OffGridInTheCity Build

ALL NEW - Battery Finder Search for 12/24/36/48v or by capacity www.batteryfinder.net
New & used Batteries, Solar, accessories, LifePo4 cells & more 5% Coupon "Powerwalls" www.batteryhookup.com
kje said:
Happy to hear and happy new year! 😊 Are they still holding voltage?
Click to expand...
Thank you and happy new year to you/all as well! :)

Yes, the fixed packs are still steady. I made this a big deal / put it off (in my head) but the find/fix was straightforward and pretty low effort (really).
1768231392472.png
 
OffGridInTheCity said:
Updated Jan 2026....

Living off-grid can bring to mind moving to the country... but the 'country' has it challenges so why not transform my city home to be off-grid capable? Water via rain-harvest (20,000g/year), Solar power to run a 100% electrified home (15,000kwh/year). Wood based heat (unfortunately) is not an easy option - and winter months are not enough power - not sure how to overcome this yet.

The Solar power design goal is to consume all that is produced. Its an ongoing, off-grid, power production focus. I'll use later posts to show details/pics. If there's additional metrics you're interested in, let me know and I can add here or share.

Power / Water / Maintenance:
View attachment 33815

Powerwall Cycles:
View attachment 33816

Powerwall Detail - 52v@260ah = 13.5kwh per battery x 8 batteries = 108kwh Powerwall
View attachment 27288
View attachment 31196
View attachment 32976

2026 Goals
* Wood based heat - boiler or forced-air or even fireplace (as city allows). During winter months (Nov, Dec, Jan, Feb) there isn't anywhere near enough PV for the heat-pump to keep things warm.
* More powerwall
Click to expand...
My own very small project, pv and 16s battery, zero export to grid continues with lessons learned.

My initial design for limiting the inrush current to the battery GTI involved placing a 22R NTC in series with the high (+) side to the GTI, after battery power on, this limited the inrush current to about 2.5A and after a delay of about 3 sec an SSR would short out the NTC however, with SSR on and generating it had about 1v across it, the lesson learned is that the a full battery under discharge is about 52v so 1v drop causes the battery GTI to sense an apparent SOC, a big loss of charge, meaning it cuts out early on its lower limit.

The design work around is to use a current sensing relay (Geya GRI8-01) that shorts out the NTC after a delay once the GTI starts generating. This arrangement is fail-safe in that if the NTC fails open circuit the GTI cannot start generating, preventing inrush damage to the GTI dc input components. Again, the lesson learned is that the dc supply to the GTI must come straight from the battery ideally without any interposing resistance. The GTI design would be better served by having separate voltage sensing wires to eliminate even very small resistance in connecting cables carrying high dc amps. :)
 
Update: Work on battery #11 thru the winter coming along... nearing 1/2 way mark.
1772930272955.png

These Battery Clearing House cells are fantastic. Doing diligence with a capacity test and a 3 week self-discharge test - but every single cell is 3.5v out of the modem packs, OPUS reporting 2650-2750mah in capacity tests (spec is 2600mah), and have been 100% pass for self-discharge.

Looking forward to a good, 11th edition to the powerwall. And I have enough cells for battery #12.
 
Last edited:
OffGridInTheCity said:
Update: Work on battery #11 thru the winter coming along... nearing 1/2 way mark.
View attachment 33951
These Battery Clearing House cells are fantastic. Doing diligence with a capacity test and a 3 week self-discharge test - but every single cell is 3.5v out of the modem packs, OPUS reporting 2650-2750mah in capacity tests (spec is 2600mah), and have been 100% pass for self-discharge.

Looking forward to a good, 11th edition to the powerwall. And I have enough cells for battery #12.
Click to expand...
Fantastic work!

It's amazing you've done #11 battery packs. 😊

Where did you get these battery clearing house cells and what was the price?
 
Update: Battery #11 hooked up! Parallel'ed onto the powerwall 'live' - getting quite cavelier these days :)
Up to 154 longmons / 148.7kwh on paper. *At 2,570 cycles, overall capacity has deteriorated 10-15% I'm guesstimating - so 148.7 * 85% = 129kwh current capacity.

Not sure what happened with 3 errant pack voltages - spiking blue bars to the right. I use an iCharger X8 to pull down the finished packs to a "Storage" voltage of 3.7'ish but apparently it didn't pull packs #144, #148, and #153 all the way down. I didn't double-check - getting 'sloppy' a bit these days.
1775941592404.png

#141 - #154 are the used longmons I bought earlier this year and at first I thought they were mis-calibrated? but a voltmeter shows them to be accurate. And the Batrium Sync went flawlessly, so they seem to be working. In any case, auto-level and individual pack discharging (using hobby charger) will take care of this reasonable soon.


Battery #11 located on top of another one. Used 8 (8" x 8") plastic dividers spaced between the bottom row of packs to help support a shelf above them for this battery. A bit of a house of cards but should let me pull out individual packs on the bottom row if I need to work on them. Planning to repeat this for battery #12 (on top of #11).
1775941076082.png
 
Last edited:
Nice work Offgridinthecity! 😊

Almost 130kwh current capacity! 😃

Did you ensure the connection of pack #144, #148, and #153 was properly secured?
 
kje said:
Nice work Offgridinthecity! 😊

Almost 130kwh current capacity! 😃
Click to expand...
Thank you!

kje said:
Did you ensure the connection of pack #144, #148, and #153 was properly secured?
Click to expand...
Yea... the lugs + copper plate connectors are bolted with 'ken torque' :) - e.g. as much torque as I can put on the wrench!. It's just a bit of sloppiness following my process. Got the 1st pack back inline and working on the remaining 2 packs...
1776092733929.png


What's (always been) interesting to me is the 'max difference variance' that occurs over the charge/discharge voltage range among the packs.
Right now (time of this post), near the 'bottom' battery voltage for last night's cycle, the max difference between packs is minimal - 80mv - but as this charges up today, the 2 'errant packs' will rise faster than the others and the difference will be 170mv till I bring these inline.
 
Last edited:
You must log in or register to reply here.
Back
Top