Central Vac overload

-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

Here's a unit that will open up whenever there is a vacuum pressure increase.

'm sure others have similar products.

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.

Oh, yeah, you could also wire this up so that a relay cuts off the motor, and locks out, AND sounds an alarm.

Is it possible that your "silensing" cabinet is restricting the cooling air to the top of the motor? Wasn't your central vac in the garage? Do you really need a silencing cabinet?

You're right about the overload safety switch. It is not designed to operate repeatedly.

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.

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).

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.

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.

>

You mean something like this?

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.

Yikes! No- I was thinking about $3 switches- not $300. More along the lines of what they mention in this thread-

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. . ]

Jim

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

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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, 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.

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.

This is one of those things that I am going to have to check out for myself because it is so counter-intuitive because the motor whine gets so loud when it's blocked. But now that you mentioning, a laboring motor *shouldn't* speed up at all, so that fact alone means you're mostly likely correct that I'll see a drop in amperage.

There are a number of possible issues, from problems with the automation system that controls the vacuum, to the motor heat overload to an issue with 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.

Most of this has been rendered moot by Art T's location of a ready-to-go valve system designed to detect such problems and remedy them.

Thanks again, Art. (And thanks to you, EA, too.)

-- Bobby G.

Which I may do despite ordering the device that Art T. pointed me to

I have a home automation controller (Ocelot) that's able to sense varied voltage conditions and take an action. That part's pretty easy. Well, at least for me. Someone without such a controller would have more difficulty.

Determining what conditions variable current levels represent will be a little trickier. A small "sail switch" in the output pipe that could detect the lack of strong air flow might work well, too. But Art's relief valve seems to be the most cost-efficient solution so far. If that fails (or succeeds) I'll come back and make a report. I'm hoping that I'll be able to report "problem solved" with.

Thanks for your input!

-- Bobby G.

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.

Mine is connected to an outlet pipe and muffler to the outside, so it's doable, but hopefully not necessary with Art's relief valve.

Otherwise,

Not sure about this issue. I suppose I could test it. For now, I am going to mount a temperature sensor in the unit and hook it up to my home automation controller to shut the unit down if the temperature exceeds a certain level. That will probably have to be a trial and error sort of thing.

Exactly. Which is why the temperature sensor might be a good thing to add in addition to the relief valve. In fact, what I should do is hook up a recording thermometer to a probe inside the silencing box to monitor a few sample runs to try to estimate the temperature rise and where it plateaus.

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. Now only if I could fan my bad knees and get them working again!

And those failures would be heat-related, as in winding insulation and bearing lube.

it > still "picks up" a piece of pocket litter.

The point that Art made applies here. An electrically driven motor brush head will appear to be picking up dust but in reality is just sucking it into the brush head. If there's not much dirt, it's very easy to think you're vacuuming when you're not. The motorized carpet sweeper head make enough noise that you really can't hear the change in the motor RPM or the lack of vacuum hiss.

-- Bobby G.