Fusing Lithium Battery Bank

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ligwyd
ligwyd Registered Users Posts: 209 ✭✭
in Off Grid Solar & Battery Systems #1
HI there,

When using the 250A DC breaker that comes standard in the Schneider full size PDP, if short circuit rating of battery bank is higher than 10kA is it best practice to install and in line t-class style fuse to protect equip?

Also what fuse would be recommended?

Schneider XW pro manual info relating to this discussion.....
see pg 43(44of157) and pg 44(45 of 157)

David Poz covers fusing 6 life power batts in a rack in this video for reference.
https://www.youtube.com/watch?v=A0bqClj5urg
 


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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,758 ✭✭✭✭✭✭
    #2
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    In a closed loop power system, the battery has it's own overcurrent protection.
    XWP panel breaker is to protect the wiring to battery.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • ligwyd
    ligwyd Registered Users Posts: 209 ✭✭
    #3
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    What if an owner shorts the main bus bars for a giant lithium bank by accident somehow? The short circuit current would be "HUGE".....The fuse would just be a fail safe to protect equip from over-current of more that 10kA.......if the batt bank was capable of that.....
    Thoughts?

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  • SteveK
    SteveK Solar Expert Posts: 387 ✭✭
    edited October 2023 #4
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    The fuse protects the wire not the components. It's gonna be the unlucky thing between the busbars that'll vaporize. David Poz sized his fuse to the wire gauge and his wire gauge to his load.

    As Dave A. said the Schneider (in my case the miniPDP) has a 250A fuse. I went to 4/0 wire because of it because my bank is capable of 600A and is protected by a 250A breaker. In reality I'll only ever see ~200A briefly. Good news is I have very little loss!

    Keep in mind that a blown fuse in the middle of a normal high load is a great way to kill an inverter.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,758 ✭✭✭✭✭✭
    #5
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    A giant commercial battery or residential battery has over current designed in. At lease the ones I use do. 

    For DIY, you are the designed in 😉
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • ligwyd
    ligwyd Registered Users Posts: 209 ✭✭
    #6
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    It "was" my understanding that the breaker protects the wire and the fuse protects equip....... The 250ADC Breaker that comes in the full size PDP, as stated in the XW pro install manual, can handle up to 10kA of in rush current but exceeding that could damage equip.....
    Appreciate the dialogue....
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  • ligwyd
    ligwyd Registered Users Posts: 209 ✭✭
    edited November 2023 #7
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    Below from XW Install manual:

    DC SHORT CIRCUIT INVERTER PROTECTION
    When the inverter is installed with a PDP, the integrated DC breaker is rated for 10 kA DC short
    circuit. If the inverter is installed with DC equipment (batteries, charge controllers) having
    aggregate DC short circuit contribution capability greater than 10 kA, XW Pro inverters and DC
    breakers must be protected by current-limiting fuses. Example fuses with ratings and part
    numbers are included in Table 4.


    Spec sheet for the EG4 LL V2 says 300A short circuit but sicker on batts says 2000A short circuit for 6ms?

    2000A X 12 batts in parallel = 24000A for 6ms. Do I need a current limiting fuse in the main positive 4/0 cable before the 250ADC breaker in the full size PDP?





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  • SumPower
    SumPower Registered Users Posts: 48 ✭✭
    edited November 2023 #8
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    I looked at the Spec sheet for the 48 voly EG4 LL V2, it says "greater than" 300A short circuit has a "less than" 0.01 mS response time to trip the breaker.
    300 Amp x 12 = 3600 Amps.
    Part of calculating the available fault current is the wire size and length of the conductor in the circuit. With the resistance of a 4/0 cable in your circuit somewhat limiting the fault current, I don't think I would be concerned about it to much. 

    "When the inverter is installed with a PDP, the integrated DC breaker is rated for 10 kA DC short
    circuit. If the inverter is installed with DC equipment (batteries, charge controllers) having
    aggregate DC short circuit contribution capability greater than 10 kA, XW Pro inverters and DC
    breakers must be protected by current-limiting fuses."

    "DC SHORT CIRCUIT INVERTER PROTECTION
    When the inverter is installed with a PDP, the integrated DC breaker is rated for 10 kA DC short
    circuit. If the inverter is installed with DC equipment (batteries, charge controllers) having
    aggregate DC short circuit contribution capability greater than 10 kA, XW Pro inverters and DC
    breakers must be protected by current-limiting fuses. Example fuses with ratings and part
    numbers are included in Table 4."

    The battery may be capable of  2000 Amp short circuit for 6mS but the breaker should trip at .01mS. Thats the way I read it, YMMV?
    If I was concerned about this I would be contacting the reseller of the batteries for this information.


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #9
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    In these cases--A very large AWG set of cables has low resistance and can supply high surge current--Even at 12-48 VDC.

    For utilities--They will actually require special "high interrupt capacity fuses" for breaker panels installed near the pole/ground transformer (typically industrial installations). For panels located further away (more voltage drop in wiring), then circuit breakers are acceptable.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SteveK
    SteveK Solar Expert Posts: 387 ✭✭
    edited November 2023 #10
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    Here is the t vs ln curve for the breaker installed in my EG4 LL V2. It is the C curve variety.


    As you can see even at 10ln which is ~1000A it will trip in .01 second. At 5ln it will trip in 5 seconds. At 2ln it will trip in 15 seconds.

    Then you have the BMS discharge protection. In my instance it is configured for 99A


    Then you (hopefully) have the armored 4/0 battery cables. So many systems don't have this and I'm not sure why.



    So, initially you were concerned with shorting the busbars. I fail to understand how this would transfer all that current to devices further down the circuit. The unlucky thing shorting the busbars would take the hit.

    And of course the Panduit busbars are totally protected too....

    It would take an axe wielding Michael Myers to short this system. In that case I want it to ignite and take him with it!
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  • SteveK
    SteveK Solar Expert Posts: 387 ✭✭
    #11
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    It just dawned on me.

    You are trying to protect the device at the other end of the battery cable from super high short circuit style currents. But really, if you are truly not trying to protect from wiring and busbar short circuits, you are trying to protect the same device that is the root cause of these high currents. This makes less sense to me because haven't you now already lost the battle? The device causing the high currents has already failed so there is no protecting it.

    Just trying to wrap my head around this. This is all considering that we know to switch off the battery before we approach lugs with a wrench.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,758 ✭✭✭✭✭✭
    #12
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    It never hurts to be careful !   It sometimes is called overthinking it 😉
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • SumPower
    SumPower Registered Users Posts: 48 ✭✭
    edited November 2023 #13
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    My first experience with DC systems and rectifier yards made me a believer of the "be careful" department as I performed my work. It was all safe and fun, until someone didn't follow safe job procedure.
     Watched one time as a 6" cast axle on a larger forklift vaporized, turned to sparks and shot molten metal 40 feet in every direction when it shorted out on 700 VDc at 110,000Amps. Proved to me that following all safety procedures, written instructions and codes was in my long term best interests.
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  • SteveK
    SteveK Solar Expert Posts: 387 ✭✭
    edited November 2023 #14
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    Looking at the charts above I think we can agree the Nader breakers alone should do a fine job addressing the OP's concerns. They preempt any deficiencies with the Schneider breaker as they would cascade rapidly below 10kA allowing the 250A Schneider breaker to function properly.

    Besides that, the BMS(s) would limit his total current produced 1200A (or 3600A if EG4 says 300Ax12), also allowing the Schneider breaker to perform correctly.

    But there would be no saving the faulty Schneider inverter that caused all the trouble though nor would the chrome on the errant wrench be spared.

    I need a different trap for Michael Myers, I fear.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,758 ✭✭✭✭✭✭
    #15
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    Would say the Schneider Breaker does what it is suppose to do. It is the reason UL 9540 treats the Inv/Chg and the battery as one.

    For homes that I do, I want 9540 because it covers my arse. Below is one system that works for me but not my favorite. If the home is insured and you do not want a claim denied, you better have the permits also. Some AHJ require UL 9540.   

     Mr Myers is always lurking.

    OCTOBER 7, 2021

    https://solar.se.com/us/en/press-releases/simpliphi-power-and-schneider-electric-receive-ul-9540-fire-safety-certification-for-complete-line-of-scalable-energy-storage-systems/

    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • ligwyd
    ligwyd Registered Users Posts: 209 ✭✭
    #16
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    Install complete. Appreciate all the dialogue. As always here.... Great forum......


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  • SteveK
    SteveK Solar Expert Posts: 387 ✭✭
    #17
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    That has to be one of the cleanest systems I've seen so far. Great job!
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  • ligwyd
    ligwyd Registered Users Posts: 209 ✭✭
    edited November 2023 #18
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    Thank you! Originally the box was built for some FLA's. It was my first ever and so I was giving it my best. A little overkill, but 12 of the 100Ah EG4 LL V2's just happen to fit in nicely.......otherwise it would have been server racks...... 

    A lot of time I can never get back in that box, but customer is happy, I'm happy! On to the next one :) 

    Couple of these 30mm frame Longi panels will be replaced since the bus bars in a couple of them are quite visible compared to the rest.... If it was on a roof no big deal, but this array in winter angle will be visible from the ground, so I am swapping them out....

    Thanks again guys for all your feedback. What a great resource that can be shared with others :)
    Peace
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