LiFePO4, drop in replacement for NiMH lights?

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Pablo de Llama
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LiFePO4, drop in replacement for NiMH lights?

I'm going to use a Thrunite Ti3 as an example in this question, because I have one.

The Ti3 driver is specified for a voltage input of between 0.9V and 3V , according to Thrunite. Yet some people have used 4.2v 10440 Li-ion cells, sort of successfully. Sometimes it doesn't break anything, sometimes it does. If it does work, heat is a problem due to increased brightness, and the circuitry lifespan is probably reduceed. It appears that the Boost Driver(I think?) inside can go into a sort of direct drive operation.

 

What about LiFePO4 cells? Their max charged voltage is about 3.6v, which is about where you'd consider a 4.2v Li-ion cell discharged.

Will they break anything? What are your experiences with them?

jmm244
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Sounds like you already know the answer. Since the LiFePO4 is still above the stated design voltage, some Ti3s may still blow up, and some may not. If you’re one of the lucky ones whose light survives, you are rewarded with a whole ~280mAh(!) of battery capacity.

I tried some of the those 10440 LiFePO4s in my MecArmy PT10 and the runtimes were even more ridiculous than a 350mAh 10440 Li-ion, as expected.

The ThruNite Ti3 is a very nice little light but it’s never going to be a lumen monster so why not just feed it something that will give it the best chance of working when you need it, like Eneloop Pro 950mAh AAAs (the black ones)?

Pablo de Llama
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I don’t really care about decreased runtimes so much, as I already carry a spare cell. Smile

My train of thought was on the lines of safely getting more lumens out of my Ti3, though now I realise that is a bit ridiculous, as even an extra 30 or so lumens on top of 170 lumens is not very noticeable. Big Smile

Lightbringer
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I’m using LFPs now for a lot of AA lights, no major issues. Haven’t really A/B tested them (too long between swapping) so can’t really measure differences between alkaleak/NiMH/LFP.

I got a bunch of Baseline LFPs from Amazon, rated 600mAH, but they seem to clock in at only 490mAH or so on my almighty Miboxer. Still, they’re okay, and the price wasn’t too bad.

On some cheaper lights, meant for alkies, sticking in a higher voltage cell will still work, but it pops something so that from thence on it’ll only work on higher-V cells, no more on alkies.

Btw, their running voltage is a nice flat 3.2V, not 3.6V. 3.6V is the CV phase of charging, the very tail end of an otherwise flat terminal voltage. Just letting them rest will let the voltage settle back down to around 3.2V.

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jmm244
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Lightbringer wrote:
I’m using LFPs now for a lot of AA lights, no major issues.

I agree and have also been using LiFePO4s in some of my AA/14500 lights.

Just to be clear, it’s the 200-280mAh AAA/10440 size LiFePO4s applicable to the OPs light that I have come to consider ridiculous in terms of runtime/capacity and have more or less abandoned. They also didn’t provide enough current to make a triple emitter mini-monster like a MechArmy PT10 really happy.

jon_slider
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Pablo de Llama wrote:
My train of thought was on the lines of safely getting more lumens out of my Ti3

consider a light built to take LiIon, such as the reylight pineapple
bear in mind they do not have built in overdischarge protection, neither does the Ti3

jmm244 wrote:
They also didn’t provide enough current to make a triple emitter mini-monster like a MechArmy PT10 really happy.

that makes sense
the PT-10 spec for Working Voltage: is 2.5-8.4V

The PT series are LiIon only, not an Eneloop compatible driver
ICR protected 10440 battery: 3.7V 320mAh is included
fwiw the PT series do not have built in Overdischarge protection.