MAGNETICALLY ACTUATED GARBAGE DISPOSAL

[B2]

I recently mentioned that I had built a MAGNETICALLY ACTUATED GARBAGE DISPOSAL several years ago and @francist ask that I post it.
I never never thought to post this to HM as I did not think it was a machinist topic, but ...

@francist

I think that’s one of the coolest ideas I’ve heard in a long time!

When remodeling our home in 2012 we wanted a clean looking kitchen island counter top, just flat. We had put in a granite counter top and did not want to have electrical out lets nor a dirty looking push vacuum switch to operate a disposal cluttering the counter top. At the same time we did not want to have to open the cabinet below the sink to turn the disposal on and off. From an electrical code stand point this is a bit in conflict with safety issues. In Europe they sometimes put the electrical outlet at the kick plate of the cabinets rather than on a shelf that sits on the counter. However, this is still rather unhandy in that you have to plug things in at the floor level. However, I had not seen a solution to the garbage disposal switch, but came up with a solution. Our solution to these are in the attached file.


@pontiac428
@Bone Head

 

[solo]

I'm impressed! You should have scored points with your wife!
I'm going to use your idea for outlets on our kitchen island.
We have a septic system so no can do a disposal. It doesn't look like a rare earth magnet.
I'm surprised it can pass through the granite. Very cool!!!

 

[francist]

Sweet! Thanks for posting that, it’s a great write-up and easy to follow. I mentioned the idea to my sister the other day and she also thought it was pretty cool. I like the receptacles concealed behind the pilasters too — nice touch (heh, heh).

 

[B2]

Hi @solo Thanks.

Yes, it is a rare earth magnet. I worked in magnetism (and a variety of other areas) most of my life. While the Samarium Cobalt (SmCo) magnets do not rust, due to their high Co content (>$$), the Neodymium Iron Boron alloys do as they are largely Iron (<$). So they commonly plate a Ni-alloy onto the surface of Neo magnets to slow this down. This makes them look like a Ni metal. Once this plated layer is broken or cracked then they start to rust. This particular magnet was taken from a magnetron sputtering cathode (vacuum deposition, sputtering of thin films). They used to coat them with epoxy paint, but you seldom see this any more. By the way, the magnetic energy product is a term used to describe the strength/unit volume of a magnet . In this case it is about 30Mega Gauss-Oersted (I do not actually recall the exact value for this one). 30MGO is pretty run of the mill these days. The theoretical limit of this material is ~ 64 MGOe. The rare earth magnets are made by hot pressing of powders then sintering, hence they are not quite 100% dense. This allows rust to propagate down the grain boundaries. Hence, when they start to rust there are lots of magnetic dust particles stuck to their surface. Because of the hot pressing geometry most of the magnets have a magnetization anisotropy (orientational preference) direction along the pressing direction. That means most of them are magnetized perpendicular to the flat surface of a coin shape. However they can be oriented in the plane and these were. If you stack up some coin shaped magnets the external field will be larger as they now look more like the geometry of an old style bar magnet producing the magnetic field out the ends. By the way, ferrite magnets (Ba-Ferrite or Sr-Ferrite), only have an energy product (~4MGOe) that is 1/10 that of the Neo magnets. When the ferrite is ground up and put into rubber/plastic for refrigerator magnets the binder dilutes the magnetic material a little and the value drops to ~1.5MGOe. Its greatest virtue is that it is mostly Iron oxide so it is really cheap!

I understand septic systems. Been there, done that! Every time I run the disposal I feel like I am polluting the world, but know that the stuff decays after/during the expensive waste water treatments.

Dave L.

 

[B2]

@francist

I like the receptacles concealed behind the pilasters too

Thanks. "Pilasters".... I was racking my brain trying to come up with what they were called. I finally used the term balusters, which I knew was not very descriptive, but wanted to move on!

 

[Gaffer]

That's very clever. I've used air activated switches below the lip of the countertop on the cabinet face frame. It's a clean look, but not as high-speed as your solution. Well done.

 

[Provincial]

Nice work!

I'm currently working on using a Reed switch to trigger a time-delay light switch for an overhead door. The actuator for the door did not have provision for a light circuit/delay, and I've spent 10 years leaving the lights on in the vehicle until I reach the light switch on the wall. I bought a time-delay circuit board and a Reed switch. I've determined that a magnet the size of a half-dollar will trigger the switch from almost 2" away, so it is a matter of making brackets for the magnet and an enclosure to protect the switch. The circuit board will be located in a 4" square box on the wall nearby, and will be about 4' above the floor for easy access.

I'll have to test the circuit board and see what voltage and AC/DC current it uses for the sensor circuit, but the Reed switch is rated for up to 200V. I'm leery of using the built-in relay in the board (rated 10A 250V AC) but I will only be using it to run one 1200 lumen LED floodlamp bulb.

I won't be needing a manual override, so I'll just put a normal light switch in the circuit as a disconnect.

 

[B2]

Hi @Provincial

Good idea! Yes, it is amazing what we will put up with for so long. Sometimes we get so used to an inconvenience that we don't even recognize it. I have my own list and my wife has an even longer one ... for me!

You could probably provide the time delay with a 555 time IC or maybe something even simpler. Either way you seem to need constant power to the electronics. If I understand correctly you only need for the Reed switch to contact as the door is moving. Then the contact is broken as the magnet move on past the sensor. You might be able to get around needing a power supply and only need a battery by using an FFT transistor to control the SSR input and resistors and capacitor at the FFT gate to provide the delay timing. There would be no power drain for the control when the operation is complete.

If you would like I can see if I can figure out a very simple circuit to fit in my disposal controller. Then with the cheap SSR that I used you could power the lights to most of or all of the house! But if you already have a plan and have spent the money then ....

Put some sort of thick coating on the magnet to protect it. Dip it in epoxy or anything (RTV, construction glue, etc.) to keep the salts and water a way. Maybe connect the sensor like I did and the drill a deep hole in the end of a longer board to hold and protect the sensor and then use the board for attaching.

By the way, connect a switch to near the house door to activate the circuit might be nice so that you can turn out the light, get in the car with the garage door light on and then open the garage door.

Another thought. If you have an old garage door opener system it is probably chain or belt driven. Attach the magnet to the belt or chain and put the sensor a few feet from the motor box. Just depends on your configuration, but I would prefer to have it up and out of the way. Mount the electronics box on the garage door motor box. Once every 10 years or so you would have to climb a ladder and change the batteries. Or their might be a DC power source at the door opening motor. I am assuming you have a wireless door opener and their would be DC for the receiver.

Dave L.

 

[solo]

Thank you for the education, I'm a bit smarter today.
My grandfather played with a perpetual motion machine using rare earth magnets. He mounted even number on one board with bearings.
And another fixed with an odd number. It was only about 16" in diameter, but it would spin a long time. It was fun when I was a kid.

 

[B2]

@solo

Sounds like the device was a form of levitation to remove most of the friction from the bearings. It would still be fun to see.

The other thing that is really fascinating as a kid it to see magnetic braking (eddy current effects). If you have never seen this take a rare earth magnet and drop it through a 3 or 4 foot long copper pipe of inside dimension similar/close to the magnet size. Mentally time the fall. Then drop the magnet outside of the pipe and compare the two times. You use Copper because it is a good conductor and is non-magnetic.