Problem with my SF M6 (Self-discharging batteries)

[Flea Bag]

Been having a problem with my CR123s self-discharging in my SF M6.

Incident 1: A few months ago, I used the M6-MN20 for about 30 minutes spread out over about 4 or 5 on/off cycles. After that, I twisted off the light. I also added an extra 1/4 revolution twist in the off-direction to ensure the tailcap isn't in an intermittent off-on position. Then I put it back on the shelf next to my bed.

A few weeks after that, the light wouldn't switch on and the batteries were dead. I was puzzled and thought that maybe the cells were already partially dischaged when I previously used it. However, if this was the case, then the M6-MN20 would have looked quite orange and dim towards the end of usage. I did not remember noticing this and so I suspected something was wrong with the tailcap. I emptied the M6 and left it battery-less, deciding to return to it another day when I have more time to investigate. For the time being, I would have to settle with my other lights...

Incident 2: A week ago, I found some time and picked up the M6 again. I put in a new batch of Sanyos measuring about 3.25 v. Then did the 30 second test and switched the light off and added the usual 1/4 revolution to keep it off. I then left the M6 alone for four or five days and yesterday, I took the batteries out and they measured 3.02 v. That's low! A 3.02 v reading would usually be associated with a half-discharged M6, not one which has run only 30 seconds! :shakehead

Has anyone had a similar incident in the past or know someone who has? is this a problem with the tailcap? Tried researching CPF but couldn't find a precedent tailcap problem, at least not with this newer version of the M6.

 

[scott.cr]

There's not a whole lot to go wrong with the SF tailcap. You might try removing the head and lamp assembly but leave the battery and tailcap on as you would normally store it. Then probe the battery + terminal and the flashlight chassis to make sure there's no voltage. If there is, that's a tailcap problem (maybe something conductive, like dirt/carbon?, bridging the gap enough to pass a little current through the lamp but not enough to light it).

You might want to probe the battery pack's terminals to make sure there's no leakage between them.

Finally, maybe you just have bad CR123s. Perhaps an initial high-rate current draw is somehow damaging the cells and initiating a rapid self-discharge state.

 

[jayflash]

Regarding incident #2: did the M6 light up with normal brightness? If so, your cells may be OK and no problem exists. The 3.02 volt reading is meaningless unless the cells were placed under a load of, say, approximately 200 - 500 mA.

Open circuit voltage measurement is accurate for rechargeable, secondary, cells (LiIons) but not the, primary, CR123 type.

If your second set of cell was drained and the M6 didn't light up, then you may have a problem with the carrier. An ohm meter check should reveal if a resistance (load) exists between the + & - cell carrier terminals.

Also keep in mind that the cells are heavily loaded even with the MN20 and may have suffered a common occurrence of dying after use. CR123 cells will sometimes provide normal light and then die between uses.

 

[Flea Bag]

Thanks for the replies guys!

There's not a whole lot to go wrong with the SF tailcap. You might try removing the head and lamp assembly but leave the battery and tailcap on as you would normally store it. Then probe the battery + terminal and the flashlight chassis to make sure there's no voltage.

You might want to probe the battery pack's terminals to make sure there's no leakage between them.

I'll give those tests a try and report back!

Regarding incident #2: did the M6 light up with normal brightness? If so, your cells may be OK and no problem exists. The 3.02 volt reading is meaningless unless the cells were placed under a load of, say, approximately 200 - 500 mA.

Open circuit voltage measurement is accurate for rechargeable, secondary, cells (LiIons) but not the, primary, CR123 type.

The light did light up with normal brightness as it would if the batteries were just half used. The batteries are fine and I trust they're not the problem. I've used plenty of Sanyos in my lights and they've always been reliable.

Regarding the open circuit voltage measurement of the CR123s though, I know there are variations between brands but I've found that cells of the same brand usually exhibit quite a strong correlation between open circuit voltage and remaining capacity as long as we're talking about voltages above 3.10 or 3.15V. Below that figure, I agree that voltage becomes less and less of a reliable indicator of remaining charge and by the time we get to around 3.05v or lower, it starts becoming a lottery.

However, an open circuit voltage of 3.02/3.03 volts for all six of my Sanyo cells is very low considering the light has only run for less than a minute and then stored for five days in the M6. The cells all read 2.85/2.86 volts after another 10 second test. Given a few hours rest outside of the M6, they return to the 3.02/3.03v figure as mentioned above. Right now, after over a day's rest outside the M6, they all read 3.05/3.06v for all six of the cells. That indicates to me that all the cells are performing consistantly and uniformly but that voltage figure is still too low. I've never had any of my CR123 (be it Sanyo or Energizer/SureFire) read as low as 3.05 volts after just a minutes usage plus some storage time! A Sanyo CR123 with 98% capacity remaining shoud read at least 3.20v or 3.18v in the very worst scenario.

Regardless, I'll run them in the M6-MN20 tomorrow and see how much more usable runtime I get out of them. That'll be another $12 worth of batteries down the drain though... Sigh... :candle:

 

[Patriot]

Those lithiums add up don't they. I've been buying Duracells and Energizers from Botach. It might help ease the battery burden some while your figuring out what the issue is.

http://www.botachtactical.com/du1236.html

 

[Tempest UK]

Which version of the M6 is it (Magnumlight, Guardian, etc)? I know the M6's tailcap design has been changed at least once due to some problems with it, but I'm not sure if they would have anything to do with this.

Regards,
Tempest

 

[Flea Bag]

Okay... With the KT4 head and LA removed and the tailcap twisted off in its usual storage position, I get an open circuit voltage reading of about 20-23mV. As I untwist the tailcap further, this low voltage reading stays constant until it gets to near the lock-out position where the first o-rings becomes exposed and the reading becomes 0v.

Resistances test on the MB20 battery holder show nothing wrong with it.

Does this confirm there to be a tailcap issue? If yes, what can I do to fix it?

Patriot36, thanks for the Duracell bargain find! I remember Silverfox's measurements of those cells to be really good!

Tempest UK, mine is a Guardian but it's a second-hand purchased about 2 years ago so it is possible that the original owner sold me a Guardian body but with an old design tailcap. I took a look at the currently active thread about the different versions of the M6 and saw a picture of the different tailcap designs. Mine seems to match the appearance of the newer improved design so I don't think the tailcap was swapped for an older one.