2xPowerwall whole house backup - HVAC sure start problem

[Ampster]

This is making a strong case, for the idea that any Heat Pump running off grid
should utilize inverter drive, variable speed motors. Beside the potential of
using much less energy, the starting surge problem is gone. Bruce Roe

Yes, it may take some time for those older less efficient compressors to wind out of the system. As you pointed out it is only an issue when trying to run off a Powerwall when the grid is down. However in the long run these systems are more efficient because they are variable speed and can be modulated based on the need for heat or cold based on the temperature differential.

I breathed some life into an old compressor when a friend found the leak, fixed it and recharged it. I am still looking forward to replacing it and my natural gas FAU with heat pump technology. For sure it will be inverter based.

[Mike90250]

If you are wedded to your existing gear, hire a real electrician with a $400 peak reading meter, and find out for sure, what your starting demand surge is. Without knowing what that value is, you are just going to keep going in circles. Can you find a nameplate on the compressor motor and see what HP it it ? The following chart may give you some idea what the actual starting surge is. 3 wire motors have an external capacitor, that's likely the closest to your compressor motor style.

Well Pump Motor Specs.jpg

[bcroe]

This is making a strong case, for the idea that any Heat Pump running off
grid should utilize inverter drive, variable speed motors. Beside the potential
of using much less energy, the starting surge problem is gone. Bruce Roe

[arf88]

Sure enough after the test today the Compressor does not run when it is off and tries to start in battery backup. Very upset about this and I'm holing the Solar company responsible for telling me it can run with 2 PW. Waiting to see how they want to rectify the problem.

[J.P.M.]

You're compressor will never draw anywhere near the Locked Rotor Amperage rating of 134 amps. 3 Tonnes, is ~10.5kW, or about 44 amps @ 240V worse case. Most likely only 50-70% of this. Starting current might, be 2 or 3 times this but only for less than a second thanks to the normal start/run cap. But this data will be in the spec sheet for the compressor.

Unfortunately, the PowerWall can only be configured for load shifting (with daily cycling) or backup (no cycling) -- not both. There still seems to be some debate on whether this can be modified post install (or at least how difficult it is to change).

3 tons of cooling = 36,000 BTU/hr.

10.5 kW electrical input to A/C unit ? You sure about that ?

[arf88]

You can do both, however i have mine set to Backup mode only. The other option will still backup the home and you can set a reserve for backup as you wish.

[JSchnee21]

You're compressor will never draw anywhere near the Locked Rotor Amperage rating of 134 amps. 3 Tonnes, is ~10.5kW, or about 44 amps @ 240V worse case. Most likely only 50-70% of this. Starting current might, be 2 or 3 times this but only for less than a second thanks to the normal start/run cap. But this data will be in the spec sheet for the compressor.

Unfortunately, the PowerWall can only be configured for load shifting (with daily cycling) or backup (no cycling) -- not both. There still seems to be some debate on whether this can be modified post install (or at least how difficult it is to change).

[arf88]

Tomorrow will be another true test to see if the compressor will turn on after it goes to battery backup. I learned a lot more about the AC system than I thought I would from this experience. Good to be informed.

Another thing i learned is if the Powerwall is fully charged the Solar Edge inverter will not allow the solar to operate until the capacity on the battery goes down a bit. This was a surprise to me b/c i expected it to be on but apparently the PW sends a signal to shut it off initially to prevent back flow into the grid but it also only allows it to turn back on once the capacity is reduced to a point where the solar production can be used either by the home or the battery to charge itself because the PV system can't just produce as the power has to go somewhere. Very interesting.

[arf88]

Thanks for the feedback guys, I had an HVAC expert come out and they removed the sure start and replaced it with an OEM Carrier Soft start kit made for this compressor. They also discovered since the sure start was not wired properly the Run Capacitor 7uF side was burnt out due to miss wiring so they replaced it and all is working with 2 PW with the AC running on a single test shutting off shore power the compressor continued to run on the PW. Will test again tomorrow with the compressor off and on battery power to see if it fires up. I suspect it will but will test to confirm.

This guys has been doing this for a long time and said the sure start is a generic module not compatible with all compressors. Coincidentally hyper engineering (maker of sure start) said it could be a compatibility issues with the logic board which could have been the issue as well.

Long story short without the sure start b/c of the 134 LRA there is no way the compressor would work switching to the batteries. But I will do a test tomorrow with the compressor off initially than go to battery and than turn the compressor on to see what happens.

[Ampster]

Very interesting. You have the PowerWall2 x2? SO theoretically, you should be able to supply up to ~60 amps @ 240V for 10s. Have you tried running the HVAC on the PowerWall's without the SureStart?

The LRA of that compressor is 134 Amps.

I've seen a lot folks on this board talking about PowerWalls (and other storage solutions), but there aren't too many that have bought them. I've not seen any discussion about folks trying to run larger loads like their AC.

Yes experience on this board for that situation is not deep. There is a parallel discussion going on another forum and the problem appears to be the Sure Start as far as I can tell. The problem occurs when ON the grid so the Powerwalls apparently are not the issue. Hopefully the OP will post the solution here when it is resolved.

[JSchnee21]

One other thought, you might need to wire the sure start to ONLY power the compressor and keep everything else on regular power.

[JSchnee21]

Very interesting. You have the PowerWall2 x2? SO theoretically, you should be able to supply up to ~60 amps @ 240V for 10s. Have you tried running the HVAC on the PowerWall's without the SureStart?

I've seen the sure start used for RV and smaller portable units running on gas generators (or poor campground power). I don't think I've ever seen one used for a house. Did you go through the appropriate "learning steps" to set it up?

My experience over the years with various leading waveform gizmos to "save energy" (essentially Caps that recover lagging generation current from spinning armatures and converting them into leading waveforms for consumption) is that many newer electronics either don't like the harmonics or in the case of my washing machine cause a strange humming in the circuit boards/power supply which I assume isn't good for them.

My really old and inefficient 4 ton unit (1997 el cheapo Goodman) only draws 29 amps continuous (Of course instantaneous starting current is much higher for the first second or so) perhaps a bit less now that I've replaced the start/run Caps.

I've always wondered this myself. I'd love for PV storage to become as cost effective as solar has. But most storage units just have really under sized inverters. I'm not interested in a backup solution that cannot run the whole house. My hope was that two or three PowerWalls in parallel might be able to run the HVAC as well. Of course generators are still cheaper and better for longer term outages.

I've seen a lot folks on this board talking about PowerWalls (and other storage solutions), but there aren't too many that have bought them. I've not seen any discussion about folks trying to run larger loads like their AC.

[wayne23836]

I used the Sure Start by Hyper Engineering on a 2 ton scroll compressor and had no problems. if your outdoor unit has an ecm fan motor I could see problems and it does sound like this may be the case. With the fan at such low speed the compressor will go out on high pressure.
I recently installed a Bosch 2.0 (seer 20) inverter Heat pump with variable speed compressor and it has absolutely no surge at all starts off at less than 2 amps and ramps up slowly from there the indoor and outdoor fans likewise (both have ecm motors) . it also has good low temp performance .
Hope this helps thought I would mention the Bosch as it does so well, if you are near a replacement you would do well to check into it.

[arf88]

I don't know if my solar company made a promise they can't keep. They told me 2 PW will support whole house with HVAC.

House is already very energy efficient, lets say just a couple of small electronics on during the day and AC running. I want the AC to work so they recommended a sure start be installed, they installed it but not correctly compressor fan would only run at half speed. Contacted Hyper Engineering and they confirmed it is wired correctly now.

What happens is the compressor (Carrier 3 ton 134LRA single stage scroll compressor) outside runs than after 2-3 mins just shuts off than starts again a 2-5 mins later. There is no fault code on the sure start (SS1B16-32SN). The fan in the house continues to run while the compressor has shut off. I called a dozen HVAC experts and none of them are familiar with sure start modules. Hyper Engineering thinks it is a compatibility issue with inherent controls of the AC unit and suggested calling an HVAC expert.

Has anyone had success with 2 PW and a sure start on their HVAC working properly?

Any tips or advice is appreciated.