New battery bank

lee1lee1 Registered Users Posts: 7 ✭✭
Hi 
I have just purchased 3 fullriver dc85 batteries and have them in parrell 
Don't think the connecting wires are substantial enough what gauge should I use they are stacked together so connections are only 4 to 6 inches apart and would I need a inline fuse 

Comments

  • mcgivormcgivor Solar Expert Posts: 3,815 ✭✭✭✭✭✭
    The gauge would be dependent on the loads, the overcurrent protection would be sized according to the gauge. To maintain ballance between the batteries is important to configure the wiring correctly, this link explains the rationale between different methods http://www.smartgauge.co.uk/batt_con.html
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  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    In cars, they either use very heavy copper cables for connection to the starter--Without fuses(?)--Or use a "fusible link" (wire) for the intial protection to the car's electrical system.

    If your electrical loads/charging are small, you can use small AWG wiring and a fuse/breaker to protect each wire back to its battery.

    Or you can use much heavier cables and a single fuse/breaker to the rest of the electrical system... The chances that a single lead acid battery would fail "shorted" is small--The bigger issue is that something falls on the bank (metal tool), or somebody (like a child playing) shorts the bank. The costs of good quality fuses/breakers and the space to install them--Many people choose to go without.

    And example of small form factor fuses and fuse holders that can manage 100's of amps are those from BlueSea. The MRBF holders (you have to buy fuses separately) are really nice:
    5191 product image2151 product image
    https://www.bluesea.com/products/category/16/72/Fuse_Blocks/Terminal_Fuse_Blocks (holders)
    https://www.bluesea.com/products/category/0/42//Marine Rated Battery Fuses (fuses)

    Using circuit breakers are also a good (larger) solution... They give you circuit protection, but also allow you to shut down power (switch function) too.

    https://www.solar-electric.com/residential/circuit-protection/circuit-breakers.html?nav_breaker_type=500&product_list_limit=all

    Using McGivor's link for parallel battery wiring:

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

    I like method #3 as this gives you obvious wire connection to the + bus where you can mount breakers or fuses.... If you use the BlueSea fuse mounts above, you can attach one to each battery + terminal, then wire as needed using any of the other suggested wiring methods.

    Those are 85 AH batteries, that supply upwards of 85 amps into a load (AGM have very low internal resistance).... Using fuse or breaker is one solution, using heavier cable is another. This simplified NEC table shows you wire ratings:

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    4 or 2 AWG wire would be heavy enough to support any "normal/maximum current loads". If you are planning on 10% of rated load (8.5 amps charging or discharging max)... A 14 AWG cable is going to carry that current. Fusing currents:

    https://www.powerstream.com/wire-fusing-currents.htm

    A 14 AWG wire will fuse around 123 amps. If you are "OK" if a 14 awg wire "fuses" (gets red hot an melts) or there is nothing that can draw >~15 amps--Then per battery protection is not really needed (battery in metal box/on concrete floor, nothing flammable nearby). 14 AWG is good for 12-20 amps pretty easily and probably appropriate to this level of current for these 85 amp cells.

    If you use 6 or 4 AWG cable (6 AWG is around 500-600 amps fusing current)---They will carry and "reasonable" fault current for this size battery bank.

    One issue with parallel power systems (power supplies, batteries, etc.)... As you add more parallel devices, the total current available increases... 3x85ah (at 1C discharge rate) = 255 amps into a fault. And you start needing to look at "per device" fusing/breakers. Why N+1 power systems are a pain in the behind (additional costs for protection of the individual N's against N+1 faults.

    Many decades ago--An old ~1954 Chevy/GMC shop pickup. The battery was under the passenger floor board with a metal cover. And the metal cover had a large steel "latch rod"... The latch rod assembly failed and dropped on the battery causing lots of smoke... Replaced the battery and tossed the broken latch assembly into the garbage... My quick fix (no other damage, no more latch assembly to fall onto the pickup's battery battery box).

    -Bill "things happen" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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