2xPowerwall whole house backup - HVAC sure start problem

[CrazyRabbit]

I want to start a 3 hp well pump which draws 16 amps, w/ LRA of 125 amps, so i'm going to go with 8 power walls which "should" be able to supply 240 Amps of start current. I have two 3 ton AC units and one 2 ton, will also be replacing my hot water heater with a Rheem hybrid after solar is installed.
Powerwalls will be paid by Apple/nVidia and federal tax credit.
I'm all electric, no gas in neighborhood. So generator would have to be propane or preferably diesel, my truck is diesel. Then on extended outage I'm at the mercy of being able to buy fuel. Diesel generators cost 20K plus installation, and require maintenance.

 

[af88]

propane tanks are not cheap, if you have natrual gas which most homes do that is the easiest and cheapest option for whole house backup. they sell sound dampening boxes you won't even know its on. With 8PW that should last you for some time if you dont run the AC and have a good solar system to charge it during the day.

 

[daniel]

At least your installer was honest with you and not worried about making a quick buck. When you get used to that humidity it sure is paradise

I've been to Florida and the Caribbean. The humidity here is nothing like that. My outdoor activity is mostly in the mornings (the wind comes up in the late morning or the afternoon and makes paddling on the ocean problematic) and it's not really humid at all. It can get humid later in the day but if you're under a roof with a good cross-breeze blowing through it just isn't all that bad. It's 3:30 p.m. right now and overcast and the humidity is 56%. Not Arizona dry, but not New Orleans humid either.

propane tanks are not cheap, if you have natrual gas which most homes do that is the easiest and cheapest option for whole house backup. they sell sound dampening boxes you won't even know its on. With 8PW that should last you for some time if you dont run the AC and have a good solar system to charge it during the day.

I had LP gas in rural North Dakota. The gas company must have owned the 500-gallon tank because I don't remember paying for it. I certainly could not have afforded to pay an awful lot for it back then. The house was all-gas except for lights, washing machine, and water pump. Gas heat, gas hot water, gas clothes dryer, gas stove.

 

[af88]

Sounds like you got it made. Kudos

 

[ArizonaJon]

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.

 

[Tk18]

Hard starts increase start amperage slightly.

‘hyper engineering video:

Would have been great had it worked...

 

[Tk18]

Could you share more information about the soft start device you used?

Spent 6 hours yesterday with an HVAC guys... the SureStart device went in, compressor started making a huge amount of noise... the contractor tried to debug... he tried a new capacitor that almost blue in my face, then compressor died... after more debugging found it overheated.., cooled it down with water... removed the SureStart, and an hour later compressor restarted... I have a very quiet carrier unit single phase compressor 17.9RLA/LRA 112... SureStart ss1b16-32n - Solar glass roof - 2PW.

I wish I had searched this forum earlier... Wasted time and money without talking about what might be the long term impact on my AC unit.

Seeing the number of threads about this issue, it is difficult to understand how Tesla would not provide better support for this... They should at least learn from all the cases they encountered with their customers and provide a KPNS for HVAC installers. It will damage the brand and slow adoption.

So, interestingly enough late today the ac turned on with 1.4kw from solar and 3kw form batteries (peak start) from solar: compressor had no problem starting without SureStart! So I guess I don’t need it... as far as there is some solar production, it should be fine...

of course at 3-3.4kwh, it can deplete the 2 people pretty fast (dropped 20% in 2hours running AC with partial low solar Complement)

based on the technical spec of the PW (https://www.tesla.com/sites/default.../Powerwall 2_AC_Datasheet_en_northamerica.pdf), it can provide 7kw for 10s peak... which should be plenty for the AC... not sure why some posts mentioned that Tesla said 3PW were needed to start the AC in full backup mode... was that to start? Or to run comfortably without running out of juice?

 

[af88]

The 10sec peak is a bit misleading. Sure they bump up the volts because Tesla doesn't even tell you what the nominal voltages of the cells are. Just like you can assume 100% charged is not 4.x volts per cell, think about storm watch mode. The increased wattage during that 10 seconds is a result of increased voltage not current. The only way your ac works is with additional current from the solar system without it, let's say at night when it's 90° out it won't start or worse trip to battery and potentially cause damage your compressor. Tesla also says up to a specific LRA is fine for two power walls, that's not true either.

Bottom line is they need to design these systems properly for homes with AC not relying on these soft start systems that may or may not work. Most of the solar companies are just out to get a buck. Either they are too ignorant because they don't know enough about the system or they are greedy seldo, you'll find honest ones.

 

[RKCRLR]

I just got 2 Powerwalls installed. I have a Carrier 5 ton heat pump with a 2 stage reciprocating compressor. 25.6 RLA and 130 LRA.
The first attempt of the SureStart installation resulted in the compressor not even attempting to start while connected to the grid. Tesla sent out their HVAC expert and he followed the wires back to figure out how to correctly install the SureStart.
The low stage now starts both when connected to the grid and with the Powerwalls in backup mode with no solar being generated.
I haven't tried running the AC long enough to see what happens when the system switches to high stage.

 

[af88]

If you have a variable speed or 2 stage you can probably get away without any assistanted start. You should have tested on PW without solar and see how it does by itself first.

 

[RKCRLR]

If you have a variable speed or 2 stage you can probably get away without any assistanted start. You should have tested on PW without solar and see how it does by itself first.

That was going to be my backup plan if they couldn't get the SureStart to work. I like having the extra margin the SureStart provides when there are other loads and the AC attempts to start.

 

[af88]

Makes sense, You are fortunate enough that you don't actually need the sure start, either your solar company new what they were doing and verified your compressor type or it was just pure luck. In any case you should be fine

 

[MIT_S60]

I recently had a 4-ton Lennox XC16 two-stage AC installed, which looks like uses a Copeland scroll compressor inside (109 LRA, 17 RLA). Any idea if the Emerson Copeland SecureStart will allow the AC to be backed up on two Powerwalls?
SecureStart™ for Copeland Compressors | Emerson US

I'm working with the HVAC company on getting the SecureStart installed while getting quotes to install the two Founders Series Powerwalls.

 

[nwdiver]

will also be replacing my hot water heater with a Rheem hybrid after solar is installed.

That's AWESOME

Take note that there are now two models out there. Not sure if Rheem is phasing out the old one but the new 'Proterra' is ~20% more efficient.

 

[af88]

Looks like a rebranded hyper unit.

To answer your question you need to know the aggregate load of the home. It's not just a matter of will x pw be sufficient and you will need assisted start. This is where you solar company should look at your MSP and subs to determine the totals before setting you up with a backup system.

 

[darhall993]

That's AWESOME

Take note that there are now two models out there. Not sure if Rheem is phasing out the old one but the new 'Proterra' is ~20% more efficient.

Nwdiver is right on the Rheem heat pump Hot water heaters, amazingly efficient. I have three of these and one of them in a rental property with heavy usage. I have the first gen units not the Proterra’s, if the new units are ~20% better that’s incredible. The 65 gallon units sips power at 4.5watts just maintaining 120 degree temps, remote control via WiFi for rental or remote locations is fantastic

 

[Tk18]

I just got 2 Powerwalls installed. I have a Carrier 5 ton heat pump with a 2 stage reciprocating compressor. 25.6 RLA and 130 LRA.
The first attempt of the SureStart installation resulted in the compressor not even attempting to start while connected to the grid. Tesla sent out their HVAC expert and he followed the wires back to figure out how to correctly install the SureStart.
The low stage now starts both when connected to the grid and with the Powerwalls in backup mode with no solar being generated.
I haven't tried running the AC long enough to see what happens when the system switches to high stage.

How did you manage to get support so quickly? Which area? (I’m I the Bay Area)

 

[RKCRLR]

How did you manage to get support so quickly? Which area? (I’m I the Bay Area)

I'm east of Sacramento. I don't think the Tesla installers are as busy in Sacramento as they are in the Bay Area.

 

[Tk18]

So, interestingly enough late today the ac turned on with 1.4kw from solar and 3kw form batteries (peak start) from solar: compressor had no problem starting without SureStart! So I guess I don’t need it... as far as there is some solar production, it should be fine...

of course at 3-3.4kwh, it can deplete the 2 people pretty fast (dropped 20% in 2hours running AC with partial low solar Complement)

based on the technical spec of the PW (https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall 2_AC_Datasheet_en_northamerica.pdf), it can provide 7kw for 10s peak... which should be plenty for the AC... not sure why some posts mentioned that Tesla said 3PW were needed to start the AC in full backup mode... was that to start? Or to run comfortably without running out of juice?

Update: finally got the visit of a Tesla service guy: he did not fix anything because he was alone and would need a small crew to efficiently pinpoint the issues and address them, but he explained that SureStart are supposed to be installed by the Tesla folks installing the batteries: it should not be the responsibility of the home owner...

He also explained that, after installing the device, it takes about 12 starts cycles for the device auto calibration ... after that the AC should not make more noise than usual... right after install, it is expected the AC unit will make a lot more noise.

I hope this helps!

 

[RKCRLR]

I just got 2 Powerwalls installed. I have a Carrier 5 ton heat pump with a 2 stage reciprocating compressor. 25.6 RLA and 130 LRA.
The first attempt of the SureStart installation resulted in the compressor not even attempting to start while connected to the grid. Tesla sent out their HVAC expert and he followed the wires back to figure out how to correctly install the SureStart.
The low stage now starts both when connected to the grid and with the Powerwalls in backup mode with no solar being generated.
I haven't tried running the AC long enough to see what happens when the system switches to high stage.

I thought I'd post a followup to this. I initially thought the SureStart was working correctly after the 2nd installation. But it turns out my AC was working intermittently and started throwing error messages. I won't go into the gory details of going through a heat wave with a malfunctioning AC unit and waiting weeks for Tesla to address it.
I decided to take matters into my own hands and contacted Hyper Engineering directly. It turns out my compressor is wired to allow reverse running and SureStart is not compatible with it. They said this is the first system they've come across with this "fairly recent technology" (my outside unit was installed in 2008).
I've told Tesla this and asked them what their plan forward is but I haven't heard back.
I've attached a description of the system that Hyper Engineering sent to me.