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Old 07-26-2021, 02:37 PM   #1
zman78
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Default J107 Tantalum cap burning inside a USB hub?

I have a USB hub specifically to fit in my car. It stopped working and i saw a burned J107 capacitor (see picture). It looks like it might have briefly caught fire as you can see the plastic under the capacitor deformed. It was hot enough that the other side (outside of the plastic box) also melted a little.

I'm curious - does anyone know what might cause a cap like this to catch on fire like that? Is it just a random manufacturing defect that can happen to anyone, or was there a design issue with the USB hub?

Also, does anyone know if these can burn hot enough to actually ignite a fire? I.e., was all that was ever going to happen was the melted case, or was there a possibility of something more serious?

The hub is plugged into the car 24/7, and likely it burned while unattended. So in case the manufacturer replaces it under warranty I wanted to know if there are any safety concerns with having something like this always plugged in?
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Old 07-26-2021, 02:38 PM   #2
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Default Re: J107 Tantelum cap burning inside a USB hub?

Oops for some reason the photo didnt post in the original, I'm attaching the photo again.
Attached Images
File Type: png Jeda1.PNG (1,022.2 KB, 49 views)
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Old 07-26-2021, 03:10 PM   #3
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Default Re: J107 Tantalum cap burning inside a USB hub?

yes it's possible to get hot enough to catch fire, likely it's due to manufacturer defect whether it's a bad capacitor or an improperly assembled PCB. MLC and tantalum capacitors are known to go up in smoke.

Whether there's enough stuff around it to fuel the fire is the question whether it goes beyond the device. Most electronics stuff are housed in plastic that's made self extinguishing for this reason.
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Old 07-27-2021, 03:28 AM   #4
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Default Re: J107 Tantalum cap burning inside a USB hub?

100uf 6.3v???
bastards!!!

thats under-rated for a tantalum - you really need a 16v part there.
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Old 07-27-2021, 10:13 AM   #5
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Default Re: J107 Tantalum cap burning inside a USB hub?

Ahhh interesting, so the USB is a 5V power supply, and the J107 is a 6.3 volt cap?

So do you think there wasn't enough voltage margin for spikes that may have caused this failure?

Last edited by zman78; 07-27-2021 at 10:13 AM.. Reason: Typo / Voltage 6.7 -> 6.3
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Old 07-27-2021, 12:07 PM   #6
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Default Re: J107 Tantalum cap burning inside a USB hub?

exactly.
you need some headspace with tantalums because overvoltage or reverse-polarity will make them burn.
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Old 07-27-2021, 12:54 PM   #7
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Default Re: J107 Tantalum cap burning inside a USB hub?

Tantalum caps can fail that way. Circa 1997, after a burning tantalum cap led to a large computer center being shut down (and a VERY POed customer!), Sun Microsystems banned tantalum caps from all new designs and required a partial redesign of then-current equipment.

At another former employer (Brandt Electronics, now defunct I think) I saw several times a burnt tantalum cap damage a DC-DC power module so badly that the module has to be scrapped. There, too, the company designed tantalum caps out of that product line.
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Old 07-28-2021, 04:32 AM   #8
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Default Re: J107 Tantalum cap burning inside a USB hub?

it is rare though,
apple and sgi used to pack there boards with tants and you never heard of a fire in one.
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Old 07-28-2021, 07:48 AM   #9
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Default Re: J107 Tantalum cap burning inside a USB hub?

Ooow that could have been very nasty :-(
Maybe put a switch and fuse in series with the +12v input, so you can turn it off.
Im happy it didn't take your car with it :-D
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Old 08-01-2021, 07:38 AM   #10
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Default Re: J107 Tantalum cap burning inside a USB hub?

Quote:
Originally Posted by stj View Post
it is rare though,
apple and sgi used to pack there boards with tants and you never heard of a fire in one.

I once saw macbook air with burnt tant (cpu vcore) anyway not pcb or nearby parts burned
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Old 08-01-2021, 09:05 AM   #11
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Default Re: J107 Tantalum cap burning inside a USB hub?

vcore would have been an smd polymer cap
the black ones with laser-etched numbers
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Old 08-04-2021, 01:33 PM   #12
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Default Re: J107 Tantalum cap burning inside a USB hub?

Quote:
Originally Posted by zx8401 View Post
Ooow that could have been very nasty :-(
Maybe put a switch and fuse in series with the +12v input, so you can turn it off.
Im happy it didn't take your car with it :-D
The problem is that when it occurred, I wasn't in the car. The car is constantly powering the USB port to record data to a dashcam, so even if there was a switch on it -- most likely the failure happened when I wasn't there to notice it.

Hopefully the manufacturer put the appropriate fire-resist/self extinguishing plastic around the USB hub. (Maybe they did since the plastic only melted and didn't fully catch fire).
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