home router battery backup

Tue Jan 18 15:11:57 UTC 2022

On 1/18/22 00:26, Jordan wrote:

> Wow, that's a nice program.  Do you know what they keep the
> "reserve percentage" set to, the proportion of stored energy that
> will never be discharged for grid-support, but held back for
> island-mode use in case of an outage?

I don't use the Tesla Powerwall, but Li-Ion is generally the same 
regardless of who packages it. The difference will be what the OEM 
decides to set the low-voltage cut-off to on the inverter and/or BMS.

I'm not sure how much the owner can configure a Tesla Powerwall, but 
with other installations, you can decide when your battery kicks in to 
run loads, or when it hands back to the grid or generator. This assumes 
evening time, when solar irradiation is unavailable, of course, as that 
is generally the preferred source of energy.

I've heard that Tesla will monitor the weather in your area to 
"pre-charge" the Powerwall to account for possible power disruptions. 
While I find that rather invasive, it's a cool feature for folk who 
"don't want to know". Then again, I also hear that Tesla will limit or 
withhold support and/or warranty if you do not connect your Powerwall to 
the Internet for them to "manage". The downside I hear, with that, is 
that they can remotely adjust SoH (state of health) thresholds to 
lengthen battery life in order to meet warranty promises. Not sure how 
true that is, but I've heard it a lot.

In terms of "reserve" capacity, Li-Ion can go much deeper than Lead 
Acid. Some inverters are setup to disconnect the battery anywhere 
between 3% - 20% SoC, depending on the OEM. For LFP chemistries, the BMS 
will usually turn the pack off at 2.50V, while for NMC, that will be 
around 2.75V. But different battery OEM's may be more or less aggressive 
with their BMS's, depending on who you choose to buy from.

Mark.