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Told by Tesla I can't run AC on Powerwalls

stevemc

Member
Sep 22, 2018
82
64
California
I received an estimate from Tesla for a 12kw + 2 Powerwalls system. But I was told that the Powerwalls cannot support the air conditioners. I have 2:

3 Ton: RLA 24.4, LRA 140.0
4 Ton: RLA 16.0, LRA 82.0
Has anyone ran into this issue or have any idea on how I'll be able to support having air conditioner in case of a power outage?
 

Raechris

Member
Nov 21, 2017
643
298
Boston
I just had two PW installed and they handle mine fine so it must be the size and running amperage. I think each PW can handle 30 amp, so maybe with more PW you can run them? They install a unit that provides initial surge capability for AC units.
 
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boaterva

Supporting Member
Apr 2, 2016
7,565
3,736
Northern Virginia, USA
I have 3 PWs and a standard AC for NoVa suburban home... they also installed the slow-start box in my unit (only one AC compressor).

It may be the fact you have 2 PWs, but as was said, more PWs can handle about anything. Surprised they didn't say how many you would need to handle the load.
 
Jun 22, 2017
526
337
Bay Area, California
I have same setup as OP (2PW, 3T+4T A/C). Same story--cannot backup. Strong technical justification: compressors not compatible (non-scroll type) with soft start electronic add-ons. Just one A/C will choke.

Solutions:
1. The PW system can monitor A/C draw and offset it when the grid is up. Wrap the current transducers (CTs) around the A/C conductors (wire). The electrician will likely do this. Just mention it to confirm. This is how it is done for me. Works good. I will get heat during the winter as the rest of the HVAC system is on backup. Downsides: If the grid is down, the HVAC system blower will kick on to attempt to cool on a hot day, which circulate air, which acts like PG&E's SmartAC program if you are familiar with it. That is okay when you are home for a cooling effect; however, if not home, the 200W blower will run and not stop given worse cases scenarios (smart thermostat thinks you home, or home and should intervene to conserve energy during a blackout). Half solution, but probably the most sensible unless you want to spend more.
2. Replace the A/C units with scroll type or ones with built-in soft start electronics at the tune of $15,000+.
3. Add more PWs to handle the surge for LRA of 140A. All 4 ton units are about LRA 140A unless equipment with soft starters. If spending money, I recommend this.

Like others said, A/C deplete batteries quick. They run about 8kW when running. That's two hours of run-time before I hit my 40% reserve. The run-time was spread between 4-6pm during peak, and the shortfall 6-9pm came from the grid... a typical heat advisory day near the car factory.

3F4D5245-A1DE-4434-8C7E-E8071A4605CB.png
 
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miimura

Well-Known Member
Aug 21, 2013
6,186
5,778
Los Altos, CA
LRA is the main problem. Soft starter can help this but I don't know how much they actually bring down the startup surge amperage. The Powerwalls are 30A surge each, so you can see why 140A surge is not workable.
 

TSLA Pilot

Active Member
Mar 12, 2013
1,707
2,332
United States
Question: How high a SEER does one have to reach to be assured of getting a scroll compressor that will work with Powerwalls?

Long Story.

We have supposedly "EPA Energy Star" HVAC units, but it's turned out that our HVAC contractor (and the builder) can lie as long as the day is long so we'll have to check the AHRI website to know for sure:

www.ahridirectory.org

Examples of just how badly we've been robbed:

1. Submitted and city-approved building plans called for 8 tons of cooling capacity. They installed 6 tons. (We actually have it better than some; a neighbor's city-approved plans require 9 tons; she also got 6 tons.)

2. Swapped the locations of the air handlers--5-ton unit where the 3-ton is supposed to be, and vice-versa. (But they actually installed 4- and 2-ton units. Perhaps the HVAC installer had a boat payment coming due?)

3. Ducting plans: thrown out the window. With the swap of the air handlers, the Manual D Ducting Plan they submitted for approval was ignored; they seemingly made up the ducting plan up as they went along, or so it appears. And there are missing returns and registers as well.

4. Furnace constantly "short cycles" since it has far too little airflow; safety overheat system kicks it off-line as temps exceed 160F just aft of the plenum . . .

5. Is anyone surprised that the HVAC systems can't cool the home properly? Yes! The builder (and HVAC contractor, both scum) report that it's our fault we have all these issues. They're all due to the Nest Thermostats we installed(!) and because of our insufficient window coverings and lack of furniture! (The home remains vacant because it's uninhabitable: too friggin' hot, and it turns out the trusses are "fake" as what's installed doesn't match the PE-stamped paperwork Oooops. The City of Phoenix is on a recorded telcon advising that the "home should never have passed inspection." So it also has a fraudulent Cert of Occupancy, but they won't help us in any way. Nor will they visit any other home in the neighborhood to inspect theirs now either, despite promising to do so.)

It's been an ongoing 3-year nightmare with an expensive, brand new home, but we've had verbal estimates of some $40k to rip out these incorrect systems and install the proper equipment. If we have to do that, we may as well get units that will work with Powerwalls . . . .

Long Story Complete.
 
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hodad66

Supporting Member
Apr 26, 2019
104
58
Indialantic, Fl
It's the LRA that is important. I have 2 Powerwalls & the LRA (one unit) had to be 56 or less.
Also MUST be scroll compressor. With 3 Powerwalls the LRA can be higher but scroll is a must!
 

StarLog

Supporting Member
Mar 11, 2019
434
181
MCO
By one of those portable A/C units from Home Depot or Lowes.
We have one for our masterbed room when power drops, we plug into 120ac and go
 
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hodad66

Supporting Member
Apr 26, 2019
104
58
Indialantic, Fl
Most inverter driven systems should be fine.

It doesn't have to be a scroll compressor. A rotary compressor is would probably be fine.

I had an AC (rotary) with an LRA of 58 and they wouldn't OK a whole house
install. I ended up spending 9K for a new scroll unit with an LRA of 55.2 before Tesla's
tech team would OK the full house install.
 
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Dan123

Member
Jun 19, 2018
451
297
Miami
I received an estimate from Tesla for a 12kw + 2 Powerwalls system. But I was told that the Powerwalls cannot support the air conditioners. I have 2:

3 Ton: RLA 24.4, LRA 140.0
4 Ton: RLA 16.0, LRA 82.0
Has anyone ran into this issue or have any idea on how I'll be able to support having air conditioner in case of a power outage?

It is the LRA number that's a problem. The 82.0 LRA may work, if it is possible to install a sure-start condensator.

Alternatively, you may consider replacing the 3 ton unit (if it is old) with a smaller (2 ton) variable speed unit.
 
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Dan123

Member
Jun 19, 2018
451
297
Miami
3. Add more PWs to handle the surge for LRA of 140A. All 4 ton units are about LRA 140A unless equipment with soft starters. If spending money, I recommend this.

Like others said, A/C deplete batteries quick. They run about 8kW when running. That's two hours of run-time before I hit my 40% reserve. The run-time was spread between 4-6pm during peak, and the shortfall 6-9pm came from the grid... a typical heat advisory day near the car factory.

View attachment 441671

I have a 4-ton AC with 22 LRA.
 
Dec 2, 2017
358
339
Arizona
Our air conditioning units were pretty old and inefficient, so I proactively replaced them with Lennox XC20 variable speed units so the Powerwall system we are installing could back them up. LRA is only 20A. They are more expensive units that won’t ever fully pay back even with the higher efficiency, but they can be backed up and make the house more comfortable than traditional units since they circulate the air more consistently.
 
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d21mike

Active Member
Aug 28, 2017
1,097
722
Torrance, CA 90503
I ordered the same system. 12k and 2 PowerWalls. I was told my house with 1 AC (below) is fine for Whole Home Backup.

Here is my AC. Can anyone tell me the size as it relates to this thread?

IMG_0969.jpeg
IMG_0968.jpeg
 

cwied

Member
Jan 13, 2015
869
617
San Mateo, CA
I ordered the same system. 12k and 2 PowerWalls. I was told my house with 1 AC (below) is fine for Whole Home Backup.

Here is my AC. Can anyone tell me the size as it relates to this thread?

View attachment 442028 View attachment 442027

It's the LRA number that matters. The maximum for two Powerwalls would be 60A. Will they install a soft-start device on your AC? If not, it won't start with just two Powerwalls.

FWIW, Tesla put my AC on the backed up panel even though it has no chance of starting during a power outage (I have whole-house backup). I wouldn't count on things working just because Tesla says so.
 

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