Sure Start/Soft Start Question but Still Grid Connected

[aesculus]

I am fully aware of the need for a Sure Start/Soft Start when the Powerwalls are isolated from the grid and powering my home for starting certain high current devices.

My question for this thread is this scenario:

My PW's are full and any solar is going to the utility, house being fed from PW and Solar. Or I am in peak time using Cost Savings mode and all my energy is being supplied from the Powerwalls. In both cases I still have an active grid.

If I have a device that exceeds the starting current of the PWs will the system get sufficient current from the grid or will my devices fail because the PWs are trying to supply the energy solely and they cannot handle that much current?

I am curious because I have a well pump that suddenly seems to not work intermittently but I have not been able yet to determine all the scenarios that it works or does not start in. It does not have a Soft Start on it but up until now did not seem to be an issue.

Heck it may be that the well supplying the water has run dry, or I have a bad starting capacitor, bad pump etc.

Just trying to understand the possibilities here to eliminate various things.

 

[jjrandorin]

If you are still grid connected, power "should" come from the grid I would think, if your solar + powerwalls is not enough to provide. I have plugged my car in when my powerwalls were full, solar going to home and grid, (about 2 kW of solar generated when home was only taking 1kW). I have a 60 amp breaker so the car charges at 48 amps and pulls 12.8 to 12.9 wK.

The system seamlessly added the grid to the powerwall and solar (all three lines were going toward the home. Wife turned on the double wall ovens during this time too, and the grid number just went higher at that time.

I didnt want the car to drain the PW so switched from self powered to backup only. Within a few seconds, PW went off, and car was still charging from solar + grid. I was sitting in the car at the time as well, looking at this, and the car never blipped lower than 48amps so it didnt even notice the changeover.

Now.. I run in self powered mode, so I never have solar going to the grid when my powerwalls can still be charged, unless they are almost full and can not take what my solar panels are putting out.

When my solar can no longer supply the house load, the PWs kick in and power the home for the rest of the evening, until the next morning (my "self powered" score for a normal sunny day is 100% currently). I have plugged in the car in the evening, and seen the Powerwalls provide up to 9.9 kW of power (I never recall seeing more than that ).

I am not sure the car creates the same draw your a motor without a soft start might create, but the grid should still cover it. Seems to me that the issue should be with that piece of equipment when there is no grid, but when there IS grid, it should be transparent.... I think.

Only speculation based off my limited experience above however.

 

[aesculus]

Doing a little internet query I found this:

A 1HP 240 volt pump pulls 10 amps while running. On start it will pull 35ish amps, but only for . 5-1 second. 240 x 10= 2400 Watts but you will need a surge capacity of around 8000 watts as the start amps are much higher.

I think I may have a 3/4 hp pump and Tesla did look over the start amps on another similar pump and thought it was OK but perhaps this one draws more current at start.

So if it does try to get 8kW for a second or so and this cannot come from the grid, my PW would not be able to handle it. And it would probably be too short of a period for the PW to trip. I have a Pump Saver on the pump and that might be what is tripping off. Still need to do more investigation here.

 

[power.saver]

You will pull any excess power demand from the grid. It is a near infinite source of energy and can respond much faster than the PWs. My 4 ton A/C starts fine when the grid is up and the PWs are providing all house power during the peak. Once they get going, they will be supplied by the PWs. The grid will cover your surge demand.

 

[aesculus]

I'll need to dig in deeper into other causes. Probably a water issue or perhaps the pump saver needs to be tuned.

Usually we don't have water issues this time of the year but this is a totally weird year in Nor Cal with water at about 50% of normal. We had nothing at all from the 2nd week of Jan until the end of March.

 

[bob_p]

If grid power is present and any devices are failing, it seems more likely a problem with the device and not with having the device powered through the Tesla Backup Gateway.

The issues with sure/soft/hard start only happen when the grid is offline and all power is coming from the solar panels and PowerWalls. PowerWalls can provide continuous 5KW of power each with a short-term peak of 7KW. Without the HVAC sure/soft/hard start upgrade, it's possible to exceed the peak power available in the system, which prevents the compressors from starting up.

But while the grid is available, any power surge is taken from the grid as long as you don't exceed the rating of the breakers for the circuit and the house.