re: Why don't A/C condensing units come installed with soft start devices?

Here’s my review of the Micro Air. I have almost 30k starts on them and installed them myself in 2021.

LINK

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So you’re trying to say resistance doesn’t affect phase angle in a 60hz RLC system? Put it in the textbooks!
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This isn't the thread but I did get it from the text books. I'm an electrical engineer with BS and MS.

Resistance has a direct impact as V=IR. For resistance, that is all you ever need/use. There is literally nothing in resistance that can change the phase of either the voltage or the current as its value lies completely in the "real" and contains no value within the "imaginary."

When you get to inductance and capacitance, they have no resistance but still provide impedance. Their values lie completely in the "imaginary" realm.

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Edit:
Capacitors increasing alternating current also breaks the first law of thermodynamics.

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No it doesn't. They cannot maintain an increased current. They absorb an increased current level when they are first energized (they charge up). They store that energy until discharged into a load (discharging during startup to provide extra starting current to compressor). Capacitors are nothing but buckets of energy. Think of them as water towers. You pour the water in slowly so you can use it faster later but you can never get more water out than you put into it. It is just there to handle changes in flow rates in transient responses.

The cap is in series with the resistive and inductive winding. Not doing the math but maybe there is a window where it could decrease impedance if so small that it was only to correct power factor. Not the case with a run cap. It is adding enough impedance to get as much phase shift as possible while having a low enough time constant to deliver full power. Current is measured in RMS so storing and releasing has no affect. Also reactive power is not imaginary. That is just a trick to use phasor math instead of much more complex polar calculations.

Since you like phasors: 1 -j has a phase angle of -45. 0-j has an angle of -90. Resistance has a big affect.

Edit: with common single phase motors 60hz and 1-10 HP. Aux reactance >> resistance after transient analysis alone. Still need to account for correct transient to send correct power which means matching capacitor to auxiliary winding resistance.

Capacitors control current in an AC circuit. Especially for "run" capacitors that remain in the circuit after the motor is running. Some units have starting capacitors where there is a mechanical switch in the motor itself or a potential relay that runs on back-EMF to remove them from the circuit after the motor has reached 70% - 90% of its max running RPM but most residential units made in the last few decades only use run capacitors. Here's a great YouTube video of a HVAC tech demonstrating what a capacitor does and how changing out capacitors with different values impacts start and run winding current values.

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I had never heard of the devices until a month ago...

now that I am considering a generator, I am being told to install them.

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We have been using them for years in industrial applications. They became popular when there was a steep difference in price between VFDs and Soft Starts for applications that didn't require variability in motor speeds. This is particularly true when running on generators due to large inrush currents (the rule of thumb is to assume six times the listed running current for a motor). Soft starts achieve much lower inrush by stepping up the voltage when starting the motor.

Where this comes in for you (or anyone setting up a backup generator) is the AC is usually the single current draw in your house when running so a 6 times inrush current may significantly impact the size of the generator you need. By using a soft start you may be able to downsize the generator you need by a bit.

I dissected a schematic a couple weeks on here. A good kit will:
1. Delay fan or compressor so they don’t start at same time.
2. Add resistance to compressor windings.
3. Subtract secondary capacitance to correct for time constant and phase shift.
4. Revert back to normal operation. Maybe check to make sure things went well first.
Main thing is just make sure it at least roughly matches your tonnage rating and don’t use on a unit that is over 25 years old. I dont live near hurricanes and wouldn’t use one, but there are no likely scenarios where these should ever damage anything.

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I think the more surprising thing than why don't they come installed, but why don't more AC installers offer to add them during the initial install. I'm assuming because they are 3rd party and may affect the warranty?

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It could be they want more work and dont want equipment to last longer or could be they just aren't familiar enough with them to understand their operation/benefits and promote them. I dont blame someone for not selling something they dont fully understand the point. They might also create more difficult troubleshooting such that it makes training techs harder.

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VFDs are better than soft starts. Soft starts are an intermediate between across-the-line starters and VFD-controlled motors.

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A VFD has soft starting capabilities since there are power electronics between the motor and the line voltage. But as I stated earlier, they are also more complex and more proprietary. Expect your unit to be down much longer than a single stage unit if you have issues with the parts.

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The Micro Air Easystart that I have starts the fan, then the air handler, then the compressor. All about 3-4 seconds apart. The description states that once the start up phase ends it pulls itself out of circuit, but my compressor runs noticeably much quieter after I installed the Easystart. Not sure if that's due to the inrush being less harsh or what.

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The fan technically does not run through the soft starter so it’s still fed directly off the contractor. But yes the compressor is delayed for 5 seconds before it starts. I also have been extremely impressed at how quiet mine are since installing. I can hear some of my neighbors’ units buzzing across the street and mine are barely audible from my driveway.

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and don’t use on a unit that is over 25 years old

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Not sure where you’re getting this from. I have one installed on an R22 compressor built in 2003. It is insanely quiet on startup compared to before and runs great. Has about 30k soft starts on it.

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I’m giving consideration to installing a soft start on my HVAC single stage condensing unit - same reason as everyone else - use of a portable gen-set

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You will be very impressed. And others who state the starter doesn’t help the compressor or extend the life hasn’t seen one in person. Both of my compressors start quieter and run quieter despite the soft starter only being in the circuit on startup. I don’t know how it does it but even a coworker of mine had to put his ear up to his 5 ton unit to make sure it was actually on after we installed one for him. Very impressive.

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Threw us a curve ball, so I’ll shut up and listen to others as I’m giving consideration to installing a soft start on my HVAC single stage condensing unit - same reason as everyone else - use of a portable gen-set - to run the HVAC - I’m now set up to back-feed the house through the main panel with an interlock transfer switch with a tri-fuel portable generator.

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I installed a micro-air on my 4ton about a month ago. Even though the app usually says my starting amps is around 34 amps, I can run it off my general 5500 using a 30amp plug.

I’ll eventually get something with a 50 amp but I’m glad that I at least have the option to just run central air if another storm comes through.