LIFEPO4 Battery discussion thread

wingnut771 said:
Fuses are to protect the cable, so the fuse goes before the cable melts.

So cable should be able to handle 25% more than the fuse imho, so 150A fuse and 200A cable.

@denmendez65, what do your fuses look like?
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Not really.

A cable is rated for that "continously". So if your cable is rated for 100A for example, you can use a slightly slower rated 100A fuse. One that pops say 5 seconds later if it sees 100A.

A 100A continiously rated cable can handle 125A for maybe 30 seconds and 150A for maybe 10 seconds etc. There is a graph for this stuff.
 
wingnut771 said:
Oh you have breakers not fuses. Each 5kWh battery would be 100A plus 25% so 125A fuse. So if 2 batteries, then cable feeding inverter should have 250A fuse and 300A cable?
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So if the battery has a breaker no fuse it required? I have the 160A fuse disconnect before the inverter.
 
cavedog said:
100A as per the spec sheet. Not sure if it matches the bms but BMS will probably max at 110a

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Screenshot 2026-05-20 105949.jpg

I see this. I assume your cables are rated similar?
 
denmendez65 said:
Not really.

A cable is rated for that "continously". So if your cable is rated for 100A for example, you can use a slightly slower rated 100A fuse. One that pops say 5 seconds later if it sees 100A.

A 100A continiously rated cable can handle 125A for maybe 30 seconds and 150A for maybe 10 seconds etc. There is a graph for this stuff.
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Yes, but how much efficiency/energy are you wasting to heat?
 
wingnut771 said:
Oh you have breakers not fuses. Each 5kWh battery would be 100A plus 25% so 125A fuse. So if 2 batteries, then cable feeding inverter should have 250A fuse and 300A cable?
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I have both. A 125A breaker and 32A fuses between each battery string.

Fuses are to avoid thermal runaway issues and cell shorting. Cable protection is there but that was an afterthought. My cables are overrated for the batteries between each string I have.

My main cable is rated for 200A. The 125A breaker was sized to protect the batteries themselves from over discharge since I had to llimit to 25A per string (the max safe discharge for GELs).

That was my design philosphy for how I did my stuff.
 
wingnut771 said:
I would still have a fuse as breakers can also fail.
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So the victron mega fuse on each terminal with a fuse holder is the best solution then. I would need battery cable like this then because those fuses won't fit directly onto the battery terminal.

Screenshot 2026-05-20 110816.png
 
denmendez65 said:
I have both. A 125A breaker and 32A fuses between each battery string.

Fuses are to avoid thermal runaway issues and cell shorting. Cable protection is there but that was an afterthought. My cables are overrated for the batteries between each string I have.

My main cable is rated for 200A. The 125A breaker was sized to protect the batteries themselves from over discharge since I had to llimit to 25A per string (the max safe discharge for GELs).

That was my design philosphy for how I did my stuff.
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Lets stick to LFP here and not banks of 12 gels.
 
wingnut771 said:
Lets stick to LFP here and not banks of 12 gels.
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In his case he needs a load disconnect switch which he says he has and fusing between each positive leg.

My breaker is my load disconnect switch and I still have fuses on each positive leg. I fail to see how LFP is different to GELs? A battery is a battery. Parallel batteries are treated the same for every installation.
 
cavedog said:
So the victron mega fuse on each terminal with a fuse holder is the best solution then. I would need battery cable like this then because those fuses won't fit directly onto the battery terminal.

View attachment 1909366
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1779268261264.png
1779268386114.png

There are these terminal fuses which saves you making another cable but I hear they are not very reliable:
1779268428215.png
 
denmendez65 said:
In his case he needs a load disconnect switch which he says he has and fusing between each positive leg.

My breaker is my load disconnect switch and I still have fuses on each positive leg. I fail to see how LFP is different to GELs? A battery is a battery. Parallel batteries are treated the same for every installation.
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Yes, its just we dont use puny 30A fuses in LFP land. :P
 
wingnut771 said:
Yes, its just we dont use puny 30A fuses in LFP land. :P
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Well yes, obviously 🤣 .

He needs to size it according to his stuff. If his cable can handle 200A like mine, then size the fuse to the max discharge of the battery which may be 100A or 150A. Depends on his. Fuses are cheap, I wouldn't rely on electronics to limit discharge.
 
wingnut771 said:
I dont want cables to be hot with 5000W load.
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Cables we use on instllations hit 90 degree to 100. They are designed to run like that. Hot is subjectve. XLPE insulated cable if I recall correctly.

Not battery installations. But DC for motor fields.
 
denmendez65 said:
Well yes, obviously 🤣 .

He needs to size it according to his stuff. If his cable can handle 200A like mine, then size the fuse to the max discharge of the battery which may be 100A or 150A. Depends on his. Fuses are cheap, I wouldn't rely on electronics to limit discharge.
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I would make it multi layered.

Layer 1: BMS (100A)
Layer 2: Breaker (125A)
Layer 3: Fuse (150A)
Cable: 200A
 
denmendez65 said:
Well yes, obviously 🤣 .

He needs to size it according to his stuff. If his cable can handle 200A like mine, then size the fuse to the max discharge of the battery which may be 100A or 150A. Depends on his. Fuses are cheap, I wouldn't rely on electronics to limit discharge.
Click to expand...

Not the Victron mega fuses. They are R500+ each
 
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