Powerwalls + Air Conditioning

[cr0ntab]

Hey All,

I recently got 2x powerwalls installed for the purpose of a whole home backup that was capable of running my AC.

I installed a SureStart in the AC unit as well to reduce inrush current demands.

I've been running a few tests but no matter what I do I can't get the powerwalls to fire the AC unit.

I get a huge voltage drop in the house when the AC kicks in and the powerwalls are in backup mode.

Various devices not on a UPS will restart (like my google homes).

In my testing I've gone so far as to turn off all the breakers, except the AC condenser, and then manually trigger the contactor. Voltage sags and the SureStart errors out for low voltage.

With line power on the house I've measured a 6kW (~25A) draw spike when the AC fires up. This is well within the 10kW/14kW max for two powerwalls.

I checked the wiring on the powerwalls and each one has a 30A breaker with #10 wire, which seems fine?

The AC has an 8-2 NMB wire that goes over to it, which should be enough, as the name place calls for a minimum ampacity of 32A.

So for me at least, all signs are pointing at the powerwalls.

Have any of you folks successfully fired up your AC units running in backup mode?

 

[boaterva]

Is your AC ‘built for Solar’? Don’t have my panels or PWs yet, but my Lennox AC compressor has a sticker that says it’s ‘Solar ready’ and will only take 15 Amps under single phase when using Solar. No idea what this means precisely or how you hook it up, need to research more. Sounds like the normal connection is like yours, as it says 240 VAC 30 Amps.

Edit; your calculations seem right if the absolute max is the 25 Amp max theoretical.

 

[electracity]

Should work, I've used a surestrart like device running AC in a vacation house off grid. You can probably get some free consulting from the company that makes the surestart.

Are you allowing time for the surestart to charge before engaging the compressor?

 

[Dan123]

What kind of AC unit is it? How many tons, make/model? Is the air handler and compressor on the same circuit breaker? What size circuit breaker do they use?

How did you measure the draw 6KW spike on the house?

Maybe the surestart thing is not working properly.

 

[arnolddeleon]

Make sure both Powerwalls are actually on. First few days for me I had one accidentally off. It wasn't obvious.

 

[Lloyd]

Make sure both Powerwalls are actually on. First few days for me I had one accidentally off. It wasn't obvious.

If it is not obvious, how do you verify that all are providing power?

 

[Shygar]

If it is not obvious, how do you verify that all are providing power?

Try to draw a load of more than 5kW. It should be up to 10kW with 2 PW's.

Instead of backup mode have you tried self powered to see if it behaves any differently? Originally I noticed that my single powerwall only outputs 1.7 kW in backup mode, but in self powered or TOU mode it outputs 5kW. Maybe when you say you are on backup mode you mean backup only mode? If that's the case then the max you can get is 3.3 kW I think. Try setting it to self powered and put your reserve at 100%.

 

[MP3Mike]

If it is not obvious, how do you verify that all are providing power?

I would think you could turn the circuit breaker for each Powerwall off to make sure the other one is providing power. We have seen at least one report that the second Powerwall wasn't provisioned correctly and wasn't providing power.

 

[cr0ntab]

Is your AC ‘built for Solar’? Don’t have my panels or PWs yet, but my Lennox AC compressor has a sticker that says it’s ‘Solar ready’ and will only take 15 Amps under single phase when using Solar. No idea what this means precisely or how you hook it up, need to research more. Sounds like the normal connection is like yours, as it says 240 VAC 30 Amps.

Edit; your calculations seem right if the absolute max is the 25 Amp max theoretical.

I doubt it's "solar ready" it's 12 years old, so probably not a huge selling point back then

Are you allowing time for the surestart to charge before engaging the compressor?

I'm not sure what you mean by this. The sure start is in line with the circuit so it sits before the motor. If the contactor on the condenser is closed it should charge itself right away correct?

What kind of AC unit is it? How many tons, make/model? Is the air handler and compressor on the same circuit breaker? What size circuit breaker do they use?

How did you measure the draw 6KW spike on the house?

Maybe the surestart thing is not working properly.

It's a Trane 5 ton unit
XR 13
M/N 2TTR3060A1000AA

Here is the nameplate:


The air handler and condenser are on different circuits, but the same panel. Everything (including the two powerwalls) is connected to the same panel.

I have a Sense home energy monitor, the graphs indicate a peak of 6kW when it fires up and is connected to regular power.

I tried to get the number with my meter, but it's too cheap and doesn't see the spike.

 

[cr0ntab]

Try to draw a load of more than 5kW. It should be up to 10kW with 2 PW's.

Instead of backup mode have you tried self powered to see if it behaves any differently? Originally I noticed that my single powerwall only outputs 1.7 kW in backup mode, but in self powered or TOU mode it outputs 5kW. Maybe when you say you are on backup mode you mean backup only mode? If that's the case then the max you can get is 3.3 kW I think. Try setting it to self powered and put your reserve at 100%.

When I say backup mode I mean that I disconnect the mains to the house and the powerwalls cover all the load. In app TBC is selected.

I will switch back to self powered to see if they'll put out more than 5kW.

 

[cr0ntab]

Should work, I've used a surestrart like device running AC in a vacation house off grid. You can probably get some free consulting from the company that makes the surestart.

Thanks for this anecdote! I'll definitely reach out to SureStart to see what they say.

 

[power.saver]

The key piece of information on the nameplate is the 148 LRA. That is the Locked Rotor Amps, and the SureStart needs to be able to handle that amount. They make different size units. Check to see if yours is rated for at least 148 LRA.

 

[cr0ntab]

The key piece of information on the nameplate is the 148 LRA. That is the Locked Rotor Amps, and the SureStart needs to be able to handle that amount. They make different size units. Check to see if yours is rated for at least 148 LRA.

I based the unit choice according to the submittal

Full Load Amps (FLA) (Corresponds to Compressor Run Load Amps (RLA))

This is the model I have:

SS1B16-32SN (230V, 60/50Hz, 16-32 FLA)

 

[Dan123]

So the instructions for SureStart say the following:

"When properly designing a backup generator application, you should expect 60% reduction in single phase HVAC system compressor locked rotor amperage (LRA)."

It seems like the SureStart does not sufficient reduce the LRA, and it still exceeds the 60amps

For comparison, the newer variable speed XV18 has LRA of 12 amps. So if you ever decide to get a new AC compressor, variable speed is the way to go.

https://www.bayareaservice.com/wp-content/uploads/2015/02/Download-Trane-XV18-Product-Data.pdf

 

[cr0ntab]

So the instructions for SureStart say the following:

"When properly designing a backup generator application, you should expect 60% reduction in single phase HVAC system compressor locked rotor amperage (LRA)."

It seems like the SureStart does not sufficient reduce the LRA, and it still exceeds the 60amps

For comparison, the newer variable speed XV18 has LRA of 12 amps. So if you ever decide to get a new AC compressor, variable speed is the way to go.

https://www.bayareaservice.com/wp-content/uploads/2015/02/Download-Trane-XV18-Product-Data.pdf

Oh for sure, when this equipment kicks the bucket variable speed all the way!

I saw what a difference it made with my pool pump, so it's a no brainer for anyone considering it!

 

[electracity]

I saw what a difference it made with my pool pump, so it's a no brainer for anyone considering it!

I'm fascinated by the AC compressor mods that heat the pool with the waste heat. In certain climates that tech must be very efficient.

 

[NuShrike]

I based the unit choice according to the submittal

Full Load Amps (FLA) (Corresponds to Compressor Run Load Amps (RLA))

This is the model I have:

SS1B16-32SN (230V, 60/50Hz, 16-32 FLA)

40% * 148 LRA = 59.2A. I think you're right at the edge beyond what the PW2s can support. How many times have you cycled the SureStart? I read it takes ~10 full-runs before it properly calibrates for your AC.

I'm about to pick up that same SS model for my 1999 AC which has a 105 LRA which reduced down to 42A should be in better range, if PW2s stock will ever deliver.

 

[Dan123]

40% * 148 LRA = 59.2A. I think you're right at the edge beyond what the PW2s can support. How many times have you cycled the SureStart? I read it takes ~10 full-runs before it properly calibrates for your AC.

I'm about to pick up that same SS model for my 1999 AC which has a 105 LRA which reduced down to 42A should be in better range, if PW2s stock will ever deliver.

There is probably something else working in the house at that time, like the air handler, so that it pushes it over 60. And I thought that powerwalls are rated for 7kw, with is about 28-29 amps each.

 

[cr0ntab]

So I was doing more tinkering today and I think this might be a case of a bad power wall.

Today I noticed that I wouldn't discharge more than 5kW at any given time. I went out to look at the powerwalls and only one was pulsing (Powerwall enabled and charging or discharging - from the manual).

So as a test I disabled the one powerwall that was pulsing and I left the other online.

The only concern is that the malfunctioning powerwall is the second in the comms wire daisy chain, so hopefully the first powerwall doesn't need to be on for things to work on the second.

I just set this up and changed to self consumption with 100% backup, we'll see how long it takes for the config update to roll out to the gateway.

If any one has any other tips on how to isolate if a powerwall is working or not I'm all ears!

 

[Ulmo]

It seems like you found a problem, then. My PowerWalls have a tiny switch near the top of the unit by the pulsing light. Do yours too? Are they both set accordingly (i.e., on)? If not, turn them both on.

Otherwise, I recommend you contact your installer and have them fix it. Call them and try to get live contact with them. Tesla is notoriously bad at returning missed calls or emails, but if you wait long enough, often they will email back within a few weeks. Best to try calling and getting ahold of someone directly until they set up an appointment, and if you don't succeed right away at that, also get them by email.