# What Caused Hoverboard Lithium Ion Fires? [closed]

Purpose of this question:

In the interest of making my own BMS circuit designs safe and robust, i seek to understand causes of BMS failures in known systems. I'm not seeking consumer advice or general tips.

History:

## Fact

The only reason LiPo's catch fire is they reach a critical temperature where thermal runaway causes unavoidable fire. But there are many causes of overtemp, some of which are unstoppable such as membrane leaks.

A Thermal sensor on each cell is good insurance unless the short is internal before the microwire fuse. ( even if there is one on each cell)

Examples of counterfeit batteries (substandard)
Which ones don't have them? Probably the cheap ones that went up in flames.

Why are the root causes not publicized?

Even if you were Samsung, would you want everyone to know why? Their mechanical tolerance stackup was too large that caused cell laminate to puncture and caused a cell self-short. Others under internal pressure with thermal duress from charging and talking at the same time or long after being dropped. (face explosion)

It just isn't good for your reputation.

Another reason is poor matched voltage cells result in mismatched ESR which under load means mismatched temp. rise of the battery. The other is aggressive mechanical stress to the batteries. ( I remember my 1st cordless drill that my old g/f threw down carpeted stairs and never worked properly again )

• Each cell must have a good active balancer if you want extended life on the battery and this adds a SMPS to each cell to bypass when under/overcharged and adds to the cost.

• Passive balancers are inefficient and rarely handle more than 5~10% Ah capacity mismatch and no cell balancers or poor quality cells are cheap and a good reason to follow the analyst's advice.

It also requires much tighter capacity and ESR balance on battery cells and this takes a lot of know-how from the supplier. Considering the imbalance accelerates to 100% when dead and << 1% when new, the rate of discharge on each cell if not actively balanced during charge AND discharge using SMPS bypass switched inductors which cost a lot, I think of a lot of design reasons why they can burst into fire. Overweight-user, over accelerated, unprotected from mechanical shock that can deform electrode foil and short out etc.

Reminds me of the cheap 5000 mAh rated LiPo cells on Bangood site, that were only 1000mAh. Don't go cheap on new unknown products.

## p.s.

Having been in R&D, Mfg DVT Test Engineering (& Mgr), Mfg Eng Mgr of Electronic products and design Services Mgr over a 40 yr span, I can say with high confidence that;

A design is only good as its specs with verified MTBF to those specs (Design Validation Test) with Process Verification Test plans (PVT) on all components, sub-systems and final product. Any missing or overlooked specs and verification tests makes them all high risk.

I have done ever test imaginable (DVT) on the reliability of HDD's from dry ice to high altitude, vibration with Radar pulses and although not a health risk can be a financial risk if bank records are corrupted. ( Circa 80's.) I've done the same on many other technologies, since then.

If the same tests are not done to hoverboards with ORT ( On going reliabilty test plans) there is high risk of repeat failures. Just ask if you need a consultant for better specs than UL's.

• Doesn't address design of the specific devices in the question. As i mentioned in the question, offer details about the specific devices, not "general tips". It's ok to say "i don't know" :D – johny why Dec 7 '17 at 1:19
• You speculate about what MIGHT have caused the problem in hoverboards, but that's just speculation. Comments like "don't do such and such" is consumer advice. StackExchange Electronics is not a consumer advice resource. – johny why Dec 7 '17 at 1:25
• "mechanical tolerance stackup was too large... Others under internal pressure with thermal duress from charging and talking at the same time" Do you have any data or documentation to back up that claim? Or are you just speculating? – johny why Dec 7 '17 at 1:35
• A possible cause is confused sensor performance, such as the temperature measurement sensors, or current sensors or voltage sensors. In interference-laden situations, what can anyone trust from an important sensor, if the magnetic and electric interferences are not well controlled. – analogsystemsrf Dec 7 '17 at 3:33
• There is a difference between speculation without experience and that with. – Tony Stewart Sunnyskyguy EE75 Dec 7 '17 at 4:39