Parallel Lifepo4 cells, to fuse or not to fuse

mcgivormcgivor Solar Expert Posts: 3,063 ✭✭✭✭✭
Currently in fabricating bus bars to parrallel series 30 ×100Ah cells 4P 8S, between reading on various sites to gain ideas, one is the use of fuses for each individual cell to prevent a bad cell being back fed by the other cells, some say fuse individual cell blocks and there are other schools of thought that say it's unnecessary. 

To me it makes sense, for the same reasons Tesla uses fuses on each cell, although I do realize they are using much smaller cells in greater numbers, thousands in fact, but the rationale would still be the same, the practice of using fuses in multiple parallel strings of series lead-acid or other type batteries to prevent a similar event should one battery in a string fail. The sizing of the fuses would have to be capable of carrying the cells share if the maximum antisapated load or charging current whichever is greater.
Ivor 
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.

Comments

  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Ivor, I would think that is partly the job of the BMS, at least for between the strings of 8.   Same as for multiple strings of FLA's.
    Aren't the blocks made up from multiple cells inside the block?
    Have you decided on that piece of the system yet?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • mcgivormcgivor Solar Expert Posts: 3,063 ✭✭✭✭✭
    Eric, Yes I have a BMS, it's job is to look after the voltage in each block of cells, 4 in my case, but as the voltage is equal across the block, a failed cell could accept the current the good cells in the block have to offer, without nesesarally changing the voltage, which the BMS restricts, hopefully the voltage would collapse and shut everything down. Just attempting to turn over any stones which may reveal a supprise, the fusing of independent cells is probably not that common, but if it can be incorporated into the initial build, perhaps it's something worth looking into was my thought. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    edited August 2018 #4
    Well I too am wondering why it  is not inside the cells blocks  since some  of the Tesla's have self immolated?
    Along that vein, Have you heard of other self igniting car models with LiFePO4 cells?  OOPS my bad.. see next post
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    Eric, Tesla uses NMC cells BTW.  All cars that I know of use NMC for the maximum power density per pound.
    LFP is not as much concern here for Ivor.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • EstragonEstragon Registered Users Posts: 3,940 ✭✭✭✭✭
    Not sure about LFP, but I've read some nasty fumes can be generated by shorted lithium even if it doesn't actually catch fire.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    All batteries have risk right?  As a user or designer the risk must be acceptable and the reward must be worth the risk.

    I was pointing out that many people mix-up all the u-tube hype of lithium and most of it is centered on NMC type lithium.

    LFP cells are much safer from the hazards (gas, fire, explosion) compared to NMC cells. 

     NMC can be made safer with BMS protection and fail safes for over charging and short circuit that include the inverter and charge sources.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • EstragonEstragon Registered Users Posts: 3,940 ✭✭✭✭✭
    Agreed. The leading cause of death is life, and life has risks. It's up to each of us to try to understand the risks as best we can, and avoid them to the extent practical and desirable.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 3,063 ✭✭✭✭✭
    From my understanding problems occur  with high discharge in automotive, E bike applications  associated with top ballancing, for those applications, bottom ballancing iwould be the preferred method, but then again I'm not an expert. Most automotive applications don't use LFP, that's understood, the Tesla reference was merely an example, the other applications where this was suggested were with LFP, here is one site I happened to bookmark http://nordkyndesign.com/assembling-a-lithium-iron-phosphate-marine-house-bank/ Building safeguards into a system will "minimize" the potential of catastrophic failure but never eliminate it,  the information seems to focus on negative aspects primarily, as well as putting all lithium  chemistries into one group, the fear of the unknown prevails, reports or videos of failure are far more dramatic than those of success.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    The auto failures also happen not just on discharge but also during high amp charging where there is a cooling issue that may have caused the failure. Not much of an issue for you as yours will be passively cooled and you are not in a contest to see how fast you can charge.

    It is impressive how fast they do charge with round trip on 48v near 95%. Most lead acid when new are lucky to hit 80% round trip. And then the big long fade of LA.

    The one issue I bring up with my clients is a fire caused by something else and how they want to deal with it. It often is a bigger issue offgrid as we want the long life of lithium and have to control the temperature in the extremes. This means that the battery is in an attached garage or part of the structure to keep the battery logging good temperatures for warranty. This is probably not an issue for you but you may want to research and have a plan for an external fire. You are lucky you don't have the wildfires we do but not bad to have plan :)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mcgivormcgivor Solar Expert Posts: 3,063 ✭✭✭✭✭
    The purpose of building safeguards is to provide multi layer protection, how I propose to achieve this is using a BMS, selected for the application by providing all specifications to the manufacturer which includes over/under  charging disconnect internally, the second layer is a another  BMS which monitors the battery in the same manner as the first, but has external disconnects, the third layer is to limit the charge/discharge parameters of the equipment involved, the charge controller and inverter, Adding a forth layer, the fuses of individual cells would protect individual cells within a cell block. Granted it may sound complicated ,but it's actually quite simple, perhaps a fifth level would be a fire/smoke suppression system, should everything else fail, but then again concrete construction limits fire propagation  to some degree. There are no low temperature issues regarding charging which would be a factor in my case, the batteries will not be within the dwelling but in the same structure..
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    Ivor what size of buss bar did you use?
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • mcgivormcgivor Solar Expert Posts: 3,063 ✭✭✭✭✭
    Ivor what size of buss bar did you use?

    What I ended up using is aluminum flat stock 20mm × 2mm , finding copper stock proved fruitless in Thailand, in fact aluminum is not commonly available, found some at a window frame supply shop, $3 for a 6 meter length, cut and drilled to parrallel 4 × 100Ah cell blocks then series the blocks using link plates. This allows for ease of separation to reconfigure all blocks in parallel to ballance charge with a 3.65V charger. The current carrying capacity is approximately 125A for the 40mm^2  which is well above what is typically used, all terminal  contact points were sanded and coated with antioxidant and bolted with stainless bolts and lock washers.
      
    Perhaps not the best material choice but what was available and it actually works well. Voltage drop checked under moderate load between cell terminals is <0.001V.  There are many bolts to torque I suggest marking each afterwards to ensure none are missed and test every terminal under load. The links provided information on busbar current carrying capacity. From the other thread you question  1/8 × 3/4 this would be~ 60 mm^2 .

    http://dolstardeltastarterdata.blogspot.com/2011/08/current-carrying-capacity-of-aluminium.html
    http://dolstardeltastarterdata.blogspot.com/2011/05/current-carrying-capacity-of-copper-bus.html
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • just startingjust starting Registered Users Posts: 228 ✭✭✭
    Thanks ivor
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Back to the original post I think it is only worth fusing small cells. The reason being the amount of heat generated by different sized cells when they are short circuited.

    The total amount of electrical energy stored in an 18650 LCO cell is ~12Wh (3.6Vx3.4Ah). If we say a sustained short circuit current of 10C which gives a 'burn time' of ~6 minutes we get the power dissipated in the cell at ~120W. It is quite possible that a well designed battery pack with well designed thermal management could cope with this, there is an interesting NASA technical paper on this.

    On the other hand if we have a 100Ah LFP cell which is storing around ~325Wh of energy with the same burn time of ~6 minutes we have to dissipate ~3.25kW without raising the temperature of the cell to the point where it catches fire!

    Because of this and because it is so easy I would say it is worth fusing individual 18650 cells but not large prismatics.

    Simon
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    Hi Simon,  did you see that LG came out with a 48V 13.5kwh for the EU? Were you not installing one for a client?

    Back to fusing, the way they did it was brilliant I thought. They were looking at protecting the battery from an inverter fault known as a shorted power bridge. Basically a short circuit on DC in to the inverter. The first time it happens the 200 amp breaker trips. The internal 48 volt circuit that is still alive looks for a reset on the breaker, if this happens, it crowbar blows the 200 amp fuse. We tested it and it was a bit scary, but worked fine. The fuse keeps the uninformed out as it required a bit more than taking the top off the battery.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • karrakkarrak Solar Expert Posts: 326 ✭✭✭✭
    Hi Simon,  did you see that LG came out with a 48V 13.5kwh for the EU? Were you not installing one for a client?
    Hi Dave, I think you have mistaken me for someone else. I am based in Australia

    I am a bit confused  by your statement
    The internal 48 volt circuit that is still alive looks for a reset on the breaker, if this happens, it crowbar blows the 200 amp fuse.
    Do you mean if the circuit breaker doesn't trip the crowbar will blow the 200A fuse?



    Sorry, I might have not been very clear with my last post. I was talking about a short circuit fault within an individual cell. With a small cell as long as there is no extra current from other cells it is possible that the amount of energy dissipated within the individual cell will be small enough to limit the damage to the individual cell. With the larger amount of energy stored in larger cells it is much harder if not impossible to limit the damage and maybe fire to the individual cell. Under these circumstances I think it might make little if any difference if there is  fusing between the paralleled cells.

    Simon

    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 2p16s (48V), MPP Solar PIP5048MS 5kW Inverter/80A MPPT controller/60A charger, 1900W of Solar Panels
    modified BMS based on TI bq769x0 cell monitors.
    Homemade overall system monitoring and power management  https://github.com/simat/BatteryMonitor
     

  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    Nah you were clear Simon, I just hijacked the individual cell thing to the bat system protection. I agree with your last sentence above.
    I use a commercial LFP for some of my clients that uses prismatics and they pretty much do what you are saying. Also the larger cells are less prone to damage just by being that large. They can't be hurt by 150 amp loads which was LG's problem with the 6KWH batteries.

    No to your question "Do you mean if the circuit breaker doesn't trip the crowbar will blow the 200A fuse?

    The first fault in the shorted inverter trips the  battery breaker, if the user resets the breaker again within 1 hour, the breaker trips and the crowbar blows the fuse so the user can't keep resetting without finding the cause. At this point a person with the smarts has to be involved as the inverter is blown and now the top of the battery has to be removed to replace the fuse also.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    To make things a bit clearer... "Crowbar" is a term used in electrical/electronic systems. It literally means that "something" (like a large transistor or even mechanical switch) placed across (closing the switch) the output of a power supply or battery bank as a last ditch method to ensure that there is zero output (or zero power transfer to the battery bank).

    For a power supply, it is a backup circuit to protect the loads if the power supply goes out of regulation (instead of 12 VDC, the supply goes out of regulation and tries to output >15 VDC).

    In Dave's discussion, LG placed a 200(?) amp fuse between the battery and the DC input of the AC inverter/charger. If there is any electrical fault from the downstream electronics that the battery management system "does not  like" (in the above case, manually resetting the master battery breaker without diagnosing the reason for the fault), the system "crowbars" (short circuits) the battery output and pops the fuse (very quickly). Preventing any further risk to the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    In my discussion, all of this is internal to the LG battery.

     A standard way to circuit breaker protect the battery from a fault one time. A very rare one I might add but possible. I have not seen an XW fail this way. The few I have seen from lightning were wide open on DC in.

     A nice way (blowing the fuse) to protect the battery from a non-informed user as the fuse is not easily accessible.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • mike95490mike95490 Solar Expert Posts: 8,370 ✭✭✭✭✭
    So if a user turns a breaker off, fiddles with something for less than an hour and turns the breaker  back ON, will that set the crowbar, or is it smart enough to sense a overcurrent trip and restore ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 29,489 admin
    If I understood the explanation correctly, the BMS remote trips the breaker (circuit breaker with a separate "trip coil" internal to the breaker), if the BMS thinks something is going wrong (battery overcharged/undercharged/overcurrent, cell to cell balance issues, etc.).

    If the circuit breaker is manually reset without any other intervention (I am guessing--in less than 60 minutes), then the BMS has a second option to blow the battery pack "master fuse" with the crowbar to stop/reduce potential damage to the battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,659 ✭✭✭✭✭
    Bill gets the cupie doll!
    The circuit breaker can be manually turned off for any length of time. It has 3 positions, on, off and tripped.
    If it is the tripped position, because of a fault, the timer is running to protect the uninformed from themselves.

    It works flawlessly, or has been since the start of my testing 2 years ago. Yes we did test the shorted DC inverter input. They gave me an XW+ to do it in the field :)

    I think that it is overkill for the guy's here doing DIY but good to think about how the Big guys do it. They probably have to as they are listed for indoor use. One of their videos has one installed next to a dishwasher in a home.


    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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