Central Vac overload

[Robert Green]

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!

[---MIKE---]

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---

[Jim Elbrecht]

-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

[Existential Angst]

=================================================

How did you build this current sensor??

[Art Todesco]

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

'm sure others have similar products.

[trader4]

New Hampshire

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?

[Existential Angst]

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.

[Existential Angst]

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

[jamesgangnc]

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.

[AZ Nomad]

you would measure the voltage crop across a series resistor.

[George]

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?

[---MIKE---]

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---

[Art Todesco]

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.

[hrhofmann]

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).

[John Gilmer]

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.

>

[Robert Green]

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.

[Jim Elbrecht]

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

[John Simpson]

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

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[Robert Green]

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.

[Robert Green]

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.