Soft Start on 2 Stage AC

[GSXR1000]

xr17 is a single speed compressor so a soft start would be fine.. it just closes a scroll bypass selniod to use 100% of the compressor

 

[maxandtara]

BentleyJ,

Thanks for the FYI, now it make when the tech support from Soothstarter/Ziller told me that the Emerson PCB on Goodman GSXC18 has builtin smooth starting capabilities.

 

[BentleyJ]

The PCB pic is a newer design and it has the ComfortBridge technology vs. the older ComfortNet system. That said, the fan motor on the condensing unit and the Blower motor on the air handler/Furnace are both ECM (electrically commutated) type. Very efficient and they do ramp up to speed and thus are soft start by virtue of the variable speed controller.
However, the GSXC18 still uses the 2 stage (not 2 speed) Copeland Scroll compressor. This compressor only has one speed. Low stage is provided by a bypass valve in the scroll compressor that relieves pressure thus the motor runs with lower amps. When this compressor starts up it has a large surge current. If this is the model number condenser you have, I would highly recommend a HyperEngineering or MicroAir Soft Starter.

BTW: Goodman does make a true variable speed condenser its model GVXC20, and this does have the soft start feature built in. Last time I compared variable speed HVAC units I come to the conclusion the Trane XV20i is far superior to Goodman. Trane has a built in static pressure gauge to self calibrate the modulating dampers for zone systems.

 

[maxandtara]

Each training trial is actually just during the half second start up period. Beyond that 0.5 second startup time the Easystart bypasses itself

Easy start instructions... on "Comfort Alert control board systems"

Enter “EasyStart_” in the entry box (with the underscore but without the quotes). Press “connect”. When the connection is complete, press the relearn tab. Change the switch for “No Start delay”

Did I understand this correctly.

• Easy start Learning is in initial 0.5 seconds.
• Turn on "No Start delay"

Does this mean:

• Are you turning off learning mode?
• Easystart will be on "Default mode" only

I am confused. I thought learning is essential to reduce the inrush requirements.

 

[maxandtara]

BTW: Goodman does make a true variable speed condenser its model GVXC20, and this does have the soft start feature built in. Last time I compared variable speed HVAC units I come to the conclusion the Trane XV20i is far superior to Goodman. Trane has a built in static pressure gauge to self calibrate the modulating dampers for zone systems.

You may be correct that Trane may be better.
But both use inverter technology. If you are using inverter technology, smooth starters are no longer required.

 

[keyblue]

BentleyJ,

Thanks for the FYI, now it make when the tech support from Soothstarter/Ziller told me that the Emerson PCB on Goodman GSXC18 has builtin smooth starting capabilities. View attachment 159018

I have the same board in my goodman 5 ton 2 stage. Decided to go for it and connect a hyper engineering sure start. Works perfect! I can now run AC from battery backup system.

 

[RCinFLA]

Easy start instructions... on "Comfort Alert control board systems"


Did I understand this correctly.

• Easy start Learning is in initial 0.5 seconds.
• Turn on "No Start delay"

Does this mean:

• Are you turning off learning mode?
• Easystart will be on "Default mode" only

I am confused. I thought learning is essential to reduce the inrush requirements.

The startup period of LRA (locked rotor amps) current is just the period of an induction motor where the motor is spinning up and has not reached run rpm's. Motor draws very high current during this spin up period.

The startup surge period will vary depending on motor initial mechanical load. It should never be greater than about 1 second. The LRA load current during startup will likely trip the compressor's overcurrent internal safety breaker if it lasts longer than about 1 second.

All the 'softstarter' like Comfort Alert and Easystart are actually a combination of voltage ramp softstart (via a 'light dimmer' triac) and a large mfd hardstart start capacitor placed across run capacitor of air conditioner. The starter capacitor provides a 90 degree current phase shift during the high LRA startup period and is disconnected after motor achieves running rpm. The start capacitor 90 degree current phase shift to start winding of motor increases motor torque during startup period. Once motor reaches running rpm's the start capacitor is disconnected and there is a relay to short across the dimmer triac to avoid it overheating from its approximately 2 volt drop, during run period.

The 'Run' capacitor mfd value also provides 90 degrees current phase shift to auxiliary (start) winding at the lower run current level. When run capacitor is correct value, providing 90 degs phase shift, the relationship between run winding current, start winding current, and compressors common wire current is: Common wire current = sqrt (run winding current ^2 + start winding current ^2).
Example: clamp-on amp meter reads 10A on run winding, 7A on start winding during run current. Common wire current should be square root of ( run winding current ^2 plus start winding current ^2) = sqrt( 10^2 + 7^2) = sqrt (149) = 12.2 amps. If the common compressor current is off by more than 10% from this calculation it means the run capacitor value is not the correct mfd value to provide the optimum 90 degs phase shift.

The start capacitor mfd value has to be selected based on motor size so it provides the optimum 90 degree current phase shift to start winding of compressor motor. Generally, the larger the motor horsepower, the larger the mfd value required of the start capacitor.

The training periods are typically five, first turn-on's after installing softstarter, where the microcontroller changes the initial startup voltage and rate of voltage ramp up during the startup period. The softstarter unit measures startup surge current and duration of time to achieve running rpm to make its decisions. As it progresses on its five startup training adjustments, it may overdo it, and this results in a compressor stall during one of the attempts. It terminates powering compressor if has not achieved running rpm's in about 0.6 seconds and ignores results of that attempt.

The unit selects and stores the 'best' training attempt to use from that point on. 'Best' startup is lowest startup surge current with no longer than about 0.5 second startup period.

It is important that training be done with a reliable AC source, like grid. It is better if you do not do its learning cycles on a generator as any generator load AC voltage slump can affect the training detection results. Most likely result of training on a generator is non-optimum startup determination.

Most units have a five minute short-cycle timer that prevents attempting a restart within five minutes of last turn off. This is to allow refrigerant pressures in air conditioner to equalize preventing more startup mechanical load on compressor due to higher compressor head pressure.

If softstarter unit is moved to another air conditioner it must be reset so it can train on new unit. Also, if a run capacitor or softstarter's start capacitor is changed it is best to have it relearn with five new training cycles.

There are two timers that can be confusing.

One is delay after outside unit's contactor turns on outside unit which causes fan to immediately come on and after a few second delay, the compressor startup begins. Softstarters do not have power during contactor off period so they require at least a few milliseconds for their microcontroller to boot up. Then they start a compressor turn on delay timer of about 3 seconds. On an inverter-generator, having the fan kick on first usually causing the inverter-generator to speed up its rpm's when in ECO mode which gets generator better prepared for the high compressor startup surge that is coming in a couple of seconds.

The 3 second compressor startup delay for inverter-generator can be disabled if it causes problems to air conditioner controller. It has no negative side effect other than losing the inverter-generator ECO mode startup benefit.

Other is the short-cycle 5 minute hold off timer to prevent restart of compressor when refrigerant pressure has not equalized.

Some air conditioners have their own 5 minute short cycle timer and require detection of an active compressor within a short period of time after activation or it shuts down air conditioner as a protection method for compressor. The startup delay of the softstarter may cause the air conditioner control unit to think there is something wrong with compressor. You can disable the softstarter's five minute short-cycle timer but this should only be done if the air conditioner has its own timer and is being 'confused' by the softstarter's short-cycle timer.

You should always have a 3 to 5 minute short-cycle timer, whether it be in the thermostat, air conditioner's control board, or softstarter.

A warning on short-cycle timers in thermostats, they only work for power glitches if you have 'C' wire connected to thermostat. It provides 24vac from air conditioner control transformer that allows thermostat to detect a power glitch. Without 'C' wire connection the thermostat runs only on its internal batteries and does not have AC power glitch detection.

The five minute short cycle lockout period will also be triggered when there is a short power glitch in grid power, like due to lightning hitting nearby power lines or wind causing tree limb to brush a power line.

A scroll type air conditioner compressor can actually immediately reverse direction and start to run backwards if subjected to less than a half second power glitch. It is hard on compressor if it runs backwards. It will overheat and trip internal compressor protection. Should be avoided by having a short-cycle timer that detects the power glitch and triggers a five-minute shutdown of compressor.

 

[RCinFLA]

BentleyJ,

I am mainly concerned if my 5 ton goodman hits Stage 2/ Hi at initial startup.

Ecobee - Hi/stage 2 is programmable. I programmed mine to 2 degrees of target temp.

Would ecobee interfere with the Goodman board during initial start up?

This thread is great. I should have seen this thread before I bought my smooth starter (SS). I have a Goodman 2 stage and installed a SmoothStarter by Ziller. It did not work. At least that there are nice enough to give me a refund if I mailed their product back.

Most install instructions of SS only show connections to simple mechanical contactor, except for Easystart. For systems using "Comfort Alert" Control Board, there is an added step of programing "No start Delay"

Does anybody know why this needs to be done? Or what is the significance?

Other smooth starter products do not have this option.

What do you guys recommend for Training the system. Hi or Low? From the post easystart recommends training the system on Hi.

With the help of air handler controls (ecobee) Scheduling , "Reverse Staging" for my 5 ton unit, separate whole house dehumidifier, as well as a mini split (2 ton). All of this to minimize the engagement of Hi of my 5 ton unit. (I do notice a power consumption difference in keeping minimizing Hi/stage 2 )

A two stage scroll compressor has a solenoid that controls when part of the scroll compressor is bypassed to reduce capacity of compressor. It just lightens load on compressor motor reducing its power consumption.

In partially bypassed mode the compressor runs at about 65% capacity. Any lower runs the risk of insufficient oil circulation through system back to compressor, allowing oil to potentially collect in evaporator coil.

Compressor startup is in bypass mode and requires the bypass solenoid to be energized to go to full power mode. Scroll compressors have a differential pressure plate that makes them startup unloaded. I doubt there is much difference in startup surge current between starting up in full power mode or low power mode. It is mostly the spin up of the mass of the motor rotor driving the surge current.

This means any softstarter is training in compressor low power mode unless there is special override setup to cause it to startup in full power mode. This capability is in air conditioner unit as this is also required to check refrigerant charge level although I am not sure if it works during startup. There is usually a jumper in a control board in outside unit to force full power mode.

If two stage air conditioner always starts up in low power mode it should not matter that softstarter trains in compressor low power mode.

Once startup is achieved, the soft starter is bypassed so any change of power mode, reverse cycle activation, or defrost activation has no effect on soft starter. There is a several amps jump in current going from low power to high power mode but this is minor compared to startup surge current. Motor is already at running rpm's when any power mode switching is done.

 

[RCinFLA]

BTW: Goodman does make a true variable speed condenser its model GVXC20, and this does have the soft start feature built in. Last time I compared variable speed HVAC units I come to the conclusion the Trane XV20i is far superior to Goodman. Trane has a built in static pressure gauge to self calibrate the modulating dampers for zone systems.

ECM blower motors control CFM rate by measuring their power consumption versus motor rpm's. They will increase their rpm's to compensate for high static pressure.

Squirrel cage blower fans bite into more air when static pressure is lower. This means a PSC motor draws less power when there is high static pressure. A PSC motor will slightly increase rpm's and draw significantly less power when there is high static pressure, like dirty air filter, clogged evaporator coil, or poor duct design. On a PSC motor, the result of high static pressure is significantly less CFM of air movement.

Although ECM motor can compensate for high static pressure, they draw more power to do it, run hotter, and can result in shortened lifespan of ECM motor.

ECM motor replacements are ridiculously overpriced. About $1500.

Be careful of using high MERV rated air filters. They can create a lot of air resistance increasing static pressure.

 

[BentleyJ]

Although ECM motor can compensate for high static pressure, they draw more power to do it, run hotter, and can result in shortened lifespan of ECM motor.

Good info. That is the beauty of a 2 stage system that runs on Low most of the time. Much less stress on the components.

 

[RCinFLA]

I do like the two-stage compressor. Least amount of additional complexity to go wrong, compared to noisy digital dancing scroll or full variable speed scroll's complex three phase inverter electronics.