Class T vs ANL fuse

alanapar

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Correct, they take the measurement at 1 kHz. I don't have a way to translate that to DC.
But, people also have BMS reporting internal resistance which I recall were similar. I think that is delta voltage at some moderate current. (I'm not finding example posts at the moment.)
So it appears DC measurements at moderate currents match my V = I x R approach.
I suspect your number of 20kA (which of course needs to be quoted for a particular cell) is well on the high side. I'm not seeing any real data to back this up.

Do you have discharge curves for this cell at different rates? That would provide some data.
 

Hedges

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I don't. I haven't used lithium cells. I'm just going by the IR numbers people report here, either from manufacturer or their own BMS or IR measurement device. I don't typically see anything like Peukert curves or other charts with voltage vs. current like we do for lead-acid. I expect IR figures to predict that (up to some point where chemistry of cell can't keep up with current, could be non-linear so you may be correct that 20kA is high.) It has been 280 Ah or so cells which had the 0.17 milliohm figure.

I saw one paper reporting 4000A from 100 Ah AGM. I assumed 16kA as a conservative figure for my 405 Ah bank, probably much less than 4x 100 Ah in parallel due to construction. We know lithium delivers higher current, can crank a car with a tiny jumpstart pack. People have welded contactors and blown fuses (including class T, I think) connecting an inverter to lithium batteries.

Of course, almost any battery included lead-acid could blow a class T fuse in some amount of time, if able to reach parts of its time/current trip curve. But blowing with inrush means the limited amp-seconds to charge capacitors have to occur in short enough time for the I^2 to overheat the fuse. My math said this might be feasible with the capacitor bank of some inverters - I think it was on the order of 100,000 uF.

On the other hand, my inverters are spec'd for up to 10,000 Ah battery bank, and no mention of precharge. For lead-acid & NiCd, wiring such a large bank might have more resistance and inductance (although it takes a lot of wire to reduce short circuit current much), but likely cells aren't optimized for low resistance high current.

 

upnorthandpersonal

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Ahttps://www.sbsbattery.com/PDFs/VRLAshortCurrentsStorageBatterySystems.pdfI suspect your number of 20kA (which of course needs to be quoted for a particular cell) is well on the high side. I'm not seeing any real data to back this up.

Do you have discharge curves for this cell at different rates? That would provide some data.

Here's a paper that has some results:


This is one of the graphs, during short circuit of LiFePO4 160Ah battery (single cell):

The-plot-of-current-and-temperature-during-short-circuit-of-LiFePO4-160Ah-battery.png


This is at 3.6V with a single cell at 160Ah. Cells with a larger capacity will have a larger short circuit current. If you then make a 48V battery with them, and you parallel e.g. two of those, you're going to see some massive currents.

This paper confirms:


"A battery's short circuit current is typically estimated by dividing its open circuit voltage by its internal resistance. While the true DC internal resistance can be determined using a series of discharge tests, it is often simpler to directly measure the battery's impedance or conductance using an AC test signal".

So the internal resistance is a good estimate. Therefor, I believe that the current in the first paper and represented in the graph is on the low end. Calculating the internal resistance in that short gives a number of around 3mR. My guess is that the leads used were a large contributing factor. If this is the case, the current could be much larger in that case. The other reason I suspect this is because of this test by GWL:


The 160Ah cell in this case was overcharged and already had a higher internal resistance because of this. The short still generated 1000A.
 
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Hedges

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More real data:


> 200C for 1/100th of a second, followed by 50C

Those weren't LiFePO4. If applicable, 280 Ah would deliver 50kA briefly. IR would limit it to 20kA. The time limit is on the order of class-T time to blow, so fuse should remain physically intact. But supports the idea of sufficient current to open the fuse in that time.

Full second at 50C (15kA) would best be protected by class-T.

Again, not LiFePO4 cells but worth considering.

This is at 3.6V with a single cell at 160Ah. Cells with a larger capacity will have a larger short circuit current. If you then make a 48V battery with them, and you parallel e.g. two of those, you're going to see some massive currents.

I actually don't think I believe those results. 160Ah can only deliver 1000A into a short? A fraction of what a lead-acid battery can do? My truck battery can deliver 800A into 8.5V, 1/3 of a short?

I suspect they have way too much series resistance and it swamps out IR, limiting current to a fraction of what the cell can deliver.
 

upnorthandpersonal

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My personal opinion on all this is to use Class T fuses, always. I've personally seen properly sized ANL fuses just sit there and get hot, melting the plastic case around them, in combination with LiFePO4 packs. At 48V, you can't use ANL anyway since they're only rated to 32V.
 

time2roll

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My personal opinion on all this is to use Class T fuses, always. I've personally seen properly sized ANL fuses just sit there and get hot, melting the plastic case around them, in combination with LiFePO4 packs. At 48V, you can't use ANL anyway since they're only rated to 32V.
That sounds more defective or poor installation vs failing to stop 1000+ amps.
 

Dzl

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I just happened to notice, while shopping, that not all Class-T fuses share the same ratings.

For example, when looking at 300A Class-Ts:
  1. Blue Sea: 20 kA @ 125VDC
  2. Littelfuse: 50 kA @ 160 VDC, but with a lower rating product also available
  3. Eaton Bussman: many options
  4. Mersen/Ferraz Shamut: 50kA I.R. DC & 100kA I.R. DC
Maybe that was already known to most, but I'm less dumb today.
Furthermore, there can be differences within a line of fuses at different currents.
For instance the JLNN Class T Littelfuse from the link above is only rated for 160VDC under 60A, over 60A its rated for 125VDC. And AIC is 50kA under 30A and 20kA over 35A.
Class T is a class/type of fuse, there are still devil's in the details.
 

alanapar

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I just happened to notice, while shopping, that not all Class-T fuses share the same ratings.

For example, when looking at 300A Class-Ts:
  1. Blue Sea: 20 kA @ 125VDC
  2. Littelfuse: 50 kA @ 160 VDC, but with a lower rating product also available
  3. Eaton Bussman: many options
  4. Mersen/Ferraz Shamut: 50kA I.R. DC & 100kA I.R. DC
Maybe that was already known to most, but I'm less dumb today.

A.

Looking at the Littlefuse data sheet


they list for voltage ratings of JLLN fuses (the 300VAC series):

Dc: 160 V (1–60 A)
125 V (70–1200 A)

and for interrupting ratings:

Dc: 50 kA (1–30 A)
20 kA (35–1200 A)


Mersen (Ferraz Shawmut) at


state for the corresponding A3T series:

DC: 1 to 1200A 160VDC, 50kA I.R.


BTW, there are two series of Class T fuses, generically identified as the 300VAC and the 600VAC series. It is the latter that has the 100kA IR for 300VDC (A6T series) in Mersen's range. I have not used the higher voltage series, but I suspect you will find they have significantly higher voltage drop at normal currents.
 
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Hedges

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I have not used the higher voltage series, but I suspect you will find they have significantly higher voltage drop at normal currents.

The trip curves differ too. Littlefuse JJLN vs. JJLS 400A, 2500A vs. 5000A for 10 milliseconds to clear.
 

carbon60

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BTW, there are two series of Class T fuses, generically identified as the 300VAC and the 600VAC series. It is the latter that has the 100kA IR for 300VDC (A6T series) in Mersen's range. I have not used the higher voltage series, but I suspect you will find they have significantly higher voltage drop at normal currents.
The voltage drop is a concern to me,I didn’t realize. A Mersen was easily available locally while there is an undefined lead time for the Blue Sea, which I also ordered.
 

alanapar

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The voltage drop is a concern to me,I didn’t realize. A Mersen was easily available locally while there is an undefined lead time for the Blue Sea, which I also ordered.
As long as you ordered the Mersen A3T (300VAC) series, you will be fine.
 

Posplayr

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FYI, These are still apparently available. The ad says "Slowblow" but the JLLN is the "Fast blow".

 

smoothJoey

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FYI, These are still apparently available. The ad says "Slowblow" but the JLLN is the "Fast blow".


I found this https://www.invertersupply.com/media/data/Go-Power_SPC_FBL_vB.pdf
No sign of a trip curve plot though.
 
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