Lithium OVP

[robotix3]

I am designing a 2-cell lithium polymer battery protection/charge management board. It is a software-defined board so I wanted to have some secondary over-voltage protection on each cell (with a circuit that I didn't design, to make sure I don't have any fires). I found the TI bq2945xxes chips chips (datasheet) and it seems exactly what I need. When the IC detects an over-voltage condition, it triggers a FET to blow a fuse.

Annoyingly, the datasheet doesn't say anything about this mystery fuse, it just says it blows one and shows a schematic with a three pin fuse with a heater. After reading a forum post at TI forums it seems that getting one of these fuses is a big pain, since they only seem to be available in high volumes. I just don't get why the IC is so openly available when the main aspect to the circuit is impossible to get a hold of, even the EVAL board doesn't come with the fuse...

So, is there an easy way of getting one of these fuses? Or is there a reliable equivalent circuit for this? (needs to be able to handle ~20 Amps)

[NiHaoMike]

NC relay with a SCR to activate it until the external voltage is removed?

[robotix3]

NC relay with a SCR to activate it until the external voltage is removed?

That would work, but it would be too large and too expensive for my application.

[robotix3]

There has to be a device out there that behaves like one of these fuses. Maybe something like a spring loaded contact that is released by melting something that is holding it down (like when dave used the resistor to melt the fishing line holding down the mouse trap arm). Of course I could build this but it would be too large and expensive to be practical.

[amyk]

Have you tried looking on AliExpress?

[robotix3]

Have you tried looking on AliExpress?

Yes, and I have found some that claim to be the parts I need, but they look counterfeit.

Why don't just use a Li-ion protection board? They have a pair of back to back FETs connected in series, to cut off both charging and discharging current.

I didn't want to add any more FETs since this would be a single use emergency device. Also, my board already has the functionality of these off-the-shelf boards. I also need everything to be on one PCB.