LiFe cell internal resistance

13

Comments

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 9 #62
    My RV has solar power!
    Voltage represents panels facing east. I expect 80+ volts when dialed in south.
    For AC, I chose Frigidaire model FFRE053WAE (5000 BTU). It uses half the amps for my application, best energy star, remote control and inexpensive. 
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Congratulations!

    One thing I forgot to type about... Your split sleeve/loom wiring tubing... Make sure whatever you do--That it is rain/wind/snow/waterproof.

    It looks like right now, is rain/water can come in through the slit and be brought right in through the ceiling and into the walls and electrical bay... Not a good thing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭

    Thnx Bill and for the help!  Yeah the sleeve isn’t waterproof, it’s added UV protection (though PV wire is sun resistant).  And it loops upward entering the cabin, water shouldn’t be an issue.  But to heed your advice I’ll silicone in and outside the sleeves at the point of entry.  Appreciate the comment.

  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    You might punch a drain hole in the low point of the sleeve so that water drains rather than pushes backup into the cabin (or into the solar array j-box).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Ok and there’s no j-box, a direct run to the scc.
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Bill, good point about the sleeve.  So I tried to fill a section with water but leaked like a sieve, good news. 
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 13 #68

    Here’s the roof install...panel tilt-up mounts secured to rafters with ss lags. PV and ground wire enclosed in a split sleeve anchored with cable mounts and Eternabond tape (no drilling).

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 13 #69
    Sun reflection 
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 14 #70
    8 LiFePO4 cells are passive balanced at 3.301V.  It’ll be interesting to see voltage differences as I bottom balance.
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 17 #71
    Last night a crazy hailstorm pummeled the RV; bullet holes in roof vents and tire cover but the solar unscathed, no leaks.  👍


  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Custom lithium battery to power the RV, 24V 280AH. The approx. dimensions and weight/12x14x8, 92 lbs.  Next cut busbars.  
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Identify the battery in an 12V RV system 
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
     I mentioned about replacing appliances that don’t meet solar standards (amp hogs); the factory microwave and AC window unit. Now I have an Instant Pot and efficient 12.1 seer window unit...they use half the amps (cheap conversion). A must in the middle of nowhere 
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited August 28 #75

    A milestone today connecting 8 lithium cells to create a 24V solar battery...we have ignition ; )  https://youtu.be/KPxHXzd4iM0

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Busbars w/heat shrink tubing. 
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭

    Can someone elaborate on connecting a 24-12 step down converter to my RV DC load panel?  Thnx!

    I think this will work:  The ac/dc converter yellow pos output wire (12v) connects to a 40 amp dc fuse aka reverse battery protection fuse.  The 30 amp fuse was for the FLA house battery (removed).  I’d like to replace the 30 amp fuse with the 40 and connect the 24-12 step down converter there.  This will power the 12vdc panel and disconnect the ac/dc converter.  

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    As I wire a question pops up...the ac neutral busbar in my RV is isolated (no ground bond) so this is a sub panel, correct? That means shore power is the main service.
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Yes, when connected to shore power (which should have Neutral+Ground bond at their "main panel")--And all other connections (i.e., RVs) should have floating AC (N and G not bonded).

    However, if you have an AC inverter or Genset--In theory, you should have N+G bonded in your panel--Or at the genset or AC inverter.

    It is common for RV AC systems to have "switched" N+G grounding depending if Shore Powered (N/G open), or running from AC inverter/Genset (N+G connected at Main panel/single point).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited September 6 #80

    Got it, shore power Or inverter acts as the main panel to bond N & G.  The RV panel remains a sub panel with isolated neutral busbar-no modification necessary.  Very helpful, thnx Bill. 

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Wiring coming together....

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭

    Making different length battery/inverter 2/0 cables. 

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited September 10 #83
    More wiring...getting there.
    Positive battery 2/0 cable run:  battery-battery fuse-cutoff switch-shunt (monitor system performance)-relay (safety shutdown)-inverter-positive busbar.
    Negative battery 2/0 cable run:  battery-inverter-negative busbar-chassis ground.
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Drilling positive, negative busbars.
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited September 13 #85
    Progress....

  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited September 15 #86
    Solar system is (chassis) grounded.  Luckily there’s an existing conduit (removed factory sealant) for 2/0 cable.


  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    edited September 26 #87
    Prep living in the wilderness, solar ready.


  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    Yay!  Off grid wiring complete, next prep and install lithium battery bank. 
  • buckleystephaniebuckleystephanie Registered Users Posts: 1
    Yay!  Off grid wiring complete, next prep and install lithium battery bank. 
    Hi Suntrekker. This is a great guide. I will add this to my favorites on my computer. May I know where you get all these products from? I'm currently in quarantine and looking for a place to shop online.
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭
    buckleystephanie, get well!  As for ordering parts, my go to websites are Amazon, eBay and Walmart.  At times i’ll use google too.  ...hope this helps.  
  • SuntrekkerSuntrekker Registered Users Posts: 84 ✭✭

    l’m building a discharger for LiFePO4 280AH cells (bottom balance) and trying to estimate time to 2.5V. 

    The discharger has four 50W/0.5 ohm power resistors in parallel on a heat sink.  Each cell is currently at 3.301V (70% SOC).  To estimate discharge time, I used formulas I=V/R and 1/Rt=1/R1+1/R2+1/R3+1/R4.  If RT=.125 ohms, then I=26.4 amps (I’m using #10 stranded).

    280AH cell x 70% SOC=196AH to discharge. 196/26.4=7.5 hours.

    Bill, can you or members review and comment, is 7.5 hours accurate?

    Thnx a lot!  Rich

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