Class T vs ANL fuse
- Thread starter MarvRVHam
- Start date
Regarding BS88 type fuses: remember you need to pick the fast acting ones. In practice, that means something like a 200FM or 200LMT (sticking to 200A for reference, a 100LET for 100A for example should do).
These fuses are used with the main purpose to prevent a short circuit and its consequences (fire, destroyed wires, damaged cells). The wires will survive with 1000A for 1 second. Especially if you are creating a system that can operate at 200A continuously.
What matters is what is the short circuit current, the time that the fuse will take to trip under it and if your wires system will survive with that.
curiouscarbon
Science Penguin
- Joined
- Jun 29, 2020
- Messages
- 3,024
the wires should be specified to tolerate that sort of condition.
fast blow fuse is appealing to some for the impression it will clear the fault before more advanced damage might occur.
eg if the BMS shorts closed, the wires might be ok for a huge surge but some component in the BMS might ignite with a "long/slow" 1 second fault.
it is for this reason that fast blow class-t are my preferred fuse for my DIY stuff. it should pop quickly and reduce chance of secondary fire
disclaimer i am an amateur
fast blow fuse is appealing to some for the impression it will clear the fault before more advanced damage might occur.
eg if the BMS shorts closed, the wires might be ok for a huge surge but some component in the BMS might ignite with a "long/slow" 1 second fault.
it is for this reason that fast blow class-t are my preferred fuse for my DIY stuff. it should pop quickly and reduce chance of secondary fire
disclaimer i am an amateur
These days, fuses are also specifically useful to protect semiconductors (google "semiconductor fuse"). With a fast acting fuse, your BMS will likely survive (I tested this). With a slower fuse, your wires will be fine, but you will likely fry the BMS. Keep in mind that short circuit current with a BMS that starts to smoke/burn might be much lower than a direct short on the battery terminals outside the BMS. LiFePO4 by the way also has a more limited short circuit current compared to e.g. LiPo or other chemistries.
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
The BMS should trip on short circuit current in microseconds.
The semiconductor fuse should blow in milliseconds.
Therefore if the semi fuse blows it means the BMS has already failed.
The question I have is, will the really fast blow fuses prevent the already failed BMS from causing a fire?
Last edited:
So, from personal experimentation: I have used a 100A JK BMS, with a 225A class T fuse, and shorted the whole thing (48V LiFePO4 battery). The class T fuse blew before the BMS knew what happened. The BMS survived in all tests (I did this multiple times; this was when I could get a class T fuse for €20).
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,694
"High Speed Fuse", 350A FE, FM fuse at 2200A clears in 0.01 second
(Clears? or "virtual pre-arcing time", whatever that is?)
These have a graph for "Total clearing I^2 t", don't also see what current is guaranteed not to clear or damage them. Maybe it is "pre-arc" in the table.
Class T JLLN 300V is similar.
Class T JLLS 600V, needs 4200A to clear in 0.01 second. 2200A would clear in 0.3 seconds
(You may need to search Littlefuse site to get datasheet; those links may have been served to me.)
https://www.farnell.com/datasheets/712509.pdf semiconductor fuses
350FM, 2200A "virtual pre-arcing time" 0.01 seconds, below that time (half a 50 Hz line cyle) curve extends to 12,000A 0.0001 seconds
These also have "pre-arc" and "clearing" in a table (energy given as current x current x time), I think only for AC not DC. Time to clear DC might be longer, at least where time works out to more than half a line cycle (which helps stop AC current)
I had expected class T to be slower, time delay compared to high speed semiconductor which is used to protect transistors. Looks like class T is fact acting, confirmed by Up North's tests. An by people blowing them with capacitor pre-charge.
Whichever you choose, make sure intended surges are well below clearing current/time. Deal with precharge of capacitors if needed.
John Frum
Tell me your problems
- Joined
- Nov 30, 2019
- Messages
- 15,233
What was the short circuit current duration set to in the BMS?
That I don't remember. Whatever the default was - I did not change that.
Good to know. Thanks!
The Bussmann 100FE fuse that I'll be using is a pretty fast one. It clears 500A in 0.01s.
I just discovered this post from a few months ago which discusses using "BS88" style fuses in the LET and LMT series including the idea of bolting directly to the battery terminal. This forum is great. There are actually lots of options in the BS88 Style and all have at least 40kA interrupt ratings.
In fact almost every series in this whole Bussman "IEC High Speed Fuses" catalog is rated for >100VDC and usually 50kA interrupt. There are lots of cheaper options out there, they just require a lot of digging any may have low availability. Many are high cost. Any then you have to have a proper fuse holder....I wonder if any of these sizes happen to be compatible with the dimensions of Class T holders? I know there are already two sizes of Class T holders for <=200A and >=225A which seems to cause lots of confusion and ordering mistakes.
For class T fuses: The blue sea systems product pages are vague. They seem to just be selling other manufacturers fuses but they don't list the actual part numbers or give the datasheet so you can't actually look up the specs of the Class T fuses they sell.
I also found this cool cross reference guide from Edison. The 300V class T are the ones I believe blue sea systems sells. Maybe they change manufacturers based on availability and price.
In fact almost every series in this whole Bussman "IEC High Speed Fuses" catalog is rated for >100VDC and usually 50kA interrupt. There are lots of cheaper options out there, they just require a lot of digging any may have low availability. Many are high cost. Any then you have to have a proper fuse holder....I wonder if any of these sizes happen to be compatible with the dimensions of Class T holders? I know there are already two sizes of Class T holders for <=200A and >=225A which seems to cause lots of confusion and ordering mistakes.
For class T fuses: The blue sea systems product pages are vague. They seem to just be selling other manufacturers fuses but they don't list the actual part numbers or give the datasheet so you can't actually look up the specs of the Class T fuses they sell.
I also found this cool cross reference guide from Edison. The 300V class T are the ones I believe blue sea systems sells. Maybe they change manufacturers based on availability and price.
Last edited:
True, but for a good reason: so you can't put a 500A fuse in a system that needs to be protected under 225A.
As far as I know, those BS88 fuses (I have not checked/tried them all) don't fit a class T fuse holder. Even if the space between the holes matches on some (160 LET iirc), the size of the fuse itself makes it not fit in the Class T holder.
hoosierrun
New Member
- Joined
- Aug 24, 2022
- Messages
- 1
I have accidentally shorted out my Battleborn batteries before and they are quick to open up with their internal built in resettable breaker. That is probably why they are supplying ANL fuses in their package.
I mean that's one reason. It provides a small amount of protection from putting a wildly wrong sized fuse on a system, but you can still put a 400A fuse on a system designed for 225A. And there are actually 5 sizes in the Class T fuse lineup catalog. Blue sea systems only carries 2 of the sizes. On the smallest size they range from 0.5A to 60A so you could potentially fit a 60A fuse into a system designed for 0.5A. I think the primary reason they have different physical sizes is that the engineering requirements of the fuses demand different physical sizes of fuse. They struck a balance between having a different fuse holder for every amp rating and having one huge fuse size which would make all the smaller rated fuses bulky and overpriced.
It actually looks like the BS88 LET series (25A to 180A) would fit in the 101-200A class t holder. Am I missing something?
Bussman class T holder:
Last edited:
tigerwillow1
Solar Enthusiast
- Joined
- Sep 20, 2021
- Messages
- 194
And I found a Mersen data sheet that gives the DC breaking capacity of 40 kA at 240 volts. Either way, on paper this is superior to class T.
https://ep-us.mersen.com/sites/mersen_us/files/brochure_BS88_Low-Voltage-Fuses-and-Fuse-Holders.pdf
On the Bussman spec, it's showing the 100 amp fuse breaking at over 150 amps after infinite time. The Mersen specs show the same thing. I had always assumed a 100 amp fuse would open up very close to 100 amps over a long time period.
It's possible that the Bussman fuse has superior performance to the Mersen one and yet they both meet the BS88 requirements set by the queen herself back in 1988. (/s) It's also possible that they are equivalent and were simply tested/qualified at different conditions.
I find those time vs current breaking curves to be very interesting. People are talking about fast blow vs slow blow, but for example, in response to a 300A overload, a 150A fast blow might perform similarly to a regular 100A fuse. The Class T are described as "extremely" fast. But you also have to consider the Amp rating and look at the charts.
Last edited:
curiouscarbon
Science Penguin
- Joined
- Jun 29, 2020
- Messages
- 3,024
thanks everyone! learning a lot here.
