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I'm curious as to what the actual internal resistance of the LiFePO4 batteries are. I see the data sheet is marked at .8 or .9mOhm for 12.8v batteries. Has any one done any testing to confirm? Looking online at other batteries I'm seeing much higher resistance .1 to 1ohm. If the datasheet is accurate I would need to fuse every battery with a class T fuse (20,000AIC) per ABYC E-13 for the dead short current. 12.8/.0008=16,000amps in dead short fault.
I just measured my DIY 180AH LiFePo battery and it has a resistance of approx. 2,7mOhm. This is including the BMS, some connection cables, the busbars and the battery terminals.
So indeed, a short current could reach some kAmps... But what do you mean or want to fuse this so high? What is your usecase for such a 12V battery?
@Jetlag the fuse rating would not be 20,000A. For lithium you need fuses that can break the circuit when subjected to an overload where the current might reach 10,000 or 20,000A, this is the AIC of the fuse, the Ampere Interrupting Capacity. Simple fuses may only have an AIC of 5,000A (even if the rated current is say 400A), a fuse with an AIC of 5,000A when subject to a dead short causing a current of 20,000A will blow BUT the current will continue to flow as an arc because the fuse gap is too small so the device does not offer protection to the cabling / rest of the system.
T fuses, NH fuses can all do this well.
I just measured our 10 year old motorhome 300Ah 4 cell LiFePO4 battery with a YR1035+ meter.
No BMS involved. Total = 0.9mΩ.
Sure it COULD deliver just a few kA if directly shorted at the terminals but hopefully the inline 300A circuit breaker and auxiliary lower valued fuses will prevent that if a dead short o curs further down the line.
Ah, now I got it. I was not familiar with this english abbreviation. Thanks for that!
An yes, you should choose a fuse that is capable to interrupt such a high current.
Just recently, there was published a youtube video to this topic. "Unfortunately" it is in german, - the channel is called Elektronik "EXTREM".
The guy tested some Megafuses, and it turned out, that the fuses from iMaxx (as well as the models from victron) perform very well, and can even interrupt a shorted 16S LiFePo battery with >50V and few kA.
