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    Battery Safety

    I have a Bicycle Motor Works 52V, 17AH battery with LG-MJ1 cells and 42V BMS shutoff...bought new earlier this year. The battery gets charged by a Luna advanced charger, usually at 3A at 80%...at 100% infrequently. The battery gets charged in a converted, metal, bottom rollaway, toolbox set up exclusively for charging in case of fire. The battery is used on a mountain bike while in a padded back pack...not mounted on bike. This battery never feels warm while charging or in hard use...always ambient temp. The battery has been flawless in use and charging.

    I've read a lot of good battery info on this site and others concerning the potential safety issues, storage issues, and operational procedures. The big issue of potential battery fire has one element that isn't clear to me. When I've seen videos or read reports about fires, I've only seen them occur while in use or while charging. Can you battery gurus provide some insight on that period of time when the battery is already charged or in a state of proper discharge for some storage when you're not going to ride the next day?

    If the battery is brought indoors so it can be kept in a climate controlled temp, is that a state that has that much potential for a spontaneous fire? I know there is no such thing as an impossibility, but how likely is that to occur under these conditions? The main reason I ask is that I read that batteries shouldn't be stored in extremely hot or cold conditions when not in use. Here in TX the temps in my shop building when the evap AC isn't on can be brutal. I don't really want to leave the battery sitting in the building at those temps. I charge the battery at night in that converted toolbox in the middle of a concrete floor as it's cooler at night. The next morning I bring the battery inside the house.

    So...how volatile is a charged or partially discharged battery kept indoors well after it has charged or been used?

    #2
    Well first it depends on the specific chemistry of the cells - if you are talking LiPo's that's a whole different animal than say LiFePO4

    Batteries have absolutely been known to enter thermal runaway spontaneously and catastrophically without load or being charged, but it's is far less frequent

    The batteries most of us are using in bikes are reasonably safe, low probability of catastrophic thermal runaway but it can happen, ambient conditions and power going in or out will generally affect those odds

    How they were manufactured affects those odds too

    So there are no hard and fast ways to calculate those risks in any practical fashion... do your homework - you are your own risk manager

    OTOH I've heard of very few fires on this board - heard of a few over on ES tho

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      #3
      AZ, I was hoping you would be one of the respondents. OK...without me doing more research through google, can you give me the lazy man's rundown on the LiPo vs. LiFePO4 comparison? I'd rather hear it from someone as it relates to ebike use anyway. Here's a link to my battery. I'm a pretty good mechanic, but these ebike batteries are a new animal to me. I'm not certain which category my cells fall in as to your description. I know they state "lithium ion", but that's where my brilliance ends...LOL!

      52v 17.5ah LG MJ1 Lithium ion E-Bike Battery | Bicycle Motor Works

      These LG cells are allegedly from Korea. One other confusing thing about battery storage seems to be the "fully charged" vs partially or 50% charged condition. Again, my main concern is to store off the bike in a more temperature friendly environment like inside my home. You're in AZ...you know hot...and you probably know my area of west TX is about as hot...LOL! It doesn't seem healthy to store in a metal shop building that when not in use can see 130 degrees on a good day inside. And to clarify when I say "store", I'm not meaning long term storage. I can ride pretty much all year here, probably like you...as long as it's in the AM in the summer...LOL! I'm going to put the battery in some form of metal box for indoors...just haven't come up with one yet. Still, I have no plans to charge indoors at any time.

      Comment


        #4
        LiPo's (lithium polymer) are generally considered one of the least safe. They are made for very light weight, mostly the RC market. The have thin flexible plastic film for the outer layers and their electrodes are also flexible. The electrolyte is flammable and they have a nasty potential to have "thermal runaway" since they have a negative temperature coefficient of internal resistance so as they get hotter the can produce more heat, particularly under heavy load. They are capable of delivering very high currents and not too many people use themin electric bikes, but some do since they are inexpensive and light.

        LiFePO4 (Lithium iron phosphate) are on the other side of things although they can deliver pretty high currents. The electrolyte is typically not flammable and they don't have a negative temperature coefficient of internal resistance so they don't normally enter thermal runaway. They have a lower voltage than LiPo's or Lithium nickel manganese cobalt oxide ("NMC", LiNixMnyCozO2) or Lithium Nickel Cobalt Aluminium Oxide ("NCA", LiNiCoAlO2) which are about 4.2V max and less Ah so in the end only about half the energy mass density.

        Lithium nickel manganese cobalt oxide ("NMC", LiNixMnyCozO2) or Lithium Nickel Cobalt Aluminium Oxide ("NCA", LiNiCoAlO2) are the most common for electric bikes and EV's in general. They are far safer than LiPo's and Lithium Cobalt Oxide (LiCoO2, "LCO" - you see these in vape devices, etc.) but still can enter thermal runaway and have flammable electrolytes.


        We all have to come up with our own risk management IMO. There are some folks that leave/charge batteries in hot/cold sheds/garages and others that always store and charge in flameproof containers that are in some corner of a controlled temperature environment that's not connected to their house


        Me I always keep LiPo's in flameproof boxes - I only use those in RC's regardless, not bikes. I have a work shop for my business that doesn't get much warmer than 33C (that's how hot it was last week when we had five days in a row over 47C/116F), has roof sprinklers and very little flammable items nearby and that's where the majority of my batteries hang. I don't mind keeping one or two of my bike batteries at the house but don't charge them when I'm not home... but agin, everyone should do what they can to educate themselves and do what they feel comfortable with... it's like the paralleling debate... me I don't see a good reason to parallel batteries, if I want more capacity I may carry two and just switch between them and if I want more current handling I'll buy a larger battery built for those currents... but that's just me... plenty of folks parallel batteries but I honestly can't think of much in the way of good reasons to do that...

        Comment


          #5
          OK, with your info I was able to determine that my LG cells are LiNiMnCo02 which appear to be the "NMC" version if I'm reading correctly. That was some heavy duty detail there, AZ. Very informative. I expected my battery to get somewhat warm while charging, but this thing always feels ambient temp. What you posted may explain that. As mentioned before, I charge on the 3A selector, and that probably helps too.

          With this info I feel better about keeping the battery in the house in a fireproof box after it's charged outside. That extreme heat of the metal shop building just doesn't sound good to me.

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