Mechanism to actuate lever switch...

[Tom18991]

I have an air compressor out behind my garage.  I like to turn it off at the end of the day, but it's a pain to get to, so I'd like to create a little remote do-hicky to turn the switch off remotely.  I'll use a couple Arduino's with a wireless link between them, and have that part covered.  I'm not a robotics guy, so am mulling how to set up a mechanism to throw the switch.  Is there a 'right' way to actuate a switch like this?  Rotating cam of some kind?   Push-pull solenoid?  Something else?  Here's the switch in question....

[moffy]

Perhaps something like this: https://www.amazon.com.au/Wireless-Household-Appliances-Electrical-Equipment/dp/B08NC447JS
You are just trying to turn the power ON/OFF to the compressor?

[Tom18991]

Thanks, I'd love to use something like this, but I forgot to mention this is a 240 volt single phase compressor.  It's also hard-wired to the service disconnect, so there isn't even a plug, although I suppose I could add one if someone offers a 30amp 240v remote controller like the one you linked...

[moffy]

If you want to actuate it mechanically you are dependent on the force required and stroke length, and you need it to work both ways, it really is more direct to use an electrically operated relay or such.

[inse]

A universal central locking actuator would be the most cost effective solution.
Use a lever or limit the current if the stroke length does not match.

[erotichamster]

What kind of force / torque is required? If it is low, could an RC servo (the ones for steering on radio controlled cars etc..) work?

[CaptDon]

Since you have to run control wires anyway why not do the right thing and include a motor contactor which is nothing more than a heavy duty relay or perhaps add a manual disconnect indoors? Circuit breakers are allowed to be used as 'switches' in many instances according to N.U.E.C. here in the states. Just turn the breaker off (if it is easily accessable) I often see circuit breakers used as 'light switches' in factories. Is that pressure switch one of the types used on a well where if you are starting at zero pressure you have to manually hold the lever in place until pressure starts to build? Those types of pressure switches were designed to prevent pump burnout if the well ran dry and pressure was lost.

[pcprogrammer]

What kind of force / torque is required? If it is low, could an RC servo (the ones for steering on radio controlled cars etc..) work?

There are servos that can handle high force / torque. Not very cheap, but they exist. (For instance: URUAV Deluxe Line BLS3211)

But indeed in this instance a heavy duty relay would make much more sense. Could even be solid state. https://www.newark.com/c/switches-relays/relays/solid-state-relays-contactors?load-current=30a

They exist with opto isolated control input and can be controlled from an arduino if wanted, but a simple solution like CaptDon suggested, with a circuit breaker mounted in the garage will be far less of a hassle.

[Ground_Loop]

I have a large compressor in my shop that has a timing relay connected to the lights.  When the lights are turned on the normally closed relay contacts open a valve on the tank drain.  After a ten second time out the relay activates and the normally open contacts close to energize and open the hose valve while opening the normally closed contacts to de-energize and close the tank drain valve.  In addition, another set of normally open contacts close to enable the motor starter.  So without the lights on, the outlet hose is dead and the motor starter is disabled preventing inadvertent operation or pump up due to any leaks.  This is all done with a single timing relay with two form-C contact sets mounted in a handy box on the wall.

I gave some initial thought to a programmable controller and even went as far as buying the pressure sensors, but the the KISS principle prevailed.  The hose and drain valves are 120 VAC motor operated ball valves that auto close on power loss.

[CatalinaWOW]

What kind of force / torque is required? If it is low, could an RC servo (the ones for steering on radio controlled cars etc..) work?

There are servos that can handle high force / torque. Not very cheap, but they exist. (For instance: URUAV Deluxe Line BLS3211)

But indeed in this instance a heavy duty relay would make much more sense. Could even be solid state. https://www.newark.com/c/switches-relays/relays/solid-state-relays-contactors?load-current=30a

They exist with opto isolated control input and can be controlled from an arduino if wanted, but a simple solution like CaptDon suggested, with a circuit breaker mounted in the garage will be far less of a hassle.

Depending on the OPs skills and background the servo approach could be easiest for him.  And the switches associated with these moderate sized compressors don't require enormous amounts of torque.  Servos that can handle that level of torque are comparable to, or cheaper than contactors and high power SSRs.

[Nominal Animal]

Since you have to run control wires anyway why not do the right thing and include a motor contactor which is nothing more than a heavy duty relay or perhaps add a manual disconnect indoors? Circuit breakers are allowed to be used as 'switches' in many instances according to N.U.E.C. here in the states. Just turn the breaker off (if it is easily accessable) I often see circuit breakers used as 'light switches' in factories. Is that pressure switch one of the types used on a well where if you are starting at zero pressure you have to manually hold the lever in place until pressure starts to build? Those types of pressure switches were designed to prevent pump burnout if the well ran dry and pressure was lost.

I was thinking the same.  Mouser has several contactors rated for 32A and above for approximately USD $50.  Stick one between the existing switch and the compressor.  To actuate it (most use mains alternating current for the coils), you can just use a remote controlled mains socket; I'd prefer the IR ones, as all radio-based ones are too easy to exploit.  At least with IR, you need to be within sight.

If you want to make your own key fob for it, I'd suggest a contactor from Mouser, controlled by a microcontroller with mains-rated relay, say Olimex ESP32-EVB (also available at Mouser; two 250VAC/10A 120VAC/15A 24VDC/15A relays).  It includes an IR LED receiver, Bluetooth, and WiFi.

[pcprogrammer]

Depending on the OPs skills and background the servo approach could be easiest for him.  And the switches associated with these moderate sized compressors don't require enormous amounts of torque.  Servos that can handle that level of torque are comparable to, or cheaper than contactors and high power SSRs.

True it all depends on his skill set and budget which solution fits best.

A solution with a servo requires some mechanical skills in making brackets and arms to attach the servo near the switch and have it function properly. It also involves controlling the servo which is easy with an arduino, but combined with a radio link it is a bit more complex. Also the arduino near the compressor needs a power supply, which adds to the equation.

A single circuit breaker and copper wire and maybe a box in the garage will be a bit more expensive, but certainly easy to install.

I myself would go for the simplest solution not using an arduino or other controller. A light switch and a big relay if it needs more distance from the compressor or the circuit breaker if possible.

[Ian.M]

If the switch in question incorporates an unloader, then leaving it on and switching power remotely isn't an option as even a slight leak in the check valve that will be between an unloader type pressure switch and the tank would result in the motor having to start against full back pressure, which it isn't designed to do.  You'd have to blow the tank down or manually operate the switch to vent the line to restart, which is a PITA if you just need to switch it off for a few minutes for a phone call!   

Its easy enough to check if its an unloader type pressure switch - look for an exhaust port or let the compressor build pressure till it cycles off and see if the switch vents a burst of air as it does so.

[pcprogrammer]

I assume the compressor also has a pressure based off switch for when it is on pressure. Mine does. It also has hysteresis and only turns back on again when the pressure drops below a certain value. There is also a mechanical safety on there to allow for venting when the motor starts. Besides all that there is a normal on off switch on it.

Guess it depends on the type of compressor what kind of mechanisms it uses.

[Ian.M]

The O.P's photo shows it has a plumbing connection, and that its marked 'LEFOO pressure controller' so it certainly isn't a simple switch.   In fact I have visually matched it to Lefoo's LF10 series, some of which have an unloader valve.

[pcprogrammer]

It certainly looks the same what you have found, and when kept in the loop it will still prevent the compressor from starting under load. The text near the lever indicates either off or auto. In the off position it will cut the power, and when in auto the pressure switch will take over. Not sure if it also controls the unloader valve.

[robert.rozee]

hi Tom,
    consider using a car door lock actuator. this will give you an inch or so of movement and be easy to control remotely. type car door lock actuator into google to see pictures.


cheers,
rob   :-)

[Ian.M]

First confirm the LF10 pressure switch has an unloader, as I described above or by checking its part number against the datasheet.  If not, everyone suggesting remote switching power is on the right track.   If it has, I'd suggest removing the little red plastic sleeve from the operating lever and extending that to get a throw to match the stroke of a car central locking actuator.   

Drill a hole to fit the lever down the center of an aluminium bar, cross drill and tap for a grub screw to hold it on, and slit and cross drill the far end for a pin through a simple steel strip linkage to the actuator.   Slot the end hole of the linkage slightly so the actuator isn't forcing the lever against its stops or holding the lever back off its stops.   That's all possible with hand tools, namely a drill, hacksaw, some files and a bench vice, so you don't need a machine shop.

[Doctorandus_P]

Why not simply put an extra switch in the power cord of the compressor? (Extension cord with switch).

In the workshop I go sometimes, there is a stick welder that is mounted next to a 15 meter long bench. That welder also has a quite loud and annoying fan, so I do not want it making noise the whole day. Above the workbench, I have made a string in a horizontal loop that is connected to a switch that switches the welder on and off. If you pull the sting rightways, the welder goes on, if you pull it leftways, it goes off. In total there are four pulleys on the cord. One on the right side just to reverse direction, and two on the left side, so the cord bends downwards towards a weight that also has a pulley. The weight is just to keep the string under tension. With this setup, the welder can be turned on and off from anywhere along the 15 meter long workbench.

[Tom18991]

You guys are awesome. Lots of really good brainstorming here, thank you!  The switch in question does appear to be a LEFOO LF10, with an unloader.  I say 'appears to be' because it is supplied by Eastwood (the auto tool company) as a replacement for the original pressure switch on their 30/60 scroll compressor. It still has the Lefoo logo on it and appears identical to the standard Lefoo switch, though I don't know for sure it's identical to the off the shelf version.  But for purposes of this project, it's the same. 

I love the low-tech pulleys and strings idea, but the compressor is out behind the garage, so would require drilling holes in the wall etc., which I'd rather not do.  I've thought about a hard-wired safety switch or relay etc., but I'm not sure it that would be good for the machine if I cut the power everyday (and don't want to attract attention of the building inspector.) It was actually a power outage that killed the original pressure switch. 

So, I've picked up a door lock actuator 'kit' that comes with a controller and remote controls.  I had planned to make a wireless arduino set up, but this $25 Amazon kit covers virtually all of the electronics (other than power source).  I'm thinking I'll design and 3D-print some mounting and actuating mechanism.  Stay tuned, and thanks again for all the great ideas!

[Tom18991]

Well, here's what I came up with.  I tried the power door lock actuators, but they were not powerful enough with such a short throw, so ended up using a 4" linear actuator from Amazon.  Literally everything else (except for a bearing) is 3D printed and just clips on.  Kind of a maker's solution, but it works and allows the compressor and pressure switch to work as designed. 

[CatalinaWOW]

One of my college profs, a guy who split his time between teaching and developing semiconductor technology at TI, said that "A working circuit is a thing of beauty."  This solved your problem, using tools you are familiar with.  It is a perfectly fine solution to the problem.