AC Compressor (109 LRA) doesn't need SureStart? (2 x PowerWalls and Backup Gateway 2)

[notsure11]

I just got two Tesla Powerwalls installed with Backup Gateway 2 yesterday. It's a whole-house backup configuration and I don't have solar.

I have an A/C and the compressor outside has a label that says 19.9 RLA and 109 LRA. I thought this required a SureStart for the AC to work during power outage, but the installer said I may not need it. He said try it out once the batteries are fully charged and if it doesn't work, he will have someone come install it. I was very skeptical.

I just shut off the circuit breaker from the grid with the two batteries at 95% charged. To my surprise, when I turned on the AC, it was working! The fan on the compressor outside was spinning and it felt like cold air was coming out of the vents. The house power usage on the Tesla app jumped from 0.5kW to 4kW, so I assume the AC was actually running. Am I testing this right? Is it possible to run AC with 109 LRA without SureStart? Thank you.

 

[dailo]

The spec says it can handle 118LRA, so you should be good and seems to be working just fine. I have the same setup, but my AC is 134LRA. They initially installed without sure start saying it would work but it didn’t after testing so they just installed them for me later.

 

[yblaser]

With two Powerwalls it's not surprising it works. The say less than 98 LRA for a single Powerwall so two should support roughly twice that. That said, when I tried my 117 LRA with two Powerwalls it started but browned out the house.

 

[notsure11]

Thank you. I think I read somewhere that this Tesla page that says 1 Powerwalls can do 98 LRA is assuming SureStart is installed, but I now see that this page says 1 Powerwalls can handle 88A LRA for each Powerwall. So maybe I will be fine.

@dailo how did you know your AC wasn't working before you had SureStart installed? Did it just not produce any cold air? Or did Powerwalls shut down? Thanks!

 

[dailo]

Thank you. I think I read somewhere that this Tesla page that says 1 Powerwalls can do 98 LRA is assuming SureStart is installed, but I now see that this page says 1 Powerwalls can handle 88A LRA for each Powerwall. So maybe I will be fine.

@dailo how did you know your AC wasn't working before you had SureStart installed? Did it just not produce any cold air? Or did Powerwalls shut down? Thanks!

I did it at night when no solar was producing to simulate worst case scenario and the AC started sputtering loudly and lights flickered like crazy for a few seconds. Once the AC stopped (glad I didn’t break it) everything turned back on. My family was not happy with my test. So yeah if it doesn’t work, you’ll definitely be able to tell!

 

[notsure11]

Ah, so it was obvious it wasn't working properly. Thank you.

 

[el-guapin]

.... Is it possible to run AC with 109 LRA without SureStart? Thank you.

Just my opinion, I would still install one. Those units are affordable and easy to install. Cheap insurance. The AC would draw less power from the PWs. In turn, PWs power will last longer.

 

[Steve2498]

I second that.

After I installed one, the inrush amps (i.e. Start-up amps) went from 156 down to 78. Much easier on everything including the compressor.

 

[Zinc_Saucier]

The AC would draw less power from the PWs. In turn, PWs power will last longer.

The AC will draw less currant in that instant that they are starting up, but the overall draw will still be the same while running. So the only way that the powerwalls last longer is if that instantaneous inrush current is causing additional wear and tear and you are talking about the lifespan of the powerwall and not the backup duration during an outage.

 

[ptdusn]

We have 2 Powerwalls and our A/C has no issue starting and running off just the batteries. From what you have said it looks like you will be fine.

 

[RKCRLR]

The early Powerwalls had a low surge capacity but the newer ones (what Tesla refers to as Series 3) have higher LRA ratings.
SureStarts aren't compatible with all compressors.
Don't ask me how I know this

 

[Chaostheory]

The early Powerwalls had a low surge capacity but the newer ones (what Tesla refers to as Series 3) have higher LRA ratings.
SureStarts aren't compatible with all compressors.
Don't ask me how I know this

What was the problem? Tesla installed a surestart on one of our AC units and now the compressor won't start...

 

[RKCRLR]

What was the problem? Tesla installed a surestart on one of our AC units and now the compressor won't start...

My Carrier compressor was a Bristol 2 stage compressor that reverses direction when switching between high stage and low stage. The SureStart doesn't understand that type of operation. My HVAC system threw nearly 100 error codes (it is a microprocessor controlled communication system). When I went outside to investigate the system shut down with a large "bang". Tesla removed the SureStart and my system would no longer operate. Tesla told me to call a HVAC repair company since there must be something wrong with the HVAC system. After the tech left I compared the wiring to the schematic and found they hadn't rewired it correctly when they removed the SureStart. I rewired it correctly and the unit appeared to operate correctly but the compressor has subsequently failed (no output on low stage and low output on high stage). It cost me $11K to replace my outside unit and evaporator coil.

 

[ptdusn]

My Carrier compressor was a Bristol 2 stage compressor that reverses direction when switching between high stage and low stage. The SureStart doesn't understand that type of operation. My HVAC system threw nearly 100 error codes (it is a microprocessor controlled communication system). When I went outside to investigate the system shut down with a large "bang". Tesla removed the SureStart and my system would no longer operate. Tesla told me to call a HVAC repair company since there must be something wrong with the HVAC system. After the tech left I compared the wiring to the schematic and found they hadn't rewired it correctly when they removed the SureStart. I rewired it correctly and the unit appeared to operate correctly but the compressor has subsequently failed (no output on low stage and low output on high stage). It cost me $11K to replace my outside unit and evaporator coil.

I would send the bill to Tesla with a demand for a refund/payment.

 

[RKCRLR]

I would send the bill to Tesla with a demand for a refund/payment.

There is a little more to the story. Tesla was supposed to provide a whole home backup and negation's finally settled on Tesla installing a 3rd Powerwall (series 3) at a reduced cost to handle the required current surge. I discovered the compressor had failed after I had already signed the paperwork to install the 3rd Powerwall and relieved Tesla of responsibility for the HVAC unit not starting. I don't know exactly when the compressor failed since it was still working but not putting out full output.

Two HVAC companies verbally told me it was quite likely that the compressor failure was caused by the SureStart. However, they wouldn't put it in writing. There is nothing in it for them to put it in writing and it is hard to backup. If I were to take this to arbitration I would at least need written testimony from an expert that the SureStart caused the unit to fail. Additionally, my system is 13 years old and many HVAC repair places will tell you that is about the expected life of a heat pump compressor. Plus that particular compress was a known problem child (the company has gone out of business) and I was told I was lucky it lasted that long. Carrier had a service campaign to replace the outside unit with a different outside unit if the compressor had failed under warranty.

I decided my chances to recover any money from Tesla were slim so decided not to pursue arbitration. The SureStart may have just pushed it over the edge.