circuit design for a small dc airpump

[peter]

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC? I need to find out
firstly if it is feasible to re wire the electromagnet to take a DC
current to provide approximately 5w of power. And secondly, is it
possible to design an electrical circuit which provide the same
approximately 50 times per second oscilation?

Ideally, these oscilations would literally be the same as what is
achieved with mains power. I was hoping it will be possible to design
a circuit which firstly powers the electromagnet with current going in
one direction, then switching to power the electromagnetic with
current going in the other direction, similar to what happens in an
electric motor. This will power to diaphragm both as it contracts and
also to expand it back to rest.

If this is not possible, is it possible to design a circuit which only
powers the electromagnet briefly to contract the diaphragm, and during
the brief period when power is then switched off, relying on a small
spring to pull the diaphragm back to rest, and then pulse briefly on
again and so on

It also needs to be reliable. It will be used continuously for 12
hours daily, and will need to have a reasonable working life before
items wear out or need replacing and so on (incidentally, its use is
not like sustaining !! It will be used in a pressure management system
in an air cushion, which disabled people have to rely on to ease
pressure on bits of aging bodies that they sit on for long period of
time !!) .

Any suggestions, direct help, comments or anything else that is useful
would be much appreciated.

 

[the Wiz]

petergodfrey@dodo.com.au (peter) wrote:

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC? I need to find out
firstly if it is feasible to re wire the electromagnet to take a DC
current to provide approximately 5w of power. And secondly, is it
possible to design an electrical circuit which provide the same
approximately 50 times per second oscilation?

A DC motor with an attached wheel that moves an arm could by driven a PWM (pulse
width modulated) controller to adjust its speed. As the wheel rotates, the arm
would move back and forth to move the diaphragm (think of a steam engine drive
system).

Someone else suggested a DC->AC inverter to power the original pump. This would
work, but would require appreciably more power from the battery than a DC
solution. Inverters have fair efficiency, but typically not with small
inductive loads like the air pump.

Small DC motors are readily available, as are basic PWM speed control devices.

In the US, www.mpja.com probably has everything you need (motor, PWM speed
control kit). You might search their site for ideas, then see if you can locate
similar items locally. Some of their kits may have originated elsewhere than
the US.

Possible Australian sources:

http://www.dontronics.com

http://www.oatleyelectronics.com/

http://www.grantronics.com.au/

http://www.bettanet.net.au/gtd

http://www.dse.com.au/

http://www.cia.com.au/rcsradio/

http://www.kitz.ozware.com/

http://www1.jaycar.com.au/productResults.asp?FORM=KEYWORD&ProdCodeOnly=yes&Keyword1=K&Keyword2=K

Place to search for other kit makers: http://kitsrus.com/back.html

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter at@at mindspring dot.dot com. Fix the obvious to reply by email.

 

[Ian Bell]

peter wrote:

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

Others have given perfectly good laternative design suggestions so I just
wanted to put a different slant on it. I am part of a UK charity called
REMAP which builds technical aids for the disabled which are not available
commercially. So, if you were in the UK you could approach your local REMAP
group and they would build something for you free of charge. I know you
are not in the UK but I just wondered if their might not be an organisation
similar to REMAp in OZ? Just a thought.

Ian

 

[Gareth]

peter wrote:

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC? I need to find out
firstly if it is feasible to re wire the electromagnet to take a DC
current to provide approximately 5w of power. And secondly, is it
possible to design an electrical circuit which provide the same
approximately 50 times per second oscilation?

It is certainly possible to make a circuit which will reverse the
direction of the current in the electromagnet approximately 50 times per
second. to switch the current you would probably want an 'H' bridge,
this is just four transistors arranged so that either side of the motor
can be connected to the +12V and either side can be connected to 0V.

You would then need something to generate a 50 Hz (50 times per second)
signal to control the H bridge, there are quite a few ways to do this
for example using a 555 timer IC.

You do not need to re-wire the electromagnet to take DC, but if it is
designed to take 240V (or is it 115V or 120V?) it will not work very
well with only 12V or 24V. I wonder if there are any pumps which are
designed to work from a lower voltage, for example some aquarium pumps
may have a step down transformer so that you can keep mains voltages
well away from the aquarium, or maybe not I did a brief search but
couldn't find any.

Does it have to be this type of pump? I have seen air pumps designed to
be powered from 12V for inflating car tyres for example:

http://www.gbdriver.co.uk/acatalog/Online_Catalogue_aircomp_35.html

This type of pump may not be suitable for your application but it is
probably worth looking at.

Gareth

--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris

 

[Gordon Youd]

Peter,
Many years ago I invented a cushion and mattress for the relief of patients
who were unable to move and suffered from bedsores.

You are welcome to use my idea which is a cushion or mattress designed as
two separate sets of tubes, one set is inflated and takes the patients
wieght, then an air valve switches the air supply to the other set of tubes,
the first set then deflates through a bleed port.

The weight transfers from one set of tubes to the other, so the patient has
some relief .

As someone has suggested, you can buy 12 volt air pumps at any motor shop,
use a 555 timer to time the switching.

The cushion/mattress was made for me by a firm in the Isle of Wight, it was
two plastic sheets heat sealed into two separate patterns of tubes.

I think this is what you are trying to make!!!


Regards, Gordon.
----------------------------------------------------------------------------
"peter" <petergodfrey@dodo.com.au> wrote in message
news:fa403389.0403210043.4a2fcd0c@posting.google.com...

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC? I need to find out
firstly if it is feasible to re wire the electromagnet to take a DC
current to provide approximately 5w of power. And secondly, is it
possible to design an electrical circuit which provide the same
approximately 50 times per second oscilation?

Ideally, these oscilations would literally be the same as what is
achieved with mains power. I was hoping it will be possible to design
a circuit which firstly powers the electromagnet with current going in
one direction, then switching to power the electromagnetic with
current going in the other direction, similar to what happens in an
electric motor. This will power to diaphragm both as it contracts and
also to expand it back to rest.

If this is not possible, is it possible to design a circuit which only
powers the electromagnet briefly to contract the diaphragm, and during
the brief period when power is then switched off, relying on a small
spring to pull the diaphragm back to rest, and then pulse briefly on
again and so on

It also needs to be reliable. It will be used continuously for 12
hours daily, and will need to have a reasonable working life before
items wear out or need replacing and so on (incidentally, its use is
not like sustaining !! It will be used in a pressure management system
in an air cushion, which disabled people have to rely on to ease
pressure on bits of aging bodies that they sit on for long period of
time !!) .

Any suggestions, direct help, comments or anything else that is useful
would be much appreciated.

 

[petrus bitbyter]

"peter" <petergodfrey@dodo.com.au> schreef in bericht
news:fa403389.0403210043.4a2fcd0c@posting.google.com...

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC?

No, not using the type of pump you described.

I need to find out firstly if it is feasible to re wire the electromagnet
to
take a DC current to provide approximately 5w of power.

Well, yes and no. If you replace the 220-240V coil by let's say a 24V coil
it will work perfectly on 24VAC. But to rewind a coil may be difficult. The
coils are often moulded both to improve mecanical strength and to prevent
excessive humming. So winding a new coil by hand will be a hell of a job.
Nevertheless it can be done.

And secondly, is it possible to design an electrical circuit which provide
the same approximately 50 times per second oscilation?

Sure.

Ideally, these oscilations would literally be the same as what is
achieved with mains power. I was hoping it will be possible to design
a circuit which firstly powers the electromagnet with current going in
one direction, then switching to power the electromagnetic with
current going in the other direction, similar to what happens in an
electric motor. This will power to diaphragm both as it contracts and
also to expand it back to rest.

That's the right way.

If this is not possible, is it possible to design a circuit which only
powers the electromagnet briefly to contract the diaphragm, and during
the brief period when power is then switched off, relying on a small
spring to pull the diaphragm back to rest, and then pulse briefly on
again and so on

This will *not* be effective.

It also needs to be reliable. It will be used continuously for 12
hours daily, and will need to have a reasonable working life before
items wear out or need replacing and so on (incidentally, its use is
not like sustaining !!

What reliability do you need? Well designed electronics are very reliable
but nevertheless your radio, tvset, hearing add, computer and telephone may
fail sometimes. The most vulnerable thing is the pump but this types tend to
run for years often on a 24h/d basis.

It will be used in a pressure management system
in an air cushion, which disabled people have to rely on to ease
pressure on bits of aging bodies that they sit on for long period of
time !!) .

Are you sure that small a pump will give pressure enough for the job on
hand?

Any suggestions, direct help, comments or anything else that is useful
would be much appreciated.

My advise is to buy or build a small 12VDC to 230VAC converter first. The
Elektor issue SEPT/OCT '99 has an example although it's named frequency
converter. The only thing you have to mention is the transformer. I'd use a
10- or 15VA type for your application. But even then the overall size will
be about the same as the size of your pump. If you have to build more then
one sample - and money becomes an issue - the electronics can be simplified.

petrus







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[John G]

"peter" <petergodfrey@dodo.com.au> wrote in message
news:fa403389.0403210043.4a2fcd0c@posting.google.com...

I'm disabled, and I need help to design an electrical
circuit for a
medical item, which I don't think is available
commercially

It's a small airpump, literally the size and power of a
small aquarium
pump (about 5 watts), but it needs to be powered by 12 or
24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which
oscilates
in the face of an electromagnetic, and this motion moves a
diaphragm.
The oscilation is provided by the alternating current, ie
the diagram
is moved by a very small amount approximately 50 times per
second

Is it possible to do the same thing with DC? I need to
find out
firstly if it is feasible to re wire the electromagnet to
take a DC
current to provide approximately 5w of power. And
secondly, is it
possible to design an electrical circuit which provide the
same
approximately 50 times per second oscilation?

Ideally, these oscilations would literally be the same as
what is
achieved with mains power. I was hoping it will be
possible to design
a circuit which firstly powers the electromagnet with
current going in
one direction, then switching to power the electromagnetic
with
current going in the other direction, similar to what
happens in an
electric motor. This will power to diaphragm both as it
contracts and
also to expand it back to rest.

If this is not possible, is it possible to design a
circuit which only
powers the electromagnet briefly to contract the
diaphragm, and during
the brief period when power is then switched off, relying
on a small
spring to pull the diaphragm back to rest, and then pulse
briefly on
again and so on

It also needs to be reliable. It will be used continuously
for 12
hours daily, and will need to have a reasonable working
life before
items wear out or need replacing and so on (incidentally,
its use is
not like sustaining !! It will be used in a pressure
management system
in an air cushion, which disabled people have to rely on
to ease
pressure on bits of aging bodies that they sit on for long
period of
time !!) .

Any suggestions, direct help, comments or anything else
that is useful
would be much appreciated.

Someone from the UK has suggested getting help from REMAP
or its Australian equivalent.
Well that is TAD, Technical Aid to the Disabled, (
http://www.technicalaidnsw.org.au/ ). There are branches in
other states as well.

There have been some very complex suggestions made to answer
your problem.

Do you mean the pump will run continuously or will it be
turned on by the user to inflate a cushion ad then turned
off until another adjustment is necessary?

SuperCheap Autos has a small 12volt blower designed
specially for filing cushions and mattresses.
--
John G

Wot's Your Real Problem?

 

[petrus bitbyter]

That %(@!#)(+&%=#(* UPC newsserver failed again so I repost:


"peter" <petergodfrey@dodo.com.au> schreef in bericht
news:fa403389.0403210043.4a2fcd0c@posting.google.com...

I'm disabled, and I need help to design an electrical circuit for a
medical item, which I don't think is available commercially

It's a small airpump, literally the size and power of a small aquarium
pump (about 5 watts), but it needs to be powered by 12 or 24v dc, and
not mains powered.

A mains powered aquarium pump has a permanent magnet which oscilates
in the face of an electromagnetic, and this motion moves a diaphragm.
The oscilation is provided by the alternating current, ie the diagram
is moved by a very small amount approximately 50 times per second

Is it possible to do the same thing with DC?

No, not using the type of pump you described.

I need to find out firstly if it is feasible to re wire the electromagnet
to
take a DC current to provide approximately 5w of power.

Well, yes and no. If you replace the 220-240V coil by let's say a 24V coil
it will work perfectly on 24VAC. But to rewind a coil may be difficult. The
coils are often moulded both to improve mecanical strength and to prevent
excessive humming. So winding a new coil by hand will be a hell of a job.
Nevertheless it can be done.

And secondly, is it possible to design an electrical circuit which provide
the same approximately 50 times per second oscilation?

Sure.

Ideally, these oscilations would literally be the same as what is
achieved with mains power. I was hoping it will be possible to design
a circuit which firstly powers the electromagnet with current going in
one direction, then switching to power the electromagnetic with
current going in the other direction, similar to what happens in an
electric motor. This will power to diaphragm both as it contracts and
also to expand it back to rest.

That's the right way.

If this is not possible, is it possible to design a circuit which only
powers the electromagnet briefly to contract the diaphragm, and during
the brief period when power is then switched off, relying on a small
spring to pull the diaphragm back to rest, and then pulse briefly on
again and so on

This will *not* be effective.

It also needs to be reliable. It will be used continuously for 12
hours daily, and will need to have a reasonable working life before
items wear out or need replacing and so on (incidentally, its use is
not like sustaining !!

What reliability do you need? Well designed electronics are very reliable
but nevertheless your radio, tvset, hearing add, computer and telephone may
fail sometimes. The most vulnerable thing is the pump but this types tend to
run for years often on a 24h/d basis.

It will be used in a pressure management system
in an air cushion, which disabled people have to rely on to ease
pressure on bits of aging bodies that they sit on for long period of
time !!) .

Are you sure that small a pump will give pressure enough for the job on
hand?

Any suggestions, direct help, comments or anything else that is useful
would be much appreciated.

My advise is to buy or build a small 12VDC to 230VAC converter first. The
Elektor issue SEPT/OCT '99 has an example although it's named frequency
converter. The only thing you have to mention is the transformer. I'd use a
10- or 15VA type for your application. But even then the overall size will
be about the same as the size of your pump. If you have to build more then
one sample - and money becomes an issue - the electronics can be simplified.

petrus



---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
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