Industrial duty dimmer

[Jaggy Taggy]

For a museum exhibit I need a dimmer.
The electrical requirements are light, I want to regulate a small aquarium
pump with this dimmer, so any good old dimmer will do, really.
But it needs to be very reliable because it would be very difficult and time
consuming to get to it once it is installed in the final exhibit.

Where do I find such a dimmer??

Uwe

 

[Fred Bloggs]

Jaggy Taggy wrote:

For a museum exhibit I need a dimmer.
The electrical requirements are light, I want to regulate a small aquarium
pump with this dimmer, so any good old dimmer will do, really.
But it needs to be very reliable because it would be very difficult and time
consuming to get to it once it is installed in the final exhibit.

Where do I find such a dimmer??

Uwe

Could it be found at an industrial electrical supply store? Forget the
aquarium- SED has the perfect exhibit, it will be the world's smartest
moron, Larry Brasfield.

 

[Michael A. Terrell]

Jaggy Taggy wrote:

For a museum exhibit I need a dimmer.
The electrical requirements are light, I want to regulate a small aquarium
pump with this dimmer, so any good old dimmer will do, really.
But it needs to be very reliable because it would be very difficult and time
consuming to get to it once it is installed in the final exhibit.

Where do I find such a dimmer??

Uwe

You need one designed for a motor, so it isn't a "dimmer". Check out
the variable speed controls for ceiling fans, but be careful. If you
slow the pump down too much it may fail to start running again if the
power cuts out for more than a few seconds. Why can't you put a "Y" on
the air hose and use a small needle valve to vent some excess pressure?
--
?

Michael A. Terrell
Central Florida

 

[John Larkin]

On Sat, 26 Mar 2005 03:17:05 GMT, Jaggy Taggy <outhouse@midcoast.com>
wrote:

For a museum exhibit I need a dimmer.
The electrical requirements are light, I want to regulate a small aquarium
pump with this dimmer, so any good old dimmer will do, really.
But it needs to be very reliable because it would be very difficult and time
consuming to get to it once it is installed in the final exhibit.

Where do I find such a dimmer??

Uwe

Have you tried an ordinary dimmer with the pump? That may not work.

John

 

[Jaggy Taggy]

On 3/26/05 12:52 AM, in article
1111816319.980380.305050@l41g2000cwc.googlegroups.com, "Chris"
<cfoley1064@yahoo.com> wrote:

Michael A. Terrell wrote:
Jaggy Taggy wrote:

For a museum exhibit I need a dimmer.
The electrical requirements are light, I want to regulate a small
aquarium
pump with this dimmer, so any good old dimmer will do, really.
But it needs to be very reliable because it would be very difficult
and time
consuming to get to it once it is installed in the final exhibit.

Where do I find such a dimmer??

Uwe

You need one designed for a motor, so it isn't a "dimmer". Check
out
the variable speed controls for ceiling fans, but be careful. If you
slow the pump down too much it may fail to start running again if the

power cuts out for more than a few seconds. Why can't you put a "Y"
on
the air hose and use a small needle valve to vent some excess
pressure?
--
?

Michael A. Terrell
Central Florida

Second the motion. Most of these small aquarium pumps are actually
driven by a small solenoid that vibrates a bellows. For that kind of
setup, you would need a 20 watt variable frequency drive rather than a
line voltage phase control dimmer. ;-)

In addition to that, the R-C/potentionmeter/diac/triac setup that is
the circuit for these small dimmers requires a minimum load current to
operate properly. The small aquarium pump might not be enough of a
load, and its power factor isn't going to help things, either.

If you insist on "better living through electricity", find a small
motor-driven air pump (think automotive?) and use PWM or other means to
vary motor speed. But it would be best to follow Mr. Terrell's advice
and tee off a bleeder valve to vary the amount of air. That's an
inexpensive, reliable solution.

Good luck
Chris

The air pump I will have to use is a 2 to 3 watt aquarium pump which indeed
uses a small solenoid which vibrates the bellows.
I tried to run one of these things off of a regular $5 dimmer and it worked
fine, but as I said 'momentary' performance does not impress me when failure
means having to fly to Europe to fix it, that is where my wont for a
reliable solution comes in.

Using the aquarium pump continously and bleeding off the excess is an
interesting thought.

Controls like this, either a valve or the pot of a dimmer, see an incredible
amount of abuse in a science museum environment and the final solution
should be the one which results in the most rugged 'visitor interface', and,
in spite of its perceived ruggedness, still the one the maintenance people
can easily fix.

If needed I can get around the minimum load requirement by using an
additional dummy load resistor in conjunction with the regular dimmer.

I am aware of PWM but that doesn't seem to be a solution in my case.


What is the variable frequency drive Chris is referring to??


Thanks for the postings so far, this is helpful to me

Uwe

 

[John Woodgate]

I read in sci.electronics.design that Jaggy Taggy
<outhouse@midcoast.com> wrote (in <BE6ADD02.6645%outhouse@midcoast.com&gt
about 'Industrial duty dimmer', on Sat, 26 Mar 2005:

The air pump I will have to use is a 2 to 3 watt aquarium pump which
indeed uses a small solenoid which vibrates the bellows.

Try a 100 ohm wirewound or cermet variable resistor.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Mark Jones]

John Woodgate wrote:

I read in sci.electronics.design that Jaggy Taggy
outhouse@midcoast.com> wrote (in <BE6ADD02.6645%outhouse@midcoast.com&gt
about 'Industrial duty dimmer', on Sat, 26 Mar 2005:

The air pump I will have to use is a 2 to 3 watt aquarium pump which
indeed uses a small solenoid which vibrates the bellows.


Try a 100 ohm wirewound or cermet variable resistor.

Also consider that as the pump ages, its capacity will decline.

I like the idea of a "hidden" bleeder screw or valve.

 

[Rich Grise]

On Sat, 26 Mar 2005 12:46:19 -0500, Mark Jones wrote:

John Woodgate wrote:
I read in sci.electronics.design that Jaggy Taggy
outhouse@midcoast.com> wrote (in <BE6ADD02.6645%outhouse@midcoast.com&gt
about 'Industrial duty dimmer', on Sat, 26 Mar 2005:

The air pump I will have to use is a 2 to 3 watt aquarium pump which
indeed uses a small solenoid which vibrates the bellows.


Try a 100 ohm wirewound or cermet variable resistor.


Also consider that as the pump ages, its capacity will decline.

I like the idea of a "hidden" bleeder screw or valve.

Every vibrator-style aquarium pump I've ever seen has an adjustment
right on the pump. I've seen pumps in fountains and such that seem
to run continuously forever without human intervention. Is this what
you're going for? Why is this such a big deal? Is this thing
supposed to have some kind of customer-adjustable knob or something?

Just get an ordinary aquarium pump, set it to the right air flow,
and leave instructions, "When air flow changes, turn this knob. If
you can't bring air flow to spec, replace pump and adjust new pump
accordingly."

If you're new to electronics, and are just itching for some kind of
demo masterpiece just to show off, don't put it in a public-accessible
place until it's been tested literally to destruction. This should not
take long - I know: BTDT.

Good Luck!
Rich

 

[Jaggy Taggy]

On 3/27/05 1:19 AM, in article
1111904355.990568.22580@z14g2000cwz.googlegroups.com, "Chris"
<cfoley1064@yahoo.com> wrote:

Jaggy Taggy wrote:

The air pump I will have to use is a 2 to 3 watt aquarium pump which
indeed
uses a small solenoid which vibrates the bellows.
I tried to run one of these things off of a regular $5 dimmer and it
worked
fine, but as I said 'momentary' performance does not impress me when
failure
means having to fly to Europe to fix it, that is where my wont for a
reliable solution comes in.

Using the aquarium pump continously and bleeding off the excess is an
interesting thought.

Controls like this, either a valve or the pot of a dimmer, see an
incredible
amount of abuse in a science museum environment and the final
solution
should be the one which results in the most rugged 'visitor
interface', and,
in spite of its perceived ruggedness, still the one the maintenance
people
can easily fix.

If needed I can get around the minimum load requirement by using an
additional dummy load resistor in conjunction with the regular
dimmer.

I am aware of PWM but that doesn't seem to be a solution in my case.


What is the variable frequency drive Chris is referring to??


Thanks for the postings so far, this is helpful to me

Uwe

Hi, Uwe. A couple of points:

* Sorry -- the 20 watt variable frequency drive business was a bit of
a joke (note the "winky" ;-) ). VFDs are frequently used for speed
control of multi-horsepower AC motors.

* You've got a point -- if the museum patrons are gooig to be tweaking
this continuously, a small needle valve might not be a good idea. They
wear out fairly quickly. In addition, they can be ruined easily by
cranking them past full off.

* I did a quick Google scan, and saw a couple of manufacturers of
aquarium air pumps that have models with electronic air speed controls.
These could possibly be the R+pot-C/DIAC/triac controls in the cheapie
lamp dimmers, and one description mentioned that it had a bellows-type
motor. So, in fact, what you're talking about with a dimmer-type
controller might be possible.

* One issue with these lamp dimmers I didn't mention has to do with
the asymmetry of the DIAC triggering voltage. This results in a DC
component in the load voltage. While this isn't a problem with lamps,
it can cause issues with motors or inductive loads like solenoids. It
heats the coil, and can result in damage. It's something that has to
be taken into account.

* I believe a power resistor in parallel with your pump is a good
idea, but you shouldn't need more than a 680 ohm 25 watt resistor for
120V, or 1500 ohm, 50 watt for 240V. Since lamp dimmers are in series
with the AC load, this should provide enough load current to make sure
your dimmer works properly.

* You mentioned that this business might be shipped to another
country. You should be aware of voltage differences (if you get a
120VAC pump and send it to a country with 240VAC, the pump will have a
very short, warm and exciting life. Also, if you're building it in a
60 Hz environment, and you ship it to a 50Hz environment, you'll have
less air volume. Remember, bellows stroke frequency will be dependent
on line frequency).

* Given that this is going to a museum, you've got a couple of more
issues, if the museum patrons are going to be playing with this
control. In many countries, exhibits with electrical controls may be
classified by the local regulatory agencies as machines. If so, you
may have to deal with the requirement for low voltage (24V max.) panel
controls. This would obviously mean a line voltage lamp dimmer with
line voltage on the pot would be out.

* You also have to deal with the potential for patrons to be downright
malicious, at least by accident. Can you imagine what would happen if
a 3rd grade urchin spills a Juicy Juice on a typical dimmer control?
Bzzzt. Ouch.

* From a practical standpoint, too, you have to look at the life cycle
of the pot or dimmer control you're using. Most dimmers are basically
made to be tweaked a couple of times a day for 10 years or so, meaning
about 50,000 cycles. One busload of 3rd graders could run through that
in one day, especially if your exhibit is fun and exciting to more than
one of the little urchins. Imagine the delight of the museum tech
having to change the dimmer every month. You might want to look at an
AC control with remote pot, and use one of those Allen-Bradley machine
panel potentiometers with washdown capability. The pot itself is
mounted behind the panel mounted shaft, and joined with a flexible
coupling, which eliminates the side-to-side torque that usually results
in premature pot failure. Since the only moving part is on the front
panel, it should be fairly easy for the museum tech to replace. I
guarantee that this will be a predominant failure mode here. Get the
one with the small terminal block under the pot for the three wires.

You can buy or borrow a lamp dimmer and actually try your idea.
Measure the DC resistance of the solenoid coil. Then, after you hook
up the parallel load resistor, run it straight off line voltage for a
while with the cover off. Get an idea how hot the coil becomes at full
voltage. An educated (but careful) finger is probably good enough
here. Then hook up the lamp dimmer in series, and see what happens.
Measure the DC component by putting a DVM across the load, set for
highest range DC. Measure maximum DC voltage (this will usually occur
between 5% and 40% of maximum control voltage). Figure out how much DC
power is going to be dissipated. Try leaving the dimmer at that
setting for twenty minutes, and then see if the coil gets hot. Try
several power settings, and see. See if yuo can make the thing stall
and get stuck at lower voltage. It's a start, anyway. After you've
done this, you can look at different types of AC controls that will
work for you. There are some which work with inductive loads, some
which have forgiving minimum current requirements, and can be used with
an external speed pot. There are also others which provide an isolated
low voltage for a remote control pot which complies with EU strictures
on low voltage controls. I'd need a lot more information before
specifying something myself.

dreamland>Of course, if I wanted to nuke this problem, and money was
no object, only reliability, I'd use a 24VDC motor driving a
peristaltic pump, and use a PWM motor controller with the Allen Bradley
washdown machine panel pot as the user control. You can get everything
you need except the Alen Bradley pot, including the speed control, from
the Cole-Parmer catalog. Make sure you use the most expensive, most
durable tubing available.</dreamland> (This is very expensive, and
should be viewed as humor, unless you've got a lot of cash to spend.)

Where I live, the local science and industry museum has a tech
department, and has people who are paid to do this kind of thing. I
know if I had a problem of this type, I'd want to call them up and ask
a few good questions. They also may be able to come up with more
gotchas off the top of their heads. If you're a member of your local
science museum patron support group and you ask nicely, you might be
able to buy one of the techs or engineers a good lunch, and in
exchange, be able to ask a few questions and pick their brain about
your project.

Good luck
Chris

Chris, thank you for your very thoughtful answer, you hit on most of the
pertinent questions I can think of.

First a few points regarding the effort which often goes into these
controls. They easily cost hundreds of dollars since you can never let the
public handle a potentiometer directly, they are always isolated and
protected from radial and axial loads and from turning past their stops.

In addition to all these precautions I design the knobs in such a way that
the public does not really have much leverage on the whole assembly, for
example by using a flat knob with a shallow depression for your index
finger, hard to exert much force that way.

And then you obviously need the best pot money can buy.

And then you need to make it easy to change because it will fail anyways.


The pumps in our case are pretty much determined. I looked for the pump with
the right amount of flow and a very low noise level. I have been using this
particular one for years and will try not to change it. I supply my exhibit
with a big transformer so I can continue to use this type of pump even in
Germany with 220V!


The pump will last about a year under continuous use. I used an arrangement
to bleed of the excess in an earlier version and thought the electronic
control would allow to change the airflow similar to a bleeder arrangement
but prolong the life of the pump since it might not run continuously,
statistically speaking the visitors might leave it in the off position half
of the time.

Also, in a bleeder valve (I designed my own back then, not a needle valve
but a ported cylinder which does not need any stops, you can keep turning
it) it is not that easy to make a channel which will gradually and evenly
bleed off air over 180 or 270 degrees, we are talking a very small groove
here...

Early tests seemed to indicate that a dimmer arrangement with this pump
might work, but for how long??


The discussion here seemed to question the reliability of this arrangement
and since then I have been thinking again about the bleeder arrangement.
And indeed I think I will go with a modified bleeder valve, which I can
build as beefy as necessary, it can have a continuous turn, no stops
necessary, and I managed to find an arrangement which allows the entire
bleeding valve to be removed as a unit from the outside while no screws are
visible, another requirement of our particular set-up.


And Chris, finally, referring to the suggestions in your last paragraph, I
am one of those people one often calls for advise in these matters. I know
this must be a disappointment to you but this is how I earn my keep and it
is quite a challenge given all the other constraints and the publics
ingenuity to disassemble the exhibits to come up with good solutions.

We will see how long this one will last in Germany....

Anyways, thank you and the other posters for the input, I think I got a good
approach now.

Uwe