pulsing 24V motor with 240V - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: March 25, 2013, 02:16:39 pm
content: 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 ?

author: daedalus
author_rank: Regular Contributor
timestamp: March 25, 2013, 03:58:08 pm
content: 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).

author: Simon
author_rank: Unknown
timestamp: March 25, 2013, 04:01:05 pm
content: 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

author: daedalus
author_rank: Regular Contributor
timestamp: March 25, 2013, 04:06:48 pm
content: 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.

author: qno
author_rank: Frequent Contributor
timestamp: March 25, 2013, 04:13:14 pm
content: Usually the hairdryer motor is tapped from the heating element with a bridge rectifier.It is often a 6 or 12 DC motor.

author: mzzj
author_rank: Super Contributor
timestamp: March 25, 2013, 04:22:12 pm
content: Quote from: Simon on March 25, 2013, 04:01:05 pm700W motor in hairdryer O0Apparently you are trying to create something like thisSo why not go to nearest hardware store and get yourself leaf blower

author: Simon
author_rank: Unknown
timestamp: March 25, 2013, 04:26:15 pm
content: 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

author: mzzj
author_rank: Super Contributor
timestamp: March 25, 2013, 04:48:50 pm
content: Quote from: Simon on March 25, 2013, 04:26:15 pmVacuum cleaner motor?

author: SeanB
author_rank: Super Contributor
timestamp: March 25, 2013, 07:21:24 pm
content: 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.

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 07:56:00 am
content: Quote from: mzzj on March 25, 2013, 04:48:50 pmyea 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

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 07:57:33 am
content: Quote from: SeanB on March 25, 2013, 07:21:24 pmThey don't want heat

author: David_AVD
author_rank: Super Contributor
timestamp: March 26, 2013, 08:46:44 am
content: Why can't you use your 24V motor with a switchmode power supply? How much current does the 24V motor draw?

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 08:52:06 am
content: 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 !

author: David_AVD
author_rank: Super Contributor
timestamp: March 26, 2013, 08:53:40 am
content: 88,000 RPM sounds unlikely for a 240V AC motor.

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 08:54:44 am
content: Quote from: David_AVD on March 26, 2013, 08:53:40 amhttp://www.bavada.com/en/36-dyson-airblade-ab03-hand-dryer-steel-grey-eu.html?gclid=CJKl34__mbYCFXDKtAodHTIAFADo you mean it could be a brushless motor or something ?

author: David_AVD
author_rank: Super Contributor
timestamp: March 26, 2013, 08:57:04 am
content: Quote from: Simon on March 26, 2013, 08:54:44 amHard to say. Just because the dryer runs from 240VAC doesn't mean the motor is 240V AC. Just sayin'....

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 08:59:17 am
content: true, I'm guessing brushes will have a limited life at that speed although I beleive drill motors run at something like 20K rpm

author: mzzj
author_rank: Super Contributor
timestamp: March 26, 2013, 09:31:04 am
content: 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.

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 09:36:30 am
content: 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

author: peter.mitchell
author_rank: Super Contributor
timestamp: March 26, 2013, 10:21:10 am
content: Yeah, i'm still thinking leaf blower motor... maybe need a gearbox on the end of it to get the speed.

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 10:27:22 am
content: 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

author: mzzj
author_rank: Super Contributor
timestamp: March 26, 2013, 10:52:41 am
content: 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.htmhttp://www.amtechuk.co.uk/shop/lamb-ametek-6-6-high-suction-vacuum-motor-pid-529.html

author: amyk
author_rank: Super Contributor
timestamp: March 26, 2013, 10:58:41 am
content: All this talk of overvolting motors and vacuum cleaners and Dysons is a little photonicinduction-y...

author: Simon
author_rank: Unknown
timestamp: March 26, 2013, 11:04:58 am
content: 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

author: mzzj
author_rank: Super Contributor
timestamp: March 26, 2013, 12:38:20 pm
content: Quote from: Simon on March 26, 2013, 11:04:58 am"Simon Industries introduces the first airBLADE hairdryer to barbershops. Will cut your hair and remove your scalp without unhygienic ordinary blades!"

author: G7PSK
author_rank: Super Contributor
timestamp: March 26, 2013, 01:51:44 pm
content: 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.

author: IanB
author_rank: Super Contributor
timestamp: March 26, 2013, 02:23:16 pm
content: Quote from: Simon on March 26, 2013, 11:04:58 amDon'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.

author: peter.mitchell
author_rank: Super Contributor
timestamp: March 26, 2013, 03:10:17 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: March 26, 2013, 04:04:18 pm
content: It is a brushless motor.

author: Agony
author_rank: Contributor
timestamp: March 26, 2013, 11:04:34 pm
content: 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.htmlhttp://www.surplussales.com/fans-blowers/fansblow-1.html

author: peter.mitchell
author_rank: Super Contributor
timestamp: March 28, 2013, 05:46:12 am
content: Im sure you could find something reaaaaal nice in herehttp://www.delta.com.tw/product/cp/dcfans/dcfans_prod_sch.asp

author: Hypernova
author_rank: Unknown
timestamp: March 28, 2013, 08:16:35 am
content: Also check out EBM-Papst, they are pretty much "it" when it comes to fans.I gotthisbookmarked 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.

author: amyk
author_rank: Super Contributor
timestamp: March 28, 2013, 11:03:17 am
content: Quote from: Hypernova on March 28, 2013, 08:16:35 amOh my... 11K RPM in a 120mm fanAnd I thought Deltas were extreme...

author: grumpydoc
author_rank: Super Contributor
timestamp: March 28, 2013, 11:17:08 am
content: QuoteThat's not so bad but 78dBa - I wouldn't want to be in the same room

author: G7PSK
author_rank: Super Contributor
timestamp: March 28, 2013, 01:21:52 pm
content: 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.

author: Hypernova
author_rank: Unknown
timestamp: March 28, 2013, 03:45:54 pm
content: Quote from: G7PSK on March 28, 2013, 01:21:52 pmOr, in other words, a jet engine.

author: IanB
author_rank: Super Contributor
timestamp: March 28, 2013, 04:16:32 pm
content: Quote from: G7PSK on March 28, 2013, 01:21:52 pmIt 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.

author: ConKbot
author_rank: Super Contributor
timestamp: March 28, 2013, 04:26:37 pm
content: Quote from: IanB on March 28, 2013, 04:16:32 pmMaybe something like a miniature linear aerospike to fit in the 0.5mm slothttp://en.wikipedia.org/wiki/Aerospike_engine

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 28, 2013, 06:24:31 pm
content: QuoteTry 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.)Quote from: amyk on March 28, 2013, 11:03:17 amDo 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...

author: BravoV
author_rank: Super Contributor
timestamp: March 28, 2013, 06:47:19 pm
content: Quote from: NiHaoMike on March 28, 2013, 06:24:31 pmFor 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.