Central Vac overload

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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!
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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---

>> (44° 15' N - Elevation 1580')
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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.
================================================ How did you build this current sensor??
--
EA


---MIKE---
>>In the White Mountains of New Hampshire
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wrote:

you would measure the voltage crop across a series resistor.
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EA asked:

Its a circuit that I found on the internet years ago. Magnet wire is wound around an iron core and placed near one of the wires to the pump. A voltage is induced in the coil which is sensed by the circuit. I can't send the circuit here.
---MIKE---

>> (44° 15' N - Elevation 1580')
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On Mar 30, 7:39 am, snipped-for-privacy@webtv.net (---MIKE---) wrote:

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?
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<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.>
That's the path I was headed down but I think Art T. found the perfect answer to the problem - a "relief" valve designed for central vacuums for $10.
Thanks for your input. Say, how close are you to "the Old Man in the Mountains?" When I was a kid we took a trip to New England and New Hampshire in the summer was about the greenest place I have ever seen.
Hope it's still green.
-- Bobby G.
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-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
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wrote:

that
mean
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.
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On Wed, 31 Mar 2010 13:12:18 -0400, "Robert Green"
-snip-

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/community/Vacuum-Pump-Limit-Switch-System /

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
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wrote in message

a
$0.
While cruising cable last week I saw a show called "Smash Cuts" where they were flinging small English sports cars and flaming barrels full of something flammable from a three story trebuchet. Very impressive. Can you imagine manning the castle walls when the first one to be invented rolled up on you?
-- Bobby G.
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wrote:

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.
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On 3/30/2010 7:23 AM, Robert Green 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.
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<stuff snipped>

I
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.
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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.
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On Apr 1, 7:59 am, "B Fuhrmann" <b-fuhrmann-

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.
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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
<stuff snipped>

I
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On 4/1/2010 8:18 AM, Josepi wrote:

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.
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protected
stress on

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

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

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.
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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!
What is likely happening is that the motor is going out on temperature overload, not from current, but from lack of airflow, that cools the motor.
Still, you could use a current alarm like what Mike did, or an air flow switch (Graingers) in the exhaust, or even a thermostat switch somewhere in the exhaust, around the motor, before the motor temp overload kicks in.
Probably an airflow switch in the exhaust would be the cheapest, most straightforward. You could even build this yourself with a piece of a soda can and a microswitch from radio shack or someplace.
What I would do is connect a NO relay to the power switch (the coil of the relay). Then, in series with the relay contacts, I would put a NC microswitch operated by the soda can flapper. This way, the alarm will sound if air flow stops, but not when the unit is off.
--
EA


>
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