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2xPowerwall whole house backup - HVAC sure start problem

CrazyRabbit

Member
Apr 21, 2020
447
154
Fort Worth TX
in a nut shell you need more powerwalls then you think to start motors with everything else running... i wish powerwalls had twice the starting capacity, but they don't. so i'm sizing my powerwalls to start my well pump (3hp) times two, 4.1 should start my well pump so i'm going with 8. so my well pump should start while starting a air conditioner at the same time with the hot water heater running.
 

af88

Member
Sep 28, 2019
258
48
Cali
The moral is educate yourself. PW is not cheap, measure your load and get the data first than size appropriately unless you have unlimited budget. There is no one size fits all.
 

Vines

Active Member
Jul 20, 2018
2,081
2,520
Silicon Valley, CA
Believe me, I have enough arguments at work, don't need to add any with respect to contractors. I will definitely point this out though in the planning process. I am glad that brett's system went well. We need his time to answer basic questions from non-electricians! :)

Exactly, don't purposefully set someone a trap for your installer in the contract phase, where you knowingly don't point out a design error, then try to get a free Powerwall out of it later. No one has time to litigate that. Handle this on the front side.

Also, don't just measure one leg if you are going that far. Powerwalls do not have any auto-transformer, or other way to share load between L1 and L2. If either leg is more heavily loaded with demand at the moment of compressor startup, that is your limiting factor. In the older PW1 design there was a Solar Edge auto-transformer which would allow more imbalance, but that system was limited in its own ways.

Also, if there is a significant power outage, and the Gateway does not switch over fast enough all your loads are going to restart. Often this startup can cause additional issues by throwing everything at the PW at once, where a smoother transition wouldn't have overloaded it, especially if you are on the edge.
 

af88

Member
Sep 28, 2019
258
48
Cali
This thread should serve as a cautionary tale for all installers who don't do their due diligence up front with onsite measurements and go off assumptions and specs.

I would not expect the average customer to have the know how or even have the proper accurate equipment to know what to look for, but if you do, certainly measure, have the data on hand when discussing the details with the installer and get everything documented in the contract.

There should be no surprises if all parties do their job. I learned the hard way but hopefully sharing what I posted here will save everyone the same headache. 2xPowerwall whole house backup - HVAC sure start problem
 

BIC1

Member
Feb 19, 2020
90
16
Missouri USA
Enough to make my head spin for a while. New construction. I have a 12.1kW PV system with two AC in a reverse 1.5 story with walkout basement. The lower level doesn't really need the 2-ton AC (but does need the gas furnace). I got it more for dehumidifying, but then it overcools so I just use a regular portable dehumidifier. I do need the main level 3-ton AC, June through September.

Both Carrier 24ACB7 models have two-stage scroll compressors. Specs are:

24ACB724A0031030 (2-ton)
RLA 10.3
LRA 52.0
FLA 0.7

36ACB736A0031030 (3-ton)
RLA 16.7
LRA 82.0
FLA 1.2

I have one PW2 and due to some less than clear advertising by Tesla, I realized I need a second PW, likely to be installed next month.

I was told by a Hyper Engineering distributor that Tesla installs the Hyper SureStart on most every PW install that includes AC. I'm using a third party installer that I don't think is aware of that. Anybody know about this?

SureStart website claims about a 70% reduction, bringing my 82 LRA down to 25 amps, which should work OK with my 56 amps of twin PWs. I plan to install the SureStart on both, even though we don't really use the downstairs AC and would definitely have it shut off in an outage.

I do have a Garaventa elevator, The company says the solid-state motor limits the in-current so no worry. I could certainly make sure the rarely used elevator doesn't run with the AC running. I'll have to carefully manage all the load at night anyway, turning all AC off if need be and sleeping downstairs in the guest rooms.

Anybody see any potential problems here?

Off-topic: Tesla re-did the PW web page; don't see the price anymore. Has the price changed recently? Thanks.
 

af88

Member
Sep 28, 2019
258
48
Cali
Not sure how much more clear it could be.

Stop making assumptions based on specs and measure the loads of you don't want any surprises. Can't help those that don't want to help themselves!
 

BIC1

Member
Feb 19, 2020
90
16
Missouri USA
You're assuming we all have Fluke meters. And, we can't measure the SureStart effects until we have them installed. For now, I have to work with specs. Thanks.
 

af88

Member
Sep 28, 2019
258
48
Cali
You don't have to assume anything, tell your installer to collect the data.

Or, pony up and buy the equipment if you want to get informed. Or rely on specs, assumptions and go off a hope it all works.

You can lead a horse to water... well you get the rest.
 

Vines

Active Member
Jul 20, 2018
2,081
2,520
Silicon Valley, CA
Enough to make my head spin for a while. New construction.

I have one PW2 and due to some less than clear advertising by Tesla, I realized I need a second PW, likely to be installed next month.

I was told by a Hyper Engineering distributor that Tesla installs the Hyper SureStart on most every PW install that includes AC. I'm using a third party installer that I don't think is aware of that. Anybody know about this?

Anybody see any potential problems here?

Off-topic: Tesla re-did the PW web page; don't see the price anymore. Has the price changed recently? Thanks.

If you are going by the numbers understand that your certainty is not 100% but better than nothing. Also "Up to 70% " is exactly how it sounds. Older compressors or different models will respond differently or not at all. Sounds like yours is pretty new equipment.

If you know how to read your utility meter it will tell you the total draw at at any given time. You don't have to use a multimeter, or oscilloscope lol. (BTW, if your system designer brings an oscilloscope to your house and asks if they can camp out at dawn until dusk to measure your AC draw, all before you have signed a contract and money changed hands he's either got way too much time or is learning from this thread, don't hire them)

Understand that your baseline load at the time your AC kicks on needs to be subtracted from the available amps the PW can supply. If you ignore this it means you could run your AC, as long as you aren't running your house at the same time. Most people don't accept this as "working"

As pointed out earlier AC is a huge drain on your PW resources. Not sure how often you might have an outage event when AC is critical to you, but 3 hours of the larger AC is an entire Powerwall drained to 10%. Manage your expectations appropriately, if your PV isn't recharging the Powerwalls then you have an issue with running much AC regardless.

Also, your overall system size demands 2 Powerwalls, unless it was a very recent system (Frequency shift partial production enabled inverters, AKA Rule 21 Capable). Otherwise your issue will be that your PV system is too large for a single Powerwall in a backup event. It will never or almost never charge without fussing.

Powerwall can only charge at 5kW max. If you are in backup mode and have 12 kW of PV pumping into the backup system what does the Microgrid do with the other power? If you are using your electric dryer now, then great your Powerwalls will charge. Otherwise you will have too much PV for the PW to safely charge. The PV and PW will be constantly fighting each other, until you turn on house loads large enough to suck up 7kW.

Then the Powerwalls can charge correctly from 5kW of your solar, because the other 7 kW (assumed) needed somewhere to go now that the grid is down. The Powerwalls will frequency shift your microgrid to approx. 66 hz and this will turn off all solar production. Until you turn on 7 kW of load you will get no charge in your Powerwalls. Sometimes I have heard of customers having to manually flip the breaker on one PV inverter or string to alleviate this problem with a 1 Powerwall system and PV inverters that have no option for partial curtailment.

Newer inverters (within the last year or 2) can recognize a partial curtailment signal (62 hz approx) from the Powerwall, and throttle the pv production when needed. This gives the Powerwall some control over the generation power to be other than on or off.

Its a good thing you are getting a second one for sure but just make sure the baseline load in your house is taken into account when deciding if the Powerwalls will fire your AC. Regardless, if the Sure Start works with your AC compressors, its a good thing to have installed. Might be a good time to have the HVAC serviced as well
 
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af88

Member
Sep 28, 2019
258
48
Cali
Understand you are getting advice from a company who had to rip out a whole system b/c they didn't measure loads properly or did their due dillgence.

Who said you have to camp out to measure loads at dawn? I guess turning on the same lights or appliances you would normally at night is too much of a daunting task or concept to understand.

As the saying goes, lead a horese to water...
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
10,896
12,619
Riverside Co. CA
Understand you are getting advice from a company who had to rip out a whole system b/c they didn't measure loads properly or did their due dillgence.

Who said you have to camp out to measure loads at dawn? I guess turning on the same lights or appliances you would normally at night is too much of a daunting task or concept to understand.

As the saying goes, lead a horese to water...


Im not sure you realize how combative your posts are. As someone who has zero skin in this discussion, when I read your posts, I read someone who is frustrated, but also lashing out at almost everyone else. Maybe thats intentional, but if not, thats how the posts come across.

Only mentioning it in case its "not" intentional.
 

Vines

Active Member
Jul 20, 2018
2,081
2,520
Silicon Valley, CA
OP, nothing personal but I don't have time for more of your posts. You can lash out at your installers again and get that free Powerwall. Let the rest of the community know how it goes.

I have made mistakes in the past, and luckily as a human I can admit that and show how its resolved. In this case, our company paid for a mistake one of the designers made, it does happen regardless of your approach. The customer was happy enough with our work and moral standing that they ordered the larger system with just a phone call.

This is the cutting edge of battery backup design developing over the last 2 years and not everyone has all the answers. We suspect the issue was the design team wasn't measuring peak on both L1 and L2 that caused the issue in this case, as one was much more heavily loaded in the 30A 240V elevator feed. 2 Powerwalls seemed appropriate to the designer and we learned something there, which I shared freely here. Posts like yours make me less likely to share anything.

Others appreciate my advice, if you don't feel free to ignore it. Casting me and mine as other than a competent design professional is not a call you have any right to make.
 
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af88

Member
Sep 28, 2019
258
48
Cali
OP, nothing personal but I don't have time for more of your posts. You can lash out at your installers again and get that free Powerwall. Let the rest of the community know how it goes.

I have made mistakes in the past, and luckily as a human I can admit that and show how its resolved. In this case, our company paid for a mistake one of the designers made, it does happen regardless of your approach. The customer was happy enough with our work and moral standing that they ordered the larger system with just a phone call.

This is the cutting edge of battery backup design developing over the last 2 years and not everyone has all the answers. We suspect the issue was the design team wasn't measuring peak on both L1 and L2 that caused the issue in this case, as one was much more heavily loaded in the 30A 240V elevator feed. 2 Powerwalls seemed appropriate to the designer and we learned something there, which I shared freely here. Posts like yours make me less likely to share anything.

Others appreciate my advice, if you don't feel free to ignore it. Casting me and mine as other than a competent design professional is not a call you have any right to make.

You made a mistake and didn't learn anything form this discussion.

No one asked you to post here, you decided to participate in this thread. You don't like being called out for your mistake and level of competence, than don't discuss it.

You made the mistake by not measuring loads, your company screwed up, that is fact. Learn from it and measure loads next time, simple.

Did you learn anything at all from this thread, No, you just gave another user advice based on speculation of specs. Perhaps you should stop spouting off bad information. People don't have time to have their entire system ripped out so installers like you can come and charge them for double the original PW qt to get it right the first time. Apparently you think people have time to deal with improper installs.

The whole point of this thread is to bring awareness to measure and collect the right data, rather than relying on specs and hopes it all works out.
 

RKCRLR

Member
Apr 13, 2020
481
202
Garden Valley, CA
Does Tesla include the SureStart(s) in the overall price or is it added on extra depending on whether they're used or not? Thanks.
It was included in the "package" installation price for me, it was not specifically called in the contract. I'm now waiting to see what they do since it isn't compatible with my compressor.
 

af88

Member
Sep 28, 2019
258
48
Cali
Here is a little food for thought all soft starters are rated for 50-60Hz.

The default powerline frequency is 65Hz even if it's reduced to make the inverter happy it is out of spec for the soft start.

Will be doing some testing and working with a company to possibly make a PW variant compatible sure start. Stay tuned.
 

Left coast

Member
Apr 11, 2019
37
31
Ventura
For those who think they can't run their AC on 2 powerwalls, there is a solution. I have a 5 ton AC unit. It had a start up current of 147 amps - way too much for my 2 powerwalls. Yesterday they installed a Micro-Air EasyStart device (ASY-368-X48). The start up current was reduced to 32 amp. Note this is not a Tesla system installation. I used a 3rd party that is certified for Tesla powerwalls.

Also my SolarEdge monitoring and TEG are working. There is no conflict. But I am using a hardwired Ethernet connection, not WiFi.
Care to share a bit more about this? Is this a universal device? How is it different than the sure start Tesla installs? What did it cost to install? I have the same issue and want to have an alternative ready. Although they did misrepresented my install as well I doubt they’ll gift me another powerwall. Maybe I can get them to cover this device?

thanks!
 

af88

Member
Sep 28, 2019
258
48
Cali
I have one, it is only slightly better performance than sure start. Depending on your measurements and loads it isn't going to make a huge difference. It also has the same spec for operating frequency. Cost is relatively the same as hyper unit.
 

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