What in the hey is this component?

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I've started up a little hobby of taking apart laptop Lithium-ion battery packs that have kicked the bucket. Why? At work - I design some fairly similar circuitry and like to steal ideas "from the pros". Mostly it's interesting seeing what ICs and FETs they choose for these mass produced devices.

There's one part that I've encountered time and time again, and I simply can't explain it. It is always situated right above (literally above) or right next to two back to back FETs (or two paralleled back to back sets of FETs). It always has some sort of white crud between it and the FETs - probably a thermal goop of some sort. It is a three pin device. They all look about the same, though the package varies from board to board. Sometimes some of the pins show shorts to each other, sometimes not. This may be due to shorts on the PCB - I've never pulled the component to find out. I've seen this on PCBs that are only a year or so old, and most recently, on a PCB that was something like 10-15 years old.

I've attached some photos of it. The 8 pin SOICs are FETs. Also note the flux residue on the PCB on the leads - messy enough that it could have been hand soldered maybe?

Anybody have any ideas as to what this bugger might be?

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One more pic.

A colleague suggested it's some sort of TVSS. But I typically think of those as being two pin devices - and I don't see why it'd need to be thermally connected to the FETs.

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My hunch is temperature sensor. But only a hunch.

I've taken apart ONE protection board for LiIon batteries and saw nothing like this thing.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Maybe a polymer fuse of some sort?

Tom Pappano
Tulsa, Oklahoma

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A thermal fuse methinks - these usually look like a square.

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Kartman wrote:
A thermal fuse methinks - these usually look like a square.

The thing in the background of the last picture with a yellow wire connected to it - that's a thermal fuse in series with the battery pack.

Also shouldn't a thermal fuse always have a short across it, assuming it isn't fried? And what sort of thermal fuses are 3 terminal devices? There is no question that that part is a 3 terminal device.

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Maybe if you sit down and trace the circuit, the schematic will give a better idea. My money is on temperature sensor.

A three terminal device is mechanically more stable than a two terminal device; we can't rule out that possibility.

If you think education is expensive, try ignorance.

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emuler wrote:
Maybe if you sit down and trace the circuit, the schematic will give a better idea. My money is on temperature sensor.

A three terminal device is mechanically more stable than a two terminal device; we can't rule out that possibility.


There's tons and tons of parts on these PCBs... Tracing it out would take me weeks.

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Not all of it, of course; just the part which is connected to this thingamajig. One pin must be GND. One might be V+.

E.g. Temp sensor: GND, V+, uC.

If at least two of the pins are connected to fat power traces/lands, then the odds for it being a thermal fuse increase (one pin might be to sense the failed state).

If you think education is expensive, try ignorance.

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emuler wrote:

A three terminal device is mechanically more stable than a two terminal device; we can't rule out that possibility.

I think there is a possability of this as well, that 3 are used for mechincal reasons. Look at small002 and small003, it appears as though the reason for the thick leads and solder contacts are to put some pressure on the device to improve heat transfer. I would go for a temp sensor as well, checking if it is a thermal fuse should be simple with an ohm meter.

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This is a thermal fuse + resistor unit. One was made by Semitec. Here is info on it...

http://www.electronicspecifier.c...

Brad

I Like to Build Stuff : http://www.AtomicZombie.com

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AtomicZombie wrote:
This is a thermal fuse + resistor unit. One was made by Semitec. Here is info on it...

http://www.electronicspecifier.c...

Brad


Awesome - I knew I could count on one of you all for finding this thing.