Lipo failure

[Syonyk]

In the Floont case he was reportedly reconfiguring a number of different packs together to very high voltage and bulk charging them, so the balance was poor, and not monitored or controlled. This is a particularly high risk approach to battery configuration, and I would not recommend that.

Except that people on ES keep recommending reconfigurable lipo packs as a way to power ebikes...

I'm working on a survey of battery fires I can find, and the vast majority of them involve hobby lipo packs. I'm having a genuinely hard time finding fire reports from other battery pack types - and I know there are a lot of other batteries out there, but they just don't seem to be catching fire like the lipo packs.

As far as house fires/car fires/other structure fires, RC boards are an endless supply of them as well. Admittedly, their power sources are almost entirely hobby lipo packs, so I'd expect the bulk of the fires reported there to be hobby lipo based, but there are an awful lot of torched houses & cars as a result of them, not just on ES.

For high current applications the BMS is not generally switching the high current path, it controls power to the controller logic subsystem instead, so a short will depend not on the BMS but on the overcurrent device which many builds are lacking, or which are not rated for the proper voltage. This only works if the short is downstream of the protective device. The majority of connections and opportunities for a short are inside the battery pack where the overcurrent device or BMS is not helpful.

If you've got a million random wires and connections running around, yeah, you've got a lot of opportunities for shorts inside the pack, and the heat released will generally melt insulation and cause more shorts (or just straight up thermal runaway of neighboring cells). This doesn't seem to be the case in many 18650 packs - there isn't a way to get multiple shorts going, and a battery failing will often not be able to get the surrounding cells up to thermal runaway temperatures, so the energy released is a single, decently cooled cell (heat flowing into other cells rapidly enough that it doesn't get up to ignition temperatures).

Not many commercial packs meet the needs of high performance ebikes. They cannot deliver the current needed. Or they are too large, heavy or expensive for the application. If folks could easily and cost effectively buy packs that met their needs, they would. They just aren't very available in the configuration that fits the application.

This is certainly a problem. I think the reality is more that they're too expensive for people to want to spend money on for their 6kW ebike. That's fine, but if I can shift attitudes such that only the truly high powered bikes are using lipo packs, it's still an improvement. You don't need them for a 1000W commuter.

The people on this forum don't represent the majority of ebikers. These are the folks who want to build something, not the off-the-shelf appliance operators that represent most of the population. Not too many of this crowd live in apartments, from what I've seen. If you want to address the majority of ebikers you need to find a different venue. This isn't going to reach them. This is the DIY crowd made primarily up of engineers, technicians, inventors, experimenters, modders and tinkerers.

And if the DIY people continue to make fireball ebikes that burn down buildings, it's going to very negatively affect public opinion of ebikes.

Though I will grant you, very few people here seem to be burning things up in apartments. I'm not sure why that is, but I have noticed that.

 

[Alan B]

The number of ebike fires is minuscule compared to other fire sources. The number of homemade ebike packs is insignificant to other battery packs, and the number of homemade pack failures is a tiny percentage of homemade packs. This board tends to concentrate and collect reports of fires for a number of reasons, which creates a warped sense of frequency. So extrapolating data from that results in inaccurate estimates of overall risk. If you look on the car forums you will find toasted cars, and those are not lipo. If you look at electric motorcycle racing you will find toasted bikes that are generally not lipo. Anywhere you have very high energy density you have increased potential for conflagration.

Your experience with battery packs doesn't appear to be very significant. I wouldn't expect a lot of folks to look to you for guidance. The insulation around each cell in a cylindrical cell pack is very thin, and it is all that is preventing shorts within the pack (unless some other insulation or spacing is interposed). There are a very high number of opportunities for a short from either vibration rubbing through the thin insulation or a heated cell melting through it. We have seen this happen. One cell gets hot from a brief high current load or internal problem, melts through to the next cell, and forms an internal pack short causing a runaway event. Many 18650's are not exempt from this. They are even worse than mylar bags in this type of event.

Collecting statistics on past battery fires is also misleading in that the cells currently available are not the same as a few years ago, and most events that you find were using older cells. The chemistry is evolving, and cells that used to burst into flame at 4.5 volts are not what we're getting today. You can find tests of new cells that withstand much higher voltages. This is in contrast to gasoline, propane, methane or hydrogen, which bursts into flame the same as it always has. Batteries are improving very quickly, as is testing and regulations for shipping safety. Note that RC batteries do meet shipping safety requirements, and are tested for that.

The number of interconnects in a pack is quite similar regardless of cell type (it is more related to cell size, and 18650 is a small cell so it tends to have more). It is significantly shy of a million wires. The balancing wires are generally small enough gauge to be "self fusing", so they are not a significant part of the fire risk. The main power wires are the ones that can carry enough current to cause fires, and all packs must have those to be useful for high current applications. Cylindrical packs often have wide current carrying conductors that are not insulated, increasing the opportunity for shorts in those packs.

Enjoy your ebike and stay away from radio control toys and thin laptops as they are full of the series Lipo you fear. Avoid commercial flights as well, and don't live in an apartment or stay in a hotel as there are plenty of series lipo on board every flight and in every apartment and hotel. You cannot stop either the use of lipo or the march of increased battery capacity and series connecting cells into packs. Battery packs will become safer as that is everyone's goal. The industry has already improved the safety of cell types and will continue to do so. People will buy and use what is available and cost effective for their needs.

 

[markz]

OK OK sorry about that, I just wanted to get the fire thing behind me.

About the #9 battery. I had put it aside, along with another battery that the balance wires were'nt reading properly, the #5 battery. Balance wires were lose.

I knew my batteries were low when I got home after the ride, because my ride took 16S4p? of RC Lipo down to 62.5V I believe is the LVC on the Lyen 18fet 65A.
At the time of the fire, I had 4 batteries in parallel to give me 20Ah, then of that setup had another 4 of those in the series string to make 67.2V I believe.

I cant remember now if I checked with my cell-log 8 or not before I charged them. I would normally check out of a 6 pack brick, 2 or 3. Sometimes all.
I do remember my LV Alarm was reading battery cells of 3.2V and 3.1V, in which I reset the LVA to another battery....while riding, with similar readings.

The charging I was doing at the time. I was charging 4 batteries on the parallel board, at a rate of 6A. I remember I was having problems with my charger not being able to read one cell and the charger would stop. I would try Balance Charging mode, Charging Mode and Fast Charging Mode, sometimes it would fail immediately, other times would start charging and stop. At the time the RC Lipo destructed it was set on regular Charging Mode, 6A and had reached 14.4V in total. So 1.5A a peice? Is what? 0.25C? I dont know. Anyway, I didnt have a problem with the first 6 pack brick or my 4 pack brick. I believe I charged them to 3.3V, then balance charged them to 3.5V then moved onto next set of batteries.

I am lucky it didnt go off on the desk in the office while I was in the Kitchen.
Because by the time I heard the first pop, and second pop, to the fire wasnt long....minutes really.
It was user/operator error. Obviously I charged them too quick, or those 2 bricks there was something wrong with them which I didnt catch, hence user/operator didnt find it due to just not knowing, or ignorance whatever it was.

Scrutinize all you want.

Im moving onto to a "safer" battery chemistry/setup.

 

[Gregory]

markz, thanks for being honest, at least others can learn what not to do. I assume 16S4P means you have 16 x 4S hardcase battery packs.

16S4p? of RC Lipo down to 62.5V I believe is the LVC on the Lyen 18fet 65A.

Can't be right. Nominal for 16S is around 60V. At controller 62.5V LVC 16S cells would have been 3.9V. It must be set at something lower and you need to know this. It makes no sense given the next quote.

I do remember my LV Alarm was reading battery cells of 3.2V and 3.1V, in which I reset the LVA to another battery....while riding

Obviously the battery must have been down around 50V. You set LV Alarm at 3.1V or lower? Or ignored the beeping at 3.5V? Naughty markz.



No room for guess work with LiPo, you need to be the BMS. Else buy a BMS.

 

[cal3thousand]

In the Floont case he was reportedly reconfiguring a number of different packs together to very high voltage and bulk charging them, so the balance was poor, and not monitored or controlled. This is a particularly high risk approach to battery configuration, and I would not recommend that.

Except that people on ES keep recommending reconfigurable lipo packs as a way to power ebikes...

I'm working on a survey of battery fires I can find, and the vast majority of them involve hobby lipo packs. I'm having a genuinely hard time finding fire reports from other battery pack types - and I know there are a lot of other batteries out there, but they just don't seem to be catching fire like the lipo packs.

As far as house fires/car fires/other structure fires, RC boards are an endless supply of them as well. Admittedly, their power sources are almost entirely hobby lipo packs, so I'd expect the bulk of the fires reported there to be hobby lipo based, but there are an awful lot of torched houses & cars as a result of them, not just on ES.

Floont's issue was not reconfiguring. He did many things that go directly against best practices of LiPo safety. Reconfiguring may introduce opportunities for failure, but only if done improperly. It's not proper to downgrade a practice based on a small group's inability to execute it safely.

As Alan correctly pointed out, these fire reports are horrible data for statistical extrapolation. People tend to report and remember failures, not mundane successes.

 

[Alan B]

OK OK sorry about that, I just wanted to get the fire thing behind me.

About the #9 battery. I had put it aside, along with another battery that the balance wires were'nt reading properly, the #5 battery. Balance wires were lose.

I knew my batteries were low when I got home after the ride, because my ride took 16S4p? of RC Lipo down to 62.5V I believe is the LVC on the Lyen 18fet 65A.
At the time of the fire, I had 4 batteries in parallel to give me 20Ah, then of that setup had another 4 of those in the series string to make 67.2V I believe.

I cant remember now if I checked with my cell-log 8 or not before I charged them. I would normally check out of a 6 pack brick, 2 or 3. Sometimes all.
I do remember my LV Alarm was reading battery cells of 3.2V and 3.1V, in which I reset the LVA to another battery....while riding, with similar readings.

The charging I was doing at the time. I was charging 4 batteries on the parallel board, at a rate of 6A. I remember I was having problems with my charger not being able to read one cell and the charger would stop. I would try Balance Charging mode, Charging Mode and Fast Charging Mode, sometimes it would fail immediately, other times would start charging and stop. At the time the RC Lipo destructed it was set on regular Charging Mode, 6A and had reached 14.4V in total. So 1.5A a peice? Is what? 0.25C? I dont know. Anyway, I didnt have a problem with the first 6 pack brick or my 4 pack brick. I believe I charged them to 3.3V, then balance charged them to 3.5V then moved onto next set of batteries.

I am lucky it didnt go off on the desk in the office while I was in the Kitchen.
Because by the time I heard the first pop, and second pop, to the fire wasnt long....minutes really.
It was user/operator error. Obviously I charged them too quick, or those 2 bricks there was something wrong with them which I didnt catch, hence user/operator didnt find it due to just not knowing, or ignorance whatever it was.

Scrutinize all you want.

Im moving onto to a "safer" battery chemistry/setup.

Thanks for the details. Any cells below 3.5V would put me into "extra caution" mode and I would then use low current and only a per cell balancing charger like the BC168 to avoid any possibility of overcharging. Additionally if much below 3.5V I would split the pack into individual batteries and charge them separately at very low current. I've done the same with LiFePO4, though the voltages are slightly lower for that chemistry.

If you had a commercial BMS on that pack it probably would not have allowed charging at all. Time for a trip to either the dump or the battery hospital. That pack needed emergency care.

When we build packs from smaller batteries we take the responsibility to manage them. Regardless of chemistry.

Glad to hear that you are changing the way you manage your batteries. It is important. You will find that a completely made up pack with full protection is a lot more costly, especially for high current. Zero motorcycle has some nice ones. Your motor and controller are outside the normal ebike packs.

Series connecting BMS managed packs is not a great idea. It subjects the BMS to potentially much higher voltages than it was designed for and can cause failure of the BMS which is not what you want. It also adds the loss of the series FETs to both packs and passes full current through both BMS's. Only do this if the manufacturer of the pack explicitly permits this application.

Parallel connecting BMS managed packs is probably a better plan. Again, only do this if the manufacturer permits it. They should be fully charged when paralleled to avoid different states of charge from producing interaction currents.

Using the CAv3 to control current is not sufficient to protect batteries as it is too slow and allows temporary excursions beyond its limits. Instead you must use a programmable motor controller and set that to limit the battery current to within the BMS ratings. The CAv3 can then be used to further limit current, and any momentary excursions will be controller limited. Otherwise you risk BMS shutdown events which may require unplugging/replugging batteries to reset.

If all this seems too much, then buy a complete kit with battery, controller and motor from a reputable vendor. They have already matched the components and dealt with all these issues. Putting a system together yourself makes you the system integrator and as you can see there are many issues to take responsibility for managing.

Ride and Charge Safely!

 

[Ykick]

Here’s an 8S RC Lipo discharge graph using good new cells. As you can see approaching 3.65V everything’s fine but after that point things literally start to go downhill. It only takes a few minutes, if that, for a cell in the series string to reach critical minimum voltage.

If you think you can “guess” where that narrow window will occur without using any cell level monitoring, you probably have a career waiting as a psychic fortune teller…

 

[Alan B]

One day during my morning commute I noticed the pack voltage was lower than usual, eventually falling to near the low voltage cutoff. By that time I was a couple of miles from work with a pair of 10% climbs to go. I shut the motor off and pedaled on the level and downhill parts, and got off and pushed up the steep hills (since I don't have low gearing on this heavy ebike for climbing). I arrived at work late, but the battery pack was not damaged. I monitored the cell group balance every few minutes during bulk charging, and insured that the balance was good, and the cells were all above 3.5V and equal in voltage. The pack did not require balance charging, the balance was fine, and $800 worth of lipo was saved.

When there is any reason to suspect battery issues it must be addressed. It may be inconvenient, it may involve pushing the bike or removing the battery pack immediately. Ignoring it may lead to pack damage or even fire.

It turns out the problem here was an intermittent connection on the AC side of the charger at home (a poor quality removable power cable at the charger side), it started to charge and stopped before completing the job.

 

[Ellou]

This thread is great and I'm glad there are people in here discussing the truth about real world usage of lipos and not just speculation.

All of the people that say don't have lipos in apt, house, car etc. Do not think about how many rc plane, car, motorcycle and multicopter people are around. Where do you think they live? I've been using lipos in rc trucks, planes and multicopters for years, never had a fire and I've been in bad situations. (Over discharge, draw to many amps, crash lipo first going 30mph) Never had a fire. Even when a pack was completely deformed I only ended up with a bad cell.

My point is like anyone else in the thread that has just been saying be responsible, good charger (I've never trusted those external balance things), monitor fully charged/end cycle, LVA and best judgment and you'll be fine. Accidents do happen but for some people lipos are live grenades and it's going to ruin ebikes.