Custom bus bars for LiFePO4 batteries

just startingjust starting Registered Users Posts: 228 ✭✭✭
so I will be making my own bus bars to connect 5 cam72 LiFePO4 cells and then have 8 sets of the cells for a 24v bank I have some 1/8"x 3/4" is that going to be enough or should I double up?
200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 

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  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    I will be using a 3000w samlex inverter with a 125 amp breaker, max I figured it would work out to 20 amps max from each cell if that helps
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • BB.BB. Super Moderators, Administrators Posts: 29,009 admin
    It really depends on what the maximum current will be (discharging and charging).

    For a 24 volt battery bank, you want less than ~0.1 to 0.2 maximum voltage drop across the bus (i.e., 28.5 volts at the bus inputs for charging, 28.4 or 28.3 volts minimum at the the battery cells.

    Cell to cell, voltage variation on the bus, again, less than 0.1 volts drop during charging.

    During discharging, we generally use the NEC 3% maximum voltage drop... But to save wasted energy (and excess heat buildup), using heavier bus bars down to 1% drop works well (going heavier for less than 1% drop is just usually a waste of money on copper).

    Usually maximum charging current is less than maximum discharge current--So looking at the voltage drop for both, and having different limits is OK. Charging current voltage drop is to ensure cells are equally and accurately charged and where more than a 0.1 volt variation is significant error. And for discharging, just avoiding excess heat and voltage drop to the load (i.e., generally most 24 VDC inverters have a battery cutoff voltage of 21.0 volts--So you look at minimum battery voltage of the battery bank "chemistry" plus the voltage drop of wiring and fuses/breakers).

    For example, Lead Acid batteries are generally "dead" (and ruined) at 21.0 volts... And the minimum "operational" voltage under load is (very roughly) around 23 volts. 23 volts FLA battery voltage - 21 volts inverter cutoff = 2 volt drop for bus bars, fuses/breaker, cabling at maximum current.

    You should be able to find tables/etc. about copper bus bars... Here is one that talks about copper bus bar vs temperature rise:

    https://www.copper.org/applications/electrical/busbar/bus_table3.html

    A very detailed design guide here:

    https://copperalliance.org.uk/knowledge-base/resource-library/busbars-guidance-design-installation/

    Electrical Resistance Calculator:

    https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm

    And the old electrical equation: Voltage = Current * Resistance

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,240 ✭✭✭✭✭
    Best bus bars are tin plated copper.  next best is bare copper, and then finally, thick tin plated aluminum

    What is your material ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    C110
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • mike95490mike95490 Solar Expert Posts: 8,240 ✭✭✭✭✭
    Use a good anti-ox on the whole piece.   Thru bolt your lugs on it with SS bolts &  lock washers
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    Do you think the 1/8x 3/4 would be ok its rated for 215 at a 30c increase it's only for battery interconnect
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • BB.BB. Super Moderators, Administrators Posts: 29,009 admin
    What current do you plan on taking from and recharging the battery bank?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    edited December 2018 #9
    Charge would be 100 amps and max discharge would be 150 amps  for maybe 1 minute if the washer and dishwasher or the washer and shallow well pump kick on
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
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