t class, anl, mega or mbrf

[noelex 77]

Originally Posted by Cpt Mark

That busbar connects all 3, 280AH batteries together . So there is a potential for a lot of current to hit if there was a surge from all 3 batteries is the thinking. Am I wrong?

Lithium batteries can potentially deliver a very high current (depending on the BMS), but a fuse is required to protect the attached cable.

The capacity of the fuse needs to be less than the capacity of the wiring that the fuse protects.

In the event of a short circuit, the fuse should blow before the cable melts. There are tables to determine the maximum fuse size for each sized cable (this varies depending on the temperature specification, if the cable passes through a hot engine room, if it is bundled etc).

This is a typical (simple) table.

A 500A fuse is designed to protect a large cable:

[Cpt Mark]

Originally Posted by noelex 77

Unfortunately, yes. The fuse protects the cable.

The capacity of the fuse needs to be less than the capacity of the wiring that the fuse protects.

In the event of a short circuit, the fuse should blow before the cable melts. There are tables to determine the maximum fuse size for each sized cable (this varies depending on the temperature specification and if the cable passes through a hot engine room etc).

This is a typical table:

Yes, your are correct. Thank you.

[wholybee]

Originally Posted by Cpt Mark

Hi all,

Thank you so much for your inputs.

Yes. It is a Lifipo4 battery system. I have 3 separate batteries each with it's own BMS, Fuse and ON/Off switch. All Negs go to a central neg busbar. That busbar then feeds the DC Main distribution which also has connected the windlass and electric winch. Moving those 2 cables would be a nightmare so I installed a heavy duty busbar.

On the positive side, all cables go to a very heavy duty busbar and from there to a 500 amp fuse which then goes to the main Positive distribution busbar.

Positive cables are all 1/0 ga. Neg cables from BMS to busbar are 2 pairs of 6 AWG cables. From Neg busbar to distribution is 1/0 cable.

Original design for dc distribution was a single post. With so many cables going into them I installed appropriate sized bus bars to handle the loads.

What was running was a 1500 watt electric heater. That shouldn't have popped any fuses but 2 did.

Fuses were bought at West marine, Blue Seas.

Re: Overkill. What I can't stand is their absolute lack of service after the sale. After a couple of years I finally had 1 tech reach out to me regarding settings. It has been hit and miss, mostly miss. If anyone out here understands these settings I'd love to talk with you. Currently, even tho they shouldn't, when the battery gets very close to full I get a cell over volt fault and the FET that controls the charging gets turned off. This over volt must happen in terms of microseconds as I've not seen it as it happens and the cell voltages are all where they are suppose to be for a full battery which is below the trip point.

And their display of battery full etc. Batteries full, 100%. Switch to invert only and 1 immediately goes to 59% even tho the voltage is the same for the other batteries which are in the high 90's.

You might be wondering why it has taken me so long to get here considering I built this sytem a couple of years ago. I just installed 1080 watts of solar. i need to be able to go offgrid. 1. I'm going cruising 2. my marina picks out a number to charge for electricity. Pretty sure it's based on whatever extra money they need that month. Last year I had a bill and when I asked about it was given the excuse and blah blah blah. I pointed out I was gone for 5 weeks so, no, that can't be right.

I had a 2000 watt inverter connected to a Sterling Pro 50 amp charger. Their Ultra Pro might be fine for lead acid but not for Lifipo4 batteries.

Including my rants, sorry about that, I hope this provides the additional info requested.

Thanks again

It is disappointing to hear that about OverKill support now. That certainly was not the case when I bought mine years ago. The reason for buying an Overkill instead of a JBD (which is the same BMS) is for the excellent support they once had.

There is something wrong with your system. A single OverKill BMS can handle 1500W at 13.2V. Two of them can easily do it, and three is a cakewalk. I will be happy to discuss your settings, as I have the same BMS.

A damaged or defective cell can cause the really quick spike that would return to normal as soon as charging is stopped. But there may be something else going on. There is a setting in the BMS for delay before cutoff. Is should be a few seconds, as a few seconds won't hurt anything, and gives you time to see the issue and/or correct it before power is interrupted. Also, if you intend to charge to 3.65Vpc (14.6V total) then you need to set the HVC to about 3.7Vpc. Otherwise, you will get annoyance trips. This goes against what a lot of people recommend, but it's fine because you are not charging to 3.7Vpc, that is just the limit you set to know that something is wrong and to shut it down. I suggest charging to about 3.5Vpc though, and only charge to 3.65Vpc as an occasional test.

Also, poor connections of the sense/balance leads can cause weird problems, and can be hard to diagnose because they might look and seem perfectly fine. But some resistance in that connection breaks just about every function of the BMS.

Where did you buy your 280Ah cells, and what brand are they? There are many nightmare stories from bad 280Ah cells because the market is flooded with counterfeit, factory rejects, used cells, refurbished cells, and anything else you can think of. It almost doesn't matter where you buy them, there is still a chance that you get scammed on them.

[Cpt Mark]

Originally Posted by Cpt Mark

Yes, your are correct. Thank you.

BTW. That fuse was used to go to the main distribution post (since replaced) and the external inverter. That was why we went that large. Truly isn't needed now.

[Cpt Mark]

Originally Posted by wholybee

It is disappointing to hear that about OverKill support now. That certainly was not the case when I bought mine years ago. The reason for buying an Overkill instead of a JBD (which is the same BMS) is for the excellent support they once had.

There is something wrong with your system. A single OverKill BMS can handle 1500W at 13.2V. Two of them can easily do it, and three is a cakewalk. I will be happy to discuss your settings, as I have the same BMS.

A damaged or defective cell can cause the really quick spike that would return to normal as soon as charging is stopped. But there may be something else going on. There is a setting in the BMS for delay before cutoff. Is should be a few seconds, as a few seconds won't hurt anything, and gives you time to see the issue and/or correct it before power is interrupted. Also, if you intend to charge to 3.65Vpc (14.6V total) then you need to set the HVC to about 3.7Vpc. Otherwise, you will get annoyance trips. This goes against what a lot of people recommend, but it's fine because you are not charging to 3.7Vpc, that is just the limit you set to know that something is wrong and to shut it down. I suggest charging to about 3.5Vpc though, and only charge to 3.65Vpc as an occasional test.

Also, poor connections of the sense/balance leads can cause weird problems, and can be hard to diagnose because they might look and seem perfectly fine. But some resistance in that connection breaks just about every function of the BMS.

Where did you buy your 280Ah cells, and what brand are they? There are many nightmare stories from bad 280Ah cells because the market is flooded with counterfeit, factory rejects, used cells, refurbished cells, and anything else you can think of. It almost doesn't matter where you buy them, there is still a chance that you get scammed on them.

Hi Warren,

I bought mine years ago when there was a waiting period. In my experience, they have never had customer service let alone good customer service. Most of my emails were never answered.

I'd love to discuss with you about the settings. While I "think" I understand all the settings I'm surely missing something. We can do this offline if you'd like. By phone, video or email. LMK. If by email/text we might consider starting a new thread as I know I'm not the only one having this issue and it could be helpful for others. Thanks

[Cpt Mark]

Warren

Oops. My cells are EVE 280 AH, bought new from a reputable seller in China.
All were top balanced etc. Recently, thinking I had a problem in 1 battery I pulled it out and load tested it. Have a cool graph for my battery now. All was fine.

[paradox]

I am new to Lithium batteries. I am working on a hybrid lithium/LA system. I am using an MRBF fuse on the battery connected to a T fuse for the system. The mrbf is overkill, but I want to protect the short cable from the Lithium battery to the T fuse. Then the T fuse connects to the system. There is a great video on you tube from nigel calder on the use of T fuses on lithium batteries. He talks about the AIC rating of fuses for lithium batteries: https://youtu.be/CrwT52ehymQ?si=IqqB9l0ZTWpot1kp

The wires you are using are not matched to the fuses. A 1/0 battery cable is likely too small for the battery bank. And the 6AWG wires are certainly too small. OR, the fuses are too large to protect the wires from overheating.

Paradox4
Long Island, NY

[Cpt Mark]

Originally Posted by paradox

I am new to Lithium batteries. I am working on a hybrid lithium/LA system. I am using an MRBF fuse on the battery connected to a T fuse for the system. The mrbf is overkill, but I want to protect the short cable from the Lithium battery to the T fuse. Then the T fuse connects to the system. There is a great video on you tube from nigel calder on the use of T fuses on lithium batteries. He talks about the AIC rating of fuses for lithium batteries: https://youtu.be/CrwT52ehymQ?si=IqqB9l0ZTWpot1kp

The wires you are using are not matched to the fuses. A 1/0 battery cable is likely too small for the battery bank. And the 6AWG wires are certainly too small. OR, the fuses are too large to protect the wires from overheating.

Paradox4
Long Island, NY

Thank you for your thoughts. I ran across the Nigel Calder video too. When I was learning about Lifepo4 I read his white paper 1st. He is great.

Per BMS factory specs the 2 6AWG are what BMS needs. Not sure I can get larger wires in there. Will be looking at it next time I can get in there.
The 1/0 cable is ok for my system but as I've learned 00 would have been better.

I question your use of MBRF in your proposed system. As you watched in the video the MBRF is not up to the task of Lifepo4 batteries due to fire potential and that is the 1st one you have to protect yourself? The one you don't want in your system will be the 1st to blow? Your T Class fuse is going to be within inches of the terminal. ABYC and Nigel Calder agree this is best.

My thoughts. I've ordered T class fuses and holders.

[Cpt Mark]

In the end, after considering everyone's thoughts, watching Nigel Calder's video and learning all about the different fuses, AIC ratings etc.. the clear winner and IMHO the only fuse to use with a Lifep04 system is the Class T fuse.

It has the highest AIC rating, is the fastest blowing fuse and what I liked best is that inside that tube of metal that houses the fuse silica packed in there. This is so when the fuse blows it prevents or at least helps preventing fires.

[paradox]

Cpt Mark
I agree the MRBF is less than optimal. I have a 12 inch run from the +terminal of the battery using a 1/0 wire to the T fuse. I want to protect that short run. I cant find a way to put a T fuse at the battery post. And I cant secure a T fuse holder with only a 6inch battery cable - it will hang down next to the battery. Not ideal, Likely overkill. Unless you know a way to secure a Tfuse holder directly to the battery cable

[Americanrancher]

Originally Posted by Bellinghamster

Inrush to discharged capacitors of an inverter could possibly blow fuses, especially if the battery switches were all off initially and you turned them on one at a time, blowing each batteries fuse in turn. Caps got a bit of charge from each one so the last one could finish the job without blowing the fuse?

There are inverter precharge circuits available specifically to address this.

MEGA fuses are rated to clear 2000A fault at 32VDC
ANL fuses are rated to clear 6000A at 32VDC. (They were the original "cheap" battery fuse, not very precise in their trip curve.)
Class T fuses are rated to clear 20,000A at 125VDC.

Trip curves for each are attached. ANLs are not as precise as the other two. Class T are VERY reliable, but also expensive, and voltage rating is higher than it needs to be on a 12V system.

You should (must) have a fuse with a rated interrupt capacity (AIC) higher than the amount of current your battery can supply into a short circuit, otherwise they arc instead of breaking the circuit and are a serious fire risk.

As mentioned in previous replies, there are lots of counterfeit knockoffs of legitimate fuses flooding the market through Amazon and Ebay. No need to buy them from a marine store, but you should buy only legit brand Bussmann or Littelfuse (Blue Sea private labels fuses from them and are good) and get them from a legitimate distributor. (I prefer Digikey or Mouser for things like this).

Being ignorant I used MIDI fuses in my system for battery protection. I did this because they are more compact and less expensive than those mentioned above. Reviewing the Blue Sea Systems site they do not publish a curve for these types of fuses. Can you shed some light on this? I have not had any problems with them and they have blown when I had a starter fail. Should I replace them with one of the above? Thanks Ben S/V DAWN

[Statistical]

Originally Posted by Americanrancher

Being ignorant I used MIDI fuses in my system for battery protection. I did this because they are more compact and less expensive than those mentioned above. Reviewing the Blue Sea Systems site they do not publish a curve for these types of fuses. Can you shed some light on this? I have not had any problems with them and they have blown when I had a starter fail. Should I replace them with one of the above? Thanks Ben S/V DAWN

The issue is not the curve the issue is the AIC. People often assume that once afuse blows the circuit is open and current stops flowing. That is what is suppose to happen but electricity can have other plans. With enough current an arc can form across the fuse. The fuse is blown but the circuit is still energized and that can lead to fire melting and catching fire even after the fuse is blown. The AIC is the measure of the maximum current the fuse can stop.

There are two seperate numbers. There is the fuse rating which is the current beyond which the fuse will blow based on the curve (amount of current exceeding rating vs time). It should never blow below the rated current even if operated continually at that current. Then there is the AIC which is the current beyond which the fuse can not prevent current flow. You can think of the AIC as the limit of the fuse's protection abilities.

The AIC for MIDI fuses is usually around 5,000A at 12V nominal and 2,000A at 24V nominal. They are often not rated for higher voltage.

If you have a 24V system they would be insufficient for just about any LFP battery. If you have a 12V LFP system they would be borderline for smaller LFP packs and insufficient for larger ones.

If the LFP batteries are drop ins they should have a short circuit current listed. The AIC of the fuse should exceed the short circuit current. If the batteries are DIY or from specified cells it can be computed from internal resistance.

[Jammer]

Hello Mark


One Fact to Consider that has not yet been touched upon in this thread is that fuses are thermal devices. In essence they are heated by current passing through them, and melt and open at a certain point.


Fuses will blow below their rating if they are in a hot environment or if they are heated by smaller cables or poor connections made to the fuse block, or by adjoining fuses in the same fuse block (if present). That may explain what happened.

[Americanrancher]

Originally Posted by Statistical

The issue is not the curve the issue is the AIC. People often assume that once afuse blows the circuit is open and current stops flowing. That is what is suppose to happen but electricity can have other plans. With enough current an arc can form across the fuse. The fuse is blown but the circuit is still energized and that can lead to fire melting and catching fire even after the fuse is blown. The AIC is the measure of the maximum current the fuse can stop.

There are two seperate numbers. There is the fuse rating which is the current beyond which the fuse will blow based on the curve but it should never blow below the rated current even if operated continually at that current. Then there is the AIC which is the current beyond which the fuse can not prevent current flow.

The AIC for MIDI fuses is usually around 5,000A at 12V nominal and 2,000A at 24V nominal. They are often not rated for higher voltage.

If you have a 24V system they would be insufficient for just about any LFP battery. If you have a 12V system they would be borderline for smaller LFP packs and insufficient for larger ones.

If the batteries are drop ins they should have a short circuit current listed. The AIC of the fuse should exceed the short circuit current. If the batteries are DIY or from specified cells it can be computed from internal resistance.

Thanks, I think I am OK as my system is old school Lead Acid! I am considering upgrading to LFP so I will upgrade to different fuses at that time. Ben S/V DAWN

[Cpt Mark]

Originally Posted by paradox

Cpt Mark
I agree the MRBF is less than optimal. I have a 12 inch run from the +terminal of the battery using a 1/0 wire to the T fuse. I want to protect that short run. I cant find a way to put a T fuse at the battery post. And I cant secure a T fuse holder with only a 6inch battery cable - it will hang down next to the battery. Not ideal, Likely overkill. Unless you know a way to secure a Tfuse holder directly to the battery cable

what battery(ies) are using on the Lifepo4 side? How are they connected?