Properly fusing four 12v LFP battery packs

K8MEJ

Solar Addict
I currently have two DIY 280Ah battery packs connected in parallel to run my 3000VA MultiPlus and DC loads. I have two MPPT's for solar charging. The system is all installed under the bed in my travel trailer. I am using a Lynx Distributor with MEGA fuses for input from my batteries. Each battery pack is connected to the Lynx bus bars via 2/0 wires between about 24" in length. I have since learned that MEGA fuses aren't recommended for battery fusing due to their low interrupt capacity in short circuit situations.

I'm going to be adding two more 280Ah battery packs giving me four of these packs in parallel. I'm using 280Ah EVE cells from Amy Wan with M6 welded studs. I'm thinking instead of using the MEGA fuses in the Lynx Distributor, I should instead be using a Lynx Power In with MRBF fuses mounted directly on each of the four battery packs' positive terminal. While more expensive, I'd rather go the MRBF route than ANL fuses if I make the switch.

My questions for the group:
  1. In my 12 volt system, are MEGA fuses acceptable or should I use MRBF terminal fuses at each battery pack?
  2. The highest load in my system is the Multi, which can pull up to 200A at 12 volts. If I plan for one or even two batteries to fail or need to be brought offline, what size fuse should I use on each battery pack? I'm thinking 100A.
Thanks in advance for any help.
 

Stepandwolf

Solar Addict
Your system and mine is somewhat similar so a lot of my own research would apply to your system.

In Victron's own sample, they show two Lithium 12V batteries in parallel. On each battery, they have a 300A ANL fuse between the battery and the busbar. Then it goes through the main battery switch. From there, through a 400A MEGA fuse. From there to the 3000 VA Multiplus.

I had already bought a 300 ANL for my single battery bank, but am building my second bank and so I added a second 300 ANL per Victron.

Where I deviated from Victron was by choosing a T Class fuse for the inverter. A user on here convinced me.
  • Inverter Class T slow blow inverter fuse with holder 300 amp
  • Semi conductor fuse
  • Guarenteed to terminate power when blown
  • Specifically made for use with inverters
That is from the AZ description, and as I was told, these are specific to inverters.

If you check the Victron manual that came with the Multiplus, they specify a 300A fuse, so I wouldn't go smaller.

Another user on here said it didn't need to be 300A despite what Victron said, so I talked to the Battle Born tech and he gave me the math supporting the 300A fuse. Why Victron put a 400A MEGA instead, I don't know. I went with the 300A T Class.

So now you have a Victron and a user suggested answer and what I chose to do.
 
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