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Powerwall and Pumps

davidwpb

Member
May 17, 2019
48
10
west palm beach, florida
I know there are dozens of threads about PW and AC systems, but my question is regarding other motors like pumps.

Tesla brought out two Hyper Engineering SureStarts for my install. I'm assuming they will install one in my AHU and one in my condensing unit.

While waiting for Tesla to come back and finish install, I got to thinking, wouldn't I need this for my water pumps as well? Does anyone have knowledge of this they can share? I'd rather have Tesla handle this when they come for back for my install than be an issue down the road that needs a separate electrician for. I have two pumps for my house, one is for my household plumbing as we are on a well and one is for my irrigation system. The house pump is 1.5HP and the irrigation pump is 3HP (got it for free from an hotel that was being renovated). I can sacrifice the irrigation pump, but whats the point of having power if you cant flush toilets or take showers. Below is what I could find from the pump spec sheet, generic to all size 0.5 to 1.5 HP.
http://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2012/07/BJS-R3.pdf
Motor: • NEMA standard • 60 Hz • ½ – 1½ HP, 115/230 V capacitor start • Single phase • 3500 RPM
 

ajdelange

Active Member
Dec 10, 2018
1,077
540
Virginia/Quebec
I just checked my well pump. It draws draws 1.7 kw running and only 2 at startup. Note that the latter is measured in a 1 second window so the inrush for the first fraction of a second would be higher than that but certainly not more than 3 -4 times the running load (i.e. max 6.8 kw).

I'd check with Tesla to see if motor inrush is a problem for the Power Wall. I think the max peak they can handle is 8 kW (?). With a single PW you might be pushing things.
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
3,722
Buford, GA
I just checked my well pump. It draws draws 1.7 kw running and only 2 at startup. Note that the latter is measured in a 1 second window so the inrush for the first fraction of a second would be higher than that but certainly not more than 3 -4 times the running load (i.e. max 6.8 kw).

I'd check with Tesla to see if motor inrush is a problem for the Power Wall. I think the max peak they can handle is 8 kW (?). With a single PW you might be pushing things.

One of the issues isn't just the max draw, but the amount of imaginary power (Power Factor) that occurs. Measuring with a standard meter won't show it, because it's current flow at zero voltage.
Also, you have to work in the situation where all the motors start at once. Rare, but common after power outages.
 

ajdelange

Active Member
Dec 10, 2018
1,077
540
Virginia/Quebec
One of the issues isn't just the max draw, but the amount of imaginary power (Power Factor) that occurs. Measuring with a standard meter won't show it,
Did I say I used a standard meter? The numbers I reported are true. Beyond that I'd guess, as I am not a motor expert, that locked rotor current is almost in phase with the voltage because only the leakage inductance is there to produce VARS. The big VARS don't come until the rotor starts to spin. And beyond that modern inverters are sophisticated enough to compensate for reactive current. Certainly Telsa's inverters, developed for controlling induction motors, are capable of this.

Hadn't really thought about this but during the summer I run 1 G/W heat pump (with soft start kits) 2 A/A heat pumps and 1 old fashioned central A/C all on inverters (when the sun is shining).
...because it's current flow at zero voltage.
The meter measures amplitude and phase of both the current and voltage waveforms and is thus able to measure true and apparent power. I don't record apparent.

Also, you have to work in the situation where all the motors start at once. Rare, but common after power outages.
Modern air conditioning equipment (heat pumps AND thermostats) wait for a random period of time after a call in order to prevent this but that does not mean it can't happen. And there is no guarantee that the well pump will not come on at the same time as the random turn on time of an HVAC unit. Good system design (and the code) required that a backup system can handle whatever loads are connected. Shedding systems that bring on one load or set of loads at a time are an example of this. I am unaware of any load shedding capability for the Power Wall system and were I to consider one I would certainly be looking into that aspect of it.
 
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davidwpb

Member
May 17, 2019
48
10
west palm beach, florida
Tesla called yesterday, they are able to do my solar install this Saturday! And they added another 2 Soft Starts to my order! I wonder where they will install, there is room for them in HVAC equipment, but pumps are much smaller.
 

jsimon7777

Member
Feb 1, 2018
219
99
Castro Valley
I have a well pump (maybe 3/4 HP), a water pump (1.5HP but a variable pressure model, so it's already soft starting), and two heat pumps. With four power walls, I've had no issues. I think the larger of the two heat pumps has a Tesla-installed soft starter, but I'm not sure. If we had a long power outage, I'd turn it off anyway.
 

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