Lithium Battery banks fuse protection methods - Page 1
Forum section: electronics / projects

author: robint
author_rank: Regular Contributor
timestamp: October 22, 2023, 02:21:10 pm
content: Hi Guys, hope Im in the right category, please advise otherwiseThis concerns the construction of a 24V 100Ah LiFePo4 8 cell bank (this BTW is a tiddler compared to the off grid Solar power boys who dont get up for less than 48V 5000Ah banksIn their world they get very heated about fault current protection an AIC Amp Interrupt Capacityhttps://energytheory.com/what-is-aic-amperage-interrupt-capability/andwhich fuse to use ANL, MRBF, Class T and 20,000A fault current rating, marine battery isolation switchand I found to my surprise there is a very good reason to be concerned eg an 8Ah LiFePo cell shorted at terminals pulled over 80Amps and destroyed itself violently in 2+ minutes. A 160Ah cell pulled 960 A and destroyed itself in 12 mins. The concern is that once a dc arc has been established it is in a negative resistance region and the plasma has virtually zero resistance so the arc will draw as much as is available from the source. The you follow the logic from there on. It gets scary.If you havent considered building (or buying ) Lithium batteries to make your own bank (commercial kit is ca 2x $$$$ - hence the DIY interest) then this topic wont be of interest here.So before I dive in with be researches and experiences (links papers etc) are there any others here in the same page?

author: uer166
author_rank: Super Contributor
timestamp: October 23, 2023, 06:24:42 am
content: What exactly is the concern? You choose a fuse of an appropriate rating to protect your pack. If your pack can generate 960A short circuit current, then choose a fuse or breaker that can quench that current, at the pack's voltage, with good margins.In general up to 10s of kA is trivial, and there are parts readily available that are SMT, TH, and cartridge/stud mount.Don't forget a metal fuse is the primary protection for short circuit fire, not a BMS and its' FETs.

author: Berni
author_rank: Super Contributor
timestamp: October 23, 2023, 06:53:19 am
content: Yes high current DC fuses need extra care because of how much DC loves to draw an arc.But is is as simple as just buying a fuse that is rated to handle high DC fault currents. Usually sand filled or spring loaded fuses.But as stated above the main fuse is the last resort measure for when things go really wrong. The BMS should be the one looking after the battery, including disconnecting the output in case of a short.

author: robint
author_rank: Regular Contributor
timestamp: November 06, 2023, 12:42:43 pm
content: My concern is that, generally, those concept of fuse protection for dc battery circuits is treated trivially - as are the safety issues (except of course the Marine guys, who have for decades, been all too aware of the fire hazards associated with on board (LAB) battery systems - recently upgraded to include Lions. The have a raft of codes of practice to back it up). landlubbers seem to overlook this wealth of experienceHave you seen the cost of these Class T (EU HRC) dc spec fuse cartridges $$$ - more than my original 12v battery pack.

author: robint
author_rank: Regular Contributor
timestamp: November 17, 2023, 01:27:05 pm
content: Another week of digging through the large amount of fake news on Google on our subject and here's my findingsSome salutary vids to reset your ground zero hereWhy you cant weld with a 12v batteryYou can weld with a 2 x 12V batteriesSee how this totally rank amateur is meddling with his solar power system on his boat - if he had been on a 24Vdc system, the mistakes might have been so much worse - keep a fire axe handy to cut through cables.24vI think its important to note that an arc cant be struck at 12Vdc. At 24 Vdc it can be struck and sustained quite easily as shown by the experience welder.So If your ATO wafer type car fuse fails by gross fault current it can develop a sustained arc flash at 24Vdc and burn out until the gap gets too big ca 20mm. At 48Vdc its much more likely to become a problem with a fault condition.Once an arc flash develops it enters the negative resistance zone so that the current will increase under near zero ohms across the gap and is only limited by the source/wiring resistance. So this can escalate in milli secs - hence it can become an explosion - like a fire cracker. I think amateur dabblers are misled by the benign behaviour of a typical car battery and its electrics.It has been said that a short circuit of a Lifepo battery bank is like trying to contain the approx explosive power of a hand grenade 50g TNT 200 MJ - just to put it into context here - naysayers go pooh poohHere IMHO is a very fair vid on the range of fuse link types available for RV, Boaty, solar, off gridder - doesnt look too biased re sponsorship BUT totally deprecates the EU knife Blade NF Fuse with a very long trusted history - since 1949 (Siemens original design) and an obvious equivalent to the much vaunted Class T fuse states side.BTW the down side is that makers keep the fuse carrier system under closely guarded supply BUT the basic open ceramic has been around for a long time and can be obtained on Ali for $10 (with fuse) - cartel busting. BTW dont ever trust unbranded fuse links from Ali, buy from a reputable source.And just when you though this must be a massive hoax (its your call and your funeral) there has been a long standing workaround in the automotive industry called the fusible linkpresent on most vintage cars (14AWG x 6" insulated single core wire)https://m.roadkillcustoms.com/understanding-fusible-links/Most people dont know about thisOf course it breaks the current BUT doesnt contain the explosive force or potential fire and personal safety risk (see how many vids show amateurs messing with Lifepo banks and NOT wearing googles. Would you weld without them? Think of a stick weld x 1000 for arc flash.This is open for discussion in the hope of bringing some professionalism to the subject of my OP