Protected vs unprotected 18650 batteries ?

Scarface26 · May 4, 2014

I'm new to LED flashlights and this forum, but have recently purchased a Fenix PD35 (GREAT, by the way) and have been reading up on batteries. Why would someone choose to purchase an unprotected 18650 battery for use in their flashlights? It seems that a battery with a protection circuit would be a much better choice.

gravelmonkey · May 4, 2014

Scarface26 said:
I'm new to LED flashlights and this forum, but have recently purchased a Fenix PD35 (GREAT, by the way) and have been reading up on batteries. Why would someone choose to purchase an unprotected 18650 battery for use in their flashlights? It seems that a battery with a protection circuit would be a much better choice.

Unprotected is cheaper and more 'reliable' in the sense that there's less to go wrong. They're also smaller in size so more likely to fit.

Personally, I prefer protected cells; I've harvested a few laptop battery packs but use the cells as backup-backups.

Edit: I should clarify that the above is regarding LiCo Cells. For IMR and LiFePO4 cells, they're considered 'safe chemistry' so a protection circuit isn't needed.

tripplec · May 4, 2014

Scarface26 said:
I'm new to LED flashlights and this forum, but have recently purchased a Fenix PD35 (GREAT, by the way) and have been reading up on batteries. Why would someone choose to purchase an unprotected 18650 battery for use in their flashlights? It seems that a battery with a protection circuit would be a much better choice.

No reason not to go protected. Verify the length and buy proven cells. Why someone wouldn't is NOT because of price. There aren't expensive. Those people must think they can get away with it until all goes wrong. Much like with an without a condom, you have to know when to quit.

mcnair55 · May 4, 2014

For single cell use i have no issues using an unprotected cell but for more than one cell i would only use protected, and only ever buy protected for either for ease of use.

thedoc007 · May 4, 2014

Since your question was general, I'll take a stab at it. There are some lights that REQUIRE an unprotected cell to function properly. For my TK75vn, for example, which was current boosted, my standard protected cells would not maintain turbo mode. After just a few seconds, it would step down. So obviously I had a good reason to go unprotected in that case.

It is a fact that protected cells definitely are more expensive...maybe not by a lot, but to some people it makes a difference.

Theoretically the protection circuit always draws a little power from the battery, even when you aren't using it. This can lead to faster self-discharge. And it does reduce efficiency slightly...any time you make a circuit more complex (i.e., adding a protection circuit) it is absolutely inevitable that you will lose some efficiency. However, modern high-quality cells have VERY low self-discharge with or without the circuit.

Another reason is the size...the protection circuit usually adds at least 2-3 mm to the length of the cell. And in some cases, it adds almost 5 mm. This does lead to issues in the real world...some lights have tight tolerances, and adding just that little extra length can mean the cell doesn't fit at all.

Another reason is that the protection circuit can fail. Unprotected cells are just a simpler design.

In summary, I personally would recommend protected cells if they will work for your specific uses. Never a bad idea to have an extra safety feature. But unprotected cells clearly do show some advantages. Which one is better depends on the individual user.

RetroTechie · May 4, 2014

Personally I've always had a preference for things that aren't more complicated than they absolutely, necessary must be. And like thedoc007 said, a protection circuit introduces another potential point of failure. That said, Li-ions are not as foolproof as NiMH's or alkalines. And the chances of a protection circuit failing should be pretty slim compared to the chances of other stuff around a battery failing. So there's good reasons to use protected cells.

For single-cell lights and if you know what you're doing, unprotected cells are okay. If not (and for multi-cell lights, specifically: series configuration), better use protected cells. At least until you have a bit more experience using Li-ions. And have read a few of the horror stories... :poof:

:devil:

18650 Li-ion batteries pack a lot of punch, and deserve some respect. Choose & treat them with care, and you'll be fine.

StorminMatt · May 5, 2014

Also keep in mind that many lights have built-in overdischarge protection. And typically, this built-in protection is actually more conservative than the protection in protected batteries (ie it cuts power at a higher voltage). This eliminates ALOT of the need for protected batteries.

vicv · May 5, 2014

Personally I rarely use protected cells but mostly my cells are all Imr. That way I can use smaller cells to power powerful lights. Like an 18350 for a 4A draw xm-l or 2x 18350 to power a p91. I really don't care about the fact that lico cells have higher capacity as I charge my cells very often. Usually they're at 3.8-3.9v when they go on the charger. Get a good charger and take responsibility for your cells and the protection circuit is unnecessary

Tobias Bossert · May 9, 2014

There is another benefit of protection board build in a cell:
It makes the cell short circuit resistant!
If you use a battery connected to the device via a cable you should use protected cells to avoid hasard in case of cable failure under all circumstances.
In any case you should avoid to have a short circuit with unprotected cells - it could be dangerous even if the short circuit lasts only for a short time.

vicv · May 9, 2014

Very good point. I'll admit it here and I'll probably be ridden for it but was a stupid mistake. I use Imr cells for vaping as well as flashlights. So I carry extra 18500s with me. I always put them in a case in my lunch bag. Well one morning after not enough sleep I just grabbed a couple extra cells and put them in my pocket which really is fine. Unfortunately later I threw a bunch of change in that pocket:fail: so I'm walking around and all of a sudden my pocket is about a million degrees. Quickly emptied my pocket on the floor and half the coins and the one battery were too hot to hold. And I've years of experience with these and know better but screw ups happen. Protected cells would've avoided that. But they can't provide 6a regular use either

HKJ · May 9, 2014

vicv said:
Protected cells would've avoided that. But they can't provide 6a regular use either

Some protection does first trip at currents above 10A.

6A for short bursts is fairly easy to find, you do not need the protection much above 6A to handle that. For batteries that can continuous deliver 6A you need batteries with a trip current above 7A.

You can find the trip currents in my battery tests.

vicv · May 9, 2014

Ya there's cells that can handle it but not 18500 I think. And even then they wouldn't provide the voltage I'd need. Imr cells are just better for vaping application. Just don't put loose li ion cells in your pocket full of change!

InspectHerGadget · May 14, 2014

StorminMatt said:
Also keep in mind that many lights have built-in overdischarge protection. And typically, this built-in protection is actually more conservative than the protection in protected batteries (ie it cuts power at a higher voltage). This eliminates ALOT of the need for protected batteries.

It sounds like the protected cells would be better then as it offers safety and potentially more useable capacity.

Unless I misunderstood, it sounds like an point in favour of protected cells.

Aside from size, for stock torches, I don't see any advantage to using unprotected cells unless you simply enjoy rolling the dice. Maybe there is a price advantage?

thedoc007 · May 14, 2014

InspectHerGadget said:
Aside from size, for stock torches, I don't see any advantage to using unprotected cells unless you simply enjoy rolling the dice. Maybe there is a price advantage?

If you read the other posts in this thread, you'll see that several advantages of unprotected cells have already been covered. And yes, they are cheaper.

psychbeat · May 14, 2014

Idk - the protection adds a safety feature in some ways and a hazard in others.
If you've ever had a protected cells thin little "positive strip" short on you you'll know what I mean.
Mine burned thru the wrapper & smoked like crazy.

The other thing is instant cut off.
My p60 led modules have low voltage warning with a flicker every few seconds which is preferable to complete cutoff when riding a bike on steep mountain trails in pitch black

I'm not saying protected are worse in all cases but they're definitely not safer in all cases either.
It's a trade off like most things.
I personally have only been buying raw cells like the new panny PFs.

funkychateau · May 14, 2014

thedoc007 said:
Since your question was general, I'll take a stab at it. There are some lights that REQUIRE an unprotected cell to function properly. For my TK75vn, for example, which was current boosted, my standard protected cells would not maintain turbo mode. After just a few seconds, it would step down. So obviously I had a good reason to go unprotected in that case.

It is a fact that protected cells definitely are more expensive...maybe not by a lot, but to some people it makes a difference.

Theoretically the protection circuit always draws a little power from the battery, even when you aren't using it. This can lead to faster self-discharge. And it does reduce efficiency slightly...any time you make a circuit more complex (i.e., adding a protection circuit) it is absolutely inevitable that you will lose some efficiency. However, modern high-quality cells have VERY low self-discharge with or without the circuit.

Another reason is the size...the protection circuit usually adds at least 2-3 mm to the length of the cell. And in some cases, it adds almost 5 mm. This does lead to issues in the real world...some lights have tight tolerances, and adding just that little extra length can mean the cell doesn't fit at all.

Another reason is that the protection circuit can fail. Unprotected cells are just a simpler design.

In summary, I personally would recommend protected cells if they will work for your specific uses. Never a bad idea to have an extra safety feature. But unprotected cells clearly do show some advantages. Which one is better depends on the individual user.

Besides the protected-cell issues you mentioned, another is that a semiconductor device is in series with the battery. While the "on" resistance of the protection circuit is low, it does increase the amount of voltage sag under a particular current draw. Some applications are more sensitive to this than others. For example, a buck-only driver will fall out of regulation sooner, or a driver with low-voltage shutdown may detect sooner.

My personal opinion is that protected Li-ion cells are needed for lights that use two or more in series. They are also needed for single-cell lights which incorporate boost circuitry. For single-cell lights having buck-only or linear regulation, or direct drive, I can generally detect visible dimming before the cell is completely drained. So I'm OK with unprotected cells in that application, even if the light has no built-in voltage monitor.

psychbeat · May 14, 2014

Even on direct drive lights it's pretty darn obvious when the cells get low.
If u run em down to 2.5v yer gonna see it even with a low VF emitter.
It would suck to have a dd light switch on in yer bag with an unprotected cell but it seems unlikely that it would explode unless something happens when u try to bring it back to life by charging.
Not really worth it if cells are ~10$ or less shipped.

STORMINORMAN · May 14, 2014

OK, let me get this straight... It is safe to use two, stacked, protected Li-Ion 17500 3.7v batteries in place of 3X 123a primary batteries in a 3G Surefire (with a P60L 6-9v led dropin) or, for example, a Solarforce L2M with an 18650 extender and a 3.0-9v led drop-in? I know it would be OK to use two red AW IMR batteries, what I'm concerned about is the common warning on protected cells that the protection circuits are "designed for single cell operation" vs. "pack building": but is using two protected cells stacked an example of "pack building", or am I misinterpreting the nature of the warning?

vicv · May 14, 2014

Battery packs have their own protection circuit for the whole battery. The single cells don't need it and would only complicate the build. For stacking batteries in a light either use protected cells or safe chemistry cells and use only matched cells. Protection circuits are no excuse to not look after your cells

STORMINORMAN · May 14, 2014

vicv said:
Battery packs have their own protection circuit for the whole battery. The single cells don't need it and would only complicate the build. For stacking batteries in a light either use protected cells or safe chemistry cells and use only matched cells. Protection circuits are no excuse to not look after your cells

So... 1st of all: THANKS to vicv! for the almost immediate response.

Based upon your post it appears I was misinterpreting the standard manufacturer's warnings about protected cells: one can safely use, for example 2 X 17500 protected cells instead of 3 X 123a primary cells with an appropriate drop-in? One can safely use 2 X 18650 protected cells with (at least) a 9v led drop-in?

I'm in no way disregarding the comment about "...no excuse to not look after your cells" either. Have upgraded my charger with this specifically in mind and am looking to buy some more modestly-priced cells for multiple-cell use (as in "TWO stacked") but don't want to forego protection in that my lights don't have the built-in protection circuits like some do.

Protected vs unprotected 18650 batteries ?

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