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diy solar

Upgrading battery pack - fuse requirement

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Saucy2ubud

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Feb 15, 2022
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Good Morning all - I have been using a 24 volt (4X 12 v 100ah Li batteries) for a few years now and have had a 250 amp fuse between the inverter and battery bank. I have bought another set of batteries ( 6 in total now) and looking for 350-400 amp fuses ...and no luck. I was wondering if there as any other way to connect fuses to ensure the safety of my system?
 
I think you need to understand how many amps are going to be in the wire. Then select a fuse a bit (20%?) above the ampacity of the wire. That way the fuse protects the wire.
 
Yes it is - so does that mean that i don't have to change the fuse - I thought the fuse was based on the battery amp. A 2/0 under 50 ft will take up to 450 Amps - but my fuse is 250Amp - i assumed that the amp of the battery bank determined the fuse size - if that is not the case am I good to just hook the new set of batteries with the existing fuse?

I have used solar for a few years but a novice when it comes to upgrading so please educate
 
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hwy17 - Well I'm increasing my battery bank form 24V 200 Amphours to 24V 300 Amphours - FROM: 4X 12 v 100ah Li batteries TO 6x12V 100ah
 
Consider to wire your battery packs to a bus bar.

Use safety protection for each parallel battery string, I like to use a breaker like these blue sea 187s.

187-Series - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
www.bluesea.com www.bluesea.com

Doing it this way you can use 2 awg wire for each battery pack string.
 
Listen I appreciate all your comments and we are going in a circle, no one has really given me an answer to what I am asking and I believe the more info I give we are still not going any where.

I have a 2/0 cable the cable takes up to 400 amps - I think my 250 amp fuse should do what its supposed to do. I the current if more the fuse will blow fuse and protect the other stuff I have - 3000*1.25/24V gives me a fuse rating of 150 Amps . I hope this math is right. (3000 is my inverter wattage).

There are folks on this forum like me who don't know/ understand and would like a simple answer sometimes. I appreciate all the responses and next time don't reply if you don't have an answer- please n thanks.
 
2/0 cable cannot handle 400A. Best it can do is 285A on very short runs.


Fuses are for protecting wires. Hook a AA battery up to an LED with 4/0 cable and the right fuse is 400A. Hook a 5kW inverter to a 15kwH battery bank with an 18 ga wire and the correct fuse is 20A. Fuses have absolutely nothing to do with loads or equipment. Size the wire for the load, size the fuse for the wire. Really simple.
 
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Saucy2ubud said:
Listen I appreciate all your comments and we are going in a circle, no one has really given me an answer to what I am asking and I believe the more info I give we are still not going any where.

I have a 2/0 cable the cable takes up to 400 amps - I think my 250 amp fuse should do what its supposed to do. I the current if more the fuse will blow fuse and protect the other stuff I have - 3000*1.25/24V gives me a fuse rating of 150 Amps . I hope this math is right. (3000 is my inverter wattage).

There are folks on this forum like me who don't know/ understand and would like a simple answer sometimes. I appreciate all the responses and next time don't reply if you don't have an answer- please n thanks.
Click to expand...

We're not just here for your use and pleasure. We also have an obligation to educate especially when dealing with a safety item like this.

Now you know how to size a fuse, 1.25X (rounded up) the conductor rating. If you have oversize conductors, you can use 1.25X the maximum possible current (rounded up).

For your calculation, a 3000W inverter is not 100% efficient. .85 is a commonly used efficiency, so:

3000W/24V/0.85 = 147A

1.25X147A = 184A which puts you at a likely size of 200A. Since your wire can handle > 250A, the 250A fuse is fine.

My point was that since you didn't change your wire, you don't need to change your fuse. There is no good reason to install a 300A fuse.
 
sunshine_eggo said:
We're not just here for your use and pleasure. We also have an obligation to educate especially when dealing with a safety item like this.

Now you know how to size a fuse, 1.25X (rounded up) the conductor rating. If you have oversize conductors, you can use 1.25X the maximum possible current (rounded up).

For your calculation, a 3000W inverter is not 100% efficient. .85 is a commonly used efficiency, so:

3000W/24V/0.85 = 147A

1.25X147A = 184A which puts you at a likely size of 200A. Since your wire can handle > 250A, the 250A fuse is fine.

My point was that since you didn't change your wire, you don't need to change your fuse. There is no good reason to install a 300A fuse.
Click to expand...
I understand now - TY
 
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