LFP Ext. Regulators: Why do Volts and Amps need to be sampled?

[rgleason]

Interesting point.

How fast and what type and size of fuses should be used between FLA-FLA, LFP-LFP and that verboten FLA-LFP batteries?

[Statistical]

Originally Posted by rgleason

Interesting point.

How fast and what type and size of fuses should be used between FLA-FLA, LFP-LFP and that verboten FLA-LFP batteries?

The key thing is the AIC. The fuse needs to handle a short circuit current. For this reason if you have LFP you need class T fuses (or something similar) on each battery. Not just one after all the batteries have been paralleled. Same would apply for FLA-LFP. For FLA-FLA pretty much any fuse is possible although I would still recommend a class T fuse.

[s/v Jedi]

Originally Posted by rgleason

Interesting point.

How fast and what type and size of fuses should be used between FLA-FLA, LFP-LFP and that verboten FLA-LFP batteries?

I think you must size the fuse for the cable that connects it, like always.

If the BMS only supports less than that, it should deal with this itself.

This may not be optimal when you have a really small battery on a really big cable, but I don’t see that happen in reality (of course it will be argued over here on CF )

[Baronkrak]

Originally Posted by tanglewood

Lead batteries short out and melt down much more often than you might think.

Not really.
It is highly unlikely that all the cells of a LA battery will short out at the same time. A misused LA is more likely to explode rather than meltdown.
There are other reasons why batteries should not be paralleled. The most obvious is that paralleling cells, paralleling batteries, paralleling banks is bad engineering and this may explain why the ABYC do not endorse paralleling.

Taking into consideration the following.

Originally Posted by Maine Sail

…..Again millions upon millions of parallel banks….

Looks like ABYC recommendations are poorly adopted.

[tanglewood]

Originally Posted by Baronkrak

Not really.
It is highly unlikely that all the cells of a LA battery will short out at the same time. A misused LA is more likely to explode rather than meltdown.
There are other reasons why batteries should not be paralleled. The most obvious is that paralleling cells, paralleling batteries, paralleling banks is bad engineering and this may explain why the ABYC do not endorse paralleling.

Taking into consideration the following.



Looks like ABYC recommendations are poorly adopted.

It only takes one shorted cell. Doesn't require all of them.


Also the issue is about not paralleling cells of different chemistries, not about paralleling in general.


How is paralleling batteries in general "bad engineering"?


And it's quite ironic that you quote Rod from 11 years ago in a discussion about paralleling same-type batteries. As I recall, he was one of the big proponents of NOT paralleling different chemistries, even though he and pretty much all of the rest of the world have no issue with paralleling same-type batteries.

[Statistical]

Originally Posted by Baronkrak

Not really.
It is highly unlikely that all the cells of a LA battery will short out at the same time. A misused LA is more likely to explode rather than meltdown.
There are other reasons why batteries should not be paralleled. The most obvious is that paralleling cells, paralleling batteries, paralleling banks is bad engineering and this may explain why the ABYC do not endorse paralleling.

Taking into consideration the following.



Looks like ABYC recommendations are poorly adopted.

There is no ABYC prohibition on parallel batteries. There is only a strong recommendation against paralleling batteries of different chemistries.

I mean it is pretty obvious that parallel batteries are needed in many circumstances.

LFP cells larger than ~300 Ah are rare to non-existent from most manufacturers. So any battery bank of >300 Ah is going to have 2+ cells in parallel. Regardless of if it is done at the cell level or battery level.

[Baronkrak]

Originally Posted by Statistical

Regardless of if it is done at the cell level or battery level

And it is bad engineering

[Baronkrak]

Originally Posted by tanglewood

It only takes one shorted cell. Doesn't require all of them.

Originally Posted by tanglewood

there can suddenly be a whole lot of energy available to dump into that lead battery…

One shorted cell will not suddenly dump a whole lot of energy into a battery.
One shorted cell will drain any batteries, banks that is connected to that shorted cell, to be LFP or LA.

Originally Posted by tanglewood

Also the issue is about not paralleling cells of different chemistries, not about paralleling in general.

The issue is about to get it right.

Originally Posted by tanglewood

How is paralleling batteries in general "bad engineering"?

You normally learn that in tech school.

Originally Posted by tanglewood

And it's quite ironic that you quote Rod from 11 years ago in a discussion about paralleling same-type batteries. As I recall, he was one of the big proponents of NOT paralleling different chemistries, even though he and pretty much all of the rest of the.

The rest of the world does have issue with paralleling batteries.

[Statistical]

Originally Posted by Baronkrak

The rest of the world does have issue with paralleling batteries.

No they don't. Do you seriously think massive 2000 MWh grid storage batteries are one giant battery. Parallel batteries are used all over the world all the time under all kinds of applications.

This "never put batteries in parallel" rule is something you made up in your head.

The sheer irony is that all batteries already have cells in parallel. There is no primary cell of any kind with a voltage above 4V. So if you have a battery with a voltage 4+ volts of any kind for any application using any chemistry it has multiple cells in parallel.

[Baronkrak]

Originally Posted by Statistical

No they don't. Do you seriously think massive 2000 MWh grid storage batteries are one giant battery. Parallel batteries are used all over the world all the time under all kinds of applications.

And they will be adequately protected.

Originally Posted by Statistical

The sheer irony is that all batteries already have cells in parallel. There is no primary cell of any kind with a voltage above 4V. So if you have a battery with a voltage 4+ volts of any kind for any application using any chemistry it has multiple cells in parallel.

I think you are getting confused. Volt, parallel?

[Statistical]

Originally Posted by Baronkrak

And they will be adequately protected.

So the absolute rule of NEVER parallel batteries isn't absolute. It is you should have proper protection when putting batteries in parallel. Yeah ABYC agrees with you on that. Each battery should be fused seperately with fuses of sufficient AIC to prevent one battery from dumping amps into a battery that is shorted.

I think you are getting confused. Volt, parallel?

Yes that was a brainfart on my part.

[Baronkrak]

Originally Posted by Statistical

So the absolute rule of NEVER parallel batteries isn't absolute. It is you should have proper protection when putting batteries in parallel. Yeah ABYC agrees with you on that. Each battery should be fused seperately with fuses of sufficient AIC to prevent one battery from dumping amps into a battery that is shorted.

There is more to protection that just fuses.

Fair winds.

[tanglewood]

Originally Posted by Baronkrak

You normally learn that in tech school.



The rest of the world does have issue with paralleling batteries.

I must be missing something here. Can anyone enlighten me since the OP doesn't want to explain himself.

[wholybee]

Originally Posted by Baronkrak

Not really.
It is highly unlikely that all the cells of a LA battery will short out at the same time. A misused LA is more likely to explode rather than meltdown.
There are other reasons why batteries should not be paralleled. The most obvious is that paralleling cells, paralleling batteries, paralleling banks is bad engineering and this may explain why the ABYC do not endorse paralleling.

Taking into consideration the following.



Looks like ABYC recommendations are poorly adopted.

Virtually every cruising boat has batteries in parallel. Show me the ABYC recommendation or any statement from the ABYC that batteries should not be paralleled.

[tanglewood]

Originally Posted by wholybee

Virtually every cruising boat has batteries in parallel. Show me the ABYC recommendation or any statement from the ABYC that batteries should not be paralleled.

I think the guy is in la la land.