squowse
Solar Enthusiast
- Joined
- Jan 4, 2021
- Messages
- 600
Oh I thought you were saying to not bother using fuses.
House burned down
- Thread starter Jejochen
- Start date
Brucey
Solar Wizard
With those super cheap tyco disconnects at batteryhookup for around $15 no real reason not to.
There is nothing wrong from a safety perspective to have all string contactors controlled by the Batrium such that any failure isolates each string... beyond the nuisance factor.
There really are three elements that are needed, but two can be combined easily: a means for the BMS to isolate a string, a means to interrupt currents in excess of the BMS or wiring rating, and a means to electrically isolate a string for maintenance. Great to have all those class-T fuses... but if one needs to be replaced and you have voltage drift between your strings I sure as hell wouldn't want to be putting the fuse in "hot." (My fear goes back to telecom strings though and we aren't talking about a 4,000A plant here.)
Brucey
Solar Wizard
Yes, if there had been a contactor per string, the Batrium could have disconnected the problem string.
Personally I like Midnite mnedc250 DC breakers for ocp and disconnects
Considering the flat voltage curve of LFP, it's not really too big of a deal (yes, I've tested this).
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 21,333
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.
(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.
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.
(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.
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.
PotusGobbleBottom
Corn Pop was a bad dude.
_voltmeter_
New Member
- Joined
- Apr 24, 2022
- Messages
- 65
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.
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.
Prismatic vs Pouch VS Cylindrical LiFePO4 Batteries Cells
This article compares the advantages and disadvantages of prismatic and pouch LiFePO4 batteries to help you make an informed decision.
www.litime.com
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.
That means the wiring is sized to the load. Ppl leave that load part out…kinda critical
PotusGobbleBottom
Corn Pop was a bad dude.
OffGridInTheCity
Solar Wizard
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
Last edited:
_voltmeter_
New Member
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- Apr 24, 2022
- Messages
- 65
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
ElkPicture
New Member
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.
robbob2112
Doing more research, mosty harmless
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
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
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.
robbob2112
Doing more research, mosty harmless
Or have a contactor you can turn off
Or you know, just a regular disconnect switch.
Zwy
Emperor Of Solar
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.My point - it's not just as simple as always have 'individual battery automatic shut-off' or you're risking life and limb
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."
