Author Topic: What is this device?  (Read 1015 times)

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Offline PrehistoricmanTopic starter

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What is this device?
« on: February 25, 2020, 11:41:09 pm »
I found this odd looking 3-terminal device in a laptop battery pack. The board does the charge controlling.

Is this some kind of thermal fuse? It's glued onto these two power FETs. But why 3 terminals for a fuse and not 2?

It's been a long time since I took this picture. I might not have the board any more and I certainly don't have it immediately on hand to do any tests on, sorry.

Online ataradov

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Re: What is this device?
« Reply #1 on: February 25, 2020, 11:52:12 pm »
It looks like there is F1 poking from under the pin. It is likely to be a thermal fuse. The third terminal is likely for mechanical reasons. It does not seem to be connected anywhere as well.
Alex
 

Offline xavier60

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Re: What is this device?
« Reply #2 on: February 25, 2020, 11:53:39 pm »
I used to think it's a fuse with a built in heater. The fuse can be instructed to go open by energising the heater part. The idea is so that the BMS can blow the fuse without needing a crowbar circuit that can handle the full fusing current.
I used to be able to find info with a Google search, today I find nothing so far.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline xavier60

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HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 
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Offline Cerebus

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Re: What is this device?
« Reply #4 on: February 26, 2020, 12:08:39 am »
I used to think it's a fuse with a built in heater. The fuse can be instructed to go open by energising the heater part when the warranty timer runs out.

TFTFY
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline amyk

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Re: What is this device?
« Reply #5 on: February 26, 2020, 01:24:09 am »
 
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Offline ArthurDent

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Re: What is this device?
« Reply #6 on: February 26, 2020, 02:45:54 am »
Yes, it is a fuse as everyone has said. What is strange is I've never seen one before today. I bought a battery pack at GoodWill for cheap that I bought to get the 18650 Samsung cells for other projects. When I dismantled (read as ripped open) the battery pack I got 12 good cells and I saw the controller board that had the same thermal fuse. Here's a photo of the one I just discovered. The fuse is not glued to the chips but the white hard pasty stuff is silastic that is used all over the batteries and board to keep them from being loose in the plastic case.
« Last Edit: February 26, 2020, 02:54:14 am by ArthurDent »
 

Offline PrehistoricmanTopic starter

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Re: What is this device?
« Reply #7 on: February 26, 2020, 10:53:35 am »
Yes, it is a fuse as everyone has said. What is strange is I've never seen one before today. I bought a battery pack at GoodWill for cheap that I bought to get the 18650 Samsung cells for other projects. When I dismantled (read as ripped open) the battery pack I got 12 good cells and I saw the controller board that had the same thermal fuse. Here's a photo of the one I just discovered. The fuse is not glued to the chips but the white hard pasty stuff is silastic that is used all over the batteries and board to keep them from being loose in the plastic case.

That's pretty crazy how you just found this identical device.

Thanks for the responses guys. It also looks like it's made specifically for this application - in laptop BMSs - due to the elongated shape.


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