General battery specs question

[fredct]

Hoping I can post as this not a DIY question, but I’m looking to understand some things a bit better as I look into solar, specifically about battery backup options to go along with a solar system.

I was mostly focused on kWH of capacity and how long it could last (answer: not very long for whole house), but one guy I spoke to today emphasized another factor which is max current. Regardless of how much capacity the battery has, it can only output at a certain rate.

He was offering a Panasonic Evervolt which has a max current output listed of 31.7A. So even though I think it’s have enough kWh juice to run my AC for a bit in the evening, my old inefficient AC is on a 40A breaker for the compressor and a 20A breaker for the air handler. So it seems like that even 2 such batteries couldn’t actually run my AC at least not with the fridge etc ?? Is that correct?

The other offer I have for a decent amount of battery juice uses the Tesla Powerwall 3s. So I went to check their specs, but I’m not sure how to read them. There’s an initial brief start capacity of 185W, but that’s not continuous.

There IS a “maximum continuous current” but the spec sheet lists it in 4 columns ranging from 24A to 48A so I’m not sure how to interpret that. The 24 would be less than the Evervokt, but the 48x2 batteries if 96 seems like it WOULD be enough current to power my AC, at least for as long as the kWh last?

Am I understanding this right in general? And could the PowerWalls handle it?

 

[time2roll]

Evervolt looks like 7.6 Kw output with an 18 kWh battery. That gives about two hour run time at max power.

40 amp breaker is probably 240 volts so 9.6 kW. The Evervolt may start the air depending on the actual draw and the surge current. Still I would recommend at least two of these units stacked together. Up to four can be combined.

Powerwall 3 can produce 11.5 Kw but only 13.5 kWh of battery. So the single PW should start your air but the run time is shorter. Still might need two+ stacked together for run time. I believe there are battery only expansion units. Tesla will go over the design options to suit your needs. BTW that 185 is the start amps rating for the needed surge current.

 

[fredct]

Yes I would certainly need 2, but I’m trying to decide if 2 is enough, because 3 kinda becomes cost prohibitive as well as a space issue.

I see you’re using kilowatts and yesterday the guy was using amps. I guess that’s the real question is: which is the real limitation? Or does it have to be under both?

The Evervolt lists a 31.7A limit alongside the 7.6kW. I just noticed that that math matches 240V exactly (7600/240=31.666…). But the air handler and fridges etc all use 120 so you’ll exceed the amps before the kW.

If I’m running a large portion of 120V appliances, is it okay to exceed the amps if I’m under the kW draw? Or do I have to be under both?

Also what with that 4 columns of math power/current in the Powerwall spec?? How do I interpret that? (Image attached)

 

[time2roll]

The pair of Evervolt gives longer run time and might be best for your situation.

kW and amps are mostly the same thing when talking about energy at the same voltage. 120v appliances only pull from one side of the inverter so as long as the 120v items are balanced on each side then full power is available. If they all pull from one side then the amps are available but the power is cut in half as the voltage is half. Usually loads are balanced enough that it will not be noticed.

Not sure what the context of that Tesla attachment is illustrating.

 

[fredct]

The pair of Evervolt gives longer run time and might be best for your situation.

kW and amps are mostly the same thing when talking about energy at the same voltage. 120v appliances only pull from one side of the inverter so as long as the 120v items are balanced on each side then full power is available. If they all pull from one side then the amps are available but the power is cut in half as the voltage is half. Usually loads are balanced enough that it will not be noticed.

Not sure what the context of that Tesla attachment is illustrating.

I have to chew on what you just said as far as sides go, but thanks!

And as far as the Tesla sheet, it came from the powerwall 3 spec sheet:

https://energylibrary.tesla.com/docs/Public/EnergyStorage/Powerwall/3/Datasheet/en-us/Powerwall-3-Datasheet.pdf

But apparently it’s a configuration setting so you can just pick the highest I guess? Why would someone not pick the highest? See the installation instructions here and image attached: https://energylibrary.tesla.com/doc...UID-5DAC2670-0432-48D0-A5D6-FD031C0C6F11.html

 

[time2roll]

Yes generally most would just pick the highest. Unless there is a cost difference. Or limitation to the feed in current. Or the highest may be pointless without the expansion battery units. Gets more complicated as multiples are tied together. Tesla engineer would need to recommend what you need and answer why the recommendation works best.