Wiring 16 cells into 24v battery???

[John Frum]

Fusing on batteries gets complicated.

Its not that complicated.

The BMS has short circuit protection that will *almost* always pop before a fuse or breaker pops. However ,the BMS short circuit protection relies on a lot of complex circuits to operate and therefore a lot of people do not consider it reliable and additional protection is needed.

The additional protection can be added at the output of each battery or can be added after/at the busbar.

Adding over-current protection anywhere other than the positive terminal of the battery is a bad ideaTM.
1. A dead short that only effects a single battery is a nightmare scenario.
2. A cell failure within a battery will cause the others to dump energy through it.
For these reasons each battery needs over-current protection as close to the positive terminal as possible.

The nightmare scenario for an LFP battery is venting toxic electrolyte.

 

[McLovin]

You need a bidirectional or non-polarized breaker. The markings make me thing this is a directional or polarized breaker.

However, all is not lost with this breaker. For this function, only the positive line needs a breaker and that opens up the possibility of using a trick.

View attachment 131497

If the breaker is not polarized, it will open the circuit without a problem.... in fact it is double protected.

If the breaker is polarized, no matter wich way the current is flowing, one side of the two breakers will have the current flowing in the correct direction. This means when the breaker is opened manually or due to over-current, one side of the pair will be able to suppress the arc and that will stop the arc in the other side as well.

So this would only apply to the breaker in question that is located on the output side of the SCC? Correct?

 

[McLovin]

That should work.



Fusing on batteries gets complicated.
The BMS has short circuit protection that will *almost* always pop before a fuse or breaker pops. However ,the BMS short circuit protection relies on a lot of complex circuits to operate and therefore a lot of people do not consider it reliable and additional protection is needed.

The additional protection can be added at the output of each battery or can be added after/at the busbar. In server rack batteries, most people add it after the busbar and that is what I typically do. However, if the wiring between the battery and the busbar is long and/or exposed, there should be fuses on each battery. (I will assume you will put it at/after the busbar) perhaps something like this:
View attachment 131493


The size of the fuse (Or breaker) needs to be large enough to handle the max continuous current. That will be current to the inverter.... so the same size as the breaker you have selected for the inverter. However, if you add the protection at the battery, you don't really need another one for the breaker.

View attachment 131494
The next logical question is "can it be a breaker instead of a fuse". The answer is yes.... but....
1) I tend to stay with fuses when the current gets above 100A and certainly at 200A.
2) If a breaker is used, it needs to have a very high Interrupt capability (This is NOT the same as the trip value). In a short circuit situation, the current from LifePO4 batteries will go extremely high long before the breaker opens the circuit. That means the breaker has to interrupt this very high current.
* Most people on the forum say there should be a class-T fuse with an interrupt rating of 20KA.
* The spec sheet of your breaker indicates it has a 10KA interrupt capability but the way it is wired it has two in parallel. I don't know if you can call that a total of 20KA.
* Victron is an excelent company and their sample designs use fuses with much lower interrupt capability.

I like the idea of the breaker switch between the batteries and the inverter so I can isolate the inverter from receive any power if I need to work on it or replace it. That was my thinking in have that 200amp breaker there.

 

[FilterGuy]

Its not that complicated.

Adding over-current protection anywhere other than the positive terminal of the battery is a bad ideaTM.
1. A dead short that only effects a single battery is a nightmare scenario.
2. A cell failure within a battery will cause the others to dump energy through it.
For these reasons each battery needs over-current protection as close to the positive terminal as possible.

The nightmare scenario for an LFP battery is venting toxic electrolyte.

It is a matter of managing risk from both a mechanical and electrical perspective.

Trying to bolt a class T fuse to the terminal of a battery is not a good idea, so there will always be some amount of cable between the positive most cell and the fuse.

I think you are proposing fuse positioning like this:


I proposed this:



I am not convinced there is a substantial difference between the two.

 

[FilterGuy]

So this would only apply to the breaker in question that is located on the output side of the SCC? Correct?

Correct

 

[FilterGuy]

That works.

So I'm thinking this addition:

View attachment 131499

I did not notice that you were specifying ANL fuses. The interrupt capacity of ANL is typically well under 10KA.

 

[McLovin]

I did not notice that you were specifying ANL fuses. The interrupt capacity of ANL is typically well under 10KA.

I'm sure you're familiar with Will Prowse, I have followed a lot of his YouTube videos and information on his website, he seemed to indicate the ANL fuses were sufficient since I'm using two, however, do you have a link to a class-t version you would recommend?

 

[McLovin]

So I have updated (again) my planning graphic, adding 250amp busbars (could not find copper only), updated the wire of the double pole breaker next to the output on the SCC Rover, and included wire sizes. I'm hoping this will be helpful to others since I've accumulated so much helpful knowledge. Look forward to your feedback.

 

[FilterGuy]

I'm sure you're familiar with Will Prowse, I have followed a lot of his YouTube videos and information on his website, he seemed to indicate the ANL fuses were sufficient since I'm using two, however, do you have a link to a class-t version you would recommend?

Just do a search for class T fuse. As long as you stick with Busman/Eaton, Blue Sea, little fuse or other name brands you will be fine.

Now I am going to say something that will probably get me flamed.

You certainly won't go wrong with class-t, but I don't know if class T is absolutely necessary. I just posed this question on a different thread that you might want to follow:

Class T vs ANL fuse

It appears they could be bolted directly to battery lugs and the cable bolted to the other side of the fuse which seems safer to me than having a separate fuse block because the fuse is closer to the battery. Then, it's less likely that a short would happen between the battery and the fuse. I...

diysolarforum.com

 

[McLovin]

Just do a search for class T fuse. As long as you stick with Busman/Eaton, Blue Sea, little fuse or other name brands you will be fine.

Now I am going to say something that will probably get me flamed.

You certainly won't go wrong with class-t, but I don't know if class T is absolutely necessary. I just posed this question on a different thread that you might want to follow:

Class T vs ANL fuse

It appears they could be bolted directly to battery lugs and the cable bolted to the other side of the fuse which seems safer to me than having a separate fuse block because the fuse is closer to the battery. Then, it's less likely that a short would happen between the battery and the fuse. I...

diysolarforum.com

The first think I notice about that thread was exactly why I went with ANL, Class-T are "hard to find".

If you're ever in the Denver metro area, I'm taking you out for several beers... ;- )