BMS capacity vs fuse size

[CaptainRivet]

Originally Posted by Wandering1

I asked you a reasonable question and you respond with that!

That’s what happens if you do…
I by the way suggested that off-1-2 but for each inverter, on 1 is the precharge curcuit and OPs answer was he can manage loads…

[Wandering1]

Originally Posted by CaptainRivet

That’s what happens if you do…
I by the way suggested that off-1-2 but for each inverter, on 1 is the precharge curcuit and OPs answer was he can manage loads…

I am sure you are a really bright guy, but your ability to correspond effectively and win people to you way of thinking leaves a lot to be desired. Your confrontational style doesn't sit well. I struggle to understand a lot of what you put in print

[CharlieJ]

This will be like discussing guns on board but I will try. Through this all, to be compliant and safe, the fuse needs an Ampere Interrupt Capacity that is greater than the available short circuit current (ASCC) that may be produced by the battery/bank in response to a downstream bolted fault. The AIC of the most popular fuses is readily available.

The ASCC is not available anywhere that I can find. None of the major LFP battery/cell manufacturers publish this. They do publish a surge value which is not the same as the ASCC. Knowing the internal resistance (generally available) and applying Ohm’s Law does not provide the answer owing to the transitory nature of a crowbar fault.

Testing and SPICE simulation by a major company in the marine electrical equipment field has developed the following factor: ASCC of a LFP battery = 5kA/100Ahr of battery capacity. A 200Ahr LFP battery will have a theoretical ASCC of 10kA which matches the 14VDC AIC of a MRBF.

Let the games begin.

[CaptainRivet]

Well thats correct the issue that this is not published by the manufacturer but you need it to spec the fuse.

this short curcuit test of a single 40AH winston cell revealed up to 1600A or 40C (wrongly stated 400C).
https://youtu.be/R9xZf4p8PkQ?si=e3gUHwLxiDrTiScv
And now take 4 cells in series for a 12V battery....yes its one cell that shorts but eg the EVE have just a wrap, chassis is positive and the short creates heat...thats why i always take 400 degrees celcius resistance seperator between the cells to prevent a chain reaction when building the battery.
Due to ABYC you can only use class T or NH as main battery fuse on a lithium battery, never a MRBF.

My approach to that is always using NH fuses which have a minimum AIC of 80kA in DC in NH 00 till NH3, the highest rating you can find commonly avaliable. Additionally you can pull them under full load means you can also use them as disconnect switch and save costs, pointvof failures and added resistance.
Better safe, totally overspeced but working correctly then sorry.
I use the internal resistance of the cells only means the whole bank to roughly calculate it, so in my case 4cells parallel. That will be always higher then the actual current deliver capability of the bank as eg terminal and busbar resistance is added to that or the real internal resistanceis higher.i call it for myself theoretical possible short curcuit current capability and use this to spec the fuse. And doing that over the years I also realized that value has direct correlation to peak capability of the cells.
So meanwhile i created for myself !!!! over the thumb formula thatb is:
peak rating of cells (!!!)x10C multiplied with capacity and that fits quite well. So for dropins NOT the peak rating given as this is limit of BMS but not the peak rating of the cells used. So you need to figure out which cells used and their peak rating. If you cannot find it i use 3C as default.

Eg my 4p4S with 272AH cells or 1088AH, the cells have 2C constant and 3C peak.
So 3x10Cx1088AH=32640A min AIC rating needed
Using given 11mohm as internal resistance i end up at 30306A using the complex formulars. Means over thumb is always higher but quite close enough for specing the fuse.
For the above winston 40AH cell the spec where 3C constant and 5C peak so 5x10Cx40AH=2000A.

Learned it the hard way...
I myself burned a car down more then 15 years ago with an arced class T speced for 15kA with an approx 400AH LFP bank caused by an internal cell short. Cells had 5C peak and 4 in parallel.
With my formula i didn't know at that time 5x10Cx400AH=20000A so the 20kA rating would be correct one.

The major factor that your formula misses is that different 100AH cells will have different short current delivery capabilities, a 100AH with 1C peak and a new 100AH winston with 4C cont and 10C peak will have dramatically different short curcuit current. And peak current delivery has a direct corelation to internal resistance on Lifepo4 and derivates.

[CaptainRivet]

Originally Posted by Wandering1

I am sure you are a really bright guy, but your ability to correspond effectively and win people to you way of thinking leaves a lot to be desired. Your confrontational style doesn't sit well. I struggle to understand a lot of what you put in print

Sorry i lost some patience over the years and figured its best to confront with the truth and what can happen. I am direct and not the behind the back and/or a very diplomatic person...my friends like that and crew too as they always know where i and they stand. And i mean what i say and can be taken acounted for and if i am wrong i admit and apologize...and greatful that somebody took the time and correcting me.
Well exactly the opposite whats happen and people are overly senstive and other bs...happy i am retired and don't have to follow that bs in business.
I needed to be working 25years and did it more or less well as i was GM and CEO of successful companies but now early retired.
I really admire Jedi being still being so patient, repeating everything like bible reading in church and often very diplomatic answers..i lost it over the years. Maybe i need to smoke some weed :-)))

I give my experience and advice for free and don't wanna sell anything and need pull someone to my side.
I still have the attitude that sailor help each other like it always was and thats why i give my know how and experience and happy i get the same back from a lot here.
And yes i learned a lot here too in discussions and quality posts. But several of the.quality posters left or nearly posting anything anymore like eg Terry T1 which has an exceptional knowledge and also very interested but fed up being attack from armchair sailors being attacked or told they have no glue what they are doing.

Take my advice or tell me why mine is wrong or incomplete, always learning and i am also a humam who does mistakes and also admits them.
Usually my first post is showing the issues and give the best solution to fix or alternatives. neutral and facts, here too.

But as also Jedi stated several times a lot just wanna have a confirmation for what they did or already bought and if that doesn't fit ignoring or simply stating it works or start even attacking...
well then i am still answering very direct and tell them they got wrong stuff, what can and most likely will happen or installed wrong but they won't get a confirmation or a diplomatic answer.
Don't like it, well then ignore my post and life with the consequences.

[s/v Jedi]

Originally Posted by CaptainRivet

I really be jealous on Jedi being still being so patient and often very diplomatic...i lost it over the years.
[…]
But as also Jedi stated several times a lot just wanna have a confirmation for what they did or already bought and if that doesn't fit ignoring or simply stating it works or start even attacking...

And I still get strikes from the admins even when my post adheres to the rules but something else “can be read between the lines”.

But your last statement I quoted above is very true. People who aren’t sure make bad decisions and then post in search of support for what they did. I found that being direct (some call it blunt) is the best approach

[Sailorman Ed]

OK, I've read all of this thread twice and learned how much I didn't know.

My situation - clean slate: 280 Ahr Lithium w 200 BMS, short AWG 2 to 200 mccb single pole to 250 A bus. ( thanks to all of you for the primer). Now from the bus, I want to run a 50 A circuit to the windlass - thru a 50A breaker - no issue. Blue Seas 285 or 187? Now a 30A line to the distributed fuse panel, Another 30A thermal breaker or ATO fuse or inline fuse? And another 30A circuit to a conventional circuit breaker panel - so same as the first 30A circuit? And another fused circuit to the fridge. How far can I run the smaller circuits from the bus before I need the fuse? Is there a cleaner way to do this wo 3 or 4 fuses?


I am going with a T25 outboard w 16 a alternator, planning to feed the distributed fuse panel, same with the solar panel since it is a short run to the same fuse panel. Any reason not to do it this way?


And am I correct that ANL fuses are not appropriate for Lithium?


thanks in advance for my education.
Ed

[s/v Jedi]

Originally Posted by Sailorman Ed

OK, I've read all of this thread twice and learned how much I didn't know.

My situation - clean slate: 280 Ahr Lithium w 200 BMS, short AWG 2 to 200 mccb single pole to 250 A bus. ( thanks to all of you for the primer). Now from the bus, I want to run a 50 A circuit to the windlass - thru a 50A breaker - no issue. Blue Seas 285 or 187? Now a 30A line to the distributed fuse panel, Another 30A thermal breaker or ATO fuse or inline fuse? And another 30A circuit to a conventional circuit breaker panel - so same as the first 30A circuit? And another fused circuit to the fridge. How far can I run the smaller circuits from the bus before I need the fuse? Is there a cleaner way to do this wo 3 or 4 fuses?


I am going with a T25 outboard w 16 a alternator, planning to feed the distributed fuse panel, same with the solar panel since it is a short run to the same fuse panel. Any reason not to do it this way?


And am I correct that ANL fuses are not appropriate for Lithium?


thanks in advance for my education.
Ed

I recommend you get a SafetyHub150. You mount it close to the busbar and use the same size cable that is used between battery and busbar. This means you need no fuse between busbar and SafetyHub.

Now you have four fuse positions for circuits up to 200A and six fuse positions for circuits up to 30A. All in a compact, waterproof box. Also, it has a negative busbar too so that you can completely terminate all the fused circuits to this hub, both positive and negative conductors.

Here’s a link: https://www.bluesea.com/products/774...150_Fuse_Block

[CaptainRivet]

Originally Posted by Sailorman Ed

OK, I've read all of this thread twice and learned how much I didn't know.

My situation - clean slate: 280 Ahr Lithium w 200 BMS, short AWG 2 to 200 mccb single pole to 250 A bus. ( thanks to all of you for the primer). Now from the bus, I want to run a 50 A circuit to the windlass - thru a 50A breaker - no issue. Blue Seas 285 or 187? Now a 30A line to the distributed fuse panel, Another 30A thermal breaker or ATO fuse or inline fuse? And another 30A circuit to a conventional circuit breaker panel - so same as the first 30A circuit? And another fused circuit to the fridge. How far can I run the smaller circuits from the bus before I need the fuse? Is there a cleaner way to do this wo 3 or 4 fuses?


I am going with a T25 outboard w 16 a alternator, planning to feed the distributed fuse panel, same with the solar panel since it is a short run to the same fuse panel. Any reason not to do it this way?


And am I correct that ANL fuses are not appropriate for Lithium?


thanks in advance for my education.
Ed

Question is where is all the stuff located?
your battery, your main busbar, switchboard etc.
Best you make a quick drawing, also with approx cable length.
If possible and make sense from your drawing I would route one cable for the total potential load from main busbar to the switchboard and place there the saftey hub jedi posted. So you actuaĺy have a much bigger cable = less voltage drop and from the switchboard via safteyhub then shorter cable runs to each of your loads.
For the windlass it is common practise to have a breaker which needs to be breaker type for motors. You wanna quickly flip on a breaker switch when it switches of and not replacing a fuse...that can be the difference to end up on a reef or not. Means place the breaker at an easy to reach spot or even on your switchboard directly.

[CharlieJ]

@Sailor_Man52

The SafetyHub that Jedi recommends is a neat and compact way to start distributing power.

The issue is your “200 mccb”. I am assuming that this is a 200A single pole circuit breaker (SPCB). What breaker do you plan on using in this application? Since it is the first overcurrent device (OCPD) off of the battery terminal, you have to be mindful of the battery’s available short circuit current (ASCC) so that the installed OCPD has sufficient ampere interrupt capacity to handle the ASCC of the LFP battery.

If you review my post #48 up thread you will see that the estimation (barring battery manufacturer’s data) for ASCC is 5kA/100Ahr. So for your 280Ahr battery the ASCC is
(280/100) x 5kA = 14kA. There are no readily available SPCB with this level of AIC. The standard “A” series circuit breaker (Blue Sea 50A single pole, white toggle #7230) has an AIC of 7500A at 65VDC which is insufficient.

To be compliant and safe, recommend installing a Class T fuse between the LFP B+ and the SafetyHub.

You said you are going to use AWG 2 between the battery and the bus bar or SafetyHub. Outside machinery spaces the ampacity of AWG 2 is 147A so a 150A Class T small format fuse/fuse holder would be the correct choice.

[CarlF]

While fuses are sized to protect the wire, the ABYC specifies that fuses (and therefor the wire) should be 1.1-1.5 times the expected maximum current. You also want to size the wire to have a maximum 10% voltage drop.

But you then run up against the problem that T1 fuses over 400 amps are very expensive. So I'd probably put in a 400 amp T1 and use 4/0 cable to minimize voltage drop if the inverters are more than a few feet from the batteries.

The 2nd issue is that the ABYC requires that a fuse has to be within 7" of the battery terminal. If you are wiring your batteries in parallel with equal length cables - which is the best way to keep them balanced - then a good approach is a MBRF fuse at each battery terminal with equal length jumpers to a busbar and then put the T1 there.

[CaptainRivet]

Originally Posted by CharlieJ

@Sailor_Man52

The SafetyHub that Jedi recommends is a neat and compact way to start distributing power.

The issue is your “200 mccb”. I am assuming that this is a 200A single pole circuit breaker (SPCB). What breaker do you plan on using in this application? Since it is the first overcurrent device (OCPD) off of the battery terminal, you have to be mindful of the battery’s available short circuit current (ASCC) so that the installed OCPD has sufficient ampere interrupt capacity to handle the ASCC of the LFP battery.

If you review my post #48 up thread you will see that the estimation (barring battery manufacturer’s data) for ASCC is 5kA/100Ahr. So for your 280Ahr battery the ASCC is
(280/100) x 5kA = 14kA. There are no readily available SPCB with this level of AIC. The standard “A” series circuit breaker (Blue Sea 50A single pole, white toggle #7230) has an AIC of 7500A at 65VDC which is insufficient.

To be compliant and safe, recommend installing a Class T fuse between the LFP B+ and the SafetyHub.

You said you are going to use AWG 2 between the battery and the bus bar or SafetyHub. Outside machinery spaces the ampacity of AWG 2 is 147A so a 150A Class T small format fuse/fuse holder would be the correct choice.

Correctly formulated.
If you are US based get a class T 150A with AIC of 20kA. If you are european based i recommend NH2 Fuse 150A, cheaper then class T and with 80K AIC it will be more then enough.
Advantage of NH over class T its also a disconnect switch, just pull the fuse, even under full load no problem.

[Matt Johnson]

What about a Heinemann GJ breaker? They have a AIC of 25kA at 65vdc and the time delay is bypassed on overloads of 1000% of rating, so would trip in .008 second. The only improvement I see over a Class-t is the disconnect ability - like a NH switch - but it does seem to be an option.

[CaptainRivet]

Originally Posted by Matt Johnson

What about a Heinemann GJ breaker? They have a AIC of 25kA at 65vdc and the time delay is bypassed on overloads of 1000% of rating, so would trip in .008 second. The only improvement I see over a Class-t is the disconnect ability - like a NH switch - but it does seem to be an option.

Hi Matt,
Sadly they are insufficent for a main battery fuse as GJ Type means made to fuse motors and the delay is to avoid tripping due to startup surge.
But i need a breaker with smaller current rating of my watermaker and the GJ fuse is perfect for that and also in 50A for the OPs windlass.
If you have several batteries in parallel you can use class T or NH on each battery and then the heinemann as main battery bank fuse AND disconnect switch, for that its sufficent and spec it for overcurrent and battery protection. The other will do cable protection.

Main battery fuse as acctually 3 functions in one:
1) interrupt the connection in an short curcuit event of the battery
2) interrupt the connection at the given current rating to protect the installation from overcurrent
3) protect the cable connecting battery to device/main busbar. A cable type rating fuse needs a 400-500% immediate tripping rating in normal or fast as the cable can and should not trip due to surges and spike which are normal in common electric systems and act as a kind of buffer. Its speced to trip over a longer time when you overload the cable with the given tripping curve and the immediate trip rating is for defects like short curcuit.

So a class T, as always super fast acting type by its construction is actually a suboptimal main battery fuse type for a main battery fuse as when speced as in 3) for a cable its tripping rating and curve is too fast and cannot act as buffer sufficiently which they fixed by using a 125%-140% rating but that can endanger devices in 2) overcurrent protection. Bigger current rating fuse means higher resistance = more voltage drop in the complete system.

In contrast to NH which are normal or fast acting (you also get motor type ones) and constructed to run 24/7/365 on its current rating, means you use them on 100% spec rating which also gives you lowest voltage drop possible. And the lowest AIC rating on the smallest NH00 is 50kA so its always sufficent for your lithium while with class T you have to be also carefull and chose the correct AIC rating...i didn't as a didn't know 20 years ago and burned a car down when a class T fuse got arced by a shortened 400AH lithium bank.
Thats why a NH is actually the perfect fuse type for a main lithium bank fuse.

[CharlieJ]

@CarlF #56

While fuses are sized to protect the wire, the ABYC specifies that fuses (and therefor the wire) should be 1.1-1.5 times the expected maximum current. You also want to size the wire to have a maximum 10% voltage drop.

This is not an ABYC requirement.

The requirements are that if there is no fuse/circuit breaker (OCPD) equal to the ampacity of the conductor, than the next standard size OCPD may be use if it does not exceed 150% of the conductor’s ampacity.

But you then run up against the problem that T1 fuses over 400 amps are very expensive. So I'd probably put in a 400 amp T1 and use 4/0 cable to minimize voltage drop if the inverters are more than a few feet from the batteries.

1. There is no price differential for either the large or small format Class T fuses based on their rating.
2. 4/0 boat cable has an ampacity of 312A outside a machinery space and 264A inside a machinery space. Although, I do protect 4/0 boat cable with 400A Class T fuses for inverter/charger service and am comfortable because of the fast acting nature of a Class T fuse.
3. If NH fuses were more readily available in the USA, I would use them for high A, high AIC service.

The 2nd issue is that the ABYC requires that a fuse has to be within 7" of the battery terminal. If you are wiring your batteries in parallel with equal length cables - which is the best way to keep them balanced - then a good approach is a MBRF fuse at each battery terminal with equal length jumpers to a busbar and then put the T1 there.

ABYC has an exception for connections directly connected to a battery terminal: The conductor may be a maximum of 72” long if it is protected for its entire length. The easiest way to protect it is to put the conductor in self extinguishing split loom.