Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if there's a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

Thanks in advance

--
Bobby G.

Crossposted to alt.home.repair;comp.home.automation, follow up in AHR,
please!

A current sensor might work. I built a current sensor to let me know
when my septic pump is operating. The pump is in a tank that is buried
next to the septic tank in the yard. The sensor triggers a clock timer
and a doorbell chime when the pump operates. Your sensor would have to
be set to trigger only when the current exceeds a set point.


---MIKE---
In the White Mountains of New Hampshire
(44° 15' N - Elevation 1580')

"Robert Green" wrote:

Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I mean
pipe - the Pope has enough problems of his own. (-:

-snip-

I haven't finished my second cup of coffee yet- but my instinct is go
with 'lack of sucking'. Put a vacuum switch just before the canister
that triggers a bell/light/buzzer if it gets high.

Or put one at the inlet that flashes in your face if air flow drops
below a certain point.

Jim

On 3/30/2010 7:23 AM, Robert Green wrote:
Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if there's a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

Thanks in advance

--
Bobby G.

Crossposted to alt.home.repair;comp.home.automation, follow up in AHR,
please!


Here's a unit that will open up whenever
there is a vacuum pressure increase.
http://www.thinkvacuums.com/beam/valve.html
I'm sure others have similar products.

On Mar 30, 7:39*am, (---MIKE---) wrote:
A current sensor might work. *I built a current sensor to let me know
when my septic pump is operating. *The pump is in a tank that is buried
next to the septic tank in the yard. *The sensor triggers a clock timer
and a doorbell chime when the pump operates. *Your sensor would have to
be set to trigger only when the current exceeds a set point.

* * * * * * * * * ---MIKE---In the White Mountains of New Hampshire

* (44° 15' *N - Elevation 1580')

Perhaps a more interesting question is why is something getting stuck
so often that this is a real problem? I've used the one in my house
for 17 years and it has not gotten blocked even once. The other thing
I don't understand is how it could stay blocked long enough that the
motor overheats and the thermal cutoff shuts it down. Can't you tell
there is no suction anymore by the way the head behaves and that dirt
isn't being picked up?

On 3/30/2010 7:23 AM, Robert Green wrote:
Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if there's a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

Thanks in advance

--
Bobby G.

Crossposted to alt.home.repair;comp.home.automation, follow up in AHR,
please!


Guess I am missing something.

If you are using it and suddenly there is no or greatly diminished
vacuum wouldn't that be a sufficient indicator that there is a problem?

On 3/30/2010 10:45 AM, George wrote:
On 3/30/2010 7:23 AM, Robert Green wrote:
Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope -
I mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if
there's a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

Thanks in advance

--
Bobby G.

Crossposted to alt.home.repair;comp.home.automation, follow up in AHR,
please!


Guess I am missing something.

If you are using it and suddenly there is no or greatly diminished
vacuum wouldn't that be a sufficient indicator that there is a problem?

If you are using it with a motor
operated beater brush, you really can't
hear the loss of suction over the motor
noise. I know, both me and my wife have
had it happen in our old house. What
can alert you is that you have to go
over the same spot several times to pick
up the one little crumb.

On Mar 30, 12:51*pm, Art Todesco wrote:
On 3/30/2010 10:45 AM, George wrote:



On 3/30/2010 7:23 AM, Robert Green wrote:
Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope -
I mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if
there's a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

Thanks in advance

--
Bobby G.

Crossposted to alt.home.repair;comp.home.automation, follow up in AHR,
please!

Guess I am missing something.

If you are using it and suddenly there is no or greatly diminished
vacuum wouldn't that be a sufficient indicator that there is a problem?

If you are using it with a motor
operated beater brush, you really can't
hear the loss of suction over the motor
noise. *I know, both me and my wife have
had it happen in our old house. *What
can alert you is that you have to go
over the same spot several times to pick
up the one little crumb.- Hide quoted text -

- Show quoted text -

First the OP must see if the blocked hose speeds up or slows down the
motor, and see if the current increases or decreases.

I like the suggestion of Mr. Todesco that puts a vacuum bypass on the
inlet to the motor/vacuum pump. That guarantees you will not damage
the motor unless the spring in the bypass suddenly gets stronger or
the diaphram jams with dirt. That is unlikely to happen. If the
current does increase, a loop of wire through a ferrite core, with a
second coil of many turns on the same core can generate an increased
voltage when the current thru the motor increases, if that is what is
happening. That increased voltage could be used to do any number of
things, but that is for a different group (sci.electronics.repairor
misc).

"Robert Green" wrote in message
...
Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now
that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Believe it or not, the "motor load" is usually at a minimum when the vac is
completely blocked off.

If you want to monotor for a blocked inlet you might want to check flow in
the exhaust (after the bag). Most central vacs exhaust through a tube
which can be connected outside if your don't want to "re-cycle" the dirt the
filter bag misses.



Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I
mean
pipe - the Pope has enough problems of his own. (-:

I am going to try a test today with my Kill-0-Watt meter to see if there's
a
substantial increase in current draw. I might be able to use a current
sensor to detect the upswing and sound a chime or some other kind of
warning. I don't want to shorten the life of the motor by letting the
thermal overload shut it down after it has overheated.

In many/most central vacs (and even some "shop vacs") the cooling air for
the motor is separate from the air used to suck up dirt. If your's isn't
separate then a blockage would definitely cause it to overheat. Otherwise,
you may find that it actually runs slightly cooler when the inlet is
blocked.

Frankly, sensing overheat isn't a bad way of seeing if something has gone
wrong.

Modern motors "run hot" so don't worry about overheating shortening the life
of the motor.

If anything, the life limiting is as likely to be the motor bearings as the
windings.

If you like to worry about blockage, you can quickly check to see whether it
still "picks up" a piece of pocket litter.

"Jim Elbrecht" wrote in message
...
"Robert Green" wrote:

Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now
that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I
mean
pipe - the Pope has enough problems of his own. (-:

-snip-

I haven't finished my second cup of coffee yet- but my instinct is go
with 'lack of sucking'. Put a vacuum switch just before the canister
that triggers a bell/light/buzzer if it gets high.

You mean something like this?

http://www.inficonvacuumgauges.com/en/vacuumswitch.html

I've been looking around, but many of these switches are incredibly
expensive. Unless I can find something cheaper, I am tempted to go with a
current sensor, which I can build out of the scrap electronics bin for $0.

Thanks for your input!

--
Bobby G.

On Wed, 31 Mar 2010 13:12:18 -0400, "Robert Green"
wrote:

"Jim Elbrecht" wrote in message
-snip-

I haven't finished my second cup of coffee yet- but my instinct is go
with 'lack of sucking'. Put a vacuum switch just before the canister
that triggers a bell/light/buzzer if it gets high.

You mean something like this?

http://www.inficonvacuumgauges.com/en/vacuumswitch.html

Yikes! No- I was thinking about $3 switches- not $300. More along
the lines of what they mention in this thread-
http://www.instructables.com/communi...Switch-System/


I've been looking around, but many of these switches are incredibly
expensive. Unless I can find something cheaper, I am tempted to go with a
current sensor, which I can build out of the scrap electronics bin for $0.


That thread is 2 yrs old- Don't know what the chances are of
contacting the OP and asking what he ended up using.
[but he's still posting, so there is hope! gotta love a guy whose
handle is trebuchet. .g ]

Jim

"Jim Elbrecht" wrote in message
...
"Robert Green" wrote:

Some of you might remember my question about building a silencing cabinet
for a central vac. Well, it worked, but too well. The problem is now
that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Does anyone have any ideas how to detect the "laboring" of the motor so I
can sound a chime or some other alarm when something clogs the pope - I
mean
pipe - the Pope has enough problems of his own. (-:

-snip-

I haven't finished my second cup of coffee yet- but my instinct is go
with 'lack of sucking'. Put a vacuum switch just before the canister
that triggers a bell/light/buzzer if it gets high.

Or put one at the inlet that flashes in your face if air flow drops
below a certain point.

Jim

Or when it stops sucking dirt off the floor, it's clogged!!


__________ Information from ESET Smart Security, version of virus signature database 4989 (20100331) __________

The message was checked by ESET Smart Security.

http://www.eset.com

"Art Todesco" wrote in message
...
On 3/30/2010 10:45 AM, George wrote:

stuff snipped


Guess I am missing something.

If you are using it and suddenly there is no or greatly diminished
vacuum wouldn't that be a sufficient indicator that there is a problem?

If you are using it with a motor
operated beater brush, you really can't
hear the loss of suction over the motor
noise. I know, both me and my wife have
had it happen in our old house. What
can alert you is that you have to go
over the same spot several times to pick
up the one little crumb.

Thanks, Art, for summing it up so well. I wouldn't have asked the question
if it wasn't a problem. I was downstairs, right near the vac cabinet so I
could hear the motor noise change, but my wife, vacuuming upstairs, didn't.

Based on some other comments, I need to do some testing, especially current
draw, to see what's really happening when the vacuum becomes clogged.

--
Bobby G.

"Art Todesco" wrote in message
...

stuff snipped

Does anyone have any ideas how to detect the "laboring" of the motor so
I
can sound a chime or some other alarm when something clogs
--
Bobby G.

Here's a unit that will open up whenever
there is a vacuum pressure increase.
http://www.thinkvacuums.com/beam/valve.html

Robert Green wrote:

Anyone still reading: Why DOES the motor RPM increase quite
noticeably when the hose is clogged. Does an internal vacuum relief
valve sense the blockage and open a relief valve? Since it would be
close to the vacuum motor, probably in the head, it would not have to
draw air from the entire piping system and thus the motor RPM would
soar because of the lightened load. Sound right?

Block off the air flow, and air just goes around and around with the fan blades.
Without the block, it is constantly accelerating air from the input to the
output, which uses more power.

Robert Green wrote:


I've burned up enough gear accidentally (a few AMD CPUs, a few Fujitsu
tablet PCs, a Sony receiver and many, many many more) that I am now
hard over in the other direction, adding cooling fans to stereos and
equipment racks to make sure everything gets good airflow. I believe
heat really hastens the aging process and fans help reverse it.

Just make sure you clean the heat sinks and fans occasionally, or eventually,
dust will plug them and they will overheat. I just had a video board start to
create visual artifacts, and then crash my computer. I blew out the board fan
with compressed air, and all the problems went away.

"John Gilmer" wrote in message

I am going to try a test today with my Kill-0-Watt meter

Blocked and whining 8.83A, Unblocked free running inlet port - no house
piping attached (cleanout, open actually) 12.96A

External air output pipe ran free when unblocked but dropped to very low
flow when the hose was blocked. If there's an internal check valve, it's
venting to someplace other than the vacuum's output pipe.

I used a compresible coil type cheap plastic hose in the basement, and when
blocked at the nozzle it contracted considerably indicating that there was
still a serious vacuum being maintained.

Another theory. It takes more work to create a vacuum than maintain it, so
when the hose has contracted as much as it can, the motor has less load on
it and thus the current drops. With an open vacuum, the motor is constantly
sucking and never achieving even a partial vacuum within the tubing.

C'mon. There are smart people here.

Why would a plugged vacuum cleaner draw less current?

--
Bobby G.

"Soundhaspriority" wrote:

"I don't really have a replacement career, it's a very gnawing thing."

This post seems to have been an effort to harrass the person the poster claims
to be.

On Mar 31, 10:49*pm, "Robert Green"
wrote:
"John Gilmer" wrote in message
I am going to try a test today with my Kill-0-Watt meter

Blocked and whining 8.83A, Unblocked free running inlet port - no house
piping attached (cleanout, open actually) 12.96A

External air output pipe ran free when unblocked but dropped to very low
flow when the hose was blocked. *If there's an internal check valve, it's
venting to someplace other than the vacuum's output pipe.

I used a compresible coil type cheap plastic hose in the basement, and when
blocked at the nozzle it contracted considerably indicating that there was
still a serious vacuum being maintained.

Another theory. *It takes more work to create a vacuum than maintain it, so
when the hose has contracted as much as it can, the motor has less load on
it and thus the current drops. *With an open vacuum, the motor is constantly
sucking and never achieving even a partial vacuum within the tubing.

C'mon. *There are smart people here.

Why would a plugged vacuum cleaner draw less current?

--
Bobby G.

Somebody else answered that once already. Basically it's not moving a
bunch of air so it's not "working" any more. Now that you know the
current you should able to design a circuit that alarms at the 8 amp
range and is off at the 12 amp range. A 1/4ohm power resistor will
give you about a 1 volt variation between the two.

Thanks, Art, for summing it up so well. I wouldn't have asked the
question
if it wasn't a problem. I was downstairs, right near the vac cabinet so I
could hear the motor noise change, but my wife, vacuuming upstairs,
didn't.

Based on some other comments, I need to do some testing, especially
current
draw, to see what's really happening when the vacuum becomes clogged.

Current sensing (for slightly low current, fans spinning air take less power
than ones moving air) is one way but is likely to be more expensive than a
vane on a switch to watch for no air flow on the exhaust.
Another possibility is to look for a lower pressure (higher vacuum) just
ahead of the main unit.

Here's a unit that will open up whenever
there is a vacuum pressure increase.
http://www.thinkvacuums.com/beam/valve.html
I'm sure others have similar products.

Art, that's perhaps the best solution I've ever gotten to a question I've
posted
on the net. $10!!!!!! That's just what the doctor ordered. Thanks very
much!

If you want an alarm (other than that the vacuum tool is not picking up as
much as usual) you could add an air flow sensor in the line to the safety
valve. If there is flow, the alarm is triggered.

the "smart outlets." My original concern was based on what I thought was
a
thermal overload kickout, but when I sealed up the unit I left plenty of
room for airflow and even put in a small fan to make sure nothing
overheated. I realize now I ran those tests during an average vacuuming
session that didn't include the occasional serious clog, so I will have to
see what happens when I deliberately block the hose and monitoring the
motor
temperature.

It is very possible that the power unit uses the filtered air from the
vacuum as cooling.

It's counter-intuitive, but I guess the motor RPM would decrease while
overloaded, not obviously increase, which does make for a sort of "runaway
Toyota" feel.

Actually, the motor increases in speed because there is less load on it.
It is much easier to spin the fan in less than normal air without doing any
work to move air.
This is the reason that the noise level goes up.

External air output pipe ran free when unblocked but dropped to very low
flow when the hose was blocked. If there's an internal check valve, it's
venting to someplace other than the vacuum's output pipe.

No internal check valve on most vacuums. They expect that the increased
noise will let you know. With a check valve, almost no change in sound.

Another theory. It takes more work to create a vacuum than maintain it,
so
when the hose has contracted as much as it can, the motor has less load on
it and thus the current drops. With an open vacuum, the motor is
constantly
sucking and never achieving even a partial vacuum within the tubing.

A vacuum does it's work by pumping air. If it is not pumping air, it is not
doing as much work.

The amount of vacuum goes up when it is clogged because air is not flowing
into the system.

Read the rest of the comments. This is a moronic device for a self protected
motor / fan system.

No air movement = higher motor speed = less work being done = less stress on
motor = less current draw


"Robert Green" wrote in message
...
Art, that's perhaps the best solution I've ever gotten to a question I've
posted
on the net. $10!!!!!! That's just what the doctor ordered. Thanks very
much!

--
Bobby G.




"Art Todesco" wrote in message
...

stuff snipped

Does anyone have any ideas how to detect the "laboring" of the motor so
I
can sound a chime or some other alarm when something clogs
--
Bobby G.

Here's a unit that will open up whenever
there is a vacuum pressure increase.
http://www.thinkvacuums.com/beam/valve.html
I'm sure others have similar products.

He's been told, many time here but doesn't seems to understand that.


"B Fuhrmann" wrote in message
...
Current sensing (for slightly low current, fans spinning air take less power
than ones moving air) is one way but is likely to be more expensive than a
vane on a switch to watch for no air flow on the exhaust.
Another possibility is to look for a lower pressure (higher vacuum) just
ahead of the main unit.



Thanks, Art, for summing it up so well. I wouldn't have asked the
question
if it wasn't a problem. I was downstairs, right near the vac cabinet so I
could hear the motor noise change, but my wife, vacuuming upstairs,
didn't.

Based on some other comments, I need to do some testing, especially
current
draw, to see what's really happening when the vacuum becomes clogged.

On 4/1/2010 8:18 AM, Josepi wrote:
Read the rest of the comments. This is a moronic device for a self protected
motor / fan system.

No air movement = higher motor speed = less work being done = less stress on
motor = less current draw


Ya but .... In the central vac unit the
air flow over or through the motor is
what cools the motor. The "moronic
device" would solve that problem by
providing an inlet for air, when the
lines are plugged. I'm not sure I agree
with the vendor's picture of the house
and garage burning down. The motor
thermal protector should prevent that.
That all said, I had a central vac in my
previous house for 36 years and can
count on one hand the number of times
the thing actually plugged up. Robert,
if it is plugging in the hose, there
might be something wrong in the hose
causing it, like a tear which would
catch fuzz going by. If the plug is
occurring in the wall piping, again
there might be a reason. I remember my
2 year old dumping some small wooden
blocks in the inlet near his room. They
went through the pipe with no problem
but couldn't make it through a Tee. It
was about 1" x 1" x 3". This caused a
place for new dirt to catch and
eventually plug up.

On Mar 30, 5:54*pm, "John Gilmer" wrote:
"Robert Green" wrote in message

...

Some of you might remember my question about building a silencing cabinet
for a central vac. *Well, it worked, but too well. *The problem is now
that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. *On occasion, the unit's
motor even shuts down from the overload.

Believe it or not, the "motor load" is usually at a minimum when the vac is
completely blocked off.



Which of course then begs the question, so what's the problem? I
agree that with many pumps the speed increases when the line is
plugged, because the impeller is cavitating and just spinning freely.
That means the power and current go DOWN. So, why the need for a
system to prevent the motor from overheating?

The only logical conclusion would be that the motor depends on the air
moving through the vacuum for cooling. Even given that, I can't see
how the vacuum could stay plugged up and running long enough for that
to happen frequently. Surely after a minute or two of vacuuming
you'd notice the head is no longer picking up dirt, that the head
moves freely over carpet instead of being sucked down, etc.

It would seem to me that if this were a problem that occured
frequently enough to matter, all systems would have some built-in
protection besides the thermal cuttoff and the thermal cuttoff is OK
for something that happens once in a blue moon.

Regarding a blue moon, I ask again, how often does this occur? I've
had a central vac system for 17 years and it hasn't clogged once. If
it's happening frequently, sounds like whatever is causing it is the
real problem that needs addressing.

On 4/1/2010 8:13 AM, B Fuhrmann wrote:
External air output pipe ran free when unblocked but dropped to very low
flow when the hose was blocked. If there's an internal check valve, it's
venting to someplace other than the vacuum's output pipe.

No internal check valve on most vacuums. They expect that the increased
noise will let you know. With a check valve, almost no change in sound.

Another theory. It takes more work to create a vacuum than maintain it,
so
when the hose has contracted as much as it can, the motor has less load on
it and thus the current drops. With an open vacuum, the motor is
constantly
sucking and never achieving even a partial vacuum within the tubing.

A vacuum does it's work by pumping air. If it is not pumping air, it is not
doing as much work.

The amount of vacuum goes up when it is clogged because air is not flowing
into the system.


Yup. I learned this many years ago in
working on pipe organs. Normally, when
the blower is running, it is basically
plugged. The pressure is at its normal
operating pressure and no air is being
moved, except to any leaks. And in pipe
organs there are usually many tiny leaks
which eventually do add up. But, if a
wind line is opened, the blower current
goes up because it is now moving air and
thus, doing more work. In an organ
blower, the motor is usually an
induction motor. It doesn't speed up as
in a vacuum cleaner. In a vacuum
cleaner, the motor is usually a series
(sometimes called universal) motor.
These motors will actually generate a
back EMF. When the motor is not doing
an work, i.e. sealed off, this back EMF
will actually "self power" the motor a
little, making it turn faster. Back in
high school shop, they said that a
series motor with no load, will keep
going faster and faster until it
literally breaks apart. I've run a
small sewing machine motor, no load, and
indeed it kept going faster and faster.
I was afraid to keep going, but I
suspect it would eventually find a top
speed as even the bearings and cooling
fan blade do some loading, albeit small.

On Apr 1, 7:59*am, "B Fuhrmann" b-fuhrmann-
wrote:
Here's a unit that will open up whenever
there is a vacuum pressure increase.
http://www.thinkvacuums.com/beam/valve.html
I'm sure others have similar products.
Art, that's perhaps the best solution I've ever gotten to a question I've
posted
on the net. *$10!!!!!! *That's just what the doctor ordered. *Thanks very
much!

If you want an alarm (other than that the vacuum tool is not picking up as
much as usual) you could add an air flow sensor in the line to the safety
valve. *If there is flow, the alarm is triggered.

I like the cuirrent sensing solution tied to a triac to turn the thing
off when it clogs. That way you know right away and you don't waste
you time vacuuming an area with the system clogged. Sometimes when
you vacuum a relatively clean area with a beater head you do not
easily notice that the suction has stopped. The circuit would be
fairly straighforward and could probably be done with an opamp, an
optoisolator and a 20amp triac. An alarm would have to be pretty loud
to be heard over the beater anywhere in the house.

jamesgangnc wrote in news:b4f81cd1-dad7-4e35-85a3-
:

snip

Somebody else answered that once already. Basically it's not moving a
bunch of air so it's not "working" any more. Now that you know the
current you should able to design a circuit that alarms at the 8 amp
range and is off at the 12 amp range. A 1/4ohm power resistor will
give you about a 1 volt variation between the two.

And don't forget a delay or other override to handle the situation on startup
and shutdown as you pass through the range getting to 12 amps.

Most appliance motors do have a thermal cutout designed into them. Many
people repairing their own stuff will just cut it out of the circuit once it
goes.

Get the Vac unit into a repair place and get the thermal cutout replaced.

wrote in message
...
On Mar 30, 5:54 pm, "John Gilmer" wrote:
"Robert Green" wrote in message

...

Some of you might remember my question about building a silencing
cabinet
for a central vac. Well, it worked, but too well. The problem is now
that
if something gets stuck in the hose, we can no longer hear the immediate
increase in the motor load the way we used to. On occasion, the unit's
motor even shuts down from the overload.

Believe it or not, the "motor load" is usually at a minimum when the vac
is
completely blocked off.



Which of course then begs the question, so what's the problem? I
agree that with many pumps the speed increases when the line is
plugged, because the impeller is cavitating and just spinning freely.
That means the power and current go DOWN. So, why the need for a
system to prevent the motor from overheating?

The only logical conclusion would be that the motor depends on the air
moving through the vacuum for cooling. Even given that, I can't see
how the vacuum could stay plugged up and running long enough for that
to happen frequently. Surely after a minute or two of vacuuming
you'd notice the head is no longer picking up dirt, that the head
moves freely over carpet instead of being sucked down, etc.

It would seem to me that if this were a problem that occured
frequently enough to matter, all systems would have some built-in
protection besides the thermal cuttoff and the thermal cuttoff is OK
for something that happens once in a blue moon.

Regarding a blue moon, I ask again, how often does this occur? I've
had a central vac system for 17 years and it hasn't clogged once. If
it's happening frequently, sounds like whatever is causing it is the
real problem that needs addressing.

"Bob F" wrote in message
...
Robert Green wrote:


I've burned up enough gear accidentally (a few AMD CPUs, a few Fujitsu
tablet PCs, a Sony receiver and many, many many more) that I am now
hard over in the other direction, adding cooling fans to stereos and
equipment racks to make sure everything gets good airflow. I believe
heat really hastens the aging process and fans help reverse it.

Just make sure you clean the heat sinks and fans occasionally, or
eventually, dust will plug them and they will overheat. I just had a video
board start to
create visual artifacts, and then crash my computer. I blew out the board
fan with compressed air, and all the problems went away.

You're lucky you caught it before it fried. A full "dust cap" is a fine
heat retainer and could have easily cooked your VPU. Smart PC'ers use
programs like Motherboard Monitor that will tell them when their fan speeds
have dropped enough to indicate that they are getting clogged.

I do a lot of PC repair. I have a rough rule of thumb. In a normal
environment, it's probably OK to let fans go unchecked for 24 months.
Subtract 1 year if the equipment's on the floor. Subtract 2 months for each
shorthair dog or car in the house, 4 months for every longhair. Subtract 1
month for fans under 80 centimeters and another month for those under 40.

One neighbor with 5 longhairs and a floor tower with a teeny video card fan
needed monthly cleaning so we added some more fans and covered the front
intake with air conditioner filter material held in place by a little
magnetic frame. Now she just vacuums the front and the machine can go
almost a year without a blow-out. (For anyone considering this, the clips
on the cheap case face were so weak they broke during the procedure but we
replaced them with some neo mags and hot melt glue so snapping the face off
to vacuum the filter was even easier. Most case faces can't withstand
frequent removal without those damn little tab clips breaking.)

I *would* post a picture of a super small video card sleeve bearing cooling
fan and finned heat sink mount I removed from the 5 cat machine because I
had never seen anything so completely caked in dust. The fan spun, but
moved no air. I replaced it with a much larger ball bearing fan simply
because it was less prone to clogging and the space permitted it. However,
I see the picture police are on patrol, enforcing "laws" created when bits
were moved around via acoustic modem. Like so many rules of that era it has
been completely outmoded by technical advances. Anyone who says that
posting a link is as easy as posting a picture with a message isn't being
honest. Personally I'd rather see a relevant picture *with* the message
rather than clicking on a link to who knows where.

One reason we got the central vac is that we like to air cool in the summer
with a big attic fan and that brings in an awful lot of dust and pollen.
Switching from A/C to "free air" cooling cured my wife's allergy. Turns out
that being cloistered inside superclean, highly filtered office and A/C
house hyper-sensitized her to pollen. She used to sneeze up to nine times
when she left an A/C'ed building and stepped out into the late spring air,
which *is* mostly pollen. Our standing joke is "we don't go around trying
to mate with trees, so why are they trying to have sex with our noses?"

--
Bobby G.

"Art Todesco" wrote in message
...
On 4/1/2010 8:18 AM, Josepi wrote:
Read the rest of the comments. This is a moronic device for a self
protected
motor / fan system.

No air movement = higher motor speed = less work being done = less
stress on
motor = less current draw


Ya but .... In the central vac unit the
air flow over or through the motor is
what cools the motor. The "moronic
device"

Certainly not in my mind and I'm the OP.

would solve that problem by
providing an inlet for air, when the
lines are plugged. I'm not sure I agree
with the vendor's picture of the house
and garage burning down. The motor
thermal protector should prevent that.

Yes, the fire was a little much, but it almost never hurts to have an extra
layer of protection, especially against catastrophic outcomes.

That all said, I had a central vac in my
previous house for 36 years and can
count on one hand the number of times
the thing actually plugged up. Robert,
if it is plugging in the hose, there
might be something wrong in the hose
causing it, like a tear which would
catch fuzz going by. If the plug is
occurring in the wall piping, again
there might be a reason. I remember my
2 year old dumping some small wooden
blocks in the inlet near his room. They
went through the pipe with no problem
but couldn't make it through a Tee. It
was about 1" x 1" x 3". This caused a
place for new dirt to catch and
eventually plug up.

You've hit on the problem. A dog that loves to tear pieces of rag and
nylabone just large enough to catch on a crimped section of the hose.

When I tested the output of the unit's exhaust port with the hose blocked, I
noticed that although the exhaust flow cfm's dropped dramatically, the feel
of heat on my hand increased appreciably.

That was clear evidence that the motor depends on good hose airflow for
cooling and to let it run clogged was risking heating the bearing lube until
it evaporated and possibly burning the insulation on the motor windings.
Only a moron would expose an expensive motor system to unnecessary stress if
there was a ten dollar way around it.

I would rather notice lack of suction from a bypass opening than from a clog
that was burning up the motor. One wastes maybe 1 minute of extra
electricity and the other subjects a motor to 1 minute of unnecessary
stress, resulting in who knows how much shorter a life. That's a no
brainer.

--
Bobby G.

"B Fuhrmann" wrote in message
...
the "smart outlets." My original concern was based on what I thought
was
a
thermal overload kickout, but when I sealed up the unit I left plenty of
room for airflow and even put in a small fan to make sure nothing
overheated. I realize now I ran those tests during an average vacuuming
session that didn't include the occasional serious clog, so I will have
to
see what happens when I deliberately block the hose and monitoring the
motor
temperature.

It is very possible that the power unit uses the filtered air from the
vacuum as cooling.

Yep, when I tested the output flow with my hand, a clog caused the airflow
to drop steeply and heat up quickly. Very likely hose air used for cooling.

--
Bobby G.

"Existential Angst" wrote in message
...
"Robert Green" wrote in message

stuff snipped

I think what you'll find is that your killawatt will show a substantial
DECREASE in current. The motor is not laboring, but actually speeding up,
as there is no air to load it. Almost counter-intuitive, that as a vacuum
clogs, it works less!

Exactly correct. Very odd to see, but about 4A less when screaming like a
rocket.

--
Bobby G.

"B Fuhrmann" wrote in message
...
It's counter-intuitive, but I guess the motor RPM would decrease while
overloaded, not obviously increase, which does make for a sort of
"runaway
Toyota" feel.

Actually, the motor increases in speed because there is less load on it.
It is much easier to spin the fan in less than normal air without doing
any
work to move air.
This is the reason that the noise level goes up.

I said that backwards. The RPM does decrease when the motor is overloaded
but the key to that is a blocked hose isn't really a motor overload.

The irony/complicating factor is that the motor will thermally overload
eventually due to the blocked air flow but not from being asked to do more
work than it can handle. It's doing less work than normal (4 amps less on
the Kill-o-watt meter) but it's not getting proper cooling anymore.

Thanks!

--
Bobby G.

"jamesgangnc" wrote in message
...
On Mar 31, 10:49 pm, "Robert Green"
wrote:
"John Gilmer" wrote in message
I am going to try a test today with my Kill-0-Watt meter

Blocked and whining 8.83A, Unblocked free running inlet port - no house
piping attached (cleanout, open actually) 12.96A

External air output pipe ran free when unblocked but dropped to very low
flow when the hose was blocked. If there's an internal check valve, it's
venting to someplace other than the vacuum's output pipe.

I used a compresible coil type cheap plastic hose in the basement, and
when
blocked at the nozzle it contracted considerably indicating that there was
still a serious vacuum being maintained.

Another theory. It takes more work to create a vacuum than maintain it, so
when the hose has contracted as much as it can, the motor has less load on
it and thus the current drops. With an open vacuum, the motor is
constantly
sucking and never achieving even a partial vacuum within the tubing.

C'mon. There are smart people here.

Why would a plugged vacuum cleaner draw less current?

--
Bobby G.

Somebody else answered that once already. Basically it's not moving a
bunch of air so it's not "working" any more. Now that you know the
current you should able to design a circuit that alarms at the 8 amp
range and is off at the 12 amp range. A 1/4ohm power resistor will
give you about a 1 volt variation between the two.

Unfortunately my server delivers posts in frighteningly non-chrono order and
I reply the same way. I *do* get it now and realize why my portable
submersible pump makes the same kind of increased noise when it starts
running dry. It takes a lot less power to raise air ten feet than water.

Live and learn . . . eventually. Then go senile and repeat.

--
Bobby G.

"Ian Shef" wrote in message
3...
jamesgangnc wrote in news:b4f81cd1-dad7-4e35-85a3-
:

snip

Somebody else answered that once already. Basically it's not moving a
bunch of air so it's not "working" any more. Now that you know the
current you should able to design a circuit that alarms at the 8 amp
range and is off at the 12 amp range. A 1/4ohm power resistor will
give you about a 1 volt variation between the two.

And don't forget a delay or other override to handle the situation on
startup
and shutdown as you pass through the range getting to 12 amps.

Good point. In a home automation controller progam that could likely be
solved by taking action only if the amperage drop persisted for over three
seconds. There are times when a vacuum will suck in the end of a drape or
something large enough to block the tube obviously but temporarily. I think
it might be helpful to have Art's valve working in those cases because the
relief would open up and whatever was stuck would just fall away.

Considering how complicated this little exercise has become, it makes me
wonder what's really going on in Toyota's fly-by-wire system and whether
they truly did cover all the potential "exceptions" that might occur. We
may never know now that every scam artist who happens to own or have access
to a Toyota is looking for a quick buck or a new car by claiming "runaway."

Thanks for your input, Ian.

--
Bobby G.

You may find the current doesn't drop significantly as the power consumprion
does.

When load is removed from sysncronous motors the power factor decreses to
the bottom, the current stays relatively in the same ball park, depending on
motor design.

If you put a Kill-a-Watt monitor on it you may a huge difference in
consumption.



"Robert Green" wrote in message
...
"Existential Angst" wrote in message
...
"Robert Green" wrote in message

stuff snipped

I think what you'll find is that your killawatt will show a substantial
DECREASE in current. The motor is not laboring, but actually speeding up,
as there is no air to load it. Almost counter-intuitive, that as a vacuum
clogs, it works less!

Exactly correct. Very odd to see, but about 4A less when screaming like a
rocket.

--
Bobby G.