Just installed some EasyStarts on 5 ton AC

AntronX said:

I been thinking about dedicated VFD for single phase compressor for few years now. I guess it will still require 3 half bridges same as 3 phase inverter but 3rd half bridge can be made smaller because it would only power start winding. And soft start can be implemented in software.

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A standard available three-phase VFD drive is not really compatible with a single phase induction motor. They are designed for three phase motors with 120 degs phase difference between phases. I know people have hookup up a three phase VFD using just two phases but it is far from optimum for a single-phase induction motor, having the wrong phase shift and wrong AC voltage for auxiliary winding.

A single-phase induction motor in most air conditioners use a series connected run capacitor to synthesize a second phase AC source to power auxiliary (start) winding.

The proper run capacitor value provides 90 degrees leading phase shift to the auxiliary winding for maximum torque. This simple method of synthesizing a second phase AC source also comes with an impedance transformation. This results in the AC voltage on the auxiliary winding being greater than the main AC supply and run winding. For 240vac mains compressor, the auxiliary winding run voltage is in the ballpark of 300 vac and the auxiliary winding is designed for the higher voltage with more turns of slightly smaller gauge wire than main run winding.

Dave911 said:

I've never seen a VFD for a single phase motor.

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I did see a listing before. Here's another mention:


Given the starting winding, it should be possible to do VFD for soft-starting. And of course many motors will run on both 50 Hz and 60 Hz, probably prefer reduced voltage at lower frequency. PWM or delayed phase like a dimmer might help with that.

Hedges said:

I did see a listing before. Here's another mention:

VFD’S for Single Phase Motors?

www.wolfautomation.com

Given the starting winding, it should be possible to do VFD for soft-starting. And of course many motors will run on both 50 Hz and 60 Hz, probably prefer reduced voltage at lower frequency. PWM or delayed phase like a dimmer might help with that.

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These are basically very large automatic light dimmers.

RCinFLA said:

A standard available three-phase VFD drive is not really compatible with a single phase induction motor. They are designed for three phase motors with 120 degs phase difference between phases.

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I know that. I was going to modify phase angle to match what start/run winding needs. I was saying that power inverter from 3ph VFD would also be required for 1ph + start/run winding. I think even regular 3ph VFD can be used for 1ph but with phase angle modified. Could have 2 operation modes via menu. One for regular 3ph and another for 1ph+90deg winding. It would still use all 3 half bridges for both.

Quattrohead said:

These are basically very large automatic light dimmers.

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No, as I understand it there are VFD able to work for single-phase induction motors. With 60 Hz coming in, they produce PWM to drive the motor leads at a different frequency. Could/should use the "dimmer" or PWM function to reduce current at lower frequency (as do VFD for 3-phase). For starting, would drive starting winding with phase shift and ramp its frequency as well.

A dimmer would work well for universal motor, simply a speed control. Frequency doesn't relate to RPM. I think that's how my hand held variable speed AC powered tools work.

Your GOODMAN GSX130601 (5 Ton, 13 to 14 SEER Condenser) is a single stage, single speed unit.
I wonder how much difference a variable speed condenser unit, aka inverter, (NOT a variable speed blower inside) would make?

ifarkas said:

I wonder how much difference a a variable speed condenser unit, aka inverter, (NOT a variable speed blower inside) would make?

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Hello neighbor. You really want that variable speed indoor blower if you going to have VFD compressor. Those Goodman units are cheap garbage according to youtube hvac pros.

To save around 30% on AC you need a variable speed condenser unit, aka inverter.
Needless to say, the blower (inside) unit should be variable as well.
This the area where AC installer gaslight the public, aka bullshit, since they do not have the skill to install these more sophisticated units and steer you to your granddaddies technology, since they do not have our best interest (PC for scumbags).
Captain Obvious take: Inverter, high efficiency tank water heater, sufficient insulation -> < kW/h off-grid solar system.
In SF there is no gas.

I've had variable speed blowers for years. Variable speed condensers do not have a short ROI because of cost. The best most efficient system is the one that allows you to select your fuel. In my area that is two speed gas furnace and a two speed HP. With the right controls you decide what is cheaper to run.
I've been in the HVAC business for 40 years.

An AC induction motor rpm is fixed/related to excitation frequency. Just reducing applied effective voltage via PWM'g or conduction angle changing sinewave via SCR's or Triac's only reduces it maximum torque capability. This may be okay if motor load doesn't need the maximum capable torque and can improve power factor and efficiency at the given mechanical load on motor. Just got to make sure the torque does not fall below what is necessary to support present motor mechanical load or the motor will stall out.

Some of the slightly 'snake oil' power saving magic boxes are nothing but triac or SCR dimmers that reduce effective supply voltage.

An induction motor is called 'induction' because rotor gets induced current to create its magnetic field. In order for rotor to get induced magnetic current its rotation speed must be less than the stators synchronous speed based on its AC input excitation frequency. This is called 'rotor slip'. For a single phase, two pole induction motor driven with 60 Hz the synchronous stator field is 3600 rpms (AC freq x 60 seconds/mins), rotor slip will typically be 2% to 7% lower than synchronous speed. The amount of slip depends on motor mechanical load. More slip produces greater torque to support greater mechanical load on motor so motor rpm slows a few percent as motor mechanical load increases. A 60 Hz single phase, two pole air conditioner compressor will have an rpm in the 3500 rpm range.




Many mini-split air conditioner three phase variable speed motors have permanent magnet rotors. Their permanent magnet rotor rpm spins at stator synchronous speed based on AC excitation frequency because they do not need to induce current into rotor to create the rotor's magnetic field. Compressor rpm speed will be three phase inverter output frequency x 60 secs/min. 20 Hz = 1200 rpm, 60 Hz = 3600 rpm, 75 Hz = 4500 rpm. Misubishi Hyperheat model inverters run up to 144 Hz which produces a blazing 8600 rpm compressor speed at very cold outside temps making them sound like a jet engine. This is necessary to pump the required volume of refrigerant at high compression ratios on the compressor at low outside temps where compression vapor line pressure is very low.

Nice drawings as usual.

ifarkas said:

Captain Obvious take: Inverter, tankless water heater, sufficient insulation -> < kW/h off-grid solar system.

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Tell me again how tankless water heater provide any benefit for anyone (outside the industry), and especially connected to an off-grid system?

Tankless are great for gas situations but little else unless you have a preheat tank.

Okay, I did not read the entire thread, to long. This is just information for those persons shopping for a new HVAC system.

Our Trane XV20i 5 ton (60,000 BTU) has an LRA of 16 and running of 19 amps. 16 amps to start x 240 volts = 3840 watts to start it up and 4560 watts to run it full.

Trane is very high end equipment. I believe the XVi20 heat pump has the same stats too and there are Biden rebates on those unit.

So HVAC shoppers, have your salesperson show you the label on the condenser unit they want to sell to you. It will have the amps required to start and run the motor.

If our friend Will Prowse had a Trane, he wouldn't have wired in these soft starts in the first place.

glandpuck said:

If our friend Will Prowse had a Trane, he wouldn't have wired in these soft starts in the first place.

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"Trane" offers a range of products. Many manufacturers offer "inverter type" compressors on their very high SEER/SEER2 models. And they can easily cost 2X the lower efficiency models.

Here is a current Trane product line that has a LRA of 127.1A for their 5 ton version.


So even if Will had a Trane, he very well might benefit from a soft start.

@glandpuck
I would never recommend one of those units no matter what brand. Not that they won't work but you will never get it paid back. The ROI is just to long!

I have an EasyStart 368 X48 on my 4 ton unit. It reduced the inrush a lot, but also had a bunch of faults in the log over time. When I spoke with one of the guys at Micro-Air they recommended installing the capacitor from the X72 unit and this solved my problems. I'd recommend the X72 model if you have an older 4 ton unit.

This is a great discussion between an HVAC training company owner and the Engineer from Micro-Air who designed the EasyStart. Lots of interesting information here:

Partimewages said:

I've had variable speed blowers for years. Variable speed condensers do not have a short ROI because of cost. The best most efficient system is the one that allows you to select your fuel. In my area that is two speed gas furnace and a two speed HP. With the right controls you decide what is cheaper to run.
I've been in the HVAC business for 40 years.

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In South Florida, near Miami we do not have gas option available.

Hedges said:

Tell me again how tankless water heater provide any benefit for anyone (outside the industry), and especially connected to an off-grid system?

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You are correct Sir. I corrected my post. It should be “High Efficiency Tank WH”, like Rheem WH

ifarkas said:

In South Florida, near Miami we do not have gas option available.

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Then two speed HP with variable blower coil would still be a better ROI.