Distressed Nerd - How to increase Motor RPM 3

[DistressedNerd]

Hello!,

As an engineer who graduated #2 out of 10 in my class from a top tier university, yet I am completely, 100%, stumped on this electronics project and feeling like I a complete doo doo head and I am in dire need of help from my nerd comrades.

What I am trying to do is increase the RPM’s of this fan motor. Right now it has a 4 setting selector switch (off, speed 1, speed 2, and speed 3), but I need more power or RPM’s then the highest speed setting (speed 3) will give me. A picture and all the details is attached, anyone who can solve this problem I will worship you! Just let me know the parts and wiring and I will turn your words into a finished project.

If the rpm’s can not be increased using the motor I have now – then please let me know an easy motor setup I could install to give me more RPM’s then the current setup.

Thanks a ton guys!

 

[jraef]

So you got an EE degree from a "top tier" university and you know nothing about motors and fan loads? Sheesh...

#1, on a fan load like that, the load presented to the motor changes at the cube of the speed of the fan. So if you run the fan 10% faster, the load on that motor will increase to 133% of what it was; at 150% speed the load becomes 270& of what it was. Chances are about .0000000001% that a cheap little fan motor like that was built to handle even 101% of the design load of that fan as it is now at it's highest speed.

#2, that is most likely a simple cheap shaded pole AC motor. The motor will be designed to run at the highest of the speed selections, then lowering the speed is simply a matter of lowering the voltage. But increasing the voltage will not increase the speed, the maximum speed is based on the frequency. You could go buy a specialized Single Phase Variable Frequency Drive to make that motor go faster, for around $300 US.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

Give that one away and buy a fan suitable to your needs. If you increase the voltage the motor will probably burn out quickly, without turning noticeably faster. Spend a lot of money and time on a circuit to supply a higher voltage at a higher frequency and the motor may last a few hours rather than a few minutes.
The cheapest and easiest solution by far is to abandon that unit and buy a larger fan.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DistressedNerd]

Ok I am going to spill the beans - what I am trying to do is pressurized a sealed off button down shirt, which is tricky because it leaks air so it needs decent airflow (CFM), but it also needs pressure (PSI) . I've tried the following setups:

1. Leaf blower (Link) - backward curved centrifugal fan it has adequate pressure - barely enough air flow at ~350 CFM - and way to loud

2. Fan Blower (Link) - forward curved centrifugal fan it has ok pressure (needs little more), but adequate air flow ~460 CFM and very low noise level.

3. Inflatable Fan Blower (Link) - ok pressure, way to low air flow to account for air leaks in the shirt, ok noise level .

What can we do to get a little more pressure out of the fan blower or what's the best way to build a setup that will give me ~450 CFM of airflow, decent pressure, and low noise that it needs?

I know someone out there has the know-how to get this project complete. Thanks for the help so far guys!

 

[1gibson]

Go to a retail store that has Halloween decorations on clearance, find an inflatable nylon character, use that blower. Big Lots would be my first stop, see if there are any close to you.

You don't need more nerds, you need practical advice.

 

[Skogsgurra]

You got me really, really curious. Are pressurized sealed off button down shirts en vogue? Is it something people know about? Can they be bought at H&M? Or IKEA?

Sorry that I, that didn't graduate #2* is so badly informed. It may be because I live in a european country where the latest in fashion may be later than latest. So to say.


*I was #1, actually.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[DistressedNerd]

1gibson thanks for the reply, but if you look at the link in 3., it is exactly what you are talking about. I've already done exactly what you have recommend - your sharper than me though that was my 3rd though not my 1st.

 

[Skogsgurra]

No grammar in that top tier?

Sorry, nerds can take things like that...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Have you considered using two blowers??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zeusfaber]

Let's see if this post turns out to be as long and pompous and off on a tangent as I'm expecting...

There's a lot of what makes a good engineer that you have to learn after you leave Uni. That's not their fault; it's certainly not yours. It's just the nature of the job. If this project was meant as an education, whoever set it chose well.

What things can you learn from it? Here's a few.

Making sure you understand the overall purpose of the project. From what you've said, I suspect you're already there with this one. You haven't told us whether this is a process that has to run continuously for a long time or is a one-off stunt that just has to last until the laughter has died down - nor have you told us whether the shirt has to be fit to wear/sell post pressurisation - but so long as you know those things, that's OK.

Making sure you understand the scope you've got to influence the solution. This is much easier to get wrong than you might think. It sounds like everything you've tried so far has been focused on finding the right blower and motor to plug into that hole there. Now it might be that your brief was to find a cheap replacement for an existing blower without interfering with anything else - in which case, your approach is sensible - or it might be that you've trapped yourself in a rabbit hole and are missing opportunities as a result.

Closely related to this is making sure you understand your constraints. Budget is a good example, but not the only one. Overspending is bad. Delivering a cheap solution that doesn't fulfil the overall objective (in terms of performance and reliability) is a false economy. Everything you say you've tried seems to have been scavenged from consumer products. Was that a research-driven decision (was it actually a decision)?

Making sure your approach is guided by the problem rather than by the type of solution you're most comfortable with. There are lots of ways that lots of us get this wrong. I think your initial question about making motors run faster is as much a symptom of this as my habit of sneaking out to do field repairs when I ought to be back in the office being a "strategic leader".

Getting used to the idea of identifying the underlying problem before you start trying to solve it.

While never abandoning your own initial specialisation, learning enough of the basics of other people's disciplines. Most engineering problems don't really feel the need to be constrained by the traditional boundaries of mechanical/electrical/electronic engineering disciplines, so it helps if the people who set out to tackle them feel a similar degree of freedom.

Getting used to the idea of exploring a broad range of solutions to a problem - not just those within your comfort zone - learning how to recognise which are absolute non-starters and how to choose between the ones that are left.

With all that in mind (and accepting that I have no personal experience in your industry), here's a few questions I'm itching to ask:

Do you know how much pressure you're trying to develop between the inside and outside of the shirt? You've quoted a flowrate figure (450 cfm) but "decent pressure" strikes me as a bit vague for a project whose aim is to "pressurise". Do you know if there's an upper pressure limit? Understanding how much latitude you've got between upper and lower bounds on your key parameters tells you almost as much about the cost and complexity of a project as the absolute values do.

Is there just one of these things, or are you doing a whole row of them? If multiple, do you want to blow them individually? Why?

How long do you need this to keep working? On what duty cycle? How much does plant downtime cost the business? What about engineering time? On long-term projects, in-service costs tend to become dominant (but are frequently forgotten in the rush for much-cheapness in initial acquisition). Blowers scavenged from consumer goods won't be engineered for continuous use for year after year - especially if used somewhere well away from their initial design point. Will you still be able to buy the same product a couple of years down the line? If you decide to sidestep the obsolescence risk by buying half a dozen spare units up-front, does that still feel like good value?

Have you looked at the cost and suitability of industrial blowers? They will be designed for longer life and reliability and ease of replacement. You'll get a spec sheet which tells you before you buy what performance to expect. When they become obsolete you are more likely to find a replacement with the same interface. There is an up-front premium to pay for those benefits, but until you know the scale of that premium and how much value you set by the benefits (not a trivial question), you're just tinkering at the edges.

Where's all the airflow going? Is it leaking through the pores in the shirt fabric, is it escaping through your neck, cuff and torso seals - or is it escaping through the button line - or even somewhere else? Is there an easy and acceptable way to improve the sealing and make the blower's job easier? (Very dependent on application - a QA process in a shirt factory is going to give quite different answers to a stunt or display application).

Where's all the pressure going? Is the blower seeing the same pressure as the inside of the shirt, or is it having to force air through a duct that's too long, narrow, convoluted or kinked? How much scope is there to improve this?

If you're in the "one-off, needn't last long, must be cheap" space, then the process becomes much more one of "What can I do with what I've got without investing too much time in the whole business?". If it was me, I'd have a quick look at where I was losing pressure and flow to make sure there were no quick wins there (starch the fabric, or spray varnish on the inside, then put a football in the collar, something similar in the cuffs and Duck tape down the inside of the button line and round the waist) then go with Bill's suggestion of doubling up on the blowers.

There we go. Long, pompous and tangentially rambley. But any help?

A.

 

[DistressedNerd]

zeusfaber - Thank you for your response, your questions have been pulled and answered below:

Was that a research-driven decision (was it actually a decision)?
Research yes - did I look at the performance curve of the blower fans before selecting - no. I just needed to get a very rough idea of what would work, now it is time to get specific.

Do you know how much pressure you're trying to develop between the inside and outside of the shirt?
No I building a U-tube manometer now to get an idea of that now - I need about 50% more pressure than the Blower fan (#2) will give me - Question: Would we use the pressure developed inside the shirt and select a blower fan that could produce that amount of static pressure?

You've quoted a flowrate figure (450 cfm) but "decent pressure" strikes me as a bit vague for a project whose aim is to "pressurise". Do you know if there's an upper pressure limit?
Upper pressure limit I would imagine to be just a little bit more than that inflatable you see in your neighbors yard.

Is there just one of these things, or are you doing a whole row of them? If multiple, do you want to blow them individually? Why?
Individually - not developed for commercial operation - it's going to be used in residential operation - save on build cost, space requirements, etc.

How long do you need this to keep working? On what duty cycle? How much does plant downtime cost the business? What about engineering time?
Designed for = 500 hours of use. Maximum continuous "On" = 20 minutes.

Have you looked at the cost and suitability of industrial blowers?
This will be a residential use blower - although economizing (make it plastic, higher tolerances) industrial blower designs may do the trick.

Where's all the airflow going?
Through the fabric.

Is there an easy and acceptable way to improve the sealing and make the blower's job easier?
No.

Is the blower seeing the same pressure as the inside of the shirt, or is it having to force air through a duct that's too long, narrow, convoluted or kinked? How much scope is there to improve this?
The duct creates little headloss and there is no wiggle room to improve this.

What can I do with what I've got without investing too much time in the whole business?
Time can be invested I would rather spend a month finding the right blower setup for this application than going then going with options that double the space requirement, parts, etc. There's got to be the right setup out there - if I have to take a commercial blower that has the right draw it out in CAD and try to economize it for residential use I will try.

Starch the fabric, or spray varnish on the inside, then put a football in the collar, something similar in the cuffs and Duck tape down the inside of the button line and round the waist - there is no wiggle room for this either the design has already been concluded upon and shirt is sealed.


This forum is awesome - feeling a lot more confident about getting this thing designed properly

 

[zeusfaber]

Stand back - screech of brakes - Mental J-Turn.

Up to now, I (and, to look at the replies, everybody else) had assumed you were looking at a short project to put together a bespoke solution to some specialist low volume or one-off requirement.

Once you shift into volume production of consumer products, you're into a completely different battlespace. I'd suggest that all the disciplines I think engineers need to learn post Uni are still valid, but your development process has to fit round a significantly different set of priorities.

The product now has to be right before you launch it. Opportunities to tweak and tune afterwards will be few, far between and ruinously expensive.

Production cost becomes a significant driver. Jeff's observation (post #2 in this thread) about the degree of overcapacity engineered into successful consumer products is right, and right for a reason.

With R&D costs amortised against the whole of the first year or two of sales, you ought to able to afford to invest more in this part of the project than for a one off. You certainly need to.

So what does that mean in practice?

For starters, get used to saying "I trained as an electrical engineer, but...". From what you've said so far, the meat of this project is in every other discipline. To my mind, that's where it starts to get genuinely interesting.

You now need to understand your requirement in intricate detail. Not just minimum pressure and flow, but also how those parameters vary in service (are all shirts the same? What happens when they get choked with dust?). How much overpressure will a shirt take before it bursts at the seams or starts to pop buttons? How much variation is there in that? What is the power supply spec in your target market (and, yes, how much does that vary in practice)? Your product will have to work properly under every combination of conditions - even when you combine your worst-moulded and dirtiest impeller with the largest and leakiest shirt with a remote farmyard power supply. Consumers don't take kindly to being told it's their fault if the product doesn't always work.

Once you can put numbers to your requirement, the whole business of starting to look at performance curves starts to look a lot less daunting.

The piece about exploring a range of options doesn't go away. For instance, you'll probably want to compare costs and benefits of designing and manufacturing (including tooling) your own impeller versus buying in a suitable off-the shelf blower and explore the sensitivity of that balance to production volume. Just looking at the range of data that normally appears on the spec sheet for an off-the-shelf component will tell you a lot about what data you need to gather to define your requirement (and will probably help with your question about whether all you need to do is look at static pressure).

Prototyping becomes an option - but you need a way of evaluating your prototypes quantitatively across the complete requirement space.

The bit about understanding your constraints gets particularly important. Over here, the name of the game is CE marking. This will consume a lot of time and money - and should eventually make you an expert in all sorts of unexpected subjects.

A.

 

[logbook]

The attached tutorial file may help.

Skip over the first section on establishing the cooling requirements, but the rest is all relevant.

 

[DistressedNerd]

"I trained as an electrical engineer, but..." - I studied environmental engineering & economics - worked in mathematical modeling with a federal agency in R&D in undergrad, but upon graduation went tangential into a doctorate of physical therapy program.

Are all shirts the same? No -designed to accommodate 95% of all sizes

How much overpressure will a shirt take before it bursts at the seams or starts to pop buttons? Given the sound, size, cost, constraints to the design - we will take all the pressure we can get.

Name of the game here is UL or ETL in the U.S I have the UL standards document, but I will design with common sense 1st then smooth out the technicalities.

Zeusfaber I feel like you have the energy, know how, and curiosity to build this thing in 1 day - I would be very grateful if you did

logbook thank you for the tutorial it appears to be spot on - give me a little bit to digest.

 

[LionelHutz]

I quit reading by the time the long posts started but you ~REALLY~ need less air leakage.

Otherwise, there is probably something here that would work. Without knowing the pressure required it's hard to say but I'd start with the BLOWERS or possibly the TUBEAXIAL FANS (types on left as your scroll down). If you purchase a 3-phase motor variation then you can use a VFD to control the speed.

http://www.grainger.com/search?nls=0&searchQuery=fan

This would be an example of a candidate that is similar to that floor drying fan blower you had linked but with more flow, and probably more pressure too.

http://www.grainger.com/category/hv...0mtij/Ntt-fan?nls=0&sst=subset&ts_optout=true

Basically, a big ass furnace fan.

 

[ScottyUK]

An 'ass furnace'? Wow. I gotta see what one of those looks like.

 

[OperaHouse]

I stopped reading a while back but how about some spray starch so less air leaks through the shirt. In engineering, the answer isn't always more power!

 

[1gibson]

Starch was already disqualified, but some sort of liner that fits inside the shirt might still be on the table.

 

[ScottyUK]

Siemens have already solved this problem:

http://www.siemens-home.com/tr/TJ10500.html

 

[waross]

Nice link Scotty.

Bill
--------------------
"Why not the best?"
Jimmy Carter