Setting up LiFePO4

BoFuller
BoFuller Solar Expert Posts: 187 ✭✭✭
I’ll be switching over to LiFePO4 batteries on Monday. I have three 48V 100amp that I’ll be connecting in parallel. My question is, is it important to hook the pos to #1 and the negative to #3, like Lead acid, or does that not apply to LiFePo batteries.
12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,599 admin
    If I understand your question correctly... Yes, you need to have "balanced" wiring to each parallel connected battery--And it is probably even more critical for Li Ion batteries. You want each cell/battery to have cell/battery battery voltage to be nearly equal.

    http://www.smartgauge.co.uk/batt_con.html

    Lead acid batteries are a more forgiving on "over charging" vs lithium batteries.

    Do you have a BMS (battery management system)? Lithium batteries tend to be connected first in parallel, then series. That reduces the number of BMS connections.

    Lead Acid batteries are usually connected in series first, then paralleled at the end of each string.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Yes, they have BMS

    next question. All cabling with the lead acid is 2/0 but the connectors that came with the LiFePo are 4/0
    Should I replace the cabling going to the inverter and use all 4/0?
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Cables are expensive. Can I put a 4/0 connector on the end of my 2/0 cable?
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BB.
    BB. Super Moderators, Administrators Posts: 33,599 admin
    What is the maximum current you plan on using (size the wire)? What are your cable lengths (and current) for major components (battery to AC inverter, charger(s) to battery bus, etc.)?

    A "connector" has two sides... One is for connecting (crimping) to the cable (2/0, 4/0, etc.). The other side has a flat blade with one or more holes (#10, 1/4", etc.) to bolt to the battery/battery bus bars.

    The general answer is no--You cannot crimp a 4/0 connector onto a 2/0 cable... You need to match the cable->connector->crimp die->crimp tool.

    You can find different 2/0 cable ends with different size bolt holes/configurations:

    https://www.amazon.com/s?k=2/0+lug&ref=nb_sb_noss_1 (just a quick search)

    Generally--The loads and allowed voltage drops for your wiring is what determines the AWG of your cable (as well as insulation type, temperature rating, conduit fill, etc... if you want to get into all the details for something like NEC--national electric code).

    And you also need circuit breakers/fuses to protect the wiring from overheating/causing a fire.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Thanks.
    I’m thinking I need a bus bar so I can hook the individual batteries to it with the 4/0 and then use my 2/0 cables for running power to the inverter.
    My existing negative cable is the correct length but the positive cable is about 2 feet too long (12 foot vs the 10 ft I need)
    Any issue with using the 12 foot cable?
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BB.
    BB. Super Moderators, Administrators Posts: 33,599 admin
    What is the maximum amperage you expect to use @ 48 VDC (max continous/surge)?

    Is the 12 foot cable for the battery bank @ 4 AWG or the inverter @ 2 AWG?

    Generally, the suggestion is to run +/- cables in parallel (or even give them some twists to hold them together--Or in a conduit). When you run the cables in parallel, they have lower "impedance" (AC resistance) and are less likely to pickup (i.e., from nearby lightning) or emit radio frequency noise.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    The 12 foot cable is 2/0. So both cables running from the bus bar to the inverter will be 2/0.
    the 1 foot cables connecting the batteries to the bus bar are 4/0.

    I don’t know max amperage. I usually use about 165 amp hours a day.
    The 3 batteries are each 100 amp and will each be connected to the bus bar.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    For followup, I switched over to the lithium batteries last Friday, and after 8 days so far, everything is running fine.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • KenMorgan
    KenMorgan Registered Users Posts: 92 ✭✭
    @BoFuller I am guessing that you are using premade packs?  If so what brand etc.?
    70kw LiFePo4 battery bank, 18 JA solar 200 watt panels, 20 sharp 200 watt panels,  morningstar controller(s) and a magnum 4448 inverter with all the usual junk that goes with it. 
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    Gyll brand from Signature Solar.

    it’s now been 5 weeks and I’m liking them more everyday.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • ETS1001
    ETS1001 Registered Users, Users Awaiting Email Confirmation Posts: 9 ✭✭
    I wish that I was having as much luck with my new lithium batteries from Battleborn. I can post details later in another thread.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,599 admin
    ETS,

    Yes, please create your own thread about your experiences (keeps Q&A focused on your discussion).

    -Bill "moderator" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    BoFuller said:
    My question is, is it important to hook the pos to #1 and the negative to #3, like Lead acid, or does that not apply to LiFePo batteries.
    Generally speaking it is better to match cable lengths, but at least one LiFePO4 manufacturer (Blue Planet) says it does not matter.  Each Blue Planet battery has its own BMU, so each battery will stop charging when it is fully charged.  Blue Planet recommends that you do a full charge once a month which causes all the batteries to be balanced. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BoFuller
    BoFuller Solar Expert Posts: 187 ✭✭✭
    I connected all 3 batteries to a bus bar and used equal length cables for all 3, so I got every angle covered.
    12 Kyocera 235 panels, 3 Gyll LiFePO4 batteries (previously 16 Trojan L16 RE-B batteries), Outback 3600W 48V system, Generac 11K propane backup generator, NW AZ, off grid, 6,000 ft (system installed in April 2015)

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    Check your current matching between the batteries with a moderate load with clip-on ampmeter.   Even with matched cable resistance, variance in BMS MOSFET switches resistance can upset current loading balance between batteries.  This is somewhat self compensating as one BMS having more current heats up more causing its MOSFET's Rds_ON to increase.  This makes its current contribution drop and other batteries' current increase.  If you get better the 10-20% current difference between batteries consider it good.

    You also want to set inverter low battery voltage shut down level so it shuts down for low battery before BMS does.  You want to avoid BMS shut downs because they pull the battery supply to inverter.  The most likely BMS shutdown is for overvoltage when charging because cells are getting out of balance.  The greater the chargng current you use the more trouble-some this can be.

    Adjusting BMS parameters and some of your inverter parameters to get the best 'harmony' can be quite complicated.  Read battery manual carefully to avoid an expensive mistake.