House burned down

[Zwy]

Effectively, 7-15kwh batteries using all one singular BMS? That doesn’t sound fun at all

I run 58 Kwh on one BMS. Not hard to do. One Watchmon Core with 4 K9's.

Yes, that was my reasoning as well. A cell fails, the other packs dumping massive amounts of current into the pack, the fuses not able to handle it/arcing, cells (or even just one) venting, and the arcing fuse igniting the vent gasses. If the current was high enough, probably none of the fuses on the different packs would be able to quench the arcs (which is why a high AIC is required for these). I do wonder how that high of a current could develop even with a single cell shorted.

I also wonder what the BMS was doing...

The Batrium would see a low/high cell voltage according to the parameters set for cell low/high critical event. Also, there is a temp sensor for each group of 4 cells and if an overtemp occurs (according to parameter set), it also is a critical event.

The Batrium would trip the shunt trip breaker.

This however doesn't prevent current from flowing between each 16S set of cells. In my bank, each 16S set has a Class T 175A fuse. A solid 1/4" x 1" copper busbar runs down each side of the battery bank box. One side of the box is positive, the other is negative. All of the 16S positives have a solid busbar from the last cell to the Class T fuse and a solid busbar from the Class T fuse to the main copper busbar running down the side.Shown here during assembly with protective wooden covers over the terminals to help prevent accidental shorts.








On the opposite end, each 16S negative is connected with a short 2/0 cable, sorry, no photo, didn't think it was important.

One thing about my bank is it is contained inside a Hoffman industrial electrical box that is about 1/8" thick. I purposely used this cabinet for fire protection reasons. It would have to get pretty hot to burn thru it. That is why they are built heavy. I ensure often there are not any combustibles put around the box such as a cardboard box.

As for the OP's battery bank, yes, it should have had a Class T between each 16S set. Second, heavy construction of a cabinet in my mind is paramount. When in doubt, build it stout. Take my shelves for instance. Each one is double rectangular tubing of 1/8" wall with a center bracket welded in to prevent any twisting of the tubing. Each end has a heavy angle iron bracket welded to the rectangular tubing with a pair of 3/8" bolts thru the cabinet wall. These cells are heavy and any sag in a shelf will lead to failure down the road.

For those wanting to see more photos of my build, hit the link in my signature.

 

[Zwy]

I don't think running seven strings in parallel like was being done is a supported configuration from Orion. I believe they would spec one watchmon and shunt per string, not one watchmon and then multiple parallel strings.

No, One CORE and a K9 for each 16S (or whatever the series of cells). There is a max number of cells that can be monitored and he was at the limit I believe. It was supported, all cells are shown in the Toolkit in his battery thread.

In the OP's case, he was using the older cell monitors without a K9. It still would work just fine.

Nothing wrong with using a CORE with cell monitors, it will perform like it should when a critical event occurs. It will trip the shunt trip breaker and shut down the system, no discharge or charging can pass the shunt trip breaker.

There has to be proper over current protection between each series set of batteries. While the OP did have this in place, the problem appears to be the choice of fuses. A Class T with proper sizing would have prevented a catastrophic loss. This is why it is important to have a Class T between each battery in a bank. All the current from other batteries or sets will feed current to a failed cell.

It has nothing to do with the BMS. The Batrium does exactly what it was designed to do. A Class T between batteries will do exactly what it is designed to do, break current in an over current situation.

I'm building my second bank for my shop with Class T fuse protection between batteries and using JK for a BMS. I would not rely on a BMS to handle an over current failure, that is the job of the Class T fuse. I am also building a pair of battery boxes, one will be in addition to my house bank and each box will have a Class T added. I do not rely on breakers for this purpose.

 

[Zwy]

I don't really know much about Orion Batrium but my understanding is per normal specification each string of 16 cells would have a watchmon, and multiple blockmons, and a shunt. If there's an issue with a cell in the string the shunt will open and that battery is isolated.

Not how it works.

 

[Zwy]

Using 112 Blockmons (one on each cell) to a single Watchmon still does not sound fun.

Here’s the wiki for just the Blockmon, this wiki makes me now ponder more possibilities of the OP set up and potential failure points.

BlockMon

How to wire the BlockMon Cell Monitor, with wiring diagrams and features.

wiki.batrium.com

No different than running balance leads on any BMS.

I have 64 cells, 4 K9's and each K9 has of course 16 balance leads. All are fused and I numbered each one with printable heat shrink on each end.

 

[Zwy]

Almost every page of that document warns against running multiple strings in parallel without taking specific safety measures to be able to disconnect each string automatically, the section about the dangers of eddy currents foresees an issue where a single cell failure could cause a cascading issue that moves from string to string.

View attachment 212509

View attachment 212510

It is called a Class T fuse.

 

[Zwy]

you must be listening to @timselectric - he is the contactor king.

I have 24 sitting in a box. Was planning on possibly using these to break high voltage DC but came up with a better idea.

 

[robbob2112]

Crap, this might be my fault. I thought the two were the same. I thought one was the company name and one was the series of product

Yup, the goose talked to me and steered me wrong

 

[G00SE]

Yup, the goose talked to me and steered me wrong

My apologies sir!

And @Zwy thank you for setting us straight with your first hand knowledge too!

 

[Shimmy]

Sorry, but I am missing if the system has a single contactor or shunt-trip breaker for the battery, or one per string.

If you are backfeeding a string with a failed cell via paralleled cells (single contactor), then isn't the catastrophic cell failure a given and you are just looking for an eventual ignition source?

 

[robbob2112]

Sorry, but I am missing if the system has a single contactor or shunt-trip breaker for the battery, or one per string.

If you are backfeeding a string with a failed cell via paralleled cells (single contactor), then isn't the catastrophic cell failure a given and you are just looking for an eventual ignition source?

Have a look at his build thread and let us know what you think

LFP Powerwall

a few pictures of my own built 'home energy system'. I run my house, workshop and if needed charge my tesla model S with it. currently 3 multiplus 2 5 kVa units for 3-phase system, 48 V battery: 3 banks of 16 200 Ah cells, monitored by batrium. The victron system runs the ESS template. One of...

diysolarforum.com

 

[WindWizard]

@Zwy thanks for sharing your knowledge. After going through the explanations of the Batrium and Blockmon, I am still confused. I guess I like simplicity and that just does not seem to be simple to me. Attaching a PCB to each cell, just does not sound simple.

He does mention a shunt trip breaker. I am not sure why this failed to shut down the system. It probably has to do with the other 6 strings of batteries feeding the fire.

I am using a much simpler approach, in my opinion. To monitor my 128 cells, I am using 4 Overkill Solar BMS's. I can just pull out my phone and see if there is an issue with any of my cells. If one of the Cells fail, then the BMS will shut down the battery bank. All of the current from the Cells go through the BMS's.

OP presumably had a Cell that failed and all that happened was the fuse arced and unfortunately, his house burned down. Having the 7 strings of Cells while relying on some fuse to melt just does not sound right.

 

[Shimmy]

Have a look at his build thread and let us know what you think

LFP Powerwall

a few pictures of my own built 'home energy system'. I run my house, workshop and if needed charge my tesla model S with it. currently 3 multiplus 2 5 kVa units for 3-phase system, 48 V battery: 3 banks of 16 200 Ah cells, monitored by batrium. The victron system runs the ESS template. One of...

diysolarforum.com

Ok, fair enough; I originally went through the pictures. Smoking gun from OP in referenced thread.

Each bank will have its own fuse, and all banks together on 1 line will be connected to a shunt trip breaker, controlled by the batrium. (ABB also)

That doesn't really give the BMS a way to protect the battery.

 

[robbob2112]

Ok, fair enough; I originally went through the pictures. Smoking gun from OP in referenced thread.

That doesn't really give the BMS a way to protect the battery.

That is my take on it.

The only thing keeping one battery bank from dumping current into the others was the Mega fuse. Even had the shunt trip breaker the batteries are connected to each other, just not the inverter anymore. So, seems the protection provided the spark.

 

[rhino]

All of the current from the Cells go through the BMS's.

Just to be clear, this would still not prevent all the rest of the cells in one battery dumping all their energy into a bad cell in that same battery.

I don't know of any residential battery system that would stop a short between cells within the same battery.

 

[ScropusGobbleBottom]

Just to be clear, this would still not prevent all the rest of the cells in one battery dumping all their energy into a bad cell in that same battery.

What do you mean? A series of 16 into 1 BMS, cell shorts internal.
How would amps flow from neighboring cells in same series string?
I would imagine the only thing that would happen is that current would pass THRU and most likely the offending cell would be high stress and momentary negative voltage until load is gone. If the cell has no energy from not being maintained, it wouldnt hoard the amps from a load would it?

 

[WindWizard]

Just to be clear, this would still not prevent all the rest of the cells in one battery dumping all their energy into a bad cell in that same battery.

I totally disagree. The Cells have a negative and a positive. If the negatives are not connected because of the BMS's disconnecting them, then there is no current path between the positive and negative, so there is no way to dump the energy from a bad cell to the rest of the Cells.

It is like disconnecting the negative lead on your car battery. It disconnects all of the current flowing through the car.

I think that where OP had an issue is that there was no way to disconnect the 7 series of Cells other than the fuse. There was no BMS that disconnected the faulty LFP series string.

 

[robbob2112]

Just to be clear, this would still not prevent all the rest of the cells in one battery dumping all their energy into a bad cell in that same battery.

I don't know of any residential battery system that would stop a short between cells within the same battery.

A class T on each battery positive would have prevented the battery with the assumed shorted cell from dumping current into the other batteries. Link broken means no current flow and maybe just a mess to clean up. Might just as easy have had the same result.

This depends on the assumption that the Mega fuse blew then an arc formed and was not interupted.

 

[rhino]

I totally disagree. The Cells have a negative and a positive. If the negatives are not connected because of the BMS's disconnecting them, then there is no current path between the positive and negative, so there is no way to dump the energy from a bad cell to the rest of the Cells.

It is like disconnecting the negative lead on your car battery. It disconnects all of the current flowing through the car.

I think that where OP had an issue is that there was no way to disconnect the 7 series of Cells other than the fuse. There was no BMS that disconnected the faulty LFP series string.

You are correct, brain fart. Would only matter if that single cell is physically damaged enough from the short to physically affect the other cells around it.

 

[Shimmy]

A class T on each battery positive would have prevented the battery with the assumed shorted cell from dumping current into the other batteries. Link broken means no current flow and maybe just a mess to clean up. Might just as easy have had the same result.

This depends on the assumption that the Mega fuse blew then an arc formed and was not interupted.

The cell short is not seen by the fuse-- just a string short.

With LFP do you get cell reversals that can lead to overheating like you would with lead acid? That is the only mechanism I can understand for how you actually get a string short (or overcurrent).

All that aside, best of luck with your recovery @Jejochen and I hope you understand that the discussion is about learning and not criticizing or blaming. It definitely gives me pause with claims of LFP safety.

 

[ScropusGobbleBottom]

With LFP do you get cell reversals

You do with Lipo cobalt based.