Combined Pb acid Battery with LiPo project

[luna]

I would think that all battery manufacturers would recommend the use of a fuse or other suitable circuit protection on the output terminals. In order to select the proper device, the Isc of the battery needs to be known.

The Isc will undoubtedly vary based on voltage, temperature, SOC etc.
Fine, but the battery guys could just state the maximum Isc and then we all would have something to go on.

One wonders if the reason this info. is not front and centre is a legal one.

 

[fryedaze]

There is some very good (and recent) discussion on this here "Victron Comms" Epoch 460AH Lifepo4 8D Marine batteries. Sums up nicely what I am taking too many words to try to explain.

Without a specific statement from Epoch or any of the other manufacturers on *exactly* what the short circuit current rating is for their batteries we are left to draw our own and best conclusions. And without that number I’ve pretty much offered all I can on the subject so will probably step away from this discussion. Good luck to all.

Thanks for the help. I appreciate it.

 

[SteveK]

The Epoch has a 500A surge protection according to Will.
In the following load test after 37~ seconds/@584A it turns off.
Will Prowse Epoch 460 surge test @ 14.35
The Epoch site claims 400A continuouse for 10 seconds. Odd it did not trip at 400.
Is there more than one Epoch 460?

 

[Portage_Bay]

I would think that all battery manufacturers would recommend the use of a fuse or other suitable circuit protection on the output terminals. In order to select the proper device, the Isc of the battery needs to be known.

The Isc will undoubtedly vary based on voltage, temperature, SOC etc.
Fine, but the battery guys could just state the maximum Isc and then we all would have something to go on.

One wonders if the reason this info. is not front and centre is a legal one.

Maybe it's lack of control, regulations whatever you want to call it in Chinese manufacturing and production?

 

[SteveK]

There is no internal fuse on the Epoch Essentials 300ah version and he is using an MRBF external. In this particular case it would appear (based off existing ABYC info plus Charlie Johnsons' very relevant new info) that a 300ah Lifepo4 battery would require a minimum of 15k AIC on each battery which exceed the MRBF design of 10k AIC rating.

Now regarding the internal fuse on the 460ah Marine, Keep in mind that it is also a 500 amp fuse. If you use 2/0 wire for each battery to a buss bar then you still need to fuse appropriately for the wire as 500 amps is too high for a 2/0. I used MRBF fuses right on the terminals to protect the wire. MRBF are much cheaper and easy to hide. Also cheaper and easier to replace.
So on the 460 marine battery on my install it has a cascade of protections.

* BMS 1650 amps for .0004- Usually acts first due to time
* MRBF 300 amp fuse on each battery terminal to protect the wire run to the buss bar/lynx power in
* Internal gR 500 amps fuse designed for the specific battery for max AIC

Most people with the Epoch 460s are doing it this way.

Given Charlie Johnsons new info, which has been confirmed elsewhere, but not yet implemented, there will be additional options for fusing it would appear. For instance if you had a bank made up of 200ah batteries...it may well be that MRBF on each terminal will suffice. This may not be a bad way to go and would simplify installs.

But by the same new information, many large battery banks that use a single external class T probably will not suffice any longer. And as described by CJ its easy to see why. A Class T would seem to be good if you fused at each battery up to 400ah. Using a single fuse for a bank (for AIC) or using batteries over 400ah will require some additional thought.

The Epoch 460ah Marine is the only battery I am aware of that has an internal fuse, which as we said is a 50k AIC rating. Its actually quite telling that the Epoch engineers nailed this requirement so far in advance. I had these batteries for 6 months before anyone even found out a fuse was inside ( I think Panbo did ) . And now with the coming refinement of Lifepo4 fusing requirements..it really does look like they had their stuff together.

 

[twistedtree]

Thanks, looks like I will be adding a manual batt switch. I incorrectly assumed that the Bank Manager contactor would be my discount. It has a remote switch if needed.
Live and learn.

In the upcoming revision of E-13, the bank manager contact *might* be acceptable as the battery disconnect switch. A proposal of mine was accepted that would allow this under certain circumstances. But there is no guarantee it will survive through the whole review process, and I don't know when the new E-13 will be approved and released. The earliest will be this summer.

 

[twistedtree]

The breaker is ISO certified and has other EU certifications, but not UL. It seems the emerging trade war has created certification issues. I read that UL listings are not acknowleged in China and China's certification system is not recognized in the US (until such time as a US company rebrands them and has them UL certified). Welcome to the trade wars. Just what we needed is a more complex fusing calculation.

This certification issue is very true, but has been around for decades and has nothing to do with any trade wars. Most contries have their own certifications, and don't give a rat's a$$ about other countries' certifications. Occasionally there is reciprocity, but usually not. So a manufacturer has to get them for every country they want to sell in, assuming they want to operate legitimately. But that often doesn't happen, and enforcement is weak. And at least in the US there are only scattered laws requiring standards compliance.

 

[twistedtree]

I had a quick look at this and provide the following feedback. Seems most other readers overlooked a few things.

- If the internal resistance of each battery is 30 mΩ, that is 0.03 Ω. Not 0.003 Ω
- If we rely on these two batteries to act like two resisters, the bank resistance becomes 0.015 Ω
- To correct your result just knock a zero off, your battery short circuit current of 8,800 Amps becomes an Isc. of 880 Amps.

This revision seems to move things in the opposite direction compared to what ABYC and others are saying. In addition there must be something wrong when you consider that according to Epoch each of the 2 batteries is said to be able to deliver a Peak/Surge current of 1,200 A. With an Isc of 880 A, how?

I think a few things are at issue here.

- Epoch says the internal resistance for each battery is less than or equal to 30 mΩ. Epoch does not state the minimum resistance. A smaller resistance makes the current larger.
If the battery bank acted like a resistor with 1 mΩ resistance the Isc through the pair of batteries would, at your 13.2 volts be 26,400 Amps.

- Epoch also calls this 30 mΩ the Internal Impedance of the battery and is obtained by use of test equipment operating at 1kHz AC on a battery at 50% SOC. This appears to be a standardize test. One has to wonder what is the purpose of this 30mΩ value, why is it important. It does not seem to result in the correct Isc values. Not even in the same ballpark.
Maybe it's useful somewhere else. Maybe the calculation of battery resistance is just not that simple.

- I have not checked many of them, but battery manufacturers do not seem to provide Isc values for their products. You could easily think it is large as Epoch installs a fuse with an AIC of 50kA. This leaves the user in most instances to come up with their own assessment of Isc for use in selecting the required fuse. Not a good situation.

Bottom line, as I'm still in lead, my Class T is likely fine. Unless, when I change to LFP there is a lot more info. available, I will likely move to a NH or other series of fuse.

I'm seeing some specs that say LFP cell resistance is typically 30-40 mOhms per Ah. So a 100Ah battery would have an internal resistance of .3 to .4 mOhms. That yields a short circuit current of 40,000A for a 12V battery.

 

[fryedaze]

I'm seeing some specs that say LFP cell resistance is typically 30-40 mOhms per Ah. So a 100Ah battery would have an internal resistance of .3 to .4 mOhms. That yields a short circuit current of 40,000A for a 12V battery.

For four internal cells in series, wouldn't that be 1.2 - 1.6 milliohms for the 100 amphr battery???

 

[luna]

I'm seeing some specs that say LFP cell resistance is typically 30-40 mOhms per Ah. So a 100Ah battery would have an internal resistance of .3 to .4 mOhms. That yields a short circuit current of 40,000A for a 12V battery.

That is an enormous amount of current produced from such a small box.

This 40,000 Amps per 100 Ah is almost an order of magnitude higher than the 5,000 Amps CharlieJ spoke to as being the potential guidance from ABYC in their upcoming revision to E-11.

I’m no EE, but I thought the methods used to determine this kind of thing would have been settled long ago.
How can the result be so much different?

Please forgive us laymen when we wonder if some or all of this came from the Marketing Department.

 

[fryedaze]

I am going to keep plugging away until I have a real engineering answer on what short circuit current is on these batteries.

 

[SteveK]

I am going to keep plugging away until I have a real engineering answer on what short circuit current is on these batteries.

You have a very good point. I have been surfing the net looking for a hint of that answer. So far this video is the best answer.
I have been unable to find tests of fuses on induced short circuits.

 

[fryedaze]

You have a very good point. I have been surfing the net looking for a hint of that answer. So far this video is the best answer.
I have been unable to find tests of fuses on induced short circuits.

Here is a direct shot test of MRBF

 

[twistedtree]

For four internal cells in series, wouldn't that be 1.2 - 1.6 milliohms for the 100 amphr battery???

Yes, you are probably right. And there are other internal resistances, all of which lead to the ABYC guidance .

 

[Marco Flamingo]

The comments I've seen re this video say that it doesn't show that an MRBF can handle a 400Ah LFP battery short circuit. The +10 feet of 8 AWG wire used in the video has so much resistance that a MRBF fuse could handle the short. Try the test with one foot of 2/0 wire and see if the fuse can handle 25,000 amps from actually shorting a 400Ah LFP as used in a realistic boat scenario.

 

[SteveK]

The comments I've seen re this video say that it doesn't show that an MRBF can handle a 400Ah LFP battery short circuit. The +10 feet of 8 AWG wire used in the video has so much resistance that a MRBF fuse could handle the short. Try the test with one foot of 2/0 wire and see if the fuse can handle 25,000 amps from actually shorting a 400Ah LFP as used in a realistic boat scenario.

I have wondered how to rationalose a 300A MRBF fuse that can handle up to 10,000A. How a 300A Class T can handle 20,000A.
I expect both to trip if their rating is exceeded.
So I surmise that the 10k and 20k is their ability to withstand arcing which will jump a blown fuse and continue down the line.
ABYC has Class T is better choice for a house bank before LFP as we were using them with banks of 6V series/parrelell banks.
The expected updates must somehow be looking at whether LFP can exceed the class T 20K limit.
Short story. My 800Ah 6v bank with 300A class T fuse blew when the inverter shorted out. That was with 4/0 cable

 

[twistedtree]

I have wondered how to rationalose a 300A MRBF fuse that can handle up to 10,000A. How a 300A Class T can handle 20,000A.
I expect both to trip if their rating is exceeded.
So I surmise that the 10k and 20k is their ability to withstand arcing which will jump a blown fuse and continue down the line.

That's pretty much it. Most of us just think about the 300A rating and expect that current over that will blow the fuse. But if the available/actual current it too high, the fuse is no longer able to break the circuit and current keeps on flowing even thought it's well over the 300A rating.

 

[fryedaze]

I had a quick look at this and provide the following feedback. Seems most other readers overlooked a few things.

- If the internal resistance of each battery is 30 mΩ, that is 0.03 Ω. Not 0.003 Ω
- If we rely on these two batteries to act like two resisters, the bank resistance becomes 0.015 Ω
- To correct your result just knock a zero off, your battery short circuit current of 8,800 Amps becomes an Isc. of 880 Amps.

This revision seems to move things in the opposite direction compared to what ABYC and others are saying. In addition there must be something wrong when you consider that according to Epoch each of the 2 batteries is said to be able to deliver a Peak/Surge current of 1,200 A. With an Isc of 880 A, how?

I think a few things are at issue here.

- Epoch says the internal resistance for each battery is less than or equal to 30 mΩ. Epoch does not state the minimum resistance. A smaller resistance makes the current larger.
If the battery bank acted like a resistor with 1 mΩ resistance the Isc through the pair of batteries would, at your 13.2 volts be 26,400 Amps.

- Epoch also calls this 30 mΩ the Internal Impedance of the battery and is obtained by use of test equipment operating at 1kHz AC on a battery at 50% SOC. This appears to be a standardize test. One has to wonder what is the purpose of this 30mΩ value, why is it important. It does not seem to result in the correct Isc values. Not even in the same ballpark.
Maybe it's useful somewhere else. Maybe the calculation of battery resistance is just not that simple.

- I have not checked many of them, but battery manufacturers do not seem to provide Isc values for their products. You could easily think it is large as Epoch installs a fuse with an AIC of 50kA. This leaves the user in most instances to come up with their own assessment of Isc for use in selecting the required fuse. Not a good situation.

Bottom line, as I'm still in lead, my Class T is likely fine. Unless, when I change to LFP there is a lot more info. available, I will likely move to a NH or other series of fuse.

Here is another data point. I purchased a specialized battery resistance meter. Both batteries where 1.6 miliohms at 85% SOC. The meter was a 1Khz instrument.