When to call it quits on a protected cell runtime test?

Batteries and Chargers Rechargeable Batteries
1

I'm doing a runtime test on a four LED worklight for my first review.

The light came with a protected 18650 cell bearing the name of a reasonably well-known light manufacturer.

No LV protection is built into the light.

The light has built-in USB charging.

I can see the ridge at the bottom of the cell where the protection PC should be, the bottom of the cell is magnetic, and I can see/feel the conductor strip under the wrap from bottom to top.

The light has run on low continuously for more than 48 hrs. so far, except for a 30 second pause to check cell voltage with a DMM.

The light has dimmed to the point of being nearly useless except, maybe, in a pitch dark room.

I'm not well versed estimating on lumen output by eye, but I'd hazard a guess of under 5 lumens. It's more like moonlight.

I don't want to damage the cell by over discharging it, but neither do I want to abort the runtime test prematurely.

From what I think I understand, 2.5v is the bottom threshold of discharge before cell damage & instability becomes a consideration. The cell was at 2.591v when I tested it with a DMM a little while ago. That makes me nervous.

If it's still running in the morning I'll abort the runtime test, and check the voltage immediately after removing it, and again after resting for an hour no load. If it comes in under 2.5v, I have a decision to make:

1) try to recover the cell with a 200ma charge in my Opus 3100, or

2) recharge the cell using the charge feature built into the light, which is of unknown charge rate.

Advice please, on how to proceed.

.

2

I would consider the run time test complete and use the built in charging just to complete the review. Unless you are really mad at that poor 18650. :smiley:

3

FL1 standard considers a run over when the light has dropped to less that 10% of it’s output at 30 seconds - so that’s what I use too.

4

Best avoid being excessively dramatic, the chemistry of a cell doesn't changes overnight; depth of discharge matters too. I've recovered cells discharged under 2V without problems, cells which of course I perfectly knew how many time had slept in such state. If it is of any help, let me say that LG specifies discharge down to 2V for some of its cells like the HE2.

By the way, do or do not, there's no try LoL (well, there's try but if in doubt avoid trying if you prefer to see results).

Recharge the cell with whatever, there's no hurry there. On the other hand, when I need to recover a cell I want it fast, thus I avoid dumbass chargers with slowass “cell recovery feature/marketing gimmicks” and straight zap the cell to recover with a known good cell in parallel a few times or use a “real :-) dumbass” charger.

Cheers :-)

5

You’re measuring the cell without a load applied, the ‘working’ voltage while it’s in the light will be lower.

I’d call it quits.

6

I'd spank you in the ass for throwing away a perfectly fine cell like that one LoL. :-D

A cell can be rock bottom discharged and safely recovered for as long as the emergency time is kept low enough. Can't say how much time is that but just a few hours is safe for sure.

On the other hand, if you happen to grab a cell slept inside a drawer at 0V for an unknown amount of time and straight insert it into a charger, use the slowass recovery function to ramp up its voltage back to a valid normal value and then keep fast charging the cell… the cell ends blowing up in your face because of :-D your dumbass syndrome. This happened to some spanish fellow some time ago, he reported it at ForoLinternas LoL.

Cheers ^:)

7

The PCB usually cuts off at 2.40V. No problem for the cell.

8

Run er down until the protection circuit trips, then charge it back up. If the protection circuit doesn’t work, then what good is the cell in the first place?

9

I aborted the runtime test after 62 hrs.

Light output had dropped to essentially a near-useless firefly level.

LV protection had still not tripped.

I checked voltage as quickly as possible (under 15 sec.) after removing the cell from the light, and again after letting the cell rest for an hour. The voltages were, respectively:

2.435v immediate test and, 2.455v after 1 hour rest.

Charging the cell in the light brought it back to resting 4.13v.

A 3x discharge/charge cycle @ .5A in an Opus 3100 resulted in a capacity of 2655mAh for a cell rated at 2600mAh.

I'm waiting to post the rest of the light review until the manufacturer honors their word on PP reimbursement for purchase cost of the light.

10

As far as my wisdom goes, everything looks absolutely normal in what you described, slmjim. On one hand, protected cells use DW01A protection chips with typical ≈2.4V cut-off voltage; on the other hand, 1S emitter torches with linear/MOSFET/buck drivers do not really need to low voltage protect their li-ion power sources because the emitter barely draws current below a certain voltage thresold which still is above a standard safe cut-off for li-ion cells, this is ≈(2.5 - 2.6)V.

What's the problem with it?

Cheers :-)

11

I heard that some drivers may still draw a small current for their electronics even when the led had turned out due to low voltage, resulting in over discharge of the battery in a few days.

12

Zak tested this on r/flashlight and yes, single cell torches with no fancy drivers still very much need LVP.

13

No problem with the light.

Manufacturer offered PP reimbursement of purchase price of the light(s) in hopes of receiving reviews & feedback. I'll review the light eventually anyway. If they don't honor their word on reimbursement, I'll call them out on it in the review. I've PM'd them again about it. Just waiting for a response.

14

Please notice I said “do not really need” and “barely draws current”. If there's no low voltage cut-off, the cell is eventually going to be over-discharged, it just takes a long time which I never allow to pass. I never leave my flashlights completely unattended, not even my cells while being charged LoL. If you can't live with this, use protected cells (and enjoy instant blackouts).

Cheers and may all beings be happy :-)

15

Ooh! Ooh! I know! I know! :smiley:

16

Yeah, I was gonna suggest that. :smiley:

Don’t recall if any of my almighty or not-so-almighty chargers do a straight discharge without automagically starting to recharge immediately after, but I’d watch the voltage, wait for the charger to cut off, then just slap a simple resistor on it and wait for the pcb to kick in.

Me personally, in actual usage, I’d never let it get that low. Like, nowhere near that low. Still, 2.4V for white LEDs would barely have ’em light up at all. That’s already nearly on the horizontal part of the “knee” curve.

I like that light quite a bit, and my druthers would be to have it be a little “smarter”, have LVP, maybe do a quick off-blink every few seconds or so below 3.0V, then a faster blink below 2.8V or so, then off very soon after.

Low-stress light, would be perfect for burning down even crappy cells just fine.

17

Might still be quite a few hours to go. :smiley:

White LEDs that have “knee” voltages around 3V in general will draw hardly any current at all below that. For all practical purposes, they might as well be off.

In this case, the protection circuit probably just keeps the cell from discharging to 0 if crowbarred with a resistor or something.

I wouldn’t worry about it.

I “forewarned” ’em that I intended to actually EDC the flashlight a week or more to get a good feel for it, no problem.

The worklight I reviewed within a coupla days, as I just worked it a while and didn’t see anything wrong with it, but didn’t have the patience for a protracted runtime test like this. :smiley: I’m actually thinking of getting another to keep in the car as well, as I’ve gotten to really like the critter.

Got PPed over that weekend. Reviewed the usb cell after, also quite handy. Gave the light a run through the wringer, figuratively speaking, and after being suitably impressed, reviewed that also.

Gotta say, the light was nigh perfect. Perfect ano, very well lubed, not a hint of scratchiness on the threads, really nice “gift box”, really really nice little details covered quite well.

Frankly, another reason to not worry about it is, okay, what if they don’t come through? What’s stopping someone from returning the items to Amazon under their a-to-z policy, getting 100% of the cost right back, and even panning the items in subsequent reviews? No mfr in its right mind would want to chance that.

Now, ordering it from GB, or BG, etc., anyone but from Amazon, no way would I want to chance it. Trying to get a refund, well, you might have better luck getting an all-expenses-paid trip to Shenzhen with cute little chickies for accompaniment.