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Short circuit current LiFePO4 Battery

MrSwede

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Oct 1, 2023
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Sweden
I'm trying to find real world tests of what short circuit current LiFePO4 cells can produce.
And also what the common 16S batteries can produce (or even 16S batteries in parallel)?
Even better would be if the tests also included different types of fuses. To see if/when the arc is not put out.
I know there are theoretical calculations, but real world reviews/tests gives in my opinion a better/clearer view.

I've seen a lot of installations that have way undersized fuses/breakers, and i believe there is no clear information from manufacturers.
It's a very important protection. Does this forum have any estimates and what are they based on?
 
I'm trying to find real world tests of what short circuit current LiFePO4 cells can produce.
And also what the common 16S batteries can produce (or even 16S batteries in parallel)?
Even better would be if the tests also included different types of fuses. To see if/when the arc is not put out.
I know there are theoretical calculations, but real world reviews/tests gives in my opinion a better/clearer view.

I've seen a lot of installations that have way undersized fuses/breakers, and i believe there is no clear information from manufacturers.
It's a very important protection. Does this forum have any estimates and what are they based on?

Even with tests, the short circuit current depends on the specific battery and the connections/test method, so they're no more applicable to your system than a calculation.

V = I * R
I = V / R

I have a GoKWh 12.8V 100Ah battery that measures 4mΩ (pretty close to lead acid). That's a 3200A potential short circuit current.

The typical 280Ah EVE cells are claimed at 0.21mΩ per cell (maybe less). 16 cells in series gives you 3.36mΩ, which yields a 15,238A of potential short circuit current. This assumes that the busbars add no resistance at all. This is why class T fuses are recommended.
 
And yet you see people stacking 3 and more of batteries (with 280/300Ah cells) in parallel, that will be tripling the short circuit current, right?
I'm expanding my battery capacity and would like to know what the best option is.

How come there is so little (none?) tests of LiFePO4 batteries, when they are so common?
A normal/common 16S 280Ah cells in a Seplos/Apexium/EEL case wouldn't differ that much.

Alot of installations are prone to fire if short circuted, because the fuse is not correclty sized.
 
I'm looking to install three 48V 15kWh batteries in parallel and add a NH00 125A (80kA) fuse, that would be enough i believe.
How are all of you thinking of different bad scenarios, and what are you doing to mitigate battery problems, i mean beside low resistance, good crimps, large enough wires and so on.
I'm a bit concerned about the quality of the cells, or does the BMS handle that kind of issues?
 
I'm looking to install three 48V 15kWh batteries in parallel and add a NH00 125A (80kA) fuse, that would be enough i believe.

Per battery? If yes, and their "blow speed" is equivalent to a Class T, I agree. Note that I'm not at all familiar with that fuse type, but it appears to meet the AIC requirements expected.

How are all of you thinking of different bad scenarios, and what are you doing to mitigate battery problems, i mean beside low resistance, good crimps, large enough wires and so on.

That's about all you can do.

I'm a bit concerned about the quality of the cells, or does the BMS handle that kind of issues?

The BMS is supposed to deal with anything at the cell level. If cells short out internally, there is absolutely nothing you can do.
 
Per battery? If yes, and their "blow speed" is equivalent to a Class T, I agree. Note that I'm not at all familiar with that fuse type, but it appears to meet the AIC requirements expected.
No, i was thinking of using that fuse for the group of batteries. I will be having two more groups (each with a NH00 125A fuse), so in totalt nine 15kWh batteries.
The caracteristics is shown here:

1724097864611.png
1724098196304.png
1724098055364.png
 

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Yeah, I've done some research with these. The curves are harder to read than the ones for the US based companies.

What I focus in on typicaly is the 6x rated current. With that you have to assume it is either a short or a situation where multiple other batteries are dumping into one. i.e. the house burned down thread of 7 batteries and one with issues drawing current.

The speeds I've looked at for the Mersen gG fuses and the littelfuse class T of the same size are pretty similar. The real difference is size. The Mersen are filled with sand the same as the class T and they are assembled in an inert atmosphere the same as the class T so there is no gas to ionize.

They are typically rated at a lot higher heat than the class T are because the mounts are typically with them standing in free airflow. Originally designed for small european sub-stations to feed a block of houses.

You can get an explosive proof housing for them or for groups of 3 of them, but they are super expensive.

Another alternative is the BS88 series of fuse, the hard part with those is the mounts. Very hard to find and very expensive. One odd thing about them is they sometimes come as a matched set for higher amperages - i.e. two round fuses with the ends crimped together.
 
Yeah, I've done some research with these. The curves are harder to read than the ones for the US based companies.

What I focus in on typicaly is the 6x rated current. With that you have to assume it is either a short or a situation where multiple other batteries are dumping into one. i.e. the house burned down thread of 7 batteries and one with issues drawing current.

The speeds I've looked at for the Mersen gG fuses and the littelfuse class T of the same size are pretty similar. The real difference is size. The Mersen are filled with sand the same as the class T and they are assembled in an inert atmosphere the same as the class T so there is no gas to ionize.

They are typically rated at a lot higher heat than the class T are because the mounts are typically with them standing in free airflow. Originally designed for small european sub-stations to feed a block of houses.

You can get an explosive proof housing for them or for groups of 3 of them, but they are super expensive.

Another alternative is the BS88 series of fuse, the hard part with those is the mounts. Very hard to find and very expensive. One odd thing about them is they sometimes come as a matched set for higher amperages - i.e. two round fuses with the ends crimped together.
I was looking to get ABB XLP-1P fuse disconnector (and housing) for the fuse above.

1724099887206.png
 
I like that one better than the one where the clear face plate opens and you have to use a handle to pull the fuse out. And designed for it means it should open

You might want to make sure to get the handle to pull the fuses - they have a spot on either end of the body formed in the metal to hook on to. They are only about $10 and if you manage to get one stuck it would probably unstick it.

Mersen puts out a line with and without indicators for seeing if the fuse is blown by just looking at it. Well worth the extra $$ to me, but not sure it would fit that mount.

The NH series fuses are insanly expensive on this side of the pond unless you buy the chineese knock-offs. I have a few that claim to be certified by the german version of the UL standards body, but I dunno if I trust it. Eventually I'll wire up a test set and blow the ones I have just to see what is in them.
 
From that chart, I read:

100A fuse exposed to 180A blows in 100 seconds.
100A fuse exposed to 200A blows in 20 seconds.

View attachment 237659

So not as fast as I thought.


The class T fuses will run almost 10 minutes at 2x rated current of you look at those curves. It takes 6x to be sub second from the charts. Fast for a fuse but prevents nuisance blows.
 
Also, don't forget the fuse between the bus bar and the inverter.

I've seen people putting fuses between the MPPT and the bus bars and I'm not sure of the need other than to protect the wire in case of a short near the MPPT. Do MPPT short out and pull current so they need to be fused?
 
I'm using 70mm2 fine stranded copper cable with M8 lugs.
Each battery should have a fuse between itself and the common busbar. Full Stop.
Each battery has its own fuse aswell, like this.

Busbar
|
NH fuse
|
- ANL fuse (inside battery)
|
-ANL fuse (inside battery)
|
-ANL fuse (inside battery)
 
Also, don't forget the fuse between the bus bar and the inverter.

I've seen people putting fuses between the MPPT and the bus bars and I'm not sure of the need other than to protect the wire in case of a short near the MPPT. Do MPPT short out and pull current so they need to be fused?
I'm using the Victron Lynx busbars, and the MPPTs and the inverter/chargers will have fuses aswell :D
 
Really really not a fan of the ANL style fuse, especially enclosed, and especially where it can provide a spark if a cell shorts and vents. Low AIC and they generate a lot of heat. The ANL is plastic with gold contacts. If you must stick with that look for the ANN or CNN variety - still puts off heat but the ANN blows much faster and the CNN has an indicator that it has blown. None of them will contain sparks if there is a dead short that causes them to blow.

Were the batteries DIY? Kits? off-the-shelf?
 
Really really not a fan of the ANL style fuse, especially enclosed, and especially where it can provide a spark if a cell shorts and vents. Low AIC and they generate a lot of heat. The ANL is plastic with gold contacts. If you must stick with that look for the ANN or CNN variety - still puts off heat but the ANN blows much faster and the CNN has an indicator that it has blown. None of them will contain sparks if there is a dead short that causes them to blow.

Were the batteries DIY? Kits? off-the-shelf?
Bought EEL V3 cases including Seplos BMS, purchased cells from Jenny.
 
OK,

so were it me I would skip the ANL internally and connect the wire from the battery straight to the terminal for output. note - I am assuming the ANL is between the battery and the positive post while the BMS is between the battery and the negative post. Then I would put the NH style fuses between the bus bars and the battery packs. No fuss, no muss.
 
When calculating the short circuit current of LIFEPO4, where do we factor in the size of the battery, in amps? In good old lead days the manufacturer supplied a chart with the short circuit current for each battery based on amp size.
 
But a 10 amp cell won't have the same amount of amps flowing compared to a 1000 amp under a fault condition (ie direct short)- I'm trying to calculate fuse/breaker break load capacity (the load at which the fuse/breaker can sustain before being destroyed - not to be confused with trip current).
 

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