Are you aware of this ABYC Update

[jssailem]

Reviewing the latest electrical information on Panbo, I found this article about the revisions to the ABYC standards regarding Over Current Protection (OCP).

abyc-publishes-updated-battery-and-electrical-standards

For all who are playing with their batteries, be they FLA or LiFePO4, this is an important update.

 

[Johann]

Some good stuff in there…. MRBFs are good for LFP 200Ah or less. You can now parallel two cables for ampacity if you follow a few rules. BMS with a normally open contactor can be the required switch. Inverter case grounds got a lot smaller. But the AIC requirement for large paralleled batteries is going to complicate some installs…

 

[colemj]

But the AIC requirement for large paralleled batteries is going to complicate some installs…

They don't even have to be paralleled batteries. A single 1000Ah 12V battery constructed from 4 1000Ah cells in series requires a fuse with a 50,000A IAC rating.

This moves one out of Class T and into NH and other types of industrial fuses and their associated mountings.

Even a single 500Ah 12V battery moves one into these large industrial fuses. A 400Ah battery is the largest that a Class T fuse still fits the recommendation, and a majority of boats are using batteries larger than this.

Here, I think the ABYC got over their skis again. They finally did the right thing by relaxing the fuse requirements for smaller batteries, but went overboard on the larger ones. Keep in mind that until this revision, they were ridiculously specifying 20kA AIC fuses for 50Ah LFP batteries, so I have little confidence that they understand this issue well.

ABYC continues to fail us on LFP battery recommendations.

Mark

 

[dlochner]

But the AIC requirement for large paralleled batteries is going to complicate some installs…

They don't even have to be paralleled batteries. A single 1000Ah 12V battery constructed from 4 1000Ah cells in series requires a fuse with a 50,000A IAC rating.

Not so fast. AIC ratings vary based on the voltage they are tested at. Class T fuses are rated at 20,000 A @ 120 VDC. Presumably, the AIC rating would be considerably higher for a system voltage of 12v or 24v. Unfortunately, the AIC ratings are only published for the tested voltage.

That AIC ratings vary based on voltage is demonstrated at the published AIC ratings for a MRBF, which shows higher AIC ratings for the same fuse at lower voltages. Presumably this is not a function of the construction of MRBF, but rather the testing regimen the fuse under went. Perhaps this new standard will prompt LittelFuse to test their Class T fuses at lower voltages.

And Mark, who is going to build a 250 lbs 1000ah battery, when 4 60 lbs batteries have the same capacity?

 

[Johann]

They don't even have to be paralleled batteries. A single 1000Ah 12V battery constructed from 4 1000Ah cells in series requires a fuse with a 50,000A IAC rating.

This moves one out of Class T and into NH and other types of industrial fuses and their associated mountings.

Even a single 500Ah 12V battery moves one into these large industrial fuses. A 400Ah battery is the largest that a Class T fuse still fits the recommendation, and a majority of boats are using batteries larger than this.

Class T is fine. Note at the end of paragraph 11.10.1.3.2.2 (the paragraph with 5kA per 100Ah) there is an ”or”, followed by 11.10.1.3.2.3 which specifies a fuse rating AIC of 20kA at 125VDC (Class T) if the battery exceeds 20kA of short circuit current. So you don’t have to apply the 5kA per 100Ah to all LFP batteries. If it’s over 20kA you can use a Class T.

 

[colemj]

And Mark, who is going to build a 250 lbs 1000ah battery, when 4 60 lbs batteries have the same capacity?

What am I missing here? 4x60 = 240lbs. OK, maybe 10lbs lighter, but I don't know where you got the 250lbs or the 60lbs. The couple of 250Ah 12V batteries I quickly looked at weighed ~80lbs. Our 1000Ah bank does weigh 250lbs, so that sounds right. There is no free lunch - smaller batteries in parallel are no lighter than a single battery of same capacity, with exceptions for small differences in case weight or the weight of internal electrical components.

There are issues with using smaller batteries in larger parallel configurations. In my example of 1000Ah, most battery manufacturers limit parallel configurations to four batteries. In the recent past, it wasn't possible to reach 1000Ah with four batteries. Now, it is possible, but 1000Ah is also not very large anymore, and many boats are installing larger.

But that is increasingly possible too, with batteries getting denser. However, the issues with battery balancing, keeping multiple BMS's in sync, cascading failures, etc cannot be overcome when paralleling multiple batteries using smaller cells. These things are not issues at all for single batteries using larger cells.

Mark

 

[colemj]

Class T is fine. Note at the end of paragraph 11.10.1.3.2.2 (the paragraph with 5kA per 100Ah) there is an ”or”, followed by 11.10.1.3.2.3 which specifies a fuse rating AIC of 20kA at 125VDC (Class T) if the battery exceeds 20kA of short circuit current. So you don’t have to apply the 5kA per 100Ah to all LFP batteries. If it’s over 20kA you can use a Class T.

OK, but that is confusing. They list AIC requirements up to 200AH batteries, then say to see section 10.1.3 for larger batteries.

Why not just directly say anything larger than 200Ah requires an AIC of 20kA? After all, that seems to be exactly what it is once one shuffles back and forth in the recommendations piecing the disparate strings together for them.

Mark

 

[dlochner]

What am I missing here? 4x60 = 240lbs. OK, maybe 10lbs lighter, but I don't know where you got the 250lbs or the 60lbs. The couple of 250Ah 12V batteries I quickly looked at weighed ~80lbs. Our 1000Ah bank does weigh 250lbs, so that sounds right. There is no free lunch - smaller batteries in parallel are no lighter than a single battery of same capacity, with exceptions for small differences in case weight or the weight of internal electrical components.

There are issues with using smaller batteries in larger parallel configurations. In my example of 1000Ah, most battery manufacturers limit parallel configurations to four batteries. In the recent past, it wasn't possible to reach 1000Ah with four batteries. Now, it is possible, but 1000Ah is also not very large anymore, and many boats are installing larger.

But that is increasingly possible too, with batteries getting denser. However, the issues with battery balancing, keeping multiple BMS's in sync, cascading failures, etc cannot be overcome when paralleling multiple batteries using smaller cells. These things are not issues at all for single batteries using larger cells.

Mark

Epoch 300ah batteries weigh in at 58 lbs each. For the sake the discussion I rounded to 250 lbs for 4. For a 16k+ lbs boat 12 lbs does doesn’t make much difference. My boat weighs ~ 16k lbs when loaded for cruising.

 

[colemj]

Epoch 300ah batteries weigh in at 58 lbs each. For the sake the discussion I rounded to 250 lbs for 4. For a 16k+ lbs boat 12 lbs does doesn’t make much difference. My boat weighs ~ 16k lbs when loaded for cruising.

Sure, but I'm still confused on the comment "who is going to build a 250 lbs 1000ah battery, when 4 60 lbs batteries have the same capacity?".

There is nothing magical between a battery built with individual cells vs. a battery purchased with those individual cells put in a case before hand. They are both using the same cells, so they will weigh the same. In your case, Epoch doesn't make batteries, they rebadge and distribute batteries manufactured by RoyPow using individual EVE cells (RoyPow is owned by EVE). These exact cells are widely available to anyone who wants to build a battery.

The reasons one might build a single 1000Ah battery is to avoid the complications and operating issues with paralleling four individual 12V batteries.

But they will weigh the same, give or take minor choices of casings and internal ancillary components.

Mark

 

[Johann]

OK, but that is confusing.

One thing confusing me is the AIC requirement for larger parallel systems. If I have the required AIC fuse on each battery do I still need the main OCP to be Class T or better? Seems like I should be able to go to a Lynx with Mega fuses but I don’t see that in the wording.
Anyway I’m not changing my 3x 315Ah install as it was compliant in 2020 and the scope of the new standard is for installs 2026 or later. I will take advantage of the parallel for ampacity change though

 

[dlochner]

The reasons one might build a single 1000Ah battery is to avoid the complications and operating issues with paralleling four individual 12V batteries

it is a risk/reward situation Trade a slightly simpler system for greater risk. A one battery system has limited redundancy. If that battery goes offline the whole system goes down. In a multi-battery system the one failed battery can be isolated and taken offline.

Of course there should be a Start/reserve battery, however it most likely have a more limited capacity than 3 smaller batteries.

Combinational probability tells us that chance of 4 independent batteries failing is on orders of magnitude smaller than battery. To keep the math simple with small numbers, assume the any 1 battery has a 25% chance of failing at any given time. In a single battery system that means there is 25%. In a 4 battery system there is a .25 x .25 x .25. .25 or 0.00390625 chance of all 4 batteries failing at the same time.

 

[Johnb]

Sure, but I'm still confused on the comment "who is going to build a 250 lbs 1000ah battery, when 4 60 lbs batteries have the same capacity?".

But they will weigh the same, give or take minor choices of casings and internal ancillary components.

Mark
[/QUOTE]

But you only have to be able to pick them up one at a time

 

[colemj]

it is a risk/reward situation Trade a slightly simpler system for greater risk. A one battery system has limited redundancy. If that battery goes offline the whole system goes down. In a multi-battery system the one failed battery can be isolated and taken offline.

Of course there should be a Start/reserve battery, however it most likely have a more limited capacity than 3 smaller batteries.

Combinational probability tells us that chance of 4 independent batteries failing is on orders of magnitude smaller than battery. To keep the math simple with small numbers, assume the any 1 battery has a 25% chance of failing at any given time. In a single battery system that means there is 25%. In a 4 battery system there is a .25 x .25 x .25. .25 or 0.00390625 chance of all 4 batteries failing at the same time.

Alright, so you were focusing on the single vs. multiple battery aspect, while I misunderstood that you were talking about weight. It was confusing because I was responding to a question about fusing parallel batteries vs a single battery, and you responded to that with a focus on weight differences.

I don't think your probability analysis is correct, or at least doesn't encompass the real world of operation. For example, multiple batteries have multiple BMS's. A failure of one when under load or charge, could easily overload the others resulting in a quickly cascading shutdown of the entire battery bank. The chances of that happening is even greater given that these batteries all use inexpensive mosfet switched BMS's compared to other external contactor-based ones. BMS failures have so far been the primary cause of battery shutdown, while the cells themselves remain fairly robust. Of course, this is for batteries using quality cells, and not the cheap ones using second/third grade cells.

Mark

 

[colemj]

But you only have to be able to pick them up one at a time

Of course. If you need to routinely remove the batteries, smaller is easier. This is the same for lead too - use 68lb golf cart instead of 180lb 8D batteries.

But I don't know of many people who install a 1000Ah battery capacity of either a single bank or multiple batteries who routinely plan to remove them.

As for replacement if something goes wrong, our cells weigh 12lbs each, and if one goes bad, I can remove it (and 3 others) and reconnect the remaining 80% bank in only a few minutes. Within one minute reconnecting two bolts I can isolate just the half of the bank containing the bad cell and run on 50%.

In order to retain capacity if a battery goes bad, it is easier and cheaper to carry a spare 10"x7"x2.7" 12lb individual cell than to carry an entire spare battery.

Mark