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.
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.
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.
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.
eventually, > dust will plug them and they will overheat. I just had a video board start to
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?"
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.
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.
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.
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."
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.
Exactly correct. Very odd to see, but about 4A less when screaming like a rocket.
I always figured it has something to do with ionic chrage passing air over an aluminum exchanger.
It may be just drying the air too much or some kind of ion charge or both.
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.
eventually, > dust will plug them and they will overheat. I just had a video board start to
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?"
IMHO most nntp servers deliver messages in random order. It's up to your browser to sort them in the order you wish to read them in. (see Bob F message)
Each message to usenet moves along a different path from the originator to the server that "feeds" me. Some messages take longer to arrive depending on where they originate. This has nothing to do with my browser settings and everything to do with the delays a post might encounter in finally getting forwarded to my NNTP server. News posts aren't instantaneous.
For example, it's entirely likely that a message posted from very far away will arrive well after a post from a nearby server, even though it has an earlier send date and did, indeed, start its journey earlier than the closer post did.
Our points were: your browser sorts them out into any order you desire.
NNTP timing doesn't matter, within a few hours, of course.
Each message to usenet moves along a different path from the originator to the server that "feeds" me. Some messages take longer to arrive depending on where they originate. This has nothing to do with my browser settings and everything to do with the delays a post might encounter in finally getting forwarded to my NNTP server. News posts aren't instantaneous.
For example, it's entirely likely that a message posted from very far away will arrive well after a post from a nearby server, even though it has an earlier send date and did, indeed, start its journey earlier than the closer post did.
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