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MSP & garage fire!


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31 minutes ago, HamishTHaggis said:

I'm a little late to this but there are a couple pieces of info floating around here that are misleading.   

(1) The one that bugs me most is the repeated references to on-board protection circuits on battery cells.   It is true that many (not all) cells exist in a protected version like this.  But it's also true that the unprotected versions are nearly always what are used in these packs - for cost reasons if nothing else.  Therefore, generally speaking, there ARE no such protection circuits on each individual cell.  

(2) A few people have stated that there must be individual probe points per-cell for balancing.  Others seem to understand more correctly, but for the sake of clarity - this is false.  There are probes at each series point (i.e. between each set of cells in parallel) but that's not per cell.  Since packs are generally built by connecting 4, 6, 8 or however many cells in parallel, then connecting those sets in series to achieve the target layout (20s6p or 24s6p for example), the assumption is that 4, 6, 8 or whatever number of cells directly connected to one another will necessarily remain balanced.  This works pretty well until a cell fails.  Balancing is done per series-set (i.e. each of those packs of 4, 6, or 8 cells) but not per individual cell.  While it would theoretically be possible to build a pack with balancing probes per-cell, it would be considerably more costly and still wouldn't really fix this issue  - cells welded together generally DO self balance, so long as none of them fails.  If one fails, balancing won't help.  I suppose one could conceivably build a pack that alarms somehow with probes on every cell, but I wouldn't hold my breath waiting on it.  Not even Tesla does this in their packs.  EUC makers are not likely to start.

To many people's points - yes, overall these devices are quite safe.  Caution is still warranted - just as we don't keep cans of gasoline under our beds, we shouldn't do stupid things with Li-Ion cells.  It's just that most of us are less clear on what that really means in practical terms.  For me, the biggest takeaway is this - if your pack behaves strangely, ever, you should suddenly be suspicious of the safety of that pack and act accordingly until you can explain the behavior confidently and be assured of it's safety.  Beyond that - paranoia isn't warranted but caution is wise.

The motor industry solves the issue of many cells in parallel by connecting them on one side with fuse wire. If they internally short circuit the wire melts and the pack remains intact.

There is no point in having cell individual probe points as parallel connections share the same values.

A deteriorating cell first exzibits deviating (low) group voltages for a very long time before exceeding low/high safe voltage limits.

I think a very good measure of how balanced a pack is to fast charge it from a low charge to a high charge and immediately measure the levels before any balancing has kicked in. A healthy pack shouldn't even need balancing. When you first start to see that you depend on the balancing to stay balanced, that's the beginning of the end.

If you're a cheapskate like me you just use the probe points to occasionally balance externally and essentially ride without a bms. No fires, no risk. If a group goes below 2.5v you know that pack needs to be replaced or serviced professionally. By not going deep discharge with an old pack you automatically avoid the risk for bad groups to go under the low limit when the pack hasn't been balanced for some time. After balancing you can go for a deeper discharge if you please. Luckily for EUC use, the euc often becomes useless before any cell comes close to the lower limit. That's because at 3.5v they're essentially running on fumes, and so the lower limit 2.5v is quite far away. Only when continuously riding deteriorating packs do some voltages dip under 2.5v and the fire hazard presents itself. This would have been easily spotted long time ago with probe points.

Another nice feature is that end users could identify defective packs and get them individually replaced instead of sending entire wheels back and forth.

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Well, I had one of the worst imaginable events happen with my wheel other than injury, which I've already conquered many times in the past.    5 days ago...my MSP C30 wouldn't charge after a 10 m

I'm going to go out on a limb and say "stressing" the bad battery pack led to the ultimate failure. Even an idling wheel on a bad battery pack is probably not good. Nothing like hindsight though.

Stressing a pack with a bad cell by charging or discharging should not be done in any case! Never ever!  From the reports here there seem to be three stages of battery degradation - the firs

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i hv seen it 1st hand (3 machines in chain reaction); once thermal runaway starts forget abt moving it without serious risk of harm  - - u cant get within 10 feet of that inferno. plus the smoke is pure evil. imo if u wanna mitigate risk, u put wheels in a metal box (filing cab) on an outside wall of ur garage and u vent the box to the outdoors (like a propane insert). any unvented solution will not deal with the crazy toxic smoke that comes from a wheel meltdown. li-on fire is very ugly business - until solidstate batts are affordable, vented firebox is a cheap (vs fire consequence) mitigation tactic (for people with large number of machines like @Marty Backe only solution is abandoned missile silo)...  aptmnt dwellers? lots of smoke detectors & hv a practiced escape plan if ur wheel goes up in flames! and NEVER EVER charge ur machine overnight cuz li-on fire while you are sleeping would be terrible outcome... 

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On 11/24/2020 at 3:18 AM, Chriull said:

....From the reports here there seem to be three stages of battery degradation...

Excellent post! 

On 11/24/2020 at 7:05 AM, bcarp said:

Common advice in the FPV quadcopter world is to discharge battery packs to 0V then dispose on regular trash. At 0V, there is no risk of fire.

We can easily monitor individual cells & know when a pack is going bad, and discharge it fully on a computerized charger designed to do so (with temperature monitoring/alert/shutdown), in a fire-retardant bag, within hours-not weeks-the dendritic growths don't have time to puncture the insulator. We also run 8S1P easily removable packs & chain  them to get 16S..., so far fewer cells/lower risk right out of the box. (And some of us hook monitors to the balance wires while flying and are alerted if any cell starts to act up.) 

  

On 11/24/2020 at 1:16 AM, Zombie Batman said:

That is my worst nightmare.  I been thinking of getting some sort of large metal box to store my wheel in.  

 

https://www.amazon.com/Buyers-Products-Aluminum-Underbody-24x24x24/dp/B01ASXUSD2/

 

I'd get a steel box, the melting point is much higher (and generally they're less expensive).

On 11/24/2020 at 3:55 PM, Marty Backe said:

If I had one or two wheels I would store them in such a cabinet. What to do when you have a dozen :cry2:

Get a bigger box! (multiple boxes if needed) 

https://www.amazon.com/dp/B00L4CM3MQ/ref=emc_b_5_mob_i?th=1&psc=1

Edited by WI_Hedgehog
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