Sizing fuses

[taliv]

Started a new thread so as not to derail the one this quote came from

in a pinch the terminal block can be removed entirely whereas an ANL block spliced in not so much unless you are wise enough leave your self enough slack to bridge the gap, presuming you cant get any fuses and have rectified the situation.. but really your master battery fuse should never really pop, the fuse box downstream should start blowing easy to obtain blade fuses long before this one pops.. the main battery fuse is more to prevent the rubble of your vehicle from catching on fire after an accident..

however having said that, I do carry a spare master fuse in my trailer even though I never expect to use it.. but I do that for lots of things thanks to my time in the BoyScouts.

my victron dealer also a blue sea dealer set me up with post style fuse holder which is great. However he said it should have a 100A fuse in it for my battery which is rated for 100A continuous and much higher in a short time.
actually I have two batteries and one fuse on each.

max load I could reasonably pull would be under 200. And I’ve taken great care to ensure cables to and from batteries are same length.
Others however have said the fuse should be 20% higher than battery rating. Cable is short and rated to 300A. And there are fuses downstream close to the loads so they should pop way before the battery ones do. But In an event like a wreck or something having 100a on each May make sense. I just wonder per your post above what the odds are that a quick draw of some sort would cause that fuse to blow occasionally instead of never.

 

[dreadlocks]

If you dont have any loads expected to reach near 100A then that would be fine.. you also have to account for multiple things running.. one simple way would be to add together all the fuses in your circuit box and ensure that your main battery fuse is larger than the sum of those..

I've got a 200A fuse on my battery, thats the highest the battery is rated for output (intermittently) and I dont expect to come close to that normally.. so if it sees 200A for some reason I'd like it to pop, the wiring and bus bars down stream are all rated for >300A so they wont catch fire before the fuse does its job.. I've got a 1200VA inverter and most load I've seen is ~100A, so in my case my fuse is 50% larger than typical max loads.. very unlikely to have a nuisance trip if someone tries to run too much at the same time.. that 200A master fuse is only going to blow if something has gone horribly wrong.

The main battery fuse only job is to protect the distribution of power from the battery to protected sub-circuits.. from there the circuits should be protected with their own fuse.. all wiring between the battery and distribution circuits should exceed the main battery fuse's rating.. ideally the only likely scenario where this fuse blows is something catastrophic, its going to try and stop the battery from uncontrollably dumping its charge in a way that's sure to start a fire.. if it ever pops in the field and you cannot 100% determine the reason w/confidence, you surely dont want to hook it back up or try to bypass it or else you can pretty much expect damage.

 

[WOODY2]

You may consider using circuit breakers instead of fuses. For instance if you were to pop a fuse in BFE a replacement may not be readily available, in addition if you were to secure a replacement and didn't fully correct the original issue whoops you may need another one.

 

[dreadlocks]

most DC circuit breakers are total garbage I'd say the chances are higher your breaker will fail and you wont have a replacement readily available than a fuse, plus fuses are cheaper to carry spares than breakers.

 

[Alloy]

I like switching breakers but I only use DC rated BlueSea, Carlings Technologies and Midnight Solar breakers.

Don't think I've ever had to replace a defective DC breaker.

Our 3000w inverter has a 400A fuse which I've blown twice by being careless while working on the system.

Installing the switching breakers




After install but no wiring





After blowing numerous fuses on the USB plugs I made USB panel with a 5A switching breaker.



Some places fuses are best. Each of our 4 battery banks has a 200A fuse.

 

[Ozrockrat]

most DC circuit breakers are total garbage I'd say the chances are higher your breaker will fail and you wont have a replacement readily available than a fuse, plus fuses are cheaper to carry spares than breakers.

Also consider the thermal aspects of any circuit breaker. In my truck last summer my 100amp breakers were tripping with less than 50 amps due to the high ambient temps. (130 + in the cabinet where the solar controller resides.)

ANL fuses are cheap if you buy them early and expensive if you pick them up 1 at a time from an auto parts place. Easy to have a bunch of spares stashed somewhere in your rig. Just don’t forget where that perfect little stash place is .

 

[dreadlocks]

thats a pretty slick setup Alloy.. alot nicer quality than most mobile breaker setups I've seen..

However, even w/BluSea there's a significant performance difference between their breakers and fuses.

here's a 200A BlueSea Fuse, blowing 600% at 0.10s, with a lower limit of 0.01s

Here's a 200A BlueSea Fuse, blowing 600% in 1 full second, 10x longer to respond than a fuse.

Yeah 9/10th of a second is not a huge amount of time, but its enough time to let the magic smoke outta whatever just faulted..

 

[dreadlocks]

yeah assuming no inverter directly wired to battery with this as the primary OCPD, as most larger inverters instruct you to wire em up.. those might have internal fuses but thats even less field servicable.. alloy's 300A fuse on a 3000VA inverter seems to be too small IMO and not surprised he's had a few nuisance trips.. I know if I put a 100A fuse on my 1000W inverter it'd had numerous nuisance pops by now, like when my wife tried to run the microwave and toaster at the same time and the inverter overloaded and faulted out.

 

[Alloy]

yeah assuming no inverter directly wired to battery with this as the primary OCPD, as most larger inverters instruct you to wire em up.. those might have internal fuses but thats even less field servicable.. alloy's 300A fuse on a 3000VA inverter seems to be too small IMO and not surprised he's had a few nuisance trips.. I know if I put a 100A fuse on my 1000W inverter it'd had numerous nuisance pops by now, like when my wife tried to run the microwave and toaster at the same time and the inverter overloaded and faulted out.

400A fuse on the inverter.......No nuisance trips. Blew the 400A twice (wish they didn't blow so fast ) while working on the system with the power on....same thing happens with the breakers but those don't cost $30 when they trip.

Fuse/Breaker protect the wire. With my OCPD the wire is not undersized so 9/10th of a second won't do any harm.

Speaking of OCPD...here's the grounding block for the BMV712.







Disconnects for the 4 battery banks with 1/2" copper tying them together.


Base to protect the NAS drives while driving off road.

 

[taliv]

Lol that’s an awesome suspension on those nas drives. Need the net app part number lol

 

[DaveInDenver]

Lol that’s an awesome suspension on those nas drives. Need the net app part number lol

Yeah @Alloy, that is f'n clever.

 

[rayra]

All the spare blade fuses you could want, sitting in auto wrecking yards, for cheap. And they don't cost much if you have to have 'New'.

To the question in the OP, 10-20% under the rating of your wire, and a good bit over your anticipated max demand. whatever works between those two boundaries.

Ridiculously, my Sub's factory blade fuses come in three sizes, Mini-, ATO and Maxi. Plus the hardware I've added. I carry a lot of spares.

 

[Hillbilly Heaven]

I have to agree that is a nice suspension system for the NAS. I have to ask what do you need the NAS for?

 

[Alloy]

I have to agree that is a nice suspension system for the NAS. I have to ask what do you need the NAS for?

Same thing as home....pictures, camera system, movies. Not big on kids watching movies (60" TV) while camping......more for time spent inside on winter trips than in summer. Installing satellite internet has been a 2-3 year debate. When the Covid thing started we were out of communication for 2 weeks that was really nice.

 

[taliv]

You need help lol

On a positive note: victron has the min and max fuse size printed on the side of the device. So that makes it easy