Soft Start on 2 Stage AC

[DanielS]

Hello, I’m running 4x 48VDC EG4s and 2x LV6548. I have one 5-ton Trane XR17 AC that is two stage. Most of the time the AC runs in Stage 1 which the system starts fine, but still dims the lights for a sec. When in stage 2 it drags the system a lot harder…Enter the soft starter.

I’ve been looking around the Googles and can’t seem to find if MicroAir or any of the others support a 2-stage AC. I haven’t contact MicroAir yet, but thought I’d start here first. Ultimately would like to just soften the surges on batt system.

Thanks for any advice!

 

[acdoctor]

I don’t really know anything about “soft starts”. I do however know about the A/C unit in question. You will probably need to keep in mind that you have 2 run capacitors 1 for each compressor however high stage uses both by way of the third pole on the contactor. They also share the hard start capacitor and relay.
That’s a lot of watts by the way.

 

[DanielS]

I don’t really know anything about “soft starts”. I do however know about the A/C unit in question. You will probably need to keep in mind that you have 2 run capacitors 1 for each compressor however high stage uses both by way of the third pole on the contactor. They also share the hard start capacitor and relay.
That’s a lot of watts by the way.

Thank you! Yeah I haven’t opened up the AC yet to see how complicated the wiring looks on this unit. I’ve sent a message to MicroAir. I’ll report back once I hear from them.

 

[RCinFLA]

There are likely several different methods used to accomplish two stage operation. On the attached video, the motor actually has to stop, equalize refrigerant, and be setup to reverse motor direction by interchanging what are normally called Run and Start windings on compressor motor.

In one rotational direction it mechanically drives two compressor pistons, corresponding to 'high speed'. In the opposite rotational direction, it mechanically drives only one compressor piston for 'low speed'.

The motor is common in high/low speed, running at same RPM speed in both 'low speed' and' high speed' modes, just in different rotational direction. In low speed mode there is just less mechanical load on motor, driving only one piston.

It should be possible to wire in an Easystart soft starter but it must be done such that the Easystart booster capacitor and run wires are connected on AC input side before the Run/Starter winding reversal relay to motor for rotational direction, so the boost cap always goes to assigned start winding and run wire always goes to assigned Run terminal based on desired motor rotational direction. It should be trained in high-speed mode, which has a bit more initial startup mechanical load due to driving two pistons. If you allow softstarter to train itself in low speed mode it may stall out compressor when high speed mode is attempted.

When single phase induction motor has less mechanical loading its electrical input power drops off, but its power factor degrades so the VA apparent power does not drop off as much as real power. Two stage compressors can run down to 35% motor mechanical loading where power factor gets very poor. They may add a power factor correction capacitor across motor in low speed mode to improve low speed mode power factor.

On an air conditioner, as heat loading is reduced due to air temp and humidity, the air handler evaporator expansion valve regulates refrigerant flow to keep evaporator above freezing point of water. With a fixed compressor pumping rate, there is a limit to what the expansion valve can do since the compressor will continue to attempt to draw return refrigerant forcing low side pressure so low it would result in return low pressure side refrigerant line freezing up. Two stage or variable speed compressors are a better way to regulate pumping rate allowing lower heat loading run situations.

Reducing air handler air flow rate with a variable speed blower across evaporator coils allows more time for humidity removal without lowering air temp as much. This is how humidity control is done in addition to just air temp. Removing humidity takes more A/C btu's than just cooling air since causing water vapor to condense to liquid requires more heat removal. As humidity comes down in air-conditioned area the heat loading btu requirement is reduced on system to maintain air temperature.

An oversized A/C unit of fixed speed for given cooling area is bad because it quickly lowers air temp resulting in short ON cycles that gives very little time for evaporator to condense humidity out of air. You end up with a 'cold damp cave' feeling to air-conditioned rooms.

 

[DanielS]

Just got this response from MicroAir

Thanks for the question. The short answer is YES, but your system will require some special steps on your part after installing EasyStart. Long explanation ahead!... Yes, the EasyStart ASY-368-X72-BLUE will support your 5-ton Trane 2-stage XR17, but there is a special step you must take when you "learn" the EasyStart during its first 5 starts after installation. The reason is your 2-stage system uses a special Emerson Copeland Scroll compressor (only 1) that has a secondary pressure solenoid that controls how much the compressor is actually pumping. It doesn't change the compressor's speed, but instead it simply changes how much its rotating scroll pumps. So when your thermostat calls for the second stage to run (the Y2 wire gets energized in addition to Y1), the compressor will energize this solenoid, pump more refrigerant, AND therefore draw more current (energy) while running. Note that the amount of current that the compressor draws while starting will NOT be higher because the internal electronics of your XR17 system prevent the second stage from getting energized during startup (Y1 energized), and only lets Y2 pass through after a short delay. Note that under normal conditions when your room temp only goes 1 or 2 degrees above the setpoint, your thermostat will only energize Y1 (without Y2) and your compressor will only need its first stage to operate (i.e. special solenoid will be OFF). THIS is how the Trane XR17 2-stage saves you electricity! It's actually quite a nice design. So what does this mean to you? Simple. Install the EasyStart per the normal instructions and wiring. NOTHING changes there. BUT, when you go to run your system for the first time, make sure you set your thermostat's setpoint temperature to ***at least 5 degrees below the current room temp***. By doing this, your thermostat will energize BOTH Y1 and Y2, and will force your compressor's 2nd stage to run. Let the compressor run for at least 5 minutes EACH TIME you start it up for the first 5 STARTS after EasyStart installation. The EasyStart learns your compressor's STARTING behaviors during the first second or two during and after startup, but it then deliberately waits 5 minutes to learn and "lock in" your compressors RUNNING behaviors after everything warms up. This is why you need to make sure each learning start lasts at least 5 minutes. Hopefully this makes sense. Please contact help@microair.net if you have any further questions.

 

[DanielS]

There are likely several different methods used to accomplish two stage operation. On the attached video, the motor actually has to stop, equalize refrigerant, and be setup to reverse motor direction by interchanging what are normally called Run and Start windings on compressor motor.

In one rotational direction it mechanically drives two compressor pistons, corresponding to 'high speed'. In the opposite rotational direction, it mechanically drives only one compressor piston for 'low speed'.

The motor is common in high/low speed, running at same RPM speed in both 'low speed' and' high speed' modes, just in different rotational direction. In low speed mode there is just less mechanical load on motor, driving only one piston.

It should be possible to wire in an Easystart soft starter but it must be done such that the Easystart booster capacitor and run wires are connected on AC input side before the Run/Starter winding reversal relay to motor for rotational direction, so the boost cap always goes to assigned start winding and run wire always goes to assigned Run terminal based on desired motor rotational direction. It should be trained in high-speed mode, which has a bit more initial startup mechanical load due to driving two pistons. If you allow softstarter to train itself in low speed mode it may stall out compressor when high speed mode is attempted.

When single phase induction motor has less mechanical loading its electrical input power drops off, but its power factor degrades so the VA apparent power does not drop off as much as real power. Two stage compressors can run down to 35% motor mechanical loading where power factor gets very poor. They may add a power factor correction capacitor across motor in low speed mode to improve low speed mode power factor.

On an air conditioner, as heat loading is reduced due to air temp and humidity, the air handler evaporator expansion valve regulates refrigerant flow to keep evaporator above freezing point of water. With a fixed compressor pumping rate, there is a limit to what the expansion valve can do since the compressor will continue to attempt to draw return refrigerant forcing low side pressure so low it would result in return low pressure side refrigerant line freezing up. Two stage or variable speed compressors are a better way to regulate pumping rate allowing lower heat loading run situations.

Reducing air handler air flow rate with a variable speed blower across evaporator coils allows more time for humidity removal without lowering air temp as much. This is how humidity control is done in addition to just air temp. Removing humidity takes more A/C btu's than just cooling air since causing water vapor to condense to liquid requires more heat removal. As humidity comes down in air-conditioned area the heat loading btu requirement is reduced on system to maintain air temperature.

An oversized A/C unit of fixed speed for given cooling area is bad because it quickly lowers air temp resulting in short ON cycles that gives very little time for evaporator to condense humidity out of air. You end up with a 'cold damp cave' feeling to air-conditioned rooms.

View attachment 100033
View attachment 100034

Looks like you’re right on…it’s got some unique design, but fortunately is sound like it will work, but you just have to train it with Stage-2

 

[RV10flyer]

I have an American standard 16 seer 2 ton hp. It has a two-step compressor 65% or 100%. It has a softstarter that works fine. All you have to do is jump Y1 & Y2 together at the heat pump to ensure both are energized at the same time. Many thermostats will not energize Y2 for a while, even if you run the setpoint temperature 5° or more lower than room temperature.

I also have a 20 SEER 2 Ton American Standard that is 100% inverter driven, 26-100%. A Fujitsu mini hp, 9k 33 SEER 100% Inverter. Last, a Goodman 16 SEER 1.5 Ton Single Speed with micro-aire. All 6.25 Tons run great on two Sol-Ark 12K's.

 

[RCinFLA]

Just got this response from MicroAir

I think his explanation of the five minutes is not correct or at least confusing in its intent. Each training trial is actually just during the half second start up period. Beyond that 0.5 second startup time the Easystart bypasses itself with its internal relay so it is like it is not even in the circuit.

What you have to do is wait five minutes after turning off A/C to allow all refrigerant pressures on high and low side to equalize out so you do not attempt a start up with some amount of high side pressure which would make startup current greater, screwing up the training cycle results. Most A/C units have a 5-minute control timer that will not allow compressor to restart within 5 minutes of last shutdown. This is to prevent a short power flicker from restarting compressor under high refrigerant pressure load. However, if you attempt a startup without compressor engaging due to the A/C unit hold off timer, this will confuse the Easystart since it starts its softstart cycle from point contactor applies power.

The wiring of Easystart purposely leaves the outside unit fan directly on A/C contactor, not going through softstarter. For an inverter in standby mode, or an inverter-generator in low rpm ECO mode, the fan motor load will wake up the inverter from standby, or inverter-generator from low RPM ECO mode, so it is ready for the high surge current to come when compressor kicks on. There is a few second delay in Easystart from when you hear contactor click on and fan coming on before compressor starts up via softstart ramp.

The startup ramp is about 0.5 seconds. Training is done five times. The softstart is like a light dimmer that ramps up over the half second. Simultaneously a large value start capacitor is placed across run capacitor which is also voltage ramped. Having the extra starter cap boost differentiates these units from just a softstarter. It gives extra full rotational starting torque.

Training starts out relatively conservate with about 40% initial voltage reduction. Subsequent training tries to reduce the initial starting voltage more and more.

Copeland Scroll compressors are rugged but have very high startup surge current. My 4 ton stock had 190 amps startup surge current on 240vac.
First training cycle it dropped to about 105 amps. It progressively got lower on subsequent training starts.

Fourth training try was 77 amps. Fifth and last was 66 amps but the sound of compressor during startup indicated it was getting very close to a compressor stall. On the sixth startup which is what the unit decided to select was the 4th training value of 77 amps. It was smart enough not to risk using the marginal fifth try of 66 amps that almost stalled out the compressor.

 

[RCinFLA]

It got me investigating the various Copeland scroll capacity modulation schemes. There are actually three different methods used.

First is three phase motor with variable frequency drive.

Second is their digital bypass mode which has solenoid that allows the scroll to lift up stopping compression. It pops compression on and off every 1 to 20 seconds per on-off cycle. Motor continuously runs at constant speed. These compressors are a bit noisy.

Third is the two-stage solenoid operating scheme that bypasses a portion of scroll dropping compression from 100% to about 65% with a solenoid valve which is the two-stage model. Motor continuously runs at constant speed. It can switch modes on the fly.

I really like the two-stage version the best. It would allow power factor correction. The digital bypass version chops on and off too fast to allow power factor correction. The variable speed three phase motor has potential issues with oil circulation at low speed.

The digital bypass and partial scroll bypass just lighten load on motor, so the near constant speed induction motor power factor decreases.

Anyway, for Easystart soft starter on two stage Copeland scroll there should be no problem. As previous stated, just have to train the Easystart in full compressor 100% mode to get the maximum startup load to train with.

On air conditioner compressors, motor current is highly dependent on given operating conditions compression ratio. For Copeland scroll compressors there is also a high initial torque requirement on startup to spin up the high mass of scroll and motor rotor. Refrigerant charge, and heat loading varies the compression ratio requirements and thus the run and start current.

Typical compression ratio for air conditioners is 3 to 4. It can get as high as 8-10 under certain high stress conditions like low or high refrigerant charge conditions.

 

[GSXR1000]

Thank you! Yeah I haven’t opened up the AC yet to see how complicated the wiring looks on this unit. I’ve sent a message to MicroAir. I’ll report back once I hear from them.

if it has two contactor then it changes direction of rotation. if single contactor then is a scroll with an unloader seliniod.

 

[DanielS]

It got me investigating the various Copeland scroll capacity modulation schemes. There are actually three different methods used.

First is three phase motor with variable frequency drive.

Second is their digital bypass mode which has solenoid that allows the scroll to lift up stopping compression. It pops compression on and off every 1 to 20 seconds per on-off cycle. Motor continuously runs at constant speed. These compressors are a bit noisy.

Third is the two-stage solenoid operating scheme that bypasses a portion of scroll dropping compression from 100% to about 65% with a solenoid valve which is the two-stage model. Motor continuously runs at constant speed. It can switch modes on the fly.

I really like the two-stage version the best. It would allow power factor correction. The digital bypass version chops on and off too fast to allow power factor correction. The variable speed three phase motor has potential issues with oil circulation at low speed.

The digital bypass and partial scroll bypass just lighten load on motor, so the near constant speed induction motor power factor decreases.

Anyway, for Easystart soft starter on two stage Copeland scroll there should be no problem. As previous stated, just have to train the Easystart in full compressor 100% mode to get the maximum startup load to train with.

On air conditioner compressors, motor current is highly dependent on given operating conditions compression ratio. For Copeland scroll compressors there is also a high initial torque requirement on startup to spin up the high mass of scroll and motor rotor. Refrigerant charge, and heat loading varies the compression ratio requirements and thus the run and start current.

Typical compression ratio for air conditioners is 3 to 4. It can get as high as 8-10 under certain high stress conditions like low or high refrigerant charge conditions.

Thank you for this thoughtful reply! It should be arriving this weekend, I’ll report how it goes.

 

[BentleyJ]

I'm using a Hyper Engineering soft starter on a Goodman 2 stage condenser. Its the same type of Copeland Scroll with the 33% bypass relief valve as described above. The Goodman control board also uses stage 1 to start the compressor and then engages stage 2 later, if called for. From what I've seen by the time stage 2 engages the "start up surge" portion of operation is LONG since past and the soft starter is basically in a pass-thru mode. Based on the 1 second graphs from an Emporia energy monitor it is very clear that the initial surge spike, is being controlled by the soft starter but within a couple of seconds the compressor amp draw stabilizes and flat lines. When the second stage is triggered all that happens is the motor gets loaded, power consumption increases by about 0.5kW and stabilizes at the new value. There is no soft starter intervention during the transition from stage 1 to stage 2 so I'm a bit puzzled by the rather lengthy instructions you received from MicroAir. Just my 2 cents.

 

[RV10flyer]

The variable speed three phase motor has potential issues with oil circulation at low speed.

My 20 SEER American Standard HP will ramp up on initial start, then occasionally during continuous operation to help with oil circulation.

 

[DanielS]

I think his explanation of the five minutes is not correct or at least confusing in its intent. Each training trial is actually just during the half second start up period. Beyond that 0.5 second startup time the Easystart bypasses itself with its internal relay so it is like it is not even in the circuit.

What you have to do is wait five minutes after turning off A/C to allow all refrigerant pressures on high and low side to equalize out so you do not attempt a start up with some amount of high side pressure which would make startup current greater, screwing up the training cycle results. Most A/C units have a 5-minute control timer that will not allow compressor to restart within 5 minutes of last shutdown. This is to prevent a short power flicker from restarting compressor under high refrigerant pressure load. However, if you attempt a startup without compressor engaging due to the A/C unit hold off timer, this will confuse the Easystart since it starts its softstart cycle from point contactor applies power.

The wiring of Easystart purposely leaves the outside unit fan directly on A/C contactor, not going through softstarter. For an inverter in standby mode, or an inverter-generator in low rpm ECO mode, the fan motor load will wake up the inverter from standby, or inverter-generator from low RPM ECO mode, so it is ready for the high surge current to come when compressor kicks on. There is a few second delay in Easystart from when you hear contactor click on and fan coming on before compressor starts up via softstart ramp.

The startup ramp is about 0.5 seconds. Training is done five times. The softstart is like a light dimmer that ramps up over the half second. Simultaneously a large value start capacitor is placed across run capacitor which is also voltage ramped. Having the extra starter cap boost differentiates these units from just a softstarter. It gives extra full rotational starting torque.

Training starts out relatively conservate with about 40% initial voltage reduction. Subsequent training tries to reduce the initial starting voltage more and more.

Copeland Scroll compressors are rugged but have very high startup surge current. My 4 ton stock had 190 amps startup surge current on 240vac.
First training cycle it dropped to about 105 amps. It progressively got lower on subsequent training starts.

Fourth training try was 77 amps. Fifth and last was 66 amps but the sound of compressor during startup indicated it was getting very close to a compressor stall. On the sixth startup which is what the unit decided to select was the 4th training value of 77 amps. It was smart enough not to risk using the marginal fifth try of 66 amps that almost stalled out the compressor.

I’m installing today and wondering the best way to train the ES unit. 1) I have a bypass switch that I can isolate my inverters completely basically grid connect everything. 2) I can have the inverters in bypass mode which is grid bypass, however, only 60A breaker (should be basically the same as 1. 3) in battery mode, which would experience a larger voltage sage on the in rush. I’m wondering which would be the best for training the system.

 

[RCinFLA]

It is recommended you train with grid power source. They prefer it to get a solid indication of improvement on each successive training cycle startup.

With a generator source is may bog down from the beginning first startup attempt and confuse the training as to how much each successive training tweak to voltage ramp change is actually affecting the startup.

You can train on generator if it is only thing available, but first training attempt must be able to start up compressor. Training overall result may not be the best optimum when done sourced from a generator.

 

[DanielS]

It is recommended you train with grid power source. They prefer it to get a solid indication of improvement on each successive training cycle startup.

With a generator source is may bog down from the beginning first startup attempt and confuse the training as to how much each successive training tweak to voltage ramp change is actually affecting the startup.

You can train on generator if it is only thing available, but first training attempt must be able to start up compressor. Training overall result may not be the best optimum when done sourced from a generator.

Up and running! I ended up doing it off the more solid grid connection as you’d mentioned. Dropped me down to 45A on a 5 ton, so definitely worth it!!

 

[DanielS]

Do you happen to know how to pull the initial training values? I failed to take screenshots the first 2 training sessions.

 

[RCinFLA]

I don't think you can. It may trash the record and only save the final one it chooses. You can always do a retrain and capture each startup training startup on your clamp on amp meter. If you just bought the EasyStart I assume you received the new version with Bluetooth application. You can monitor on your smart phone. It makes retraining very easy and allows for you to monitor startup performance over time.

I did call MicroAir and they told me it does not retrain on its own and if you have to change out a capacitor due to its failure or service that adds or subtracts refrigerant you need to retrain.

I recorded mine on my clamp on meter for each training try. It selected the next to last training point as the last training startup had the lowest current but was very close to a compressor stall.

You did not happen to observe if the Trane/Copeland 2-stage compressor always starts up on lower compression mode 2? That should have a bit lower startup surge.

I believe the Copeland two-stage scroll compressor can flip between modes on the fly. The solenoid just opens a vent hole in scroll plate about a third of the way from the perimeter of scroll. This effectively bypasses the first third of the compression. Your unit has an extra wire control out to compressor to control the solenoid that selects mode 1 or mode 2.

It would seem better if they start on mode 2 (partially bypassed scroll) then switch to high output if required. That would put less stress on compressor and contactor relay contacts which I would think Copeland would take advantage of.

All the smarts for controlling the stage 1 or stage 2 comes from the air handler based on input from thermostat and evaporator heat loading. It may operate differently if your thermostat does or does not have humidity control. The Evaporator Electronic Valve has a stepper motor controlled TXV valve to let more or less refrigerant into evaporator. Humidity control is achieved by running higher evaporator cooling while slowing down blower speed to allow more time for air to pass across cooler evaporator coil giving more time for condensation of water vapor. It is less efficient but that is price you pay for better humidity control. Normal evaporator temp is 36 to 46 degrees F.

Your number for the 5 ton 2 stage of 45 amps surge is much better than my single stage 4 ton Trane scroll compressor. It might be due to refrigerant charge. The guys that installed mine seemed to dump too much additional refrigerant into mine when they installed it. I don't have a long tubing run between compressor and air handler so it should not have needed more than factory stock charge. Guess I need to check sub-cooling on my unit.

 

[maxandtara]

I'm using a Hyper Engineering soft starter on a Goodman 2 stage condenser. Its the same type of Copeland Scroll with the 33% bypass relief valve as described above. The Goodman control board also uses stage 1 to start the compressor and then engages stage 2 later, if called for. From what I've seen by the time stage 2 engages the "start up surge" portion of operation is LONG since past and the soft starter is basically in a pass-thru mode. Based on the 1 second graphs from an Emporia energy monitor it is very clear that the initial surge spike, is being controlled by the soft starter but within a couple of seconds the compressor amp draw stabilizes and flat lines. When the second stage is triggered all that happens is the motor gets loaded, power consumption increases by about 0.5kW and stabilizes at the new value. There is no soft starter intervention during the transition from stage 1 to stage 2 so I'm a bit puzzled by the rather lengthy instructions you received from MicroAir. Just my 2 cents.

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 )

 

[BentleyJ]

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

I believe the control board on the air handler starts up the blower and condenser on low stage then transitions to high stage within about 30sec even if the thermostat is calling for High Stage immediately. It also may depend on the model number and revision number of the control board in the air handler.