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'[EE] Compressed air electric generator?'
2008\11\02@153530 by Enki

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       I need to do a design for a client that will be powered by
compressed air. So I need a 10-15W electric generator moved by air.
       The generated voltage can be any.
       Have spent some time on google but couldn't find anything useful.

       Any ideas?

       Thanks.
       Mark Jordan

2008\11\02@161132 by Martin K

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Enki wrote:
>        I need to do a design for a client that will be powered by
> compressed air. So I need a 10-15W electric generator moved by air.
>        The generated voltage can be any.
>        Have spent some time on google but couldn't find anything useful.
>
>        Any ideas?
>
>        Thanks.
>        Mark Jordan
>
>  

You need what they call an "air motor" - try searching for that.

-
Martin

2008\11\02@164542 by olin piclist

face picon face
Enki wrote:
> I need to do a design for a client that will be powered by
> compressed air.

I've heard of consultants producing hot air, but never someone powered by
compressed air.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\11\02@165309 by Martin K

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Olin Lathrop wrote:
> Enki wrote:
>  
>> I need to do a design for a client that will be powered by
>> compressed air.
>>    
>
> I've heard of consultants producing hot air, but never someone powered by
> compressed air.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014.  Gold level PIC consultants since 2000.
>  
Use one of these:
<http://www.youtube.com/watch?v=G3E2tv8UgfU>

-
Martin

2008\11\02@191714 by Victor Faria

picon face

----- Original Message -----
From: "Enki" <spam_OUTenkitecTakeThisOuTspamgmail.com>
To: <.....piclistKILLspamspam@spam@mit.edu>
Sent: Sunday, November 02, 2008 03:35 PM
Subject: [EE] Compressed air electric generator?


{Quote hidden}

Mark look at this link, vane motors
http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=keyword&action=Go%21&QueryString=vane++motor

Victor


>
> --

2008\11\02@210600 by Enki

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On 2 Nov 2008 at 19:16, Victor Faria wrote:

{Quote hidden}

       Thanks for the link, but I'm looking for a generator. A very small
one, 10-15W will do the job. Size will be an issue.

       Mark Jordan

2008\11\02@214317 by Sean Breheny

face picon face
Hi Mark,

I think he was suggesting that you use one of those air motors and
attach it to the shaft of a generator. I doubt you will find something
which is intended to directly convert energy from compressed air to
electricity.

Sean


On Sun, Nov 2, 2008 at 9:05 PM, Enki <EraseMEenkitecspam_OUTspamTakeThisOuTgmail.com> wrote:
> On 2 Nov 2008 at 19:16, Victor Faria wrote:
>
>>
>> {Original Message removed}

2008\11\02@221008 by William \Chops\ Westfield

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On Nov 2, 2008, at 6:05 PM, Enki wrote:

> I'm looking for a generator. A very small one, 10-15W will do the job.

I'm not experienced in the area, but 10-15W sounds like a pretty  
substantial generator to me.  For comparison, bicycle generators look  
to be about 6W...

You may be stuck with some sort of air-powered motor (die grinder?)  
connected to a motor run "backward."

BillW

2008\11\02@224928 by Danny Miller

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Yeah those air motors are a lot bigger than that.

I have your answer.  Probably perfect.
Mini air turbine for dental tools:
http://cgi.ebay.com/Dental-Handpiece-PUSH-BUTTON-TURBINE-BIEN-AIR-BORA_W0QQitemZ260294847589QQcmdZViewItem?hash=item260294847589&_trkparms=72%3A1205|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14
<cgi.ebay.com/Dental-Handpiece-PUSH-BUTTON-TURBINE-BIEN-AIR-BORA_W0QQitemZ260294847589QQcmdZViewItem?hash=item260294847589&_trkparms=72%3A1205%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14>
That looks like a replacement rotor sans housing though.

Just eBay seach for "air turbine" or "air motor".  You will find several
dental handpieces.
Also:
http://cgi.ebay.com/GAST-Rotary-Air-Gear-Motor-Mounting-Hub-1UP-NRV-16-GR11_W0QQitemZ140278127269QQcmdZViewItem?hash=item140278127269&_trkparms=72%3A1205|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14
<http://cgi.ebay.com/GAST-Rotary-Air-Gear-Motor-Mounting-Hub-1UP-NRV-16-GR11_W0QQitemZ140278127269QQcmdZViewItem?hash=item140278127269&_trkparms=72%3A1205%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14>

Those might have 20W or 30W of shaft output power.  I couldn't say for
sure.  They are small though.

Be wary of maintenance questions.  Those don't run in continuous duty in
normal settings so I don't know how many runtime hours it would be good
for.  Also lubrication requirements, check on that.  But turbines are
simpler than piston-type air tools, that's for sure.

One other possibility.  Wankel model engines:
http://cgi.ebay.com/NSU-Wankel-30Cubic-Inch-OS-Graupner-Engine-Non-Cox-NIB_W0QQitemZ290272408900QQcmdZViewItem?hash=item290272408900&_trkparms=72%3A1205|39%3A1|66%3A2|65%3A12|240%3A1318&_trksid=p3286.c0.m14
<http://cgi.ebay.com/NSU-Wankel-30Cubic-Inch-OS-Graupner-Engine-Non-Cox-NIB_W0QQitemZ290272408900QQcmdZViewItem?hash=item290272408900&_trkparms=72%3A1205%7C39%3A1%7C66%3A2%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14>

AFAIK simply feeding a Wankel compressed air should work.  It's slightly
messed up because it doesn't even need the compression stage.  Actually
maybe you could leave the intake port open and add a port for compressed
air where the compression happens, I don't know.  Again, runtime hours
and lubrication need to be looked at.

Danny

>
>        Thanks for the link, but I'm looking for a generator. A very small
> one, 10-15W will do the job. Size will be an issue.
>
>        Mark Jordan
>
>  

2008\11\03@025102 by Luis.Moreira

picon face
We recently did just that.
I needed to do some measurements at 130KV potential and after looking at
some solutions, we decided to use a die grinder attached to a 3 phase
motor similar to the ones used for driving hard drives and such. We also
tried a brushed DC motor but that was not so good.
We manage to get around 14V DC (after rectification) @ 1A, and it worked
very well. But like some pointed out lubrication is an issue, not only
because it requires it but also this tools have no return pipe hence you
can end up with everything covered in oil. The other issue we found was
vibration. As this was a temporary setup for us, the motor to grinder
coupling was made directly, After running it for 4 hours continuously
the system stopped. At first we tough that the grinder seized but
actually it was the motor that do to the vibration damaged one of the
windings.
Most of all what we found, specially when we first tried the system with
the DC brushed motor, is that the choice and combination of air motor
and motor( as a Generator) is very important. Specially the RPM
required/supplied and torque.

Best Regards
               Luis

   



{Original Message removed}

2008\11\03@032039 by Danny Miller

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The Gast rotary vane vac pump I have says "use no oil" on it.

The dental handpieces won't eject oil, I'm fairly sure of that.  That
would annoy patients.  But, it might have a return line.  Actually...
yeah, it has to have a return line because otherwise I would have
remembered getting brushed by a high speed exhaust flow when getting
worked on.  I recall the noise but not that.  Not unless they dissipated
and redirected the flow really well.

Danny

Luis Moreira wrote:
{Quote hidden}

2008\11\03@051313 by cdb

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:: The dental handpieces won't eject oil, I'm fairly sure of that.  
:: That
:: would annoy patients.

I've only vaguely followed this thread, but if you are using a used or second hand handpiece, I would suggest dousing it in disinfectant or a steraliser before tinkering.

Many dentists do not clean the actual rotor - and it is amazing to see the amount of enamel dust and other bits of mouths that end up inside the handpiece.

Taps nose - due to inside knowledge of dentists and their habits. Mind you, I've serviced a lot of histopathology equipment, and one often wonders if hygiene and research go together!

Colin
--
cdb, colinspamspam_OUTbtech-online.co.uk on 3/11/2008

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359





2008\11\03@061049 by Alan B. Pearce

face picon face
>The dental handpieces won't eject oil, I'm fairly sure of that.

I suspect they eject water - that ends up in the patients mouth after
cooling the tool ...

2008\11\03@102102 by Walter Banks

picon face


William \"Chops\" Westfield wrote:

> I'm not experienced in the area, but 10-15W sounds like a pretty
> substantial generator to me.  For comparison, bicycle generators look
> to be about 6W...
>
> You may be stuck with some sort of air-powered motor (die grinder?)
> connected to a motor run "backward."
>

I like the die grinder idea. They can be quite small and inexpensive.
I have one in my shop that cost maybe $15 new. It may actually be
overkill.

Some of the rare earth magnet motors for slot cars should have no
problem delivering 10-15W

w..





2008\11\03@104210 by Enki

picon face
On 3 Nov 2008 at 10:14, Walter Banks wrote:

>
> Some of the rare earth magnet motors for slot cars should have no
> problem delivering 10-15W
>

       That's a good idea.
       Will try one of these motors coupled to a dentist "turbine".

       MJ

2008\11\03@110121 by Sean Breheny

face picon face
I think that they do have the option of ejecting water but I think
that is to cool the bit and the tooth, not the handpiece.

Sean


On Mon, Nov 3, 2008 at 6:10 AM, Alan B. Pearce <@spam@Alan.B.PearceKILLspamspamstfc.ac.uk> wrote:
>>The dental handpieces won't eject oil, I'm fairly sure of that.
>
> I suspect they eject water - that ends up in the patients mouth after
> cooling the tool ...
>
> -

2008\11\03@115228 by Alan B. Pearce

face picon face
>I think that they do have the option of ejecting water but I
>think that is to cool the bit and the tooth, not the handpiece.

Well, I was figuring on using water to lubricate the motor in the handpiece,
rather than cool it ... ;))

2008\11\03@122906 by Martin

face
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Enki wrote:
> On 3 Nov 2008 at 10:14, Walter Banks wrote:
>
>> Some of the rare earth magnet motors for slot cars should have no
>> problem delivering 10-15W
>>
>
>        That's a good idea.
>        Will try one of these motors coupled to a dentist "turbine".
>
>        MJ
>

Before you try one of those, or alternately, try one of the 3 phase
brushless hobby motors. They would be more efficient in that they would
give you more output power. The brushed motors might have highly
advanced timing which would make it a terrible generator.

-
Martin

2008\11\03@122942 by Danny Miller

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Yeah air motors and turbines do not need cooling.  They need heating.

Adiabatic cooling effects mean the air flow cools down quite a bit, and
the colder air loses pressure thus loses the potential to do work.  
Unfortunately, warming up a moving air mass is more problematic than it
seems.  The conductivity of air with an aluminum wall is fairly poor for
the flow speeds usually encountered.  That is, a piston expands and the
air cools itself with the change in volume.  This may happen within say
100uS.  The thermal conductivity of 65F cylinder walls will not
significantly rewarm the air within that 100uS.  This issue affects air
motors of any size or density, but of course high power density air
motors have even worse problems as it struggles to have a large warm
sink with the air and avoid freezing water or even frozen CO2 in the path.

Yeah it does make some sense to push the exhaust into a heat exchanger,
let it warm up and regain pressure, and push it through another
expansion chamber (cylinder or turbine).  That still has flow rate
issues and a whole new set of complications though.

Danny

Sean Breheny wrote:
{Quote hidden}

>> --

2008\11\03@161330 by Peter

picon face
Enki <enkitec <at> gmail.com> writes:

>        I need to do a design for a client that will be powered by
> compressed air. So I need a 10-15W electric generator moved by air.

Would my design help ? :

http://www.geocities.com/plpeter2006/piclist-airgen.html

9 W @ 9V at 2 bar or so

Peter




2008\11\04@020451 by apptech

face
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>> I need to do a design for a client that will be powered by
>> compressed air. So I need a 10-15W electric generator moved by air.
>
> Would my design help ? :
>
> www.geocities.com/plpeter2006/piclist-airgen.html
>
> 9 W @ 9V at 2 bar or so

Looks like fun.
The claimed 20% efficiency sounds a bit optimistic.

Pisothermal = Vatmosphere x Volume/second x ln(Psource/Patmosphere)

That gives about 100+ Watts for about 9W out or somewhat under 10%.
Still commendably useful.

E&OE / what have I missed?

I like the self dismantlement avoiding shunt regulator.



  Russell McMahon

Pisothermal = Vatmosphere x Volume/second x ln(Psource/Patmosphere)
Padiabatic about the same but not applicable here.
P"diabatic" lower

2008\11\04@090010 by plpeter

picon face

I wrote:
>> Would my design help ? :
>> http://www.geocities.com/plpeter2006/piclist-airgen.html

make that 8W @ 9V

> The claimed 20% efficiency sounds a bit optimistic.
> E&OE / what have I missed?

The "measurements" were done very approximately (l/sec estimated from the
pressure drop/time on a 25l air compressor tank before pressure regulator),
and generously rounded up by me (I don't like to lie to myself, it tends to
come back and haunt one).

> I like the self dismantlement avoiding shunt regulator.

Sufficiently optimally "designed" turbines that do not have one "live"
through some of exactly one load dump.

I think that the design is good and that it should be redone with a carbon
wheel and a different generator to take the 60,000 rpm where it would be
optimal (maybe 4 times better than now). I guess reaching 50% over-all
efficiency can be tried (0.7 for the turbine and 0.7 for the generator). The
shown wheel is mild steel sheet ca. 0.4mm thick and too hard to bend by
hand, and will start to visibly bend outwards after 30,000 rpm.

Peter

--
View this message in context: www.nabble.com/Compressed-air-electric-generator--tp20293599p20322786.html
Sent from the PIC - [EE] mailing list archive at Nabble.com.

2008\11\04@105858 by Enki

picon face

       Your design is interesting. What is the generator used?

       I have to power a load that draws 2A @ 7,5V during one second each
15 seconds. So I think a 40,000uF capacitor charged to 20V powering a
switcher would do the job.
       The charger circuit (air turbine generator) would need to charge the
capacitor to 20V in 14 seconds. The air pressure available is ~10BAR.
       I could use a battery instead of capacitors.

       Mark Jordan


On 4 Nov 2008 at 5:59, plpeter wrote:

{Quote hidden}

> --

2008\11\04@120641 by Peter

picon face
Peter <plpeter2006 <at> yahoo.com> writes:
> www.geocities.com/plpeter2006/piclist-airgen.html
>
> 9 W @ 9V at 2 bar or so

Make that 8W @ 9Vdc

Peter


2008\11\04@125647 by Danny Miller

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Well let's see:
Energy @ 40,000uF 20v= 0.5*C*V^2=8J
Energy @ 7.5V=1.125J (this is where a stepdown switcher would fail to
produce 7.5V anymore).

delta-energy: 6.875J

Energy needed= W*sec= 2A * 7.5v * 1 sec= 15J

Not nearly enough.  We have not considered switching losses or the
capacitor's ESR either.  2A is not a problem for many 40,000uF caps but
do not simply assume the ESR is low enough.

When reviewing the design idea, note that a cap of twice the voltage is
4x the energy.

If this is a DC motor load, it should be possible to PWM a higher
voltage cap to produce the desired speed without an additional inductor
or cap or anything.

Battery can be more complicated than you think.  A NiMH does not like to
be "floated" with a constant voltage OR constant current and
standard/simple state-of-charge detection schemes don't work for
floating NiMHs.  You could do a lead-acid batt but it will be larger and
have a somewhat limited life.  Actually a lithium CAN be floated at
constant voltage, and have long life, if you simply select the float
voltage that leaves it at only 70% charge or so.  Full charge and it may
overcharge if your float voltage is not very accurate, and the lifespan
is far lower when sitting on the shelf at 100% SOC than 70% (total
opposite of lead acid).

Danny

Enki wrote:
{Quote hidden}

>> --

2008\11\04@125900 by Peter

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Enki <enkitec <at> gmail.com> writes:
>        Your design is interesting. What is the generator used?

It's a relatively expensive dc servo motor from Japan (Japan Servo I think). Any
PM toy motor will do the job. Try a cheap type sold for RC electro racing (car).

Umm, you need 2A@7.5V 2 seconds out of 15. That's like 2 Watts for the power
source at 100% efficiency. Figure about 10W real input. Are you sure you can't
use air to do what you need to do ?

Peter


2008\11\04@131615 by Peter

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> Not nearly enough.  We have not considered switching losses or the

This is an app for a supercap I think. $$$.

Peter

2008\11\04@134013 by Enki

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       Sorry, I should have typed 1A at 7.5V (DC load) during one second
each 15 seconds. I could use 10x4,700uF in parallel charged to 25V.

       Mark Jordan


On 4 Nov 2008 at 11:56, Danny Miller wrote:

{Quote hidden}

2008\11\04@200947 by apptech

face
flavicon
face
> I have to power a load that draws 2A @ 7,5V during one second each
> 15 seconds. So I think a 40,000uF capacitor charged to 20V powering a
> switcher would do the job.
> The charger circuit (air turbine generator) would need to charge the
> capacitor to 20V in 14 seconds. The air pressure available is ~10BAR.
> I could use a battery instead of capacitors.

If you use a battery you can monitor the long term voltage. As long as you
get more energy in than neded on average you can use an extremely simple
regulator - either clamping the voltage at a desired point well below max
capacity or shutting off the input. Clamping sounds better if you use an air
turbine :-).

Battery wants to be large enough that 2A load does not constitute a nasty
load. 2AH would be sensible minimum for many chemistries. More better. The
battery is essentially floated. Two series connected LiIon cells sound about
right for this. 2 x 18650 at typically 2000+ mAh would be 'about right'.
Double would be better but you get a little into series-parallel
arrangements. Float arrangement should lead to longish life. SLA may be OK
but voltage is annoying. 7 x NimH about right. Load down to about 7.5 - 8.5
range depending on various factors and charge at up to 10+ volts. Even NiCd
may have a plave here. Got an old drill battery pack ? :-).(Watch quality).

 Russell McMahon




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