Electric Motorcycle Fire: Was It Battery or BMS Problem--Seeking Explanations

The circuit board the battery terminals is one type of BMS, the other would have a wire from the + terminal of each cell, and from the the pack-negative terminal. All the wires would lead to a fairly substantial enclosure the cycle somewhere.

As far as the speculation regarding the battery type, if not LiFePO4 what type are you speculating it is? a description of the cell's appearance or posting some photos might be helpful.

The cause of the fire is most likely NOT the batteries/cells. A short circuit anywhere in the bike could start a fire - it can happen in an IC motorcycle too.

Paul D.

A clue as to battery TYPE is to measure the cell (Charged) voltages! Lithium will be 3.4 to 4.2 volts per cell, Ni-Mh will be 1.2 to 1.4 volts per cell, and lead-acid will be 2.0 to 2.35 volts per cell, or somewhere very close to these values, depending on temperature. I have heard of ignition switches arcing and burning when turned off after getting wet, when used to switch high voltages. (Over 16 volts)

LiFePO4 Cells are very stable and cannot cause fires like the lithium polymer, or lithium-cobalt used in PC's and cell phones. I have taken older retired LiFePO4 cells, completely discharged them to zero, then completely recharged them. They were ruined as far as capacity and internal resistance, but nothing dangerous happened.

But if your cells are other lithium chemistry - all bets are off - but I simply have never seen anything but LiFePO4 in any Chinese scooter or MC - from one of about four manufacturers.

You prevent shorts in a scooter the same way you prevent shorts in your house or a car or motorcycle. Make sure the wire insulation is intact, no points of opposite polarity can come in contact, and use a fuse or circuit breaker. The 12-volt accessory circuit (powered by a step-down DC-DC converter), would normally always have a fuse - although the location of the fuse may not be very clearly labeled in many Chinese scooters.

As far as the traction power circuit (battery pack-motor controller-motor) a large capacity 200 amp or so fuse or circuit breaker is a good idea but not entirely necessary (one of my scooters doesn't have one). There is so much current capacity in the pack that the wiring is self-fusing - a short vaporizes the wire or connector (or the end of a stray screwdriver or wrench) at the point of the short in a fraction of a second - so starting a fire is not very likely unless the bike is made of some inappropriate overly-combustible materials. Although, ONE scooter I had had a mouse-nest of dry grass and mouse-hair in it - perfect fire-starting tinder - and of course mice can chew wires.

Is there any evidence of where the fire started?

Robert's speculation regarding the ignition switch is a good place to start. If the design involves switching the full 72 to 85 volt pack voltage using a off-the-shelf motorcycle ignition switch that was designed for no more than 14 volts, it is is a poor design.

LiFePO4 cells CAN contribute to creating a FIRE!-I Personally "tested" some 40 AH Thundersky cells by accidentally charging them to excessive voltage level of over 5 volts per cell, they got HOT, and vented highly FLAMMABLE gases, which IGNITED from the small spark created when power was disconnected!--Luckily, I had them in a safe place, and could quiqkly extinguish the flames, which were observed around the cell top vents, before any visible damage occurred. These cells no longer provide high current, but they do seem to retain a charge, although their usefulness is now very limited.You MUST protect against OVERVOLTAGE!---A similar cell, discharged to 1.4 volts, will not charge properly, as any attempt to charge it results in it getting VERY HOT, and I fear that if forced, it too could catch fire! If PROPERLY used, hazards should be minimal, but beware, things such as this CAN happen!

we are speculating that the battery pack was Lithium ion or Lithium polymer chemistry. (I will photo the 2nd bike batt pack and post photos) We ordered the LiFePO4, because we believed it is a more stable chemistry. Is that a valid assumption?

Hi Judy,

Just to make things more complicated, Lithium Ion and Lithium Polymer are merely cell formats, not chemistries

nearly all large format LiFePO4 cells are Lithium Ion
Some can be had in Lithium Polymer

It doesn't take as much for Lithium Cobalt or Lithium Manganese to catch fire, as LiFePO4.

A LiFePO4 cell can still burn, you just have to get it pretty hot first

If your bike was riding fine before being parked, its mostly likely the fire didn't start in the battery

These bikes usually either have no main fuse, or any fusing, or use AC rated circuit breakers.
That means if the battery were to short out, there's nothing to stop a fire

Was the bike on charge when it caught fire?

Matt

Odd, i have discharged a Thundersky LiFePO4 to zero volts then charged them back up to 3.7 volts. When discharged, they were swollen a bit, and liquid electrolyte could he heard. Recharging, (albeit at just 3 amps) the the swelling went away, the free electrolyte was re-absorbed, and thy did not get at all warm.

Yes, the electrolyte contains a flammable solvent (di-methyl carbonate) so if they were exposed to fire, or grossly overcharged, could catch fire - but nothing like a video of overcharged LiCoO2 I saw once - which burned like gunpowder.

The BMS does not have anything to do with managing discharge - only charging - with the exception of cutting power if a single cell voltage gets too low. Discharging the cells should not normally make them warm.

I do not recognize those white batteries or cells. Are the white things (cells?) in the plate-aluminum cradles the same as the ones underneath? Where are the terminal connections?

You need to provide a photo of the whole scooter, both sides, then close-ups.

The white color cell looks like HIPOWER

OK - What the picture shows just "clicked" in my head - they are views of the same thing from either side. The white cells are underneath and the white thing (plastic?) is an electronics enclosure on a shoddy jury-rigged aluminum heat sink (no cooling fins), and mounted where it will probably heat the cells up to damaging temperatures on warm days. I see two thick wires going in one side and three wires (motor phase wires) going out, so it is probably the motor controller. I would never imagine someone using a plastic case for any part of a controller - one needs to use all-aluminum, for heat conductance and also fire protection should a bad component go pfffft!

another photos of Hipower ,is it ?

Can you confirm - are those "cradles" with the white things aluminum or plastic?

If you are going to import and sell scooters from Chinese manufacturers - many or even most of which are quite unscrupulous, you really need to have a lot of technical knowledge and be quite hard-nosed in your dealings with them. You should expect to do a lot of "dealer prep" or you will have a lot of very unhappy customers.

Better yet, why don't you become a dealer for some reputable brands? Have you never heard of Vectrix, E-max, or Current Motor Company (look them up)?.

I will have my son remove the casing. The manufacturer told us this company: "The battery manufacturer is: XINXIANG HUANYU BATTERY CO., LTD" But I will check the 2nd bike. Thank you.

Hi NewAgeMa,
Where is your business located? It might help if someone is nearby to have a look at the bikes.
It appears from the fact that there is a tie-down screwed across the 5 white containers that there is where the batteries are contained, but they do not seem to be batteries themselves as I have never seen any Lithium chemistry cells with rounded corners as your pictures clearly show.
My guess it that the white containers have 3 or 4 cells in series inside, possibly multiple strings in parallel, so each container gives about 12V for a total of about 60V (5x12V) as pack voltage for each Bike. The voltage may be somewhat different, you would need to take a voltmeter to find the actual levels, they are probably present at the big yellow contact block with the big wires coming out.
As to the fire - I have been involved in one fire that happened to a pack with LiFePO4 cells, but the evidence suggests that there was a manufacturing defect in one cell in the middle of the pack, which had a strange fold in the internal structure and it appeared that is where the fire started... But most defects in packs have been either a bad contact that caused excessive heating of the surrounding material due to the large current flowing through, or a cell that had become unbalanced; was reversed or over-charged and its internal resistance had gone up to the point that it because warm during a ride from the power loss in the bad cell, even to the point that the plastic surrounding the cell melted. So it is not uncommon that a bad cell or connection can start a fire. That is why a good BMS cuts power when it sees temp go up or voltage sag.
BTW, I did browse the website of Huanyu and they have both Lithium-Polymer cells as well as LiFePO4, the latter also available as complete E-bicycle packs of 24V and 36V. But I would guess that you have those white containers filled with something like their 20Ah 3.7V Li-Poly cells as on the last line of this page: http://huanyubattery.com/en/cp.asp?page=3&id=5
When you click on the part number then you get a PDF with the specs and a drawing of the product.
Hope this helps.