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Told by Tesla I can't run AC on Powerwalls

d21mike

Active Member
Aug 28, 2017
1,097
722
Torrance, CA 90503
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.
They did not say anything about a soft-start device. I like the idea of having it on backup because I want to pull power from the Powerwalls during my PEAK period. Well as much as I can. My current PEAK is 2-8pm. In 2022 (if not sooner) it will be 4-9pm. Hoping that daily my Power Walls will charge to 100% from Solar and then I would use them thru the PEAK period. I can use credits as well but was thinking i would draw from PW. But it was a wait and see how much I use for other things. My AC here in SOCAL is about 3-4 months.
 
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woferry

Member
Mar 4, 2019
400
471
San Jose, CA
The Powerwall can offset the AC usage even if the AC isn't a backed-up load. It's just a matter of how the grid-side CTs are configured w.r.t. what house loads they measure and what they don't, the PW will (up to its inverter output and battery capacity) power any house load the Gateway measures, regardless of where the circuit connects. But the AC would only get power during a grid outage (provided the PW can provide enough power to start the AC) if it is a backed-up load.
 
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Reactions: Dave EV
Jun 22, 2017
526
337
Bay Area, California
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
Your LRA is 115A. A soft starter will lower the starting amperage to 35-46A. Two PWs are said to have a max peak load of just under 60A (read 58A by one poster). I would recommend that you double check by calling Tesla's Design Hotline yourself. Tesla Energy Advisor told me my A/C was okay, but down the road Tesla Design Hotline said no. What I did not do was call a particular soft starter company (i.e. Hyper Engineering) to see if their soft starter was compatible. My A/C units are 15 years old and did not pursue it anymore.
 
Dec 2, 2017
358
339
Arizona
When I was in talks with Tesla about backing up our new Lennox system with only 20 LRA per unit they implied there was even more to it than LRA. Still not sure what - maybe power factor? In any case I sent them the spec sheet and it worked out, but it would be nice if they published all the criteria.
 

Chancellor32

Member
May 10, 2018
711
479
Queen Creek, AZ
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?
With a sure start if you can get the LRA down to 58 or less than the two PW can work off grid capability. In terms of if grid is active then 1-2PW can run your ac despite them telling you they cant. I would ask design team to see if with a sure start the AC can be backed up by 2PW's.
 

Dan123

Member
Jun 19, 2018
451
297
Miami
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.
They did not say anything about a soft-start device. I like the idea of having it on backup because I want to pull power from the Powerwalls during my PEAK period. Well as much as I can. My current PEAK is 2-8pm. In 2022 (if not sooner) it will be 4-9pm. Hoping that daily my Power Walls will charge to 100% from Solar and then I would use them thru the PEAK period. I can use credits as well but was thinking i would draw from PW. But it was a wait and see how much I use for other things. My AC here in SOCAL is about 3-4 months.

Being on the backed-up panel doesn't matter for this purpose. You will still be able to "feed" it from the Powerwall during peak periods, even if the AC is not backed up.
 

d21mike

Active Member
Aug 28, 2017
1,097
722
Torrance, CA 90503
Being on the backed-up panel doesn't matter for this purpose. You will still be able to "feed" it from the Powerwall during peak periods, even if the AC is not backed up.
Apparently I need to learn more. This is a bit confusing. A youtube video seem to show what you are talking about but the person was confused why it was actually working. I am not that concerned during a power failure to use the AC. Might be nice but we do not have that many so I could actually just leave the house if not sleeping. So, would this work the same for my Tesla Car? I.E. It can pull from PW if needed but it would not in the case of a power failure because I normally would not power my car during a power failure. Unless last a long time which almost never happens.
 
Jun 22, 2017
526
337
Bay Area, California
Apparently I need to learn more. This is a bit confusing. A youtube video seem to show what you are talking about but the person was confused why it was actually working. I am not that concerned during a power failure to use the AC. Might be nice but we do not have that many so I could actually just leave the house if not sleeping. So, would this work the same for my Tesla Car? I.E. It can pull from PW if needed but it would not in the case of a power failure because I normally would not power my car during a power failure. Unless last a long time which almost never happens.
Similar situation with car chargers. There are three (3) options with any load: (1) Backed-up, (2) Monitored by PW, not backed up, and (3) Completely separate, not monitored & not backed-up. The Tesla Gateway has limited number of sensors to monitor individual circuits of grouped loads, so typical/convenient ones are house subpanels, pool subpanel, A/C, EV charging, water wells, etc. General recommendation from Tesla electrician is not to backup the Tesla Wall Connector because "it will drain the PWs." The Tesla Car does not have the ability to avoid being charged during a power outage by command. The current solution I elected to do was charge the EV using Option (3), and a NEMA 14-50 outlet using Option (1). I think option (2) for EV charging is as effective as most EV charging is done during off-peak when PW is on standby anyways due to Time-Based Controls, if you choose this popular option.
 

rolferic

New Member
Mar 3, 2020
1
0
Auburn
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?

Transformerless inverters typically do not have the surge capability to start a 1-ph motor load such as compressors unless it is small (mini-split have low surge). If you want to run large ACs, a transformer-based inverter will have more surge capability. Then there's the question of storage. Will you have sufficient solar/storage to run those large loads for the period you want?
 

bob_p

Active Member
Apr 5, 2012
3,660
2,786
We have 4 PowerWalls - and 3 HVAC systems (2, 4 and 5 ton air conditioners).

When off-grid, the 2 ton would run and only one of the 4 and 5 ton units would run. The 3rd unit would fail to start.

We've added "hard start" upgrades to all 3 units, and can now run all 3 systems off our 4 PowerWalls when operating off grid.

With a 2 PowerWall system, it might be tight to run a 3 ton and 4 ton unit at the same time (even with hard start to avoid the surge at startup). To avoid tripping the system during an outage, may be better to keep one of those units connected only to the grid.

Or, add a 3rd PowerWall. Tesla's website used to recommend one PowerWall per 4 KW of solar panels. Not only should this provide enough power to support both air conditioners, it should also provide enough battery storage to fully capture all of the solar power being generated.
 

Dukeybootie

Member
Nov 12, 2015
201
119
United States
@NathanielHrnblwr

I have a Carrier scroll compressor unit with an LRA of 109 and had a SureStart installed a couple weeks ago. It started up easily and ran smoothly when I performed my off grid test. I have a 20 panel PV system and 2 Powerwalls.

My usual baseline daytime home draw is < 1 kW so I'm sure that helps. Maybe give the SureStart a look if you haven't already?
 

JayClark

Member
Aug 6, 2019
223
181
Arizona
We have 4 PowerWalls - and 3 HVAC systems (2, 4 and 5 ton air conditioners).

When off-grid, the 2 ton would run and only one of the 4 and 5 ton units would run. The 3rd unit would fail to start.

We've added "hard start" upgrades to all 3 units, and can now run all 3 systems off our 4 PowerWalls when operating off grid.

With a 2 PowerWall system, it might be tight to run a 3 ton and 4 ton unit at the same time (even with hard start to avoid the surge at startup). To avoid tripping the system during an outage, may be better to keep one of those units connected only to the grid.

Or, add a 3rd PowerWall. Tesla's website used to recommend one PowerWall per 4 KW of solar panels. Not only should this provide enough power to support both air conditioners, it should also provide enough battery storage to fully capture all of the solar power being generated.

My experience is the same as bob_p. We went to 4 powerwalls to support 3 & 4.5 ton AC units here in Arizona. I had sized it at four PWs simply because of the amount of capacity I would need to be able to run the AC still (in a limited/controlled manner) during our summer utility peak periods. When I modeled our kW power usage, if I had less than four PWs I couldn't have "zero'd" out my utility peak period power usage without demand charges once the PWs ran out of juice, or otherwise without being too hot in the summer when it's 110deg outside for weeks on end. The 4 PWs have supported our two relatively large AC units with no problems. Tesla did install "Softstart"s of some kind on the AC units.
 

bob_p

Active Member
Apr 5, 2012
3,660
2,786
Our HVAC company installed the hard start. They said we probably only needed it for the 4 and 5 ton units - the 2 ton unit would probably be OK - but we had them install the hard start on it too.
 

bob_p

Active Member
Apr 5, 2012
3,660
2,786
What they didn't mention is the need for sure/soft/hard start upgrades to avoid the surge when the air conditioner starts up.
 
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boaterva

Supporting Member
Apr 2, 2016
7,565
3,736
Northern Virginia, USA
Tesla installed the start device on our AC unit (one) when the PWs were installed. Weird they aren’t taking that into consideration and doing the same. Has this practice changed?
 

Flyguy

Member
Aug 17, 2017
297
169
94062
Tesla installed the start device on our AC unit (one) when the PWs were installed. Weird they aren’t taking that into consideration and doing the same. Has this practice changed?
Looking at the LRA numbers on their website, I don’t think anything has changed. I assume they are just trying to not muddy the waters by explaining the soft start install on scroll type compressors.
 
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TSLA Pilot

Active Member
Mar 12, 2013
1,688
2,312
United States
A heads up. I noticed Tesla has a (new?) Powerwall FAQ that includes a discussion of Compatible Central Air Conditioners

What does Powerwall Backup | Tesla

Note: Posted here instead of new topic.

Wow, that was a really helpful post--thank you for sharing that info. We'll be getting two new HVAC systems in a few months or years so this is very important info.

As expected, it's another blow to our home builder as he's supposedly an Award-Winning builder with web pages filled with his DOE and EPA trophies--yet he installs the cheapest HVAC equipment he can find. So how does he get away with it?

He's very skilled at cheating . . . .

A bit off-topic, but submitting "X" for City approval for construction (which called for 8 tons of cooling), and then installing and building "Y" (with just 6 tons of cooling), is just a part of it. Other examples: Manual J, S & D documents which state the home has no doors (not a single one!), oh, and it faces the entirely wrong direction, among other gross errors.

Did the City of Phoenix PDD catch any of this? Nope. But they sure accepted all his permit and inspection fees (and perhaps a little "extra something" for the on-site inspectors, but that's 100% pure speculation, of course;-).

Just part of a nearly 4-year new home nightmare.
 
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