Main fuse size on battery ?


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Rasmusm88

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Joined
Mar 2, 2022
Messages
21
Hi all :)

I'm in the planning/ordering parts process of my build. I've build a 14s200p / 22kwh pack, I have bought an ABB s3n 200 amp main breaker with trip. But I should have a fuse on my main positive close to the battery right?

My problem is with sizing it. Am gonna run a Victron multiplus II gx 48/5000 it's rated at 4000w @ 230v continuously. So that is ~ 78amp on the battery at nom. 51.8v.
Thing is, it can peak power at 9000w for a short amount of time, so that is 175a how big of a fuse should I put there ? I doubt it will ever hit peak power but yea ... Wondering

Have a nice day :)

From Rasmus
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
2,121
Hi all :)

I'm in the planning/ordering parts process of my build. I've build a 14s200p / 22kwh pack, I have bought an ABB s3n 200 amp main breaker with trip. But I should have a fuse on my main positive close to the battery right?

My problem is with sizing it. Am gonna run a Victron multiplus II gx 48/5000 it's rated at 4000w @ 230v continuously. So that is ~ 78amp on the battery at nom. 51.8v.
Thing is, it can peak power at 9000w for a short amount of time, so that is 175a how big of a fuse should I put there ? I doubt it will ever hit peak power but yea ... Wondering

Have a nice day :)

From Rasmus
I have AIMS 12,000w that can peak at 36,000w for 20sec. I use a Heinemann 250a Breaker. 250a * 48v = 12,000w and indeed, the breaker tripped at an 18620w surge within a second or 2 - e.g. before the AIMS 20sec surge / breakers tripped.

Part of this is the type of breaker you buy. A guess a 'normal' breaker would trip within a couple of secs of overload. But a recent @DavidPoz youtube showed that breakers have different characteristics and you can buy ones that are *very* slow to trip.
View: https://youtu.be/q-uDyzkKwVA


Remember the breaker is primarily to protect the wire - not the Victron. Don't get anything too large for the wire. I'll bet like the AIMS that the Victron has it's own protection :)
 

Rasmusm88

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Joined
Mar 2, 2022
Messages
21
Hi thanks :) yea I bet the victron has its own protection.
I will watch the video tomorrow :)

It's all confusing in this new world to me hehe. So the fuse I'm thinking about is to protect the battery right? I might not be smart enough to figure it out, but in my head I figured a fuse on the battery, even tho all individual cells are fused.
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
2,121
Hi thanks :) yea I bet the victron has its own protection.
I will watch the video tomorrow :)

It's all confusing in this new world to me hehe. So the fuse I'm thinking about is to protect the battery right? I might not be smart enough to figure it out, but in my head I figured a fuse on the battery, even tho all individual cells are fused.
Above, you said you bought an "ABB s3n 200 amp main breaker with trip" as you're main breaker. I interpreted this as the main breaker between your battery and the rest of the system.

Breakers must protect the wire and secondarily protect things like the battery. So assuming you're wire can handle 200a, then the question is can the battery handle 200a. 200a in this context would be 200a @ 48v. So a 14s200p would be 200a/200cells = 1a/cell.

The question is then, can you're cells handle 1a as the max?

The next question - did you test your cells at 1a during your cell processing? If so, then you've seen them pass a 1a discharge test and 200a max should be perfectly OK.

For longevity, e.g. longer number of cycles, a lower regular load of 0.5a/cells or 100a @ 48v would be better.
 

Rasmusm88

New member
Joined
Mar 2, 2022
Messages
21
Yes, I think I get it now thanks. Planning on using 50-70mm2 cable. And using batrium to trip incase of emergency. Not sure about the trip curve of the ABB though. But both 50-70mm2 should be able to handle 200a.
My cells will rarely see much load, only ~2.5kw duing night when I'm charging my Nissan leaf, and also some load when cooking dinner.
 
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