Fuse Question for 48V System

[John Frum]

Correct. It's marketed as 6000W (2x) surge current. I could test it by hooking up my table saw. But I'm pretty sure I watched an independent review video of someone doing that with this unit already. In terms of sizing, I've planned my fuse and wire size on that 6000W surge. Am I putting too much caution into that circuit?

What wire and what fuse are you using on the battery?
What bms are you using on the battery?
What wire and what fuse are you using on the inverter circuit?

 

[Vigo]

Victron has 58 volt mega fuses

Eaton calls this selective coordination.
Littelfuse calls it fault isolation.

These are excellent tidbits to further my self-education with, thank you! Half of not being able to research something for myself comes down to not knowing the search terms!

For example, I have been wondering if putting lower-voltage-rated fuses in series would suffice by doubling the air gaps an arc would have to cross. In my mind it seems feasible but I have not been able to research it effectively because i don't know how to couch that in search terms in such a way that series is not taken as referring to the rest of the circuit rather than fuses in series with each other. Knowing specific names for things helps tremendously!

Although, by putting that out there I have to acknowledge that trying to kludge lower-voltage fuses into a system introduces other possible risks, such as that adjacent fuses in a fusebox/panel are too close to each other (arcing to different fuse/source/load) or that the design of the fuses does not passively protect you from touching a dangerous level of voltage with your bare hands, etc.

 

[thulle]

I've never seen a class-t fuse smaller than 100 amps.

Bussmann JJN and Littlefuse JLLN goes from 1A to 1200A:

https://eu.mouser.com/datasheet/2/87/Bus_Ele_DS_1025_JJN-347438.pdf

https://www.littelfuse.com/media?resourcetype=datasheets&itemid=78225034-cd5b-4006-8871-38e7378ac8f3&filename=jlln-fuse-datasheet

 

[wpduhe]

What wire and what fuse are you using on the battery?

Main battery fuse will be 200A. 1/0 AWG wire to main distribution. Circuit length less than 20 feet

What bms are you using on the battery?

Daly 16S 200A

What wire and what fuse are you using on the inverter circuit?

I had planned on sizing it for the surge power of 6000W. Fuse size was going to be 200A and I was going to repurpose some 2/0 AWG cable already on the boat. But I would opt for new wire if I size for the continuous power rating.

 

[John Frum]

For example, I have been wondering if putting lower-voltage-rated fuses in series would suffice by doubling the air gaps an arc would have to cross.

I believe that is the theory of operation for this breaker.

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

 

[John Frum]

Main battery fuse will be 200A. 1/0 AWG wire to main distribution. Circuit length less than 20 feet

Lets say you pull 140 amps continuous which is a good max continuous discharge rate for 280AH eve cells.
140 amps
48 volts low cutoff
20 feet(round trip)
1/0 awg
=0.59% voltage drop

if its 40 feet round
=1.17% voltage drop

Prevailing wisdom is to keep voltage drop under 3%, so you are well within spec.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

Daly 16S 200A

Can probably handle 140A continuous but they have very miniscule balancing capacity.

I had planned on sizing it for the surge power of 6000W. Fuse size was going to be 200A and I was going to repurpose some 2/0 AWG cable already on the boat. But I would opt for new wire if I size for the continuous power rating.

Bigger is almost always better.

 

[wpduhe]

Bigger is almost always better.

Obviously, the wire will not overheat and cause a fire if I use 2/0 wire and 200A fuse; but what of the equipment?

If the inverter is capable of 3000W continuous (3000 / 0.9) /48 * 1.25 = ~87A, and I fuse the circuit with a 200A fuse because of 6000W (eh 180A) potential, what risk do I run when it comes to the inverter? Obviously, I'd rather replace a fuse than an inverter. So perhaps I should size the wire for surge and the fuse for continuous. Making my requirements, at least, 1/0 wire and a slow-blow 100A fuse?

 

[John Frum]

Obviously, the wire will not overheat and cause a fire if I use 2/0 wire and 200A fuse; but what of the equipment?

I don't see how the fuse could protect the inverter.
There are passive devices on the circuit that the inverter can protect but the inverter is the load.
If it draws more than its rating and fails to shut down on overload its probably already toast.

If the inverter is capable of 3000W continuous (3000 / 0.9) /48 * 1.25 = ~87A, and I fuse the circuit with a 200A fuse because of 6000W (eh 180A) potential, what risk do I run when it comes to the inverter?

See above ^
I really don't think that inverter has any significant surge capacity.
Cheap and cheerful high frequency inverters usually have 2x surge for ~20 milli-seconds.
That has absolutely no bearing on wire size or over-current protection.

Obviously, I'd rather replace a fuse than an inverter. So perhaps I should size the wire for surge and the fuse for continuous. Making my requirements, at least, 1/0 wire and a slow-blow 100A fuse?

I fuse to protect the wire and the passive components.
BTW fuses with higher amp ratings typically have lower resistance so I generally like to use the largest fuse possible.

 

[John Frum]

This link shows the trip curve for a class t fuse

Fuse A3T / Class T 200 Amp - Blue Sea Systems

Use with Class T Fuse Blocks for circuit protection of devices including inverters. high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries.

www.bluesea.com

The plot only goes out to 500 seconds and at point 300 amps does not even entry the trip zone.

 

[wpduhe]

@John Frum
Thanks for your help. Now I just need to find the right fuses.