Class T vs ANL fuse

[chrisski]

That said, I would not use anything else in a Li-Ion system.

Just want to be sure we're talking about Lithium Iron Phosphate, and not Lithium Ion Batteries.

 

[upnorthandpersonal]

Just want to be sure we're talking about Lithium Iron Phosphate, and not Lithium Ion Batteries.

To be pedantic, LiFePO4 is a type of Lithium Ion. They all are.

 

[alanapar]

Just want to be sure we're talking about Lithium Iron Phosphate, and not Lithium Ion Batteries.

That's a common misunderstanding. Lithium Iron Phosphate ARE Lithium Ion Batteries, just one of several common chemistries employed in Lithium Ion Batteries.

I think the reason people do this is as an (incorrectly formulated) attempt to distinguish the relatively "safe" LiFePO4 chemistry from the other most commonly employed chemistries.

 

[chrisski]

That's a common misunderstanding. Lithium Iron Phosphate ARE Lithium Ion Batteries, just one of several common chemistries employed in Lithium Ion Batteries.

I don't think I'll go down that road.

 

[curiouscarbon]

LCO is what a lot of people maybe imply with

“Lithium Ion”

LiFePO4 = Lithium Ion Subtype

LiCoO2 = LCO = Lithium Ion Subtype

this isn’t something that should be painful.

LMO LTO LFP LYP NCA NMC LCO are all Lithium Ion chemistries. There is no more to it than this if it uses lithium ions then it’s a lithium ion cell.

 

[curiouscarbon]

saying a dog is not a mammal is strictly technically incorrect and worth pointing out

 

[robby]

Your all wimps! I just got me a Manly Sized Class T fuse for my system.




JUST KIDDING GUYS I thought that size counted in everything

 

[alanapar]

Your all wimps! I just got me a Manly Sized Class T fuse for my system.

View attachment 74115


JUST KIDDING GUYS I thought that sized counted in everything

Oversized protection can be worse than no protection (in all things) ;-)

 

[curiouscarbon]

gonna need a lot of wire! XD (what was the temperature rating of this insulation again….)

 

[robby]

Oversized protection can be worse than no protection (in all things) ;-)

Well not in "All things" A nice 50 cal is better protection than a .223 and thick wires with thin Insulation pass more electrons than thin wire with thick insulation

 

[Dzl]

Just to correct an earlier post about the ABYC standard for Lithium Ion Batteries (TE-13), it does NOT mandate class T fuses.

Good point. What is the TE-13 reference?

The standard 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.

This is true. And the ABYC E-11, barely considers LFP as it is. Considering the predicament you outlined above (unknown short circuit current) this is the relevant excerpt:

11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA, or 500 amp hours, battery
overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating at least as great as the battery
manufacturer’s short circuit rating OR be rated at a minimum of 20kA at 125 VDC or higher.

Since short circuit current is unknown, the latter should apply. It is unclear if the above pertains to LFP or not, there is no indication that it does not.
The above is probably why Class T has come to be the defacto standard recommendation (probably not a coincidence that both Blue Sea (Eaton-Bussmann) and Littelfuse have class T fuses rated for 20kA AIC @ 125VDC). So while there is no specific requirement for Class T, it is a sensible choice, and the most readily available fuse type that satisfies this standard.

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.

 

[alanapar]

Good point. What is the TE-13 reference?

TE-13 13.7.8.1 If necessary, a battery bank should be subdivided into units such that the ampere interrupting capacity (AIC) of the overcurrent protection device is not exceeded.

NOTE: Generally, fast acting current limiting fuses such as Class T fuses in an approved Class T fuse holder have an AIC of 20,000 amps at 12VDC and will be adequate for a subdivided bank.

[My comment: why only 12VDC?]

This is true. And the ABYC E-11, barely considers LFP as it is. Considering the predicament you outlined above (unknown short circuit current) this is the relevant excerpt:

A lot of ABYC standards (and standards in general) fail to keep pace with technology. I implemented a second-generation LFP system on my former boat over 5 years before TE-13 was released. And although I don't fully understand ABYC's "TE" designation, it is labelled a "Technical Information Report" and AFAIK, is not a required standard.

Frankly, I am disappointed in TE-13. There is a lot it could cover and doesn't. For instance, how can you require adequate AIC if you don't require the short circuit current to be specified? Having the 20kA fall-back in E-11 seems to be ducking the issue.

And subdividing a bank to accommodate protection devices that can't handle the full bank short circuit current begs the question of how you protect downstream devices and branch circuits.

And what about segregation of parallel strings (or groups of parallel strings) with contactors to limit fault effects and total loss of power with cell failures and BMS shutdowns. I know people who have lost all 24V power on their boats because the Li-Ion bank / BMS employed a single master contactor to "protect" the bank (while leaving all parallel strings still connected to the faulted string).

Since short circuit current is unknown, the latter should apply. It is unclear if the above pertains to LFP or not, there is no indication that it does not.
The above is probably why Class T has come to be the defacto standard recommendation (probably not a coincidence that both Blue Sea (Eaton-Bussmann) and Littelfuse have class T fuses rated for 20kA AIC @ 125VDC). So while there is no specific requirement for Class T, it is a sensible choice, and the most readily available fuse type that satisfies this standard.

Interestingly Mersen (Ferraz Shawmut) A3T (160V DC rated class T) fuses are rated at 50kA interrupting capacity. Presumably this means they were qualified to this level with UL or whomever. I bought Mersen fuses for the extra "reserve" whether it's real or not.

 

[curiouscarbon]

Frankly, I am disappointed in TE-13. There is a lot it could cover and doesn't. For instance, how can you require adequate AIC if you don't require the short circuit current to be specified? Having the 20kA fall-back in E-11 seems to be ducking the issue.

And subdividing a bank to accommodate protection devices that can't handle the full bank short circuit current begs the question of how you protect downstream devices and branch circuits.

good point

Short Circuit Ampere rating seems good for lithium cells to carry and post visibly?

people who have lost all 24V power on their boats because the Li-Ion bank / BMS employed a single master contactor to "protect" the bank (while leaving all parallel strings still connected to the faulted string)

?

 

[Dzl]

Frankly, I am disappointed in TE-13. There is a lot it could cover and doesn't. For instance, how can you require adequate AIC if you don't require the short circuit current to be specified? Having the 20kA fall-back in E-11 seems to be ducking the issue.

That is one way to look at it. Another way is that its just a statement made in recognition of the same problem that you stated--that AIC is often not listed by LFP manufacturers or assemblers--and guidance that can be followed without knowing that info would be useful to builders.

And subdividing a bank to accommodate protection devices that can't handle the full bank short circuit current begs the question of how you protect downstream devices and branch circuits.

If each subdivision was properly fused, with properly sized AIC and current ratings, downstream would be protected wouldn't it? Only the first fuse for each subdivision would need to handle the full AIC of the pack I think. Beyond that, lower AIC fuses are okay I think. I may be misunderstanding something.

Interestingly Mersen (Ferraz Shawmut) A3T (160V DC rated class T) fuses are rated at 50kA interrupting capacity. Presumably this means they were qualified to this level with UL or whomever. I bought Mersen fuses for the extra "reserve" whether it's real or not.

Nice to have a little extra breathing room, particularly considering the unknowns. The 20kA stated in E-11 is referenced as the minimum if short circuit current is unknown, so exceeding it is reasonable. Was the fuse more pricey than other class T fuses you looked at?

 

[Dzl]

NOTE: Generally, fast acting current limiting fuses such as Class T fuses in an approved Class T fuse holder have an AIC of 20,000 amps at 12VDC and will be adequate for a subdivided bank.

[My comment: why only 12VDC?]

Not sure without more context. My guess is they are just making a fairly safe generalized statement for the most popular system voltage. The Class T fuses I have looked at are all rated at 20kA for voltages above the common 12/24/48 system voltages (most commonly 125V or 160V DC)

 

[alanapar]

That is one way to look at it. Another way is that its just a statement made in recognition of the same problem that you stated--that AIC is often not listed by LFP manufacturers or assemblers--and guidance that can be followed without knowing that info would be useful to builders.

A power of standards (which I don't believe TE-13 has the status of) is to compel people to list safety-critical specification information in order to be compliant. The manufacturers and suppliers "tail" should not be wagging the standards "dog".

If each subdivision was properly fused, with properly sized AIC and current ratings, downstream would be protected wouldn't it? Only the first fuse for each subdivision would need to handle the full AIC of the pack I think. Beyond that, lower AIC fuses are okay I think. I may be misunderstanding something.

I take TE-13 to mean that if you have say 4 parallel battery system branches, you could fuse each at say 200A, and each of those fuses would ordinarily have to deal with just the short circuit current of that string. (Exception: if that strings shorts, the other three strings fault into it. ABYC did not allow for that - another flaw in TE-13?). But after those fuses, the branches are combined, and now the available fault current is four times greater.

(Perhaps I'm misunderstanding TE-13 here, but if so I have to say it is unacceptably unclear. In constructing large battery banks you often have a single large load - a good example would be electrical propulsion - so parallel strings have to be combined. And there is often good reason not to subdivide an electrical system even when it might be technically possible.)

For example, if you have say a couple of inverters downstream, each might be fused with say 400A.

Now it is a basic principal of protection that downstream protective devices should operate first for faults that occur (immediately) downstream of them, and that they should be coordinated with upstream devices (in capacity and speed) so that the downstream device clears the fault without affecting (tripping or degrading) any upstream device. For instance, the 400A downstream fuse should melt and clear a fault in one of those inverters, without any upstream device (200A battery string fuses) getting to the melt point (after which it is suspect even if it did not rupture, and should be replaced). Class T fuses are capable of fairly close coordination, but I have no idea what level of selectivity you can achieve with lesser interrupting fuses (such as Mega fuses). As a corollary, you can mess up coordination by having say a fast, high current fuse upstream of a slow, lower current fuse of a different type.

Anyhow, that downstream device is subject to the full bolted fault current of the entire bank of 4 parallel strings (assuming the wiring resistance and inductance in between are small), so it is faced with a (nearly) 4 times greater prospective fault current than the individual string fuses are (for faults external to the battery bank). If it then failed in its duty, and the fault continued, eventually the per-string fuses would operate, but this is not what you want to happen. Among other things, then all power is lost to all consumers, and you need to replace 5 fuses - rather expensive fuses if they are Class T.

AC standards like the NEC deal with this sort of thing in great detail. They cut a certain amount of slack on protection coordination for ordinary house and industrial situations, but get rigorous for mission-critical applications like hospitals or elevators. For my boat, I want the fuses in the individual battery strings sized so they will not be affected by faults in downstream devices.

Nice to have a little extra breathing room, particularly considering the unknowns. The 20kA stated in E-11 is referenced as the minimum if short circuit current is unknown, so exceeding it is reasonable. Was the fuse more pricey than other class T fuses you looked at?

I think they were competitively priced.

 

[curiouscarbon]

A power of standards (which I don't believe TE-13 has the status of) is to compel people to list safety-critical specification information in order to be compliant.

The manufacturers and suppliers "tail" should not be wagging the standards "dog".

?

I take TE-13 to mean that if you have say 4 parallel battery system branches, you could fuse each at say 200A, and each of those fuses would ordinarily have to deal with just the short circuit current of that string. (Exception: if that strings shorts, the other three strings fault into it. ABYC did not allow for that - another flaw in TE-13?). But after those fuses, the branches are combined, and now the available fault current is four times greater.

Bank of N packs in parallel.

This (N-1) fault into 1 failure mode is something my gut tells me to prepare for seriously. But it says a lot of things.

The most extreme safety design I am considering is one contactor and fuse per pack, and a single main larger contactor and fuse to parallel. Gigavac makes some Normally Open Contactors with very low power consumption (1-1.5W holding closed).

e.g.

Pack 1 Positive -> Fuse -> Contactor -> MainFuse -> MainContactor

With MOSFET BMS on pack negative and straight to negative busbar.

 

[Hedges]

Cell vendors publish internal resistance. With that and cell voltage, you can calculate an expected short circuit current.
From the numbers people have shown here, I get just about 20kA.
Maybe the chemistry can't produce current at that rate, but should be a good upper limit.

If four strings in parallel each with its own class T fuse, and one string shorts before the fuse, its fuse carries 60kA from the other three strings and probably sustains an arc. The other three strings blow their fuses, hopefully fast enough the one doesn't explode.
But that string is still shorted, because short was before the fuse. Try to not let that be possible (even if the boat capsizes)

If there is a short downstream you would like it to either trip its own OCP and interrupt whatever that current would be, or hold together long enough for the main fuse to blow. Don't want a minor appliance to disable power for propulsion and instruments.

In the AC world, you can choose coordinated breakers so branch circuit OCP stays closed long enough for main breaker to trip on a bonded fault, and everything can be reset. or you can choose branch breaker to trip faster, be rendered unusable, but leave the facility up.

Class T fuses have a "let through current" (really energy and time) such that a 200,000A AC fault is interrupted so fast that a 20,000A rated breaker downstream doesn't experience excessive energy. (we don't like things exploding). However, at 20,000A it doesn't protect others to 2000A. In DC application with 20kA interrupt rating, downstream circuits experience the full brunt of it.

Seems to me a "current limiting" fuse for DC applications would be good, but class T isn't it. Downstream loads carrying the fault will suffer, unless there is enough series resistance to reduce current.

 

[alanapar]

Cell vendors publish internal resistance. With that and cell voltage, you can calculate an expected short circuit current.
From the numbers people have shown here, I get just about 20kA.

Could you please quote some actual data in support of that number?

BTW, a lot of vendors quote cell impedance at say 1kHz - that is a different animal from the effective series resistance seen with large DC currents.

To expand a bit further, Li-Ion batteries have a complicated variation of impedance as a function of frequency (often displayed on a so-called Cole-Cole plot). This data can be used to characterize various electrochemical and other aspects of the battery, but detailed measurements require special equipment and are time consuming, especially at the low frequency end of the spectrum (a few Hz down to DC). In a production environment, often a spot measurement at 1kHz is employed, and this serves to detect certain faults allowing sub-par batteries to be rejected (or sold on the cheap).

But the 1kHz data does not necessarily correlate well with the low frequency data. One reason is that when you model the battery impedance with an equivalent circuit (to greatly simplify) you find part of the circuit consists of a resistance (the reaction resistance) in parallel with a capacitor (the double layer capacitance). At 1kHz this capacitance effectively shorts out the resistance, so you do not see it in such a measurement. But this resistance is an important part of the low frequency impedance.

 

[Hedges]

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.

3.4V / 0.00017 ohms = 20,000A

"With an internal resistance meter like the yr1035+ you can test.

My 280's are 0.15 to 0.18 Mili ohms.
Most are 0.17"

New to lithium batteries

Hi All, New to this forum. Need the expertise from the members since I’m new to lithium batteries. I have a SolarEdge system running with 13 KW panels and a 10KW inverter with zero feedback to the grid. Want to do a change with battery backup and thinking of building my own batteries. My...

diysolarforum.com