Very nice case!
However, I do have my doubts about the 250A fuse used. I've seen people complaining about its construction quality. Also, I doubt if its able to do its job properly. All fuses have 2 ratings: Its fusing capacity (250A in this case) but as important id its interrupting rating. This is the actual maximum current it can handle to disconnect.
For protecting a wire against overloading this is generally not an issue, but preventing a short circuit can cause problems. If you short the terminals of a battery, you will get a huge current. For lead-acid, this is not a big issue, since the internal resistance will limit this to a rather 'acceptable' current.
But with LiFePO4, especially with higher capacity banks (multiple in parallel) the current can become extremely high, bypassing the fuse's interrupting rating. Depending on the fuse design, the fuse will completely blow / 'explode', or just do nothing or burn. (The ones you are using look like thermally ones, so I think with a real decent short, the connections will just weld to each other, and not disconnecting the actual load.
The MEGA fuses for example are rated to approx 2000-2500A (See eg
https://www.littelfuse.com/~/media/...t-down-fuses/littelfuse_mega_ul_datasheet.pdf )
So using those as primary fuse will not fully protect your equipment!
Depending on the wires used, this will add to the resistance of the cells, thus limiting the short-current, but it will be still very high, especially if a short occurs close to the cells.
Another overlooked thing sometimes is the voltage rating. Mega fuses are generally rated up to 32V. Thus using it for a 48V battery bank is not a good idea. Depending on the margin between specs and failure it won't act as a proper fuse: The insulation between the poles should be able to withstand the voltage.
If the actual distance between the poles is low, or the insulation start to burn / become coal (=actually a resistor) it might just arc and let the current continue to pass..
For proper high-current protection for Lithium, you should at least use T-class fuses. Also able to handle higher voltages (eg 125V for the Littlefuse ones), they also have a much higher interrupting rating (20kA or more)
(See eg
https://www.littelfuse.com/~/media/...fuses/littelfuse_fuse_jlln_jlls_datasheet.pdf )
For even bigger banks you might need to go even higher. The Bussmann (Nowadays Eaton) FWP-500 eg is rated for 200kA breaking capability. These are commonly used in bigger UPS systems for example, to protect the battery bank.
To figure out the actual short current is kinda hard, since it has multiple factors (battery internal resistance, connector/lug resistance, cable resistance) which all together are defining the actual current. And the cable resistance depends on where the short is caused. (A full short after a 100m cable run will be much less than a short within 20cm of the cells)
Measuring it will be a pita also, but having a memory oscilloscope and a properly sized shunt, you will see a short voltage spike across the shunt, and you can calculate the actual current from there on. A clamp meter is not fast enough to register these currents, and if they were, they are probably not suitable for the high currents.
It would be really interesting to see some information about proper fusing a battery bank, since I think the issue of proper fusing is way underrated and lot of people are not aware of it. (A 300A Mega fuse used to protect a big 48V / 560Ah battery bank is highly likely to be completely useless, thus giving a false feeling of 'beeing safe'
Maybe
@Will Prowse can do some testing, starting with the cheap thermal ones as used in this build, to see what happens if you do a full short on a high capacity bank (12V 560Ah). I think this will give cool slowmotion footage showing how it's failing.....
With the amount of cells he has,
@Will Prowse probably can show what happens when you use a MEGA or MIDI fuse outside its voltage rating, and see what happens if you push it beyond its disconnect capability ratings.
Would be highly interesting to see
