Originally Posted by r0meboards
Looking for feedback on the most recent version of my electrical diagram.
More specifically the wiring / fuse sizes and if I've missed any components or wires going to the wrong places. Still need to add the Victron smartshunt and cerbo GX components, plus a BMS for the LiFePo4 cells that I have. This is for a 24v system. Thanks in advance!
Looks like a nice system. I have two thoughts:
1) The initial 300A ANL fuse from the battery is probably rated too low in "Amperage Interrupt Current" (AIC). This is not the amps it will blow at (300 which is fine) but is the ability to fully disconnect an extremely high amp circuit. Because a LiFePO4 battery bank has such low internal resistance, it can put >10,000 amps into a dead short. With an ANL fuse, the fuse will blow, but the current may not extinguish and you could get a hot, dangerous arc across the terminals that can light stuff on fire before the battery drains.
I think good ANL fuses are only about 600 AIC and cheap ones from Amazon may not even have a rating. Even the MEGA fuses that are part of the Lynx Power system are only rated up to about 2,000 AIC.
So you should use a class T fuse that will extinguish up to 20,000 amps. The fuse elements are encased in metal and filled with sand. If a big arc tries to develop, the sand turns to glass and quenches the circuit.
They are expensive ($75-100) but you only need one of them as the main fuse leaving the battery and the downstream ones can be cheaper.
I recently found this great link
that discusses the issue from the perspective of boats.
2) There seems to be a miss-match between your 300A MEGA fuse and the 1AWG wire to the inverter/charger. The fuse is there to protect the wire and so has to be rated less than the wires capacity. Even with pure copper, 90 deC rated insulation and in free air, a 1AWG is only rated for 220A. (And that will be a hot wire to touch).
This might be just good enough for this inverter:
- A 3000W inverter at 24 volts is maxing at 125A
- But if the battery is at minimum 20 volts the inverter uses 150A
- And because the inverter is just 90% efficient it really needs 167A to make 3000W AC from 20 volts DC
- Now add 25% headroom for the fuse and you need minimum 208A
So you could A) use a 200A fuse and risk occasional nuisance fuse blows if the inverter is maxed out - but keep the same 1 AWG wire. Or B) Boost the wire to 2/0 which can manage 300A in free air. Or C) some combination of both.