240V, I just need to find a motor. a competitor uses a 1600W motor that runs at 88'000 rpm !

[David_AVD]

88,000 RPM sounds unlikely for a 240V AC motor.   

[Simon]

88,000 RPM sounds unlikely for a 240V AC motor.   

http://www.bavada.com/en/36-dyson-airblade-ab03-hand-dryer-steel-grey-eu.html?gclid=CJKl34__mbYCFXDKtAodHTIAFA

Do you mean it could be a brushless motor or something ?

[David_AVD]

88,000 RPM sounds unlikely for a 240V AC motor.   

http://www.bavada.com/en/36-dyson-airblade-ab03-hand-dryer-steel-grey-eu.html?gclid=CJKl34__mbYCFXDKtAodHTIAFA

Do you mean it could be a brushless motor or something ?

Hard to say.  Just because the dryer runs from 240VAC doesn't mean the motor is 240V AC.  Just sayin'....   

[Simon]

true, I'm guessing brushes will have a limited life at that speed although I beleive drill motors run at something like 20K rpm

[mzzj]

Dyson website says "switched reluctance brushless"

Not cheap, difficult to find and requires something similar to VFD for control. Most probably still 240V but frequency is more like 50000Hz than 50Hz.


Motor is just one part of the problem, You also need highly specialized centrifugal fan to attach to your motor.

I would look for vacuum cleaner motor as a spare parts or replacements as SeanB already recommended. AFAIK they run something like 20k to 30k rpm.
Washing machine motors spin the drum something like 1000rpm with a 1:20 belt ratio so the motor is spinning roughly 20k rpm.

[Simon]

where does one buy vacuum cleaner spares ?

Yes i realize this is one hell of a headache. I don't think my boss realizes quite what we have let ourselves in for

[peter.mitchell]

Yeah, i'm still thinking leaf blower motor... maybe need a gearbox on the end of it to get the speed.

[Simon]

I'm looking at the Dyson marketing wank material and trying to extract some technical information, they say it is a digital (or course it is  ) motor, brushless running at 90Krpm and pulsed at 6KHz, that to me makes it a 4 pole brush-less stepper.

Looking at the impeller that is more of a simple fan, that is akin to a low pressure compressor turbine type.

Although we are not looking at the filtration so that will help us in the need for pressure.

http://www.dysonairblade.co.uk/hand-dryers/airblade-mk2/airblade-mk2/features.aspx

[mzzj]

How much airflow you want and how much pressure?
Or how fast airspeed and what size of nozzle(s) ?


Buy one Dyson for reverse-engineering and use it to fiqure out needed volume and pressure.


For vacuum cleaner motor spares look for example Ametek brand or call around few industrial brands and ask for replacement parts.

http://www.blowermotorsplus.com/Ametek_116196_00_Blower_Vacuum_Motor_4M960_p/116196-00.htm
http://www.amtechuk.co.uk/shop/lamb-ametek-6-6-high-suction-vacuum-motor-pid-529.html

[amyk]

All this talk of overvolting motors and vacuum cleaners and Dysons is a little photonicinduction-y...

[Simon]

No we have scrapped the PWM idea, now we know the power required we are happy to have a power supply.

We are looking 400m/s though a 0.5mm slot - correction, my boss is 

[mzzj]

We are looking 400m/s though a 0.5mm slot - correction, my boss is 

"Simon Industries introduces the first airBLADE hairdryer  to barbershops. Will cut your hair and remove your scalp without unhygienic ordinary blades!"

[G7PSK]

Have a look at espares.co.uk they have a whole host of vacuum cleaner motors and others and would carry a warraty as they are sold as motors not complete units.

[IanB]

No we have scrapped the PWM idea, now we know the power required we are happy to have a power supply.

We are looking 400m/s though a 0.5mm slot - correction, my boss is 

Don't take this the wrong way, but it looks like your boss should hire a mechanical engineer for this kind of project, maybe full time or consulting.

You understand that 400 m/s is supersonic, don't you? Air won't just flow through a slot at that speed, you will need a properly shaped nozzle. And it will sound louder than a jet engine as the shock wave disperses. And it will cause fatal injuries to anyone who puts their hands near it. (Just kidding about that last bit, but it won't be fun or safe  )

In general for such a design, you would work out the air volume rate required. Then you would work out the pressure needed to deliver that volume through the chosen orifice. Then you would determine a size and type of blower or compressor needed to deliver that amount of air at that pressure. Then you would determine the speed and power requirements for the compressor. Then you would select a motor (and gearbox?) that can perform that duty.

Of course, for something small you would probably just find something ready made that can sort of do the job, as others have been saying. But you still need to know how to tell if your motor/blower combo can indeed sort of do the job.

[peter.mitchell]

TBH, i'd avoid running anything at that high RPM, bearings don't like it. Also, it seems like there will be a lot of other things that are needed to take care of, eg, how to turn it on/off, how to waterproof it, how to stop the intakes getting clogged with dust ect.

[SeanB]

It is a brushless motor.

[Agony]

Wouldnt even standard centrifugal blowers be around 1000-3000 RPM? High RPM wouldn necessarily mean high pressure if it doesnt have enough torque.
http://www.alibaba.com/products/F0/blower_rpm/CID100009529------------------------------1120-134.html
http://www.surplussales.com/fans-blowers/fansblow-1.html

[peter.mitchell]

Im sure you could find something reaaaaal nice in here
http://www.delta.com.tw/product/cp/dcfans/dcfans_prod_sch.asp

[Hypernova]

Also check out EBM-Papst, they are pretty much "it" when it comes to fans.

I got this bookmarked just in case I decide to add it to my collection, as far as I know this is the most powerful 120mm fan in the world.

[amyk]

Also check out EBM-Papst, they are pretty much "it" when it comes to fans.

I got this bookmarked just in case I decide to add it to my collection, as far as I know this is the most powerful 120mm fan in the world.

Oh my... 11K RPM in a 120mm fan

And I thought Deltas were extreme...

[grumpydoc]

Oh my... 11K RPM in a 120mm fan   

That's not so bad but 78dBa - I wouldn't want to be in the same room

[G7PSK]

78dba is nothing compared to the sonic boom that Simon's boss will create if he has his way with the air speed. I think that speeds like that will require a multistage axial flow compressor, Pratt & Whitney or Rolls Royce may have something that will fit the bill.

[Hypernova]

78dba is nothing compared to the sonic boom that Simon's boss will create if he has his way with the air speed. I think that speeds like that will require a multistage axial flow compressor, Pratt & Whitney or Rolls Royce may have something that will fit the bill.

Or, in other words, a jet engine.

[IanB]

78dba is nothing compared to the sonic boom that Simon's boss will create if he has his way with the air speed. I think that speeds like that will require a multistage axial flow compressor, Pratt & Whitney or Rolls Royce may have something that will fit the bill.

It will actually be rather difficult to get an air speed greater than the speed of sound, that's what the "sound barrier" is all about. The same as you can't exceed the speed of light, you can't typically make a flow of gas exceed sonic velocity. At that point the flow "chokes" and won't go any faster.

[ConKbot]

78dba is nothing compared to the sonic boom that Simon's boss will create if he has his way with the air speed. I think that speeds like that will require a multistage axial flow compressor, Pratt & Whitney or Rolls Royce may have something that will fit the bill.

It will actually be rather difficult to get an air speed greater than the speed of sound, that's what the "sound barrier" is all about. The same as you can't exceed the speed of light, you can't typically make a flow of gas exceed sonic velocity. At that point the flow "chokes" and won't go any faster.

Maybe something like a miniature linear aerospike to fit in the 0.5mm slot 

http://en.wikipedia.org/wiki/Aerospike_engine

[NiHaoMike]

88,000 RPM sounds unlikely for a 240V AC motor.

Try telling that to my friend Brittany Benzaia who already has a turbocompressor that can run well in excess of 100kRPM, all off a common 120V plug. (Hybrid air conditioner using water vapor as a refrigerant, which means a very high RPM to get the required flow rate in a practical size.)

Also check out EBM-Papst, they are pretty much "it" when it comes to fans.

I got this bookmarked just in case I decide to add it to my collection, as far as I know this is the most powerful 120mm fan in the world.

Oh my... 11K RPM in a 120mm fan

And I thought Deltas were extreme...

Do they make a 12V version for running from a standard PC power supply? Apart from that and the high price, it looks like an overclocker's dream fan...

[BravoV]

Do they make a 12V version for running from a standard PC power supply? Apart from that and the high price, it looks like an overclocker's dream fan...

For 12 volt DC at 120mm wide and 38 mm thickness fan, currently the most powerful is Nidec G1238B12BB (Link)



Higher & crazier fans are above 12 volt like 24 or 48 volt, the wasted energy at high current at the coils is too large I guess when powered from 12 volt, example like that crazy EBM-Papst fan, or this Sanyo Denki 9HV1248P1G series (Link), capable of 11,500 rpm.