Battery fuse AIC calculations

[Robert Ibe]

I am interested in finding out the AIC requirements (or even better a simple formula to calculate the AIC requirements) for fusing my eve lf280k v3 16 cell battery banks(5) (both individually and all 5 combined ) I am building without taking the time to get a PHD in the subject of LFP chemistry/meteorology/ and how moon phase variables affect it all.
Anyone got a clue they could spare??

 

[Madco]

LiPO4 cells have an internal resistance on the order of 500uOhm, so Ohm's law would predict a fault current on the order of 48/.5 kA or about 96kA. That is really large, so large in fact, that there isn't a lot of equipment out there with that high of a SCC rating. Another issue is that it is DC. AC over current protection devices rely on phase reverse to extinguish the arc when the device opens. DC has no such phase reversal, so reliance is placed on an inert material like sand to extinguish the arc. As a result, at high fault current levels, it is tricky to safely interrupt.

One thing working in your favor is the resistance associated with the series cell wiring, wiring to "the outside world", and connections. These resistances will tend to swamp the cell resistances, maybe by a factor of two, so your available fault current may only be 1/3 to 1/2 the 96kA figure.

Perhaps Eve offers some data on cell impedance or resistance to allow a better analysis.

I would proceed assuming an available fault current of 32 to 48kA and find an OCP device with that level of AIC.

Hope this helps!

 

[Robert Ibe]

LiPO4 cells have an internal resistance on the order of 500uOhm, so Ohm's law would predict a fault current on the order of 48/.5 kA or about 96kA. That is really large, so large in fact, that there isn't a lot of equipment out there with that high of a SCC rating. Another issue is that it is DC. AC over current protection devices rely on phase reverse to extinguish the arc when the device opens. DC has no such phase reversal, so reliance is placed on an inert material like sand to extinguish the arc. As a result, at high fault current levels, it is tricky to safely interrupt.

One thing working in your favor is the resistance associated with the series cell wiring, wiring to "the outside world", and connections. These resistances will tend to swamp the cell resistances, maybe by a factor of two, so your available fault current may only be 1/3 to 1/2 the 96kA figure.

Perhaps Eve offers some data on cell impedance or resistance to allow a better analysis.

I would proceed assuming an available fault current of 32 to 48kA and find an OCP device with that level of AIC.

Hope this helps!

Thanks here is what the evlithium site says about the lf280k cells I am using ( impedance resistance:≤0.25mΩ )

I plan on placing fuses as close to each battery bank as I can and was looking at class t 300A 20ka AIC blue sea units + I want to put in high quality breakers as a disconnect for each bank , I found some with an Icu: 20KA and Ics: 20KA but didn't want to jump the gun on these close to $200 units if they are not adequate.

It looks like I will buy an IR tester to get real numbers on my assembled battery packs before proceeding. Does anyone know if the YR1035+ is capable of testing the assembled battery packs??