• Have you tried out dark mode?! Scroll to the bottom of any page to find a sun or moon icon to turn dark mode on or off!

diy solar

diy solar

Opinion on Fuse Setup

aKO

New Member
Joined
Jan 3, 2022
Messages
72
Has anyone used or have an opinion on using the Fuse Boxs in the photo , obviously with larger fuses to suit the system . The fuse box itself is well made and substantial and on the face f it ideal for connecting up to 3 batteries to a Bus bar .

I have incorporated one in my system a year ago and although with just one battery so far its worked as i had hoped , a fuse did blow when i i exceeded the 60amps that it came with however since increasing the fuse rating to 80amps all has worked well and i have never noticed any heat build up at all .

I check and monitor my own system daily but a friend is changing his batteries from 1 to 2 and intends to buy the same fuse box so i feel responsible should something go wrong , the reason forOpera Snapshot_2024-06-25_113114_www.amazon.es.png my post today .

Any advice would be very much appreciated .

Opera Snapshot_2024-06-25_113617_www.amazon.es.png
 
no way.
when you start connecting multiple batteries, part of the danger is one short will back feed ALL the batteries to the short, if the fuse melts into a fireball of plasma the fuse fails to cut off the flowing current, and fire is typical result.
No way would I use the linked fuse holder or fuses as a safety device for batteries. Use Class T fuses, of the correct size, in a proper holder.
Friends don't let friends burn down their home. ;)
 
I never use it .
I use Cube Fuse.
Direct by the battery self .
Than i know for sure the battery is save and the gear .
Cube Fuse are use on boats if a wire break in a metal boat we have a big problem.
A Cube Fuse is for this reason use.

Other like to use t-fuses .
But never i gone use those things on your picture.
Its more use for audio amplifier in cars.
 
So your saying that not only is the Fuse box no good even if connected to only one battery and using only one fuse that the fuses are no good for the application either . I am surprised because before buying the Fuse box i did read about ANL fuses and everything i read says they are good for Audio , vehicle and Solar system circuits .
 
I have used ANL fuses for some locations, but for ultimate fuse protection in LFP battery system (which can output thousands of amps, perhaps 10's of thousands) Class T are the way to go, in a correct holder.
 
Car audio and LFP batteries don't mix well. For only one battery use a MRBF fuse with holder on the post. Then you can take the wire from that to another fuse panel of any type you like.

If you decide to put another battery in parallel another MRBFon its post too.

If you parallel 3 or more batteries then additional fuses besides MRBF are needed, like the class T.

ANL fuses run hotter than MRBF because the have more resistance at a given amperage. They also don't have as high an AIC rating as a MRBF. And the time verse current curve is 10x slower.

And last but not least as mentioned above, in a short circuit situation they tend to explode into fragments and plasma. If the battery vents first and the hydrogen is in the area it can act as an ignition source. See the house burned down thread in up in smoke for an example of Mega fuse and vent. Not an ANL but similar..

 
I have used ANL fuses for some locations, but for ultimate fuse protection in LFP battery system (which can output thousands of amps, perhaps 10's of thousands) Class T are the way to go, in a correct holder.
Well if you do not use bms .
A bms will have limit so Really i do not see a point to use a t-fuses with a good bms systeem.

I have see it by my self by the first start of a inverter.
That my max 600a bms shutdown the systeem.
And my fuses that are lower dit not burn.

A Cube Fuse is a slow blow fuse.
 
Well if you do not use bms .
A bms will have limit so Really i do not see a point to use a t-fuses with a good bms systeem.

I have see it by my self by the first start of a inverter.
That my max 600a bms shutdown the systeem.
The best practice is to not rely on the BMS as a single point of failure. So the fuse or breaker is there as a backup in case the BMS fails with mosfets fused.
 
The best practice is to not rely on the BMS as a single point of failure. So the fuse or breaker is there as a backup in case the BMS fails with mosfets fused.
I agree with that .


Some more information.
 
Last edited:
I've always used breakers for solar installs, never had any problems or call backs due to breakers. I like the fact they are resettable if tripped.
 
I've always used breakers for solar installs, never had any problems or call backs due to breakers. I like the fact they are resettable if tripped.


For straight solar that would work just fine. When you start adding LFP batteries you get into the position of needing fuses. Breakers are super slow compared to fuses. By that I mean if you have 4 x 200ah 12v batteries (very modest install) and they are connected to a bus bar by 2ft of wire. Do the math and figure out what happens to the wire if you get a short from dropping something across the terminals of one of the batteries. Something that could happen. Now if the cable is sized for the standard 200amps + 20% and it suddenly has 600amps feeding it. That wire can go from 25c to 300c in under a second

In that situation the breaker takes around 10 seconds to trip but a fuse takes between 0.01 and 0.1 seconds to blow. I did the math in a thread a few months back and it surprised me how fast the wire was glowing red and the sheath melted off.

Funny thing, the heavier the battery cables slowed the heating down and longer to get hot but only by a second or so.
Longer cables made the biggest difference by giving the current more mass to heat up but that also means more waste heat during normal operations from internal resistance
And if you shorten the cable to around 12in or less the fuse blows and nothing really happens to the cable because the internal resistance is so low it doesn't heat. I suspect this is why ABYC requires fuses for battery wires over 7in.
 
so I will throw this out there since its bothering me, been reading more about fuses then I ever thought. since you guys like to quote the AIC 20k for t fuses. I asked Chat GPT what amperage a 4 gauge wire (typical it seems for a 48v rack battery to bus bar) would completely melt including the copper at less than 1 second. it said based on a math formula, less than 1 second would be between 6000 and 10000 amps. which is well inside of a normal breaker and is what is used on most rack batteries. T fuses are also not ignition protected without a specific cover, which I see almost no one use.

I would love a scenario where a t fuse is needed where both the bms's and the other lower rating fuses don't cut it. Don't forget victron and blue sea both have other fuses used in their rating charts and wiring diagrams. some labeled higher for use with higher amperage then t fuses.
 
ChatGPT is notorious for screwing up this sort of calculations.... many unit conversions and doing math. It is a LLM and not much better than a 10 year old.

If you want to coax it to a correct answer - it has to use the specific heat of copper. Figure the mass in kg of the length of wire. Then the current through the wire. vaporization temp of copper, etc... when it tries to combine all of those you have to watch it like a hawk and check over all the math to see if everything seems realistic. Then only bother doing the math for 1 to 2 seconds or you have to subtract out the lost heat from cooling air and the longer cables. I started with chatgpt 3.0 the same way and it took me a couple of hours checking everything then working it by hand before I was satisfied that I had a valid answer.

Now - in the example I pose we assume that all the BMS are working properly and limit current to 200amps. If they went over that by much or for long it would be a case of them failing which means a dead short internally then thefailure burns open.

There are examples of other fuses online where someone shorts a battery through them. But the most interesting one is on here where someone uses 4 victron batteries, no internal BMS, in series to test a MRBF and the results are carefully measured and also the fuse explodes into a shower of sparks several times.

I think we are all coming around to the idea that we need to use the class T in the ignition safe holder. For a single battery I am willing to use a MRBF and even for two, but no higher. And I am actually using class T for that now.

IMO - this is disputed by several - The house burned down thread was basically mega fuses in plastic enclosure and 7 DIY batteries in parallel. OP was using batrium with the shunt-trip after the bus bar where things were combined. So a single cell vented in one of the batteries creating a short and a 3.2v gradient and the other 6 batteries dumped into it. The hydrogen vent combined with the spark from the Megafuse failure caused the fire.

Victron uses the Megafuse in the Lynx combiners but I doubt they ever intended it to be used between 7 batteries that had no way to cut off current between them.

 
This battery fusing stuff is quite interesting…

( EDITED , For better clarity )

I discussed it with my batt manufactoer at length and as they recommended … I changed my fuses to about 10- 25% above where the bms would start to kick ..e.g. a 110 - 125a classT for a 100a battery and BMS …

I don't want the bms to be everyday my parachute , or tripping all the time .
I would rather buy another class T fuse to replace a blown one and then investigate why I had issue in the first place
J.
 
Last edited:
ChatGPT is notorious for screwing up this sort of calculations.... many unit conversions and doing math. It is a LLM and not much better than a 10 year old.
Haaaaaaaaaa ..I am simply amazed people today would rely on , or much less trust this crap…

I would believe info more from people who have been doing it for years…and not rely on a
collective tech brain of info that may be telling me somthing with an agenda programmed into it..

Yea I know they wouldn’t do that….but

History or factual revision , is a powerful tool … beware of it.

My dad taught me not to believe everything you read…and only half of what ya see….

J.
 
I've always used breakers for solar installs, never had any problems or call backs due to breakers. I like the fact they are resettable if tripped.
Same here. I prefer breakers for everything.
Until the costs go too high, and a fuse makes more economical sense.
 
ChatGPT is notorious for screwing up this sort of calculations.... many unit conversions and doing math. It is a LLM and not much better than a 10 year old.

If you want to coax it to a correct answer - it has to use the specific heat of copper. Figure the mass in kg of the length of wire. Then the current through the wire. vaporization temp of copper, etc... when it tries to combine all of those you have to watch it like a hawk and check over all the math to see if everything seems realistic. Then only bother doing the math for 1 to 2 seconds or you have to subtract out the lost heat from cooling air and the longer cables. I started with chatgpt 3.0 the same way and it took me a couple of hours checking everything then working it by hand before I was satisfied that I had a valid answer.

Now - in the example I pose we assume that all the BMS are working properly and limit current to 200amps. If they went over that by much or for long it would be a case of them failing which means a dead short internally then thefailure burns open.

There are examples of other fuses online where someone shorts a battery through them. But the most interesting one is on here where someone uses 4 victron batteries, no internal BMS, in series to test a MRBF and the results are carefully measured and also the fuse explodes into a shower of sparks several times.

I think we are all coming around to the idea that we need to use the class T in the ignition safe holder. For a single battery I am willing to use a MRBF and even for two, but no higher. And I am actually using class T for that now.

IMO - this is disputed by several - The house burned down thread was basically mega fuses in plastic enclosure and 7 DIY batteries in parallel. OP was using batrium with the shunt-trip after the bus bar where things were combined. So a single cell vented in one of the batteries creating a short and a 3.2v gradient and the other 6 batteries dumped into it. The hydrogen vent combined with the spark from the Megafuse failure caused the fire.

Victron uses the Megafuse in the Lynx combiners but I doubt they ever intended it to be used between 7 batteries that had no way to cut off current between them.


I use it every single day, I am an engineer by trade, So i fact check it constantly...

That said we are going to pretend that a shorted bms, can actually push 20,000 amps? I am doubting that as well.

I read the ENTIRE burn down house thread he had a short in a direct contact cell. I don't think any fuse would have saved him there if the pack itself is on fire.

Thats a large assumption on victron's part. It absolutely is false on Blue Sea's charts, they had large battery banks on boats long before guys were putting large packs in houses. balum was built to deal with marine alternator charging due to the larger banks


Do you have a link to this sparking MRBF video?


Again at the end of the day, the prices aren't really much different over a T fuse. I just like to understand how this stuff works and fails. Then decide how much I want to risk my life.
 
The price of good gear should not be part of the equation you use for what you own to keep you safe …I understand that not everyone can afford the best gear, hell I can’t…everyone can only do the best they can…
but if I see them talking on their iPhone 14 and wearing 80 dollars shoes while telling me they can’t afford good safty gear…well then .[ COMMENT REDACTED ]
get your priority’s straight… or be on the 5 o’clock news…
 
I use it every single day, I am an engineer by trade, So i fact check it constantly...

That said we are going to pretend that a shorted bms, can actually push 20,000 amps? I am doubting that as well.

I read the ENTIRE burn down house thread he had a short in a direct contact cell. I don't think any fuse would have saved him there if the pack itself is on fire.

Thats a large assumption on victron's part. It absolutely is false on Blue Sea's charts, they had large battery banks on boats long before guys were putting large packs in houses. balum was built to deal with marine alternator charging due to the larger banks


Do you have a link to this sparking MRBF video?


Again at the end of the day, the prices aren't really much different over a T fuse. I just like to understand how this stuff works and fails. Then decide how much I want to risk my life.

The current that can be dumped is limited by the internal impedance of the battery. For 12v/4cell it works out to around 3000amps typically.

The fuse might or might not have saved him, but not having it in an ignition safe housing doomed him once it was in a hydrogen atmosphere. The exploding fuse provided the literal spark.

Here is the link
 
The current that can be dumped is limited by the internal impedance of the battery. For 12v/4cell it works out to around 3000amps typically.

The fuse might or might not have saved him, but not having it in an ignition safe housing doomed him once it was in a hydrogen atmosphere. The exploding fuse provided the literal spark.

Here is the link
Thanks for this link, very interesting read, lots of comments of the bms actaully saving the day, personally I would have thought they would catch on fire.
 
BMS MOSFETs are probably a thousand time faster than a fuse if the controller has a high enough sample rate. The problem is when they fail they fail as a short. Of course that just means it is stuck on and can't turn off. This might be when there is an over voltage or overcharge is in progress and if it doesn't cut off it can damage the battery or cause a cell vent or other major issue. So you need a fuse so it can fail safe.
 
BMS MOSFETs are probably a thousand time faster than a fuse if the controller has a high enough sample rate. The problem is when they fail they fail as a short. Of course that just means it is stuck on and can't turn off. This might be when there is an over voltage or overcharge is in progress and if it doesn't cut off it can damage the battery or cause a cell vent or other major issue. So you need a fuse so it can fail safe

I just find it hard to believe the etching and pathing on the bms can actually do 10k amps without melting etc...
 
I just find it hard to believe the etching and pathing on the bms can actually do 10k amps without melting etc...
No, the will melt and burn away, it is how long does it take for that to happen and what else happens in the process. And even twice what is rated will melt balance wires and other bits pretty quick.
 

diy solar

diy solar
Back
Top