TN31/K40 Melted Springs

[ryansoh3]

Hi all,

Has anyone else experienced the battery carrier springs overheating and not returning to their full length after being compressed?

I first noticed this with my modded K40 with a solder bridged sense resistor. After some fiddling, I concluded that it was the driver pulling a lot of current from the cells when the cells are nearly depleted to supply constant current to the LED. I put solder braid on the three battery carrier springs and no issues since then.

This also happened to a modded TN31, no surprise there. The springs had melted and the batteries were rattling around because the springs were not exerting any pressure on them.

I did a quick search but no one seemed to have this issue?

[Ejected_Filament]

You mean the springs have compressed, collapsed or sagged due to heat. Not actually melted. That would be scary…

[Tom_E]

Been hearing vinh is now wiring up the battery carrier springs - maybe this is why. Those drivers are pretty incredible. Also, I believe if you copper braid/wire the springs, the cells will last longer - there seems to be a big difference between the power sucked from the cells, and power actually provided to the LED when the resistors are bridged.

[ryansoh3]

@Ejected Filament

You mean the springs have compressed, collapsed or sagged due to heat. Not actually melted. That would be scary…

Haha yes, that’s what I meant.

@Tom E

Been hearing vinh is now wiring up the battery carrier springs - maybe this is why. Those drivers are pretty incredible. Also, I believe if you copper braid/wire the springs, the cells will last longer - there seems to be a big difference between the power sucked from the cells, and power actually provided to the LED when the resistors are bridged.

I see, thanks for the info.
I simulated a drained cell under sag 3.5V x 3 = 10.5V and the modded driver was pulling a scary amount of current, and I remember the springs heating up significantly. It would be nice to have some of those magical copper beryllium springs without the need for copper braiding.

[fatlokwok]

Please refer to:

Do you have a firsthand Li-ion accident story?

Ever since I ordered a 2x18650 headlamp on ebay yesterday, I have been reading a lot about the dangers of Li-ion on the Internet. I understand the stated risks of avoiding rapid charge, discharge, and heat buildup. But I don’t see “Hey, I had a Li-ion explode on me” type of firsthand experiences. (Maybe they are not around to tell their stories :-).) Anyway, to get a sense of how common these incidents are, I thought I’d pose a question to BLF as there seem to be so many heavy duty Li-ion users…

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[pinkpanda3310 (Pinky)]

I’ve had softened springs in a different light. I don’t know what level of amps it seems to kick in but either way you lose energy from heating up the spring.

[comfychair]

I have seen springs glow like an incandescent filament - in a working setup, not something that accidentally got shorted. 5x XREs in parallel direct driven by 8.4v...

[Old-Lumens]

Spring steel is great for resistance and of course, the more power you try to punch through it, the hotter it gets. Yep, I have seen them get hot, turn red, turn black and loose all their spring tension. Copper braid is about the only easy answer we have.