Two protected cells in series don't fit. What if one protected and one not is used?

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xelario
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Two protected cells in series don't fit. What if one protected and one not is used?

A Convoy C8 with an extension tube and MT-G2 driven with a zener modded NANJG sounds sweet, but the light with extension tube is too short for two protected 18650s. At least 5mm too short.
So plan A would be to use unprotected batteries, but I don’t feel too comfortable with that.
Plan B would be to make some space. I have taken apart the switch, I think it’s possible to shave off quite a lot there, shorten the springs… Not sure if that would be enough, though.
And here comes the madness – what if I used one protected cell, one unprotected. Is one protection circuit enough for two cells, or is it as unsafe as running two unprotected cells?

Edited by: xelario on 04/25/2015 - 14:48
Streamer
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Should always use same type batteries in pairs/fours etc..  Especially when in series.  I definitely would not mix them.

202bigmike
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Try and make space , like you state in your Plan B.

djozz
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I have NCR18650B cells in the protected and unprotected version. If you start with new cells, those should match enough I would guess. And yes, I don't see why an overcurrent protection should be necessary on both cells, one should do the job I guess.

(but in the end I'm not a battery / electronics expert)

AlexGT
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Shorten springs and use copper rings between the tail cap and body treads to gain a few mm

antiparanoico
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I use only unprotected.
In the SR51 and TK75, NCR18650A or B (flat-top). In SRMini, NCR18650B (flat-top with magnets). In K40M NCR18650BD (flat-top). The groups are with cells from same type, date code and order, from the first charge.

Panasonic NCR have HLR tecnology, the protection is unnecessary.

For me protected are “The Murphy’s Temptation”.

If anything can go wrong, it will.
Matter will be damaged in direct proportion to its value.

jmpaul320
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Don’t do that. It’s safer to use 2 unprotected.

Would you mind keeping the wrong flashlight?
Best wish, May
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AlexGT
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Antiparanoico, what is HLR technology? Google said it means “Home Location Register” Shocked

ryansoh3
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Eek, I wouldn’t go there unless you really know what you’re doing.

Is one protected cell better than two unprotected cells? Logic would dictate so, but it just doesn’t feel right.

I guess the one would protected you from short circuits in series and would cut off when the cell’s voltage gets too low.

Make sure the protected cell’s capacity is lower than the unprotected one so that it shuts off when only one cell’s voltage is too low, not both.

BLF ≠ B-grade Flashlight Forum

 

xelario
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jmpaul320 wrote:
Don’t do that. It’s safer to use 2 unprotected.

Could you please elaborate? Why is that? Even if you took two protected cells with the same date code, from the same batch, just removed the protection circuit from one?

In any case, I’ll try to make more space first, and maybe later (after stacking more ships) get some higher drain unprotected cells…
So the question is only theoretical, but it’s bothering me Big Smile

Adoby
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The protection against high current should work fine using one protected and one unprotected cell. You can imagine that it is simply two unprotected cells and one protection circuit after those. The protection circuit works as a switch for both cells. I can't see any electrical reason for it to be different.

But you will obviously not get over/under voltage protection on the unprotected cell. And that is why you would like to have two protected cells in series in the first place. To avoid reverse charging and temperature runaway (venting/explosion) if you happen to use unmatched cells or one charged and one uncharged cell or even happen to flip one cell.

I still wouldn't recommend that you mix protected/unprotected like this, even if it theoretically should work fine. I would prefer to use two unprotected instead, and monitor the capacity of cells as they age to make sure they stay matched. And check that both cells are fully charged before using them. Preferably take them directly from the charger and immediately insert them into the flashlight. (And then do a function test on the flashlight wearing protective gear. Wink )

 

antiparanoico
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AlexGT wrote:
Antiparanoico, what is HLR technology? Google said it means “Home Location Register” Shocked
There was a typo…

It is “HRL Technology”… Heat Resistance Layer

If anything can go wrong, it will.
Matter will be damaged in direct proportion to its value.