Fusing on parallel 12V batteries - T-class required for each battery, or just MRBF?

[WorldwideDave]

I have 4 batteries. 2 are new store-bought, 2 are DIY. All are 12V lifepo4. All have 100A BMS or greater. All cells are 1C rated (I think - know for sure 2 of the packs are).

Going to connect these all in parallel, but cannot put a MRBF on the positive terminal of the DIY batteries. So i was going to run conductors from all 4 batteries to a 6 post bus bar. on the bus bar I was going to have 6 MRBF holders - 1 for A/C to D/C charger, 1 for the solar charge controller, and the remaining 4 for the 4 batteries in parallel.

Originally I was going to run all 4 batteries, each with t-class fuse, to the bus bar. But it seems that might be overkill for 100Ah 12V batteries.

I was going to consider running 4 batteries to their MRBF hanging on a 6 post bus bar, then run a t-class fuse between that bus bar and another bus bar #2, and on bus bar #2 I would then hang 2 other MRBF for the SCC and AC to DC charger.

Thoughts?

 

[wpns]

MRBF is fine for 12V. Should be as close as practical to the battery terminal.

Can you post pictures?

 

[WorldwideDave]

MRBF is fine for 12V. Should be as close as practical to the battery terminal.

Can you post pictures?

not tonight - calling it. Let me get the two new store bought batteries charged up. Also waiting for Poron to arrive to do final boxing on my DIY batteries. I have to discharge everything a bit before I can build the box. What is the best way to discharge the batteries in parallel fast without an inverter (10 A is fine - would run all day I'm sure - just need something other than inverter right now).

 

[wpns]

car headlights?

 

[WorldwideDave]

car headlights?

oh that's great - I do have some old T-3 bulbs from 1959 I can connect them up I suppose. Maybe I shouldn't be using bulbs so rare - probably have a halogen or something, too.

 

[WorldwideDave]

The bulb idea worked, thanks. Not a lot of power, but good enough. Warning - headlights get hot over time. Seeking creative way but suppose I can put it in a pot or something on the counter. also will add a fuse. Though really I'd like a tester than can discharge 3.2V and up to 60V if one exists. Thinking long term. Suggestions?

 

[WorldwideDave]

MRBF is fine for 12V. Should be as close as practical to the battery terminal.

Can you post pictures?

More pictures coming your way. Here's the preliminary idea that worked okay with just 2 batteries, but the blue sea t-class fuse, fuse holder, and cover cost as much as the eco-flow battery I just bought. So with it being 12V, looking at other options, and I already have the MRBF and fuses and bus bars, so why not change it up. Here you go...

preliminary/original, without shunt and other things in the drawing yet:



Now with MRBF and shunt, and t-class fuse moved, and as many batteries as I can put in parallel (N, N+1, up to 8) :

 

[wpns]

I like the kill switches on the individual batteries, so you can take them offline for service.
Can the DC breakers and PV Disconnect be the same device?
Why the T-class fuse in the lower picture? I like the upper one with individual switches and a single fused positive bus bar...

 

[WorldwideDave]

I like the kill switches on the individual batteries, so you can take them offline for service.
Can the DC breakers and PV Disconnect be the same device?
Why the T-class fuse in the lower picture? I like the upper one with individual switches and a single fused positive bus bar...

all great questions.
t-class fuse - with 4 batteries in parallel, I thought maybe having one there would prevent a massive surge of say 320 amps to an inverter that can handle about 150 amps.
I already have dc breakers and a pv disconnect. They can be the same device, but I prefer to keep the PV disconnect close to all the stuff at the house, and the breakers close to the panels 75 feet away. Thoughts?
Kill switch - I only have two, but I have 4 batteries. I know some use the DC breakers on the batteries and use that as a kill switch. That was on my radar, but not quite yet.
I want a battery kill switch in case there's a true emergency - flip the PV disconnect, flip the battery kill switch, and hope the inverter or solar charge controller doesn't melt.