House burned down

Precharge takes care of capacitor inrush.

For parallel strings, I think the thing to do would be put a voltmeter across the fuse holder and wait until charging or discharging brings voltage difference to zero.

Contactor would have the same issue. Unless the gizmo controlling it did that step for you, best to have disconnect only, not auto-reconnect. Shunt trip breaker would be an approach. It isn't "fail safe", the trip wire could be open and it would operate, unlike a contactor which needs continuity of the control signal to remain closed.

upnorthandpersonal said:

Considering the flat voltage curve of LFP, it's not really too big of a deal (yes, I've tested this).

Click to expand...

(i.e. you don't get equalization by paralleling strings without charging them.)
Widely different SOC, could be an issue.
So have disconnected string and rest of the pack towards middle state of charge.

Brucey said:

The Silicate batteries are interesting to potentially replace lead acid in below freezing conditions, both need to be only used to around 50% discharge for max life. Note in the listing it says "We parallel these with lithium batteries to give maxium surge capability" so maybe not as much current capability as LFP?

Click to expand...

My opinion …. The lack of surge is par for Lifepo design to remain controlled and stable with bms. Lacking uncontrolled high output of lead acid. Smaller cables too. I was amazed to see such small cables on bms….units.

The lead acid and silicate can do the surge part. Big cables. No restrictions except inverter. Proof in video above.
Question has anyone actually ran these in parallel for extended time? Video? I’ve read never mix any batteries… not even pouches and prismatic type Lifepo. Again refer back to video in prior post towards end to see the amazing part for lead acid pushing - operating higher amp loads vs lifepo.
Post in thread 'House burned down'
https://diysolarforum.com/threads/house-burned-down.83098/post-1087733

With Silicate ppl could just manually rotate them with breakers one and breaker to other side lifepo.
When in Parallel batteries try to normalize…voltages and such. Right? We use to slap fresh carbon battery in with weak one. It worked but they said not to do that with newer alkaline. Remember?

Switching load for 2 different types banks might be better. Put in separate charge systems. Solar charge controllers are cheap.

Lead acid if dead zero volts will freeze and bust. If person tries to charge a dead frozen lead acid battery it explodes. Seen these things time and time again.

There are advantages as shown in other video above….lead acid and imagine silicate can do the grunt work but time limited. Under milder condition the Lifepo could go near zero or 10%

Leaving any battery at Zero will kill it.

The charge rates change with temps for lead acid why it must always be monitored. Nasty acid… eats up metal boxes on locos - were inspected ever ~90 days. We had them eat floor out batteries try fall through. With used voltage regulation on with old locomotive - manual varied by temp for the charge dependent weather. We ran working charge voltages with 64vdc from ~70vdc-76vdc ….later we went to dvr….on EMD ….used brp-bfr panels for monitor control - cab mounted exc aux computer panels on ge. Large heavy panels….lot of monitoring - control… we’d get to aggressive charging and ruin a bank - smoke them. Mess with software. The lead acid stink and are very dangerous - Gassing. I’d never put one under my bed. I would not have a system with lead acid. I’d buy a diesel generator.

We have ppl putting lifepo battery/inverter under their beds on youtube videos. Rv - tiny homes….. is that a good idea? Everyone says lifepo is super safe…. . Are they really that safe - Lifepo/inverter in tight closed sleeping - living quarters? I think we will see more post “Up In Smoke” as they age. If the ppl survive. Dead ppl don’t post. Just kidding.

I love the light weight of lifepo. Those big Lifepo box packs weigh ~282 pounds. Hmmmm

My experience with what see…. we are trying to say we have settled and mastered what we have right now. I think Lifepo and Inverter are over drawn as safe when it is not time tested yet. I think inverters themselves are over rated…. Ever notice generators are suppose to be best is run at half loads? Highly recommended half loads. The warranty on those Silicate batteries requires buy 2x the amount of load you will need. Hmmm. How do you prove that for warranty?

I’m not sure if the silicate batteries off gas. I’d bet they do.

I’d like to see someone jump a car off with 12v lifepo 100ah battery. I thought about trying it but figure the bms might be damaged. I do have a wonderful small amazing jump pack ….
This thing is amazing.

D71 said:

not even pouches and prismatic type Lifepo.

Click to expand...

What did you read on this?
What problems could result?
I have one strong of each right now

squowse said:

Oh I thought you were saying to not bother using fuses.

Click to expand...

fuses wont protect the battery they protect the wiring.
because if a paralel shorted battery bank is charging from the others with less than the trip current of the fuse it wont help.

a bms is needed to protect the paralel bank and if you have the money a 2nd contactor for the paralel bank controlled by an other independent bms is the best protection.

but i havent seen two bms on each paralel battery bank.

some batrium users even have not a bms in each bank so they ignore the safety and risk their home or life. as you can see in the first post.

PotusGobbleBottom said:

What did you read on this?
What problems could result?
I have one strong of each right now

Click to expand...

Just my manufacturer notes from few other battery makers on websites. Which might just be them selling - marketing. My battery supplier stated do not add additional lifepo batteries in parallel after 6 months because of cell differences and wear tear mismatch. Again might be marketing.

We changed lead acid batteries on locomotives with mismatch old vs new never lasted long So replaced all. Expensive. Sent the old one out to be rebuilt or recycled - turned into bullets. Railroads use to rebuild lead acid themselves but farmed out…batteries due to liabilities.
Old lead acid lasted 10-15 years but newer versions only 5 years if lucky…. lighter weight. Not built same.

Again might be Lifepo marketing but bet the cells perform different pouch vs other. When tied in parallel they will try to normalize. Unless open is made with cut out. From one bank to another.
How do you clamp pouch cells?

My battery maker was Himassi they dried up and evaporated.

Li Time describes difference but not point of mix matching.

I am not an expert on any of this. I am cautious of ppl making those claims.

My batteries are limited to 20kWh per maker but it is assumed ….. reality they only state 4x12vdc in series make 48v.

_voltmeter_ said:

fuses wont protect the battery they protect the wiring.
because if a paralel shorted battery bank is charging from the others with less than the trip current of the fuse it wont help.

a bms is needed to protect the paralel bank and if you have the money a 2nd contactor for the paralel bank controlled by an other independent bms is the best protection.

but i havent seen two bms on each paralel battery bank.

some batrium users even have not a bms in each bank so they ignore the safety and risk their home or life. as you can see in the first post.

Click to expand...

That means the wiring is sized to the load. Ppl leave that load part out…kinda critical

D71 said:

How do you clamp pouch cells?

Click to expand...

My situation is 8 commercial pre built pouch 50ah 48v batteries in parallel with 1 48v 280k set. I have a victron shunt on each set and the results are interesting.
I can tell the discharge curves are different. And I can see that it normalizes after every hard charge or discharge

_voltmeter_ said:

some batrium users even have not a bms in each bank so they ignore the safety and risk their home or life. as you can see in the first post.

Click to expand...

Yikes - sounds like a misunderstanding of how Batrium works. Batrium is a central unit that monitors all individual cells in a powerwall (regardless of their 14s or 16s individual battery configurations) and in the aggregate the overall powerwall and provides a wide range of options to act on the metrics at both the cell level and the powerwall level. What one does when metrics get out of of bounds - e.g. trigger a global shunt-trip or individual battery shunt-trips or custom events is up to the user - not a deficiency in Batrium.

This view that it's always good to disable a single battery within a group of parallel batterys in a powerwall (as apposed to disabling current for the overall powerwall) is not always thought out. Let's say an individual battery overloads and is disabled... this could cause a cascading overload of the other batteries as the overall load is now supported by less capacity. This cascading overload of individual BMSs might cause more trouble than it's worth.

My point - it's not just as simple as always have 'individual battery automatic shut-off' or you're risking life and limb

OffGridInTheCity said:

This cascading overload of individual BMSs might cause more trouble than it's worth.

Click to expand...

if there are 4x 200a bms and one or two go offline the two other bms can take 400a. i think for the most of us this is enough.
there is always some sort of risk but with a bms in each paralel bank the risk is lower than with no bms

Hedges said:

exceeds

Click to expand...

Jejochen said:

Hi guys
-as already said, i can only post once in a while as i have a lot of other stuff going on right now
-when i was building my system, dividers between cells was not a thing yet. The thing back then was clamping cells or not. The cells have no spacers between.
-i will not participate in guessing games, my mind is not into that now, just want to give the facts.
-the cells were sitting on high density non conductive fibre boards, and metal parts of the rack got fibreboard as shieding to minimise contact issues
-dodgy heatshrink...i mean common, of course the back was cut off and completly free. If that was aan issue, it would have happened way sooner. The system was perfect for 4 years or so.
-and yes, of course i swapped the leaking cell.
-when i have a little spare time, ill pull the victron numbers

Click to expand...

Thank you for sharing and helping us learn. Just curious, did you have cement backer board on the walls? If so, Do you know the thickness and brand? 3/8" hardybacker board? Thanks for sharing.

upnorthandpersonal said:

Considering the flat voltage curve of LFP, it's not really too big of a deal (yes, I've tested this).

Click to expand...

How would you feel if the fuse blew the night before and you didn't get around to replacing it until afternoon? The other strings would have charged up... Seems like I remember a video where someone got bit by doing a hot replace of the class T, but it might have been the main line between the inverter and the battery bank

robbob2112 said:

How would you feel if the fuse blew the night before and you didn't get around to replacing it until afternoon? The other strings would have charged up... Seems like I remember a video where someone got bit by doing a hot replace of the class T, but it might have been the main line between the inverter and the battery bank

Click to expand...

Disconnect solar and let them settle (or wait until they drop under load), and then replace the fuse. They can be at different states of charge (say 30% and 80%) and still be at the same voltage.

upnorthandpersonal said:

Disconnect solar and let them settle (or wait until they drop under load), and then replace the fuse. They can be at different states of charge (say 30% and 80%) and still be at the same voltage.

Click to expand...

Or have a contactor you can turn off

robbob2112 said:

Or have a contactor you can turn off

Click to expand...

Or you know, just a regular disconnect switch.

OffGridInTheCity said:

Yikes - sounds like a misunderstanding of how Batrium works. Batrium is a central unit that monitors all individual cells in a powerwall (regardless of their 14s or 16s individual battery configurations) and in the aggregate the overall powerwall and provides a wide range of options to act on the metrics at both the cell level and the powerwall level. What one does when metrics get out of of bounds - e.g. trigger a global shunt-trip or individual battery shunt-trips or custom events is up to the user - not a deficiency in Batrium.

This view that it's always good to disable a single battery within a group of parallel batterys in a powerwall (as apposed to disabling current for the overall powerwall) is not always thought out. Let's say an individual battery overloads and is disabled... this could cause a cascading overload of the other batteries as the overall load is now supported by less capacity. This cascading overload of individual BMSs might cause more trouble than it's worth.

Click to expand...

I don't many quite understand this. The whole system should be shut down for the simple fact a critical fault exists.

Those with individual BMS's, no Class T (using MEGA) will find shutting down part of a bank on a large system can cause a situation similar to the OP. We aren't even certain that an individual cell failed in the OP's situation, it could have just as well been a shorted inverter and the result was a blown MEGA fuse which resulted in an arc and resulting fire.

But it is easier to blame the Batrium than to realize many have been looking at this possibly in the wrong light.

OffGridInTheCity said:

My point - it's not just as simple as always have 'individual battery automatic shut-off' or you're risking life and limb

Click to expand...

Yes, as I explained above and it actually might have been what happened. Individual BMS's are not a guarantee this type of event won't occur.

I refer back to this post and the quote from CaptainRivet in a boating forum.

"Yes in a short or anything >25% above (depending o quality of your BMS, some can +25%, some +100% but that is max) your BMS current rating the mosfets in your BMS will fry closed in 95% of the time leaving your plus connected, negative is always connected.your BMS with fried mosfets will most likely still show you the cell voltages...
By the way the same applies to your inverter/charger, eg Multiplus is also only protected via mosfets on plus, the negative is always connected to be able to monitor and eg remote switch on. This a lot sailors connect directly on the terminal of your battery/bank, with an extra fuse to avoid upgrading cabling and main busbars as its the only bigger source added. So this is now your 2nd main battery and main cable fuse combined and must be therefor Class T or NH too!!!

The BMS (and Multiplus) limits the currents to protect lifespan of your battery and switch loads and charge sources off to peotect it from over- or undercharging.
But these protection capabilities cannot withstand the enormous short curcuit or other catastrophic failure currents that a lifepo4 is creating, a rule of thumb is AH capacity multiplied with 20 gives you the roughly the short curcuit current reached by this bank/battery. So a 100Ah can do 2000A, a 500AH bank already 10000A. That is the job of a fuse, see above what and how to implement.

And you just think about your mosfet based BMS. Their are plenty other out there.
Eg My electrodacus BMS has only 2 shunts on the positive busbar of the bank, nothing else that will cut or protect the installation."

Zwy said:

I don't many quite understand this. The whole system should be shut down for the simple fact a critical fault exists.

Those with individual BMS's, no Class T (using MEGA) will find shutting down part of a bank on a large system can cause a situation similar to the OP. We aren't even certain that an individual cell failed in the OP's situation, it could have just as well been a shorted inverter and the result was a blown MEGA fuse which resulted in an arc and resulting fire.

But it is easier to blame the Batrium than to realize many have been looking at this possibly in the wrong light.


Yes, as I explained above and it actually might have been what happened. Individual BMS's are not a guarantee this type of event won't occur.

I refer back to this post and the quote from CaptainRivet in a boating forum.

"Yes in a short or anything >25% above (depending o quality of your BMS, some can +25%, some +100% but that is max) your BMS current rating the mosfets in your BMS will fry closed in 95% of the time leaving your plus connected, negative is always connected.your BMS with fried mosfets will most likely still show you the cell voltages...
By the way the same applies to your inverter/charger, eg Multiplus is also only protected via mosfets on plus, the negative is always connected to be able to monitor and eg remote switch on. This a lot sailors connect directly on the terminal of your battery/bank, with an extra fuse to avoid upgrading cabling and main busbars as its the only bigger source added. So this is now your 2nd main battery and main cable fuse combined and must be therefor Class T or NH too!!!

The BMS (and Multiplus) limits the currents to protect lifespan of your battery and switch loads and charge sources off to peotect it from over- or undercharging.
But these protection capabilities cannot withstand the enormous short curcuit or other catastrophic failure currents that a lifepo4 is creating, a rule of thumb is AH capacity multiplied with 20 gives you the roughly the short curcuit current reached by this bank/battery. So a 100Ah can do 2000A, a 500AH bank already 10000A. That is the job of a fuse, see above what and how to implement.

And you just think about your mosfet based BMS. Their are plenty other out there.
Eg My electrodacus BMS has only 2 shunts on the positive busbar of the bank, nothing else that will cut or protect the installation."

Click to expand...

I agree 100% that we will never know what happened in this case for sure.

And I see some valid points and will have to think hard about others. Mainly if it is ok to disconnect a single battery bank from a large set of parallel batteries. And if connecting a discharged set to all the others at full charge, might that cause the same type event from a voltage gradient?


I suppose it would depend on sensors for voltage and current draw and SOC of each bank. Lots to think about.


And at this point I hope nobody is just blaming the batrium. I suspect that like most accidents it is a chain of events and if any one of them had been broken it wouldn't have happened

Zwy said:

I don't many quite understand this. The whole system should be shut down for the simple fact a critical fault exists.

Click to expand...

your batrium cant shutdown a paralel bank if there is no extra contactor. your class t fuse is useless if the fault current that charges the damaged bank is under the trip current of the fuse.
and foam cell isolators, some people use, melt very quick causing more damage.

use heat resistant not conducting materials around the cells like fibercement, silicone, ceramic... no plastic or foam. no metals that can cause a short at the whole battery bank across positive and negative...

this will reduce the risk of a catastrophic failure.

but if you cant still understand, well... maybe other can understand and learn.

some have to learn the hard way. after that they start to understand very quickly.
i had no one to teach me stuff like in this thread, so i learned the hard way too. thankfully with no damage.

robbob2112 said:

Or have a contactor you can turn off

Click to expand...

I think I’m good. Midnite 250A breakers at the bus bar (Midnite Battery Combiner Box), Anderson Connectors, then 300A Blue Sea T fuses, then a contactor. I should be able to get a set disconnected lol. In all seriousness, this setup makes it easy to pull a battery when the need arises (in my case, a cell that wasn’t all that great).

SilverbackMP said:

I think I’m good. Midnite 250A breakers at the bus bar (Midnite Battery Combiner Box), Anderson Connectors, then 300A Blue Sea T fuses, then a contactor. I should be able to get a set disconnected lol. In all seriousness, this setup makes it easy to pull a battery when the need arises (in my case, a cell that wasn’t all that great).

Click to expand...

Be interesting to know the resistance of those three strung together? Don't suppose you have a 1035 meter? Or maybe measure the voltage difference across them all and figure it?

robbob2112 said:

Be interesting to know the resistance of those three strung together? Don't suppose you have a 1035 meter? Or maybe measure the voltage difference across them all and figure it?

Click to expand...

I do happen to have one. We tested both during the install. Nothing out of sorts. But the battery cables are all 12 ft 4/0 with great crimps from a long handled ratcheting crimpers using Ancor terminals and noox). Dunno if that lends any help in that regards.

_voltmeter_ said:

fuses wont protect the battery they protect the wiring.
because if a paralel shorted battery bank is charging from the others with less than the trip current of the fuse it wont help.

a bms is needed to protect the paralel bank and if you have the money a 2nd contactor for the paralel bank controlled by an other independent bms is the best protection.

but i havent seen two bms on each paralel battery bank.

some batrium users even have not a bms in each bank so they ignore the safety and risk their home or life. as you can see in the first post.

Click to expand...

If they stop the battery being shorted then they will stop the cells going into thermal runaway. As well as the cables. Did the op have 2 batteries with one bms then? I didn’t pick that up

squowse said:

If they stop the battery being shorted then they will stop the cells going into thermal runaway. As well as the cables. Did the op have 2 batteries with one bms then? I didn’t pick that up

Click to expand...

The OP was using a batrium. This is a type of bms that uses a board on top of each cell and does 2amp balance current. These boards all report back to a central unit. The OP had a trip shunt which disconnects the main load when there are problems. And the batrium was managing 112 cells for detailed reporting and balancing. Some find fault with this setup because there is not a disconnect between battery strings. Opinions differ but it is unlikely that this is the root cause.

We will never know what actually caused the fire, but my assumption is a single cell short and vented hydrogen in one of the 7 strings caused the others to dump into it and overheated the Mega fuse and arced and caused a spark to start the disaster.

In other words, your assumption is that the catastrophic failure would have been avoided with BMS controlled disconnect between strings?

Hedges said:

In other words, your assumption is that the catastrophic failure would have been avoided with BMS controlled disconnect between strings?

Click to expand...

My assumption is in that failure condition a class T wouldn't have provided a spark. Now the high current might have still heated the wires enough to melt the sheath and short and still caused a fire.

We will never know.

Hedges said:

In other words, your assumption is that the catastrophic failure would have been avoided with BMS controlled disconnect between strings?

Click to expand...

Fundamentally the BMS job is to protect the battery. As implemented by the OP, the BMS served as a monitoring and management system and not a complete protection system.

A fuse is a crude instrument to try to protect a battery, especially from a high impedance fault. Somewhat ironically a highly parallel system (10-16+ strings) can be better protected by a fuse than 2-3 strings in parallel, assuming there is no contactor/shunt trip/mosfet to isolate a single string. (Of course that fuse needs to have sufficient interrupting rating.)