21700 Vs 26650 Batteries

[idleprocess]

I'd like to see a side by side & top down photo of each battery, to understand their relative sizes.

Google Images delivers.

 

[orbital]

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I have both & use my 26650s' alot,, but if I had 2 seconds to choose between the two, I'd take the 21700

: all my cell purchases in almost 10 years now, have been unprotected :

 

[prof student]

: all my cell purchases in almost 10 years now, have been unprotected :

Why is that?

 

[orbital]

Why is that?

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My duration of use answers your question.

 

[ChrisGarrett]

Why is that?

People who have used li-ions for a number of years, who buy quality products and who don't run series lights, don't really have a need for cell protection circuitry, which is ultimately a point of failure.

Chris

 

[Katherine Alicia]

Protection circuits are Great! and really necessary for some applications, such as when you`re modding a light and testing it out on the bench, or you run them in Ican lights that have no circuitry (just battery, bulb and switch) if you accidentaly left one on with out protection you have to throw your new battery away or as mentioned running them in series (you really don`t want to reverse charge one of these!).
but other than that, you`re Much better off without them, and they`re more likely to fit your light as well! I have a bunch of protected 16340 batts that I can`t use because if I did manage to ram them into the tube, I`d never get them back out again! LOL

 

[WalkIntoTheLight]

Yeah, I almost always use unprotected cells, even in lights that take 4 cells in series. I'm just careful not to run the light after it gives a low voltage warning (in case the cells aren't perfectly matched).

I have some protected cells, and I'm generally unimpressed with them. IMO, the circuitry just adds resistance, and serves very little practical purpose. They're double the price, too.

Get lights with built-in low-voltage-protection, and you never have to worry.

 

[prof student]

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My duration of use answers your question.

Hate to burst your bubble (actually, I don't mind!!!! lol), but no it doesn't!

 

[prof student]

People who have used li-ions for a number of years, who buy quality products and who don't run series lights, don't really have a need for cell protection circuitry, which is ultimately a point of failure.

Chris

Wellllllllllllll, I've never owned any, sooooooo...................

 

[prof student]

I'm just careful not to run the light after it gives a low voltage warning (in case the cells aren't perfectly matched).

Well, I've never had any, so I have no idea about what the threshold is for running lights when battery is low, or at what point it would be considered too low & end up doing damage to the battery

I have some protected cells, and I'm generally unimpressed with them. IMO, the circuitry just adds resistance, and serves very little practical purpose. They're double the price, too.

Get lights with built-in low-voltage-protection, and you never have to worry.

So what is the difference between protected cells & cells that don't have that but do have built in low voltage protection?

 

[lumen aeternum]

Get lights with built-in low-voltage-protection, and you never have to worry.

So a series light with low voltage protection in its circuitry will prevent a good battery from being ruined if the other battery fails with high resistance? And it will prevent the good battery from pushing voltage into the bad battery and heating it up and perhaps a catastrophic exothermal reaction?

 

[orbital]

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Every Tesla car has a couple thousand 21700s' in it, do you believe every one of those cells has a pcb?

 

[idleprocess]

Well, I've never had any, so I have no idea about what the threshold is for running lights when battery is low, or at what point it would be considered too low & end up doing damage to the battery

I believe that 2.5V open-circuit is considered the threshold for a li-ion that should absolutely be disposed of with <3.0V considered troublesome. I generally cycle mine into the charger around 3.6V since operating voltage at that point under any significant load will be considerably less.

So what is the difference between protected cells & cells that don't have that but do have built in low voltage protection?

There is no such thing as a cell with built-in low voltage protection - that is the function of a protection circuit.

In general, a protection circuit performs 2 task at a minimum: under-voltage protection and over-voltage protection. Under-voltage prevents the cell from discharging itself below a danger threshold and over-voltage prevents a charger from over-charging the cell. Both of these were necessary for early applications shoehorning into A) flashlights that lacked any means of regulating their discharge voltage (i.e. 2x123A designs that happened to be capable of running within single li-ion's 4.2V-3.0V range and still needed for incandescent lights) and B) dumb chargers that lacked the means to terminate the charge at 4.2V.

Additionally protection circuits can limit current (sometimes needed for high-density cells with low max currents in the <3C range), and I believe that some will also cut power if cell temperature is too high.

Protection circuits are often eschewed by experienced users since A) they're something to go wrong, B) most LED flashlights of the last several years are built with LVP built in, C) chargers have been available for years with solid li-ion protocols and sensing capabilities baked-in, and D) they're generally not available for the high-current cells many high-performance flashlights demand.

 

[idleprocess]

So a series light with low voltage protection in its circuitry will prevent a good battery from being ruined if the other battery fails with high resistance? And it will prevent the good battery from pushing voltage into the bad battery and heating it up and perhaps a catastrophic exothermal reaction?

Short of taking per-cell voltage readings - ala a li-ion BMS system - there's no reliable way to prevent a single cell in a series from going too low and being charged by other cell(s) in the stack. This is what power tool battery packs do - and a large part of why they suddenly cut off when the pack is old or near the bottom of its charge.

Given the ... inconvenience ... of inserting a contact between cells in a typical tubular battery compartment, using protected li-ion cells is recommended for series lights. Lights with LVP generally run on single cells, there there's no ambiguity about state of charge. Some lights might manage LVP on multiple removeable cells - likely using a flat parallel compartment with all cell interconnects made by integrated conductors that can run sense leads to the driver/BMS - but I'm not aware of any.

Insofar as how Tesla packs work, they place 10s to 100+ cells in parallel in a module then line up modules end-to-end to hit their desired voltage. The vehicle's BMS takes readings at the interconnects between modules but takes no notice of individual cells, many of which can fail before a module's performance starts to suffer noticeably.

 

[WalkIntoTheLight]

I believe that 2.5V open-circuit is considered the threshold for a li-ion that should absolutely be disposed of with <3.0V considered troublesome.

It depends on the cell, but 2.5v is a good ballpark if you don't know otherwise.

But, for example, the spec sheet for the Samsung 30Q states that they can be recharged (slowly) even as low as 1.0v. So, read the spec sheet if you want specific safety tolerances.

I've also seen test reports that claim you can even recharge cells that have slight negative voltage (i.e., reverse-charged to below 0v). I certainly wouldn't recommend that, though!

 

[idleprocess]

It depends on the cell, but 2.5v is a good ballpark if you don't know otherwise.

But, for example, the spec sheet for the Samsung 30Q states that they can be recharged (slowly) even as low as 1.0v. So, read the spec sheet if you want specific safety tolerances.

I've also seen test reports that claim you can even recharge cells that have slight negative voltage (i.e., reverse-charged to below 0v). I certainly wouldn't recommend that, though!

I've seen more than a few cell harvesting pieces that are happy to recharge high-rate cells from 0V - braver souls than myself for sure.

 

[Lemurian]

The upcoming FourSevens 26650 flashlight looks pretty neat.

 

[lumen aeternum]

It depends on the cell, but 2.5v is a good ballpark if you don't know otherwise.

But, for example, the spec sheet for the Samsung 30Q states that they can be recharged (slowly) even as low as 1.0v. So, read the spec sheet if you want specific safety tolerances.

But you would need a "dumb" charger to do it, right? Don't almost all chargers "fail safe" below a minimum voltage?

 

[lumen aeternum]

The upcoming FourSevens 26650 flashlight looks pretty neat.

why? link?

 

[GraXXoR]

Sounds like those 46800 cells would be the bees knees for larger lights. I'd love a modern take on a 2D mag. Maybe a bigger head though.

I can definitely see the 46800 being epic for camping lights where a long life is the #1 requirement. Their size is also fine for non-pocket uses.

as an aside, I still do think it's a bit of a shame, though, that 26650 never got the love that the 18650 and 21700 got... The size is perfect for 1P handheld arrangements...