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Class T vs ANL fuse

Hedges said:
I have one battery feeding four inverters. I have two class T fuses, one for each two inverters.

How are your batteries wired? Are they lithium or lead-acid?
Maybe 6, 2V 1120 Ah cells in series? What is your peak continuous current draw, 400A? In that case you do want 500A fuse.
If you have two strings of cells in parallel, each can have one smaller fuse.

Would have suggested higher voltage, lower current.
Click to expand...
System is still being assembled. 16x 280 EVE LiFePo4 cells, 4P4S.
Peak continuous would be 250amp, but could see 400a for up to 20 seconds or so.
 
For 250A continuous, 1.25x would suggest > 312A fuse rating.

From the following chart, a 200A fuse carrying 400A is expected to blow in just about 20 seconds. That would vary with ambient temperature.
400A fuse is showing carrying 400A way beyond 300 seconds.
350A isn't shown on this chart, but you should be able to find elsewhere.


Whatever fuse you use, wires and everything else in the path should have ampacity at least as great as fuse rating. Easier to do with 350A than 500A fuse.

You could instead have a couple fused loads, if no single load is going to draw that much current.
 
Hedges said:
For 250A continuous, 1.25x would suggest > 312A fuse rating.

From the following chart, a 200A fuse carrying 400A is expected to blow in just about 20 seconds. That would vary with ambient temperature.
400A fuse is showing carrying 400A way beyond 300 seconds.
350A isn't shown on this chart, but you should be able to find elsewhere.


Whatever fuse you use, wires and everything else in the path should have ampacity at least as great as fuse rating. Easier to do with 350A than 500A fuse.

You could instead have a couple fused loads, if no single load is going to draw that much current.
Click to expand...
All my loads are individually fused. From the factory, my boat's AGM battery bank has no battery bank fuse. There are short 150mm2 (aprox 300MCM) wires leading from the battery bank to a distribution panel. Here individual loads are fused. For example, 200a fuses to each winch, 160a for windlass, 250a for main service panel, and many more. I'm adding a battery bank fuse out of an abundance of caution. It has been a bit of a puzzle figuring out sizing. If I add up all possible loads (winches, windlass, inverter, etc) it would add up to over 600a. However, it would be nearly impossible to do (electric winches would never be used at same time as electric windlass, and so on). Also, winches tend to be used for a few seconds at a time, not continuous duty. So my idea for the battery fuse would be to size it to protect the wiring going from the battery bank to the distribution panel. Best as I can tell (300MCM is off the charts of most marine ampacity charts I've found) those wires should carry over 500 amps. So I chose a 500a fuse. Maybe a 400a fuse would be a better choice and allow better margin, but I do worry about popping that fuse when my new (yet to be installed) victron Multiplus 12/3000 briefly pulls surge current, and I have other loads going. The Multiplus manual recommends a 400a fuse, and 2/0 wires (which according to my ampacity chart can only carry 330 amps?!). Anyway, I'm still a bit adrift about best choice for a main battery bank fuse (class T? 400a?).
 
Hedges said:
For 250A continuous, 1.25x would suggest > 312A fuse rating.

From the following chart, a 200A fuse carrying 400A is expected to blow in just about 20 seconds. That would vary with ambient temperature.
400A fuse is showing carrying 400A way beyond 300 seconds.
350A isn't shown on this chart, but you should be able to find elsewhere.


Whatever fuse you use, wires and everything else in the path should have ampacity at least as great as fuse rating. Easier to do with 350A than 500A fuse.

You could instead have a couple fused loads, if no single load is going to draw that much current.
Click to expand...
Thinking about time to blow is really useful, thanks for pointing that out. Also, I think mystery solved as far as the 400amp "limit". 400amp is simply the max amperage for the size that fits marine Blue Sea fuse blocks. There are larger fuses and fuse blocks available, but expensive.
 
ohthetrees said:
The highest rated class T fuse I’ve been able to find is 400 amp. I’ve decided that my 1120ah 12v system should have a 500a fuse. The only one I’ve found at that rating is ANL. What are all you class T absolutists doing about fusing for over 500a?
Click to expand...
If you can make a 400 amp work, BH has ACK forklift battery fuses for $10 each. You can't beat the price, and they interrupt 10ka. It's not a class T, but it would work. They also let much more than 400 amps through for short periods, as long as your continuous draw is under 400a, than it could easily take surges of 6-700a for a few seconds.

batteryhookup.com

Ferraz Shawmut ACK 400 0-125VDC 400a Fuse

Here are Ferraz Shawmut 400a bolt on fuses. These are the best fuses for high current applications. These are the best DC fuses for batteries and are also approved for forklift applications. They will work with any voltage from 0-125v. Salvaged from forklift battery packs and fully tested...
batteryhookup.com batteryhookup.com
 
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A.Justice said:
If you can make a 400 amp work, BH has ACK forklift battery fuses for $10 each. You can't beat the price, and they interrupt 10ka. It's not a class T, but it would work. They also let much more than 400 amps through for short periods, as long as your continuous draw is under 400a, than it could easily take surges of 6-700a for a few seconds.

batteryhookup.com

Ferraz Shawmut ACK 400 0-125VDC 400a Fuse

Here are Ferraz Shawmut 400a bolt on fuses. These are the best fuses for high current applications. These are the best DC fuses for batteries and are also approved for forklift applications. They will work with any voltage from 0-125v. Salvaged from forklift battery packs and fully tested...
batteryhookup.com batteryhookup.com
Click to expand...
Interesting, thanks. I wonder if fuse blocks are available for this thing. I’m probably going to stick with class T, because they are available everywhere, and I’ve never seen nor heard of this ACK fuse.
 
Is there any consideration to the short circuit protection of the BMS?
I realize this feature should not be relied upon to eliminate fuses... however I feel OK with less than Class-T considering the BMS protection.
 
The specs on my Overkill BMS says it takes 10 seconds for this over current protection to kick in. For a 100 amp system at operating at 120 amps, that's quicker than my fuse is likely to blow, but with 200 amps being pulled from the batteries, the fuse would blow near instantly.
 
BMS tend to claim short circuit protection. But I would discount the ability of anything based on a few FETs to deal with 20,000A. Only if current rise time was delayed (e.g. due to large inductance) so they could disconnect as current crossed 200A. But then it would have to survive the inductive kick (which is reverse polarity, so a diode snubber works.)

At 5x rating, fuses tend to have specs of about 10 milliseconds to interrupt current.
 
I see now in my Overkill manual I have short circuit protection. Some things I'll just have to finish installing to see how it works.

Seems like its configurable, but as look at the XiangXong Battery app, I don't see where to configure it.
 
chrisski said:
The specs on my Overkill BMS says it takes 10 seconds for this over current protection to kick in. For a 100 amp system at operating at 120 amps, that's quicker than my fuse is likely to blow, but with 200 amps being pulled from the batteries, the fuse would blow near instantly.
Click to expand...
I changed mine to 5 seconds and I believe it is at 130 amps. Any fuse should be fine at 200 amps.

Page 22 of the Overkill manual 3.1.10 describes short circuit protection of a few milliseconds. Not visible in the Apple app.
 
Reading up on the subject, there are several sources saying that FETs shouldn't be relied on as overcurrent protection like a fuse would because during a high overcurrent event, the doped semiconductor junction inside can overheat so severely that it can kind of melt and the device becomes unable to turn off. In other words that it can become no longer a semiconductor, and can fail in the closed circuit state.
 
The overkill has both overcurrent protection, and short circuit protection. They are different. The short circuit protection is nearly instant, and it works. I have directly shorted to test. Big spark, and it turns of for a few minutes. Reportedly, if done enough times it will damage the BMS. You still need a fuse.
 
Ok so I think I am comfortable with my simple mega fuse and the BMS combined without worry of going class-t.
 
ohthetrees said:
I got the (I guess wrong) impression that 400a was max from reading the Blue Sea fuse selection chart and seeing that the maximum class T size was 400 amp. Also, The marine stores I frequent seem to only carry up to 400 amp. Here is a link to the chart:
http://assets.bluesea.com/files/resources/newsletter/images/Choose_the_Fuse_Amperage.jpgView attachment 61620
Click to expand...
Class T fuses increase in size (in groups) with increasing current rating. The Blue Sea class T fuse holders (two sizes) only accommodate 110-400A fuses. Below and beyond that (and the fuses go much higher in capacity), you need to provide your own mounting system.
 
Just to correct an earlier post about the ABYC standard for Lithium Ion Batteries (TE-13), it does NOT mandate class T fuses. This "Technical Information Report" simply requires fuses of sufficient AIC (Ampere Interrupting Capacity). Unfortunately, as most battery manufacturers I'm aware of don't specify available battery short-circuit currents, the user is left with guesstimating instead of proper engineering to decide which fuses to employ.

ABYC do mention Class T fuses in a note, but there is no requirement to use Class T.

That said, I would not use anything else in a Li-Ion system. The cost of the right fuses and fuseholders pales in comparison to the cost of batteries and inverter-charger, etc. costs. Safety and peace of mind are much more important to me. I still can't get over a major manufacturer employing Mega fuses in this situation, when they are only rated by the inventor/manufacturer (Littlefuse) to interrupt 2000A at 32VDC and 1000A for the 58V version! (See https://www.victronenergy.com/upload/documents/Lynx_Distributor/Lynx_Distributor-en.pdf.)

I would add that for 48V systems, the Class T fuse is really the only proper option. ACK fuses could be borderline for a bolted fault, and are slower interrupting (plus you need to be careful you don't end up with the time delay versions often used in forklifts). Class T fuses also have relatively low voltage drop.
 
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alanapar said:
I still can't get over a major manufacturer employing Mega fuses in this situation, when they are only rated by the inventor/manufacturer (Littlefuse) to interrupt 2000A at 32VDC!
Click to expand...
Which manufacturer?
 
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