Hey All,

I wanted to see if I could get some advise on how to get my two power walls to fire up my AC condenser.

Here is the spec sheet on the power walls:

https://www.tesla.com/sites/default.../Powerwall 2_AC_Datasheet_en_northamerica.pdf

They're rated for 5kW output continuous and 7kW peak each.

I have two, so in theory the figures should be doubled to 10kW and 14kW

Here is the nameplace on the compressor:
https://photos.app.goo.gl/9HafSsFTEBy1Kczi6

It lists a RLA of 25.0 and a LRA of 148.

I have already equipped the condenser with a soft starter, which I was hoping would fix the issue but it hasn't:
http://www.hypereng.com/single_phase.html

The model I fitted was the

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

When the condenser tries to fire up the whole house drops voltage quite a bit. The sure start detects this and cancels the start.

In my mind there are two paths to walk down to figure this out:

1) Can I replace the soft starter with a VFD to reduce starting current even more

2) Is there a wiring issue or something else that can be changed that would prevent the voltage from sagging as much.

According to the spec sheets the two power walls should be able to fire this thing up, but I'm unsure on where to start the debug process.

 

New development.

The home has 10.89kW DC of solar on a 7.6kW AC inverter.

When the home is off the grid the power walls with adjust the frequency higher when the have a full charge to signal the solar inverter to shut off.

When the power level on the battery drops down, it brings the frequency back in line and the inverter fires up and recharges the battery.

Works quite well actually.

Now, the development is this: I noticed that when the solar was on and charging the battery if I turned on the AC there was enough power available such that the voltage didn't drop and the condenser could fire up.

I'm currently running the AC off of solar and batteries with no issue, it just needs to be timed.

So this points me in the direction of the power walls.

Each power wall is currently wired to a 30A double pole breaker using #10 AWG THHN.

The AC condenser is connected to a 50A double pole breaker using 8-2 NMB

Using this calculator:
https://www.southwire.com/support/voltage-drop-calculator.htm

With Input parameters:
Voltage: 240V
Max voltage drop: 3%
Length of cable run: 10ft
Current at end of cable run: 30A

It calculates a voltage drop of only 0.27%

1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 0.27% or less when supplying 30.0 amps for 10 feet on a 240 volt system.
For Engineering Information Only:
30.0 Amps Rated ampacity of selected conductor
1.1417 Ohms Resistance (Ohms per 1000 feet)
0.05 Ohms Reactance (Ohms per 1000 feet)
7.199999999999999 volts maximum allowable voltage drop at 3%
0.63. Actual voltage drop loss at 0.27% for the circuit
0.9 Power Factor

The copper run is pretty minimal, would it hurt to try to increase the wire size from the power walls to #8 AWG?

 

Do make sure the system has anti-short cycling. You don;t want the system powering up immediately after powering down. I would thing 2-5 minutes of off time before it turns on again. Thermostats can do this. Anti-short cycling timers can do it too.

Had fuseholders fry when the power glitched in a storm without the anti-short cycle timer.

Some inverters can actually correct power factor. They might have to be grid tie or essentially be able to be paralleled.

 

Do make sure the system has anti-short cycling. You don;t want the system powering up immediately after powering down. I would thing 2-5 minutes of off time before it turns on again. Thermostats can do this. Anti-short cycling timers can do it too.

Yep, the thermostat does have this built in, as does the sure start.

Additionally, I manually ensure that I wait 5m between failed starts.

 

... would it hurt to try to increase the wire size from the power walls to #8 AWG?

No, there’s no downside beyond the cost and hassle.