Do I Need Breakers for Each Battery

[sunshine_eggo]

Well I can find Nothing in the current 2020 NEC about fusing individual batteries. Regardless of being posted on Here or not. If its not in this edition of the Code then its not required nor needed. IF it was a common danger then the Code would have it listed.

Please cite the portion of the NEC that requires a BMS to be used on batteries made from Lithium cells.

Are you fully versed in article 706 and the requirements for ESS?

Yes my experience goes back to my USAF air craft days, never did I see a fuse between any batteries! Even those early NiCad ones.

An old NiCd isn't comparable to the ultra low resistance of lithium cells, particularly the larger capacities (280A) where the total 4S cell resistance is typically less than 0.8mΩ.

@Zwy

 

[wmgeorge]

Are you fully versed in article 706 and the requirements for ESS?
@Zwy

Yes, Are you? Besides posting over 4600 times in less than one year, what is are your qualifications? You had a field day making fun of and insulting me . .

 

[sunshine_eggo]

Yes, Are you? Besides posting over 4600 times in less than one year, what is are your qualifications? You had a field day making fun of and insulting me . .

Good. I'm not. I was hoping you could enlighten me.

I'm not touting myself as the expert listing my vast experience and expertise who shouldn't be questioned. I'm just a guy with an engineering degree and about 30 years of engineering experience, who happens to have worked extensively for the last 6+ years with batteries of all varieties.

Again, can you cite where the NEC requires the use of a BMS?

 

[timselectric]

If you don't have a fuse/breaker on each battery, then the main fuse would have to be sized to protect the smallest cable in the system, and even then, I would not feel comfortable (as others stated) with having a shorted cell or something on one pack trying to pull down on the rest of the packs, it's nice to have a battery able to break off of the pack.

And simply for maintenance purposes, I prefer to have breakers on the batteries, so I can turn an individual battery off (break it out of the bank easily) to do maintenance or troubleshooting, and then have the Class-T fuses on the main DC bus, one for each inverter.

Just remember that fuses / breakers are supposed to protect the cables / power paths, in case the highest current situation occurs, there can't be any fire hazard or meltdown.

The OP wanted to know.
I already know. lol

 

[wmgeorge]

Then you can quote me the number of LiFePO4 fires nationwide because I could find zero after searching for an hour?

The NEC is written by and for fire prevention (and electrical safety) IF LFP were prone to fires and needed fusing for each it Will be in the Code. Its Not, if you are a true EE then you know regardless a Master has control over the electrical on a construction job. I have taught engineers who were clueless about the real world in evening classes being paid for by their employers.

I do not come on here to be insulted by people like you, while you were in diapers I was in the USAF in the mid 60's sending B52's over to Guam and TDY elsewhere.

Why would BMS be listed or required in the NEC? Read paragraph 2 above. Stop insulting people.

 

[sunshine_eggo]

Then you can quote me the number of LiFePO4 fires nationwide because I could find zero after searching for an hour?

So, the only reason to do anything is to prevent a fire. Seems pretty short sighted. Not using a BMS with LFP is unlikely to start a fire, but there's a 100% certainty that one or more cells will be destroyed sooner rather than later.

The NEC is written by and for fire prevention (and electrical safety) IF LFP were prone to fires and needed fusing for each it Will be in the Code. Its Not, if you are a true EE then you know regardless a Master has control over the electrical on a construction job. I have taught engineers who were clueless about the real world in evening classes being paid for by their employers.

Right, so again, if somethings not required by the NEC because it can't cause a fire, it's never needed (see your quoted posts below).

I do not come on here to be insulted by people like you, while you were in diapers I was in the USAF in the mid 60's sending B52's over to Guam and TDY elsewhere.

Just wow. Grow up man. I was definitely in diapers. Why are you acting like you are in them now?

What are the odds of that happening and the result? Can you quote a source when that happened and how often. Is it in the NEC?

You brought up the NEC. Not me.

Well I can find Nothing in the current 2020 NEC about fusing individual batteries. Regardless of being posted on Here or not. If its not in this edition of the Code then its not required nor needed. IF it was a common danger then the Code would have it listed.

By your flawed logic, if something's not in the NEC, it shouldn't be done. I assume that you make an exception and believe a BMS is needed for long term health and operation of a battery even thought it won't cause a fire. If you don't agree, you're a lost cause.

The use of a fuse on each battery is to protect one from the other. LFP has the potential to deliver on the order of 16,000A, which is well above the rated discharge and charge currents of the cells involved.

 

[timselectric]

It is a good idea to fuse each battery in a bank, individually. If you have 5 batteries paralleled, and one develops a short. The other 4 will dump all of their power into the shorted battery.

 

[sunshine_eggo]

Then you can quote me the number of LiFePO4 fires nationwide because I could find zero after searching for an hour?

Right here on this site:

Need help Figuring this FIRE out!

Hi Guys Im new here, and this has been though to post. be lenient.. A few months ago I made a DIY Battery Golf car Replacement for a friend. Here are the Specs: 3 X 48v 20ah 16S2P A123 LFP 3.2v 20Ah Cells Interconnect was done with screws 80v fuse at the main positive The charger used was...

diysolarforum.com

 

[timselectric]

The NEC is always in catchup mode. It's just not in the code, yet.

 

[sunshine_eggo]

It is a good idea to fuse each battery in a bank, individually. If you have 5 batteries paralleled, and one develops a short. The other 4 will dump all of their power into the shorted battery.

If good ideas don't prevent a fire, they're not worth doing.

 

[John Frum]

AFAIK LFP cells are unlikely to catch fire even on an internal short.
They can vent toxic electrolyte though.

 

[timselectric]

I'm pretty sure that no good will come from 4 full batteries connected to a dead short.

 

[wmgeorge]

Well here is a link to a MSD sheet, no fire hazard listed? https://dakotalithium.com/wp-conten...ta-Sheet-Lithium-Iron-Phosphate-Batteries.pdf

Waffle guy, So you found ONE fire hazard?? Wow!!

Waffle guy... still acting like a child... Insults again. Nothing intelligent to say?

If my 3 batteries were connected to a dead short the fuse would blow.

 

[timselectric]

I don't even know how this started.
This thread has nothing to do with individual protection for batteries in parallel. (Everyone agrees that it's a good idea) the question was if it's a good idea to also have a breaker for each battery. (For maintenance purposes)

 

[John Frum]

I don't even know how this started.
This thread has nothing to do with individual protection for batteries in parallel. (Everyone agrees that it's a good idea) the question was if it's a good idea to also have a breaker for each battery. (For maintenance purposes)

My preferred method is to parralel the batteries to the main system busbars.
They are the feeders and are fused as close as possible to the battery positive.
I ensure every branch circuit(all the other circuits) have a means of administrative disconnect.
To illustrate... If you have 3 circuits and 2 have administrative disconnect all is good.

 

[sunshine_eggo]

Well here is a link to a MSD sheet, no fire hazard listed? https://dakotalithium.com/wp-conten...ta-Sheet-Lithium-Iron-Phosphate-Batteries.pdf

From your linked MSDS:

"Since the leaked electrolyte is inflammable liquid, do not bring close to fire."

You were saying?

Waffle guy, So you found ONE fire hazard?? Wow!!

Yet you couldn't find any after searching for an hour.

Waffle guy... still acting like a child... Insults again. Nothing intelligent to say?

I respond in kind. You just have the inability to separate the intelligent things from your emotional reaction when you feel threatened.

If my 3 batteries were connected to a dead short the fuse would blow.

Which fuse? Where is it?

Are they LFP? Did you go against the NEC and use a BMS?

Again, your position was that if it's not in the NEC, it's neither required nor needed. I quoted you above.

But... BMS are needed to protect cells from out-of-voltage operation.
Fuses between batteries are needed to protect parallel batteries from each other in the event of a cell short.

 

[timselectric]

I protect each power source. And the cables for each load. Breakers on everything for protection and to serve as a disconnect, for maintenance isolation.

 

[Sillyputty]

This thread has become a treatise on projection, not battery protection. Most members here don't do this - thankfully.

 

[upnorthandpersonal]

First of all, everyone behave. Name-calling is against the terms of use. Cool down. Take a break.

On the topic of fusing parallel batteries, a fuse per battery adds protection: when one cell in a battery has an issue like a short, this fuse will prevent the other parallel batteries of dumping their full discharge power into it. In addition, fusing each battery also prevents overloading of one of the batteries in case another battery (or more than one) cuts out for whatever reason. Your main fuse at the inverter won't help here.

By the way, this is also what Victron recommends, and is the way it is shown in documentation from e.g. Mersen (page 19 for example), ETI (this doc, page 35), etc.

 

[Danke]

Each positive cable from a battery should have a fuse?

Am I missing something from what I’ve seen?

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