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Samsung Knew a Third Replacement Note 7 Caught Fire On Tuesday and Said Nothing (theverge.com)
If you had started to feel sympathetic for Samsung, or safer with the Note 7, its latest flagship smartphone, don't be. Another replacement Samsung Galaxy Note 7 has caught fire, making it three of such incident this week alone. Read how poorly Samsung has dealt with the situation, via The Verge: This one was owned by Michael Klering of Nicholasville, Kentucky. He told WKYT that he woke up at 4AM to find his bedroom filled with smoke and his phone on fire. Later in the day, he went to the hospital with acute bronchitis caused by smoke inhalation. "The phone is supposed to be the replacement, so you would have thought it would be safe," Klering told WKYT, saying that he had owned the replacement phone for a little more than a week. "It wasn't plugged in. It wasn't anything, it was just sitting there."The most unsettling part is that Samsung knew of Klering's phone, and didn't say anything.
I'm beginning to wonder if it's an issue with something other than just the battery. Otherwise Samsung would be incredibly idiotic to send out replacement parts that suffer from the same problem. The alternatives are that a massive mistake led to sending out defective units as replacements without fixing them first, or that Samsung's battery supplier (I think I read that the source all or most of them from third parties) wasn't fully aware of the extend of their problems and have shipped more bad batteries.
The full Samsung text message was "Just now got this. I can try and slow him down if we think it will matter, or we just let him do what he keeps threatening to do and see if he does it"
Someone Mr. Klering conveniently failed to share with the news station what exactly he was threatening to do against Samsung that lead to that text message exchange between Samsung employees and which accidentally reached him instead. I'm guessing it was something more than just "I'm going to share what happened to my phone with the authorities".
So what is the real culprit here? I thought it could have been from using the wrong charging IC or someone in the battery department changing the chemistry and not telling the EEs. But they are catching fire without charging.
Lithium chemistry batteries are finicky little bastards. They are not just dangerous from over-charging (or charging too fast), but also from over-discharging and discharging too rapidly. If they are drawing 1A from a battery that is only designed to handle 1/2A, or worse, if their control circuitry allows the battery to fall below a minimum voltage, then the batteries can go into runaway thermal overload. The worst part is that all of the various factors change with pressure, so at 35k feet, you have to be far more conservative with the batteries to avoid a fire. With Li batteries, getting the extra capacity out of them can be very dangerous, and it only take a small error to end up with fires or explosions. Worse still parameters can vary widely from individual battery to individual battery and is made far worse when the batteries are sloppily made.
It should also be noted that it is unlikely that the phones have a dedicated battery monitoring chip as these cost a couple bucks, even in large quantities, and all they really are is a small microprocessor and a couple cents worth of transistors. Since cell phones already have the processor, they just use that, and add the couple of small transistors they need to handle the charging and discharge monitoring.
The root problem could be as simple as a badly chosen set of constants for cutoff voltage and thermal protection, or could be more insidious, such as a thermal protection sub-routine that doesn't work properly because at shutdown the processor looses power and reboots, thus continually drawing power from the battery.
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If you find yourself stranded on a desert island with an iPhone and no bars, you're screwed. If you have the superior Samsung phone, just activate the signal flare feature when a plane goes by.
Over here in facts-based land, the Note 7 has a MAX77838 keeping track of power.
The MAX77838 is a power management IC. It claims to have some other circuitry for battery management, but since MAXIMs website does not acknowledge that part number, we have no way of knowing what it really has or doesn't have. All outward appearances would suggest that it is a custom chip for Samsung (probably used in several of their product lines). Personally, I expect that the MAX77838 is similar to the MAX77829 (PMIC + single cell Lion charging circuit). This would make some sense since it looks like Samsung elected to use an external PMIC, and since they had to have one anyways, getting one that had the charging circuit built in would not be that big a deal. Unfortunately for Samsung, the charging circuit has to be relatively tuned to the specific battery being used. Generically designed Lion chargers have a habit of failing. (So much so that Tenma actually ships many of their battery chargers with a fireproof pouch to put the battery in while charging it...
This just goes to show how stupid Samsung is for designing it this way. Since the fault lies either with the Custom Maxim Chip, with the battery itself (or a mismatch between the two), Samsung has backed itself into a corner. They cannot just replace the defective Maxim Chip with an off the shelf component because there is no drop in replacement or they wouldn't have had Maxim build a custom chip in the first place. Nor can they simply change the battery easily, as the batteries are manufactured to spec as well.
If samsung had offloaded the charging and battery management control into software running on one of the processors in the phone, then they would likely have been able to fix the problem with a firmware update. Now, because they did not have the sense to do what everyone else is doing, they are fucked.
The best kept open secret in the Phone / Tablet world are the PSOC processors that are used extensively for all of the low level work in these devices. Cypress sells nearly as many processors as Broadcom, and nobody has ever heard of them. Their processors come with built in PMIC, Capacitive touch sense (which is why everyone started using them in the first place), and a host of other powerful features that reduce part count and unit cost. I have personally designed a half dozen devices that used them, two of which had battery charging circuits and charge control software. The irony is that the PSOC processors cost cost about $5 each and they are full featured processors while the Maxim ICs Cost more than that and are just a PMIC.
TLDR: Samsung is staffed by incompetent engineers. Its no wonder they have exploding phones, their engineers designed a phone with at least $5 more parts than they should have had, but skipped on the thermostat protection on the battery to save $0.50. If they used this same chip in the S5, then they lost more than 60 million dollars in excess unit cost in just the first three months of sales, and now with the S7, its going to cost them billions.
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