After adding a smart switch to the air compressor, a viewer commented that if the smart switch cut power to the compressor while the motor was running, the pressure between the compressor motor and tank would not get released, and when power was applied again, the motor would not be able to start up due to this backpressure. The compressor relies on a mechanical unloader valve that releases the pressure at the end of each cycle. For most of our use, this wasn't an issue, because the compressor loses pressure overnight and starts up in the morning at 0 psi. However, if the smart switch cuts off the power because the motor has been running too long (due to a large air leak), then the pressure in between the compressor motor and tank won't get released, and the motor won't be able to start up again.
The solution is to add an electric unloader valve in series with the mechanical unloader valve. I chose a normally open solenoid valve that must be energized to remain closed. The next issue that occurred was that the compressor pressure was too close to the 145 psi solenoid max operating pressure, which meant that the solenoid valve would not reliably open when power was turned off. The spring wasn't strong enough to retract the plunger away from the orifice. Increasing the spring strength could result in the solenoid not being strong enough to move the plunger. The solution was to make the orifice smaller, reducing the force required to retract the plunger. I machined a brass insert that press fits into the original orifice and has a 60-drill size hole. Now the solenoid valve always opens reliably.
▼ WHERE TO BUY
▶ EMBRIGHTEN 40A Smart Switch - amzn.to/3SDmhFL
▶ Electric Unloader Solenoid Valve (requires orifice reduction) - amzn.to/48hUXkN
The shop air compressor would benefit from a smart switch that could do the following.
A timer that shuts off the air compressor after hours and starts it up again in the morning. This is simple enough, except that there are times when we want the air compressor to stay on after hours, like if we have resin items that are curing in the pressure pot. A simple timer won't account for these anomalies, and we would need to add a bypass switch and remember to enable the bypass switch. With a smart switch (controlled from the SmartThings smart home app), it would be possible to add a switch or pressure sensor at the pressure pot line that gets turned on when the pots are on. This prevents the smart switch from turning off the air compressor.
The 120V air compressors I use are already on the edge of tripping 15 to 20-amp circuits. The oil air compressor will often trip the circuit breaker, usually on start-up, while the oil-less air compressor rarely trips the circuit breaker, even when running continuously. Therefore the ~2 HP motors on these air compressors won't work with 15A-rated smart home switches. There are basically no 20A 120V plug-in smart home switches because 20A outlets are less common.
This is the Kobalt Quite Tech oil-less air compressor that the switch will be used with. It has a 1.8HP motor. It's similar to the California Air Tools Ultra Quite air compressors, but the quality is a little lower. See the post where I replaced the prematurely worn piston rings with ones that I sourced myself because Kobalt doesn't offer replacement parts.
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▼ VIDEO CHAPTERS:
00:00 What's the problem with shutting off compressor power remotely using a smart switch?
00:56 Mechanical unloader valve
03:17 What is an electric unloader valve and why you need one
04:45 Connecting electric unloader valve to airlines
06:33 Electrical connections for electric unloader valve
07:41 Defective solenoid valve!
08:05 Replacement solenoid valve works
08:38 Modifying the solenoid valve orifice for higher pressure
09:06 Using solder to decrease valve orifice diameter
09:37 Turning a smaller orifice insert on the lathe
10:09 Final setup of electric unloader valve
10:33 Testing the electric unloader valve (normally open solenoid valve)
The products shown here were purchased by me with the intent to use them. I did not receive any free items, and I am not being paid or compensated for this review. The video, description, and comments may contain affiliate links. If you click on a link, I may receive a commission. Money earned helps to support my channel and bring you more informative videos about engineering, crafting, and DIY.