Flashlight cutting off

[RedForest UK]

Okay, I've recently modded a stock dx RC-G2 using a Q5 led and dx sku.15880 as a driver, it now accepts li-ion 14500's and is crazy bright, at least 200 lumens. :twothumbs

However, i have recently been playing around with the modes by soldering the stars on the back of the driver. I have settled on the two mode, but where before it would run for 36-40 minutes on a 14500, now it cuts off at about 17-20 minutes and goes to a low flashing mode.. I am assuming that this is the 'low voltage' warning mode as advertised in the drivers description, but it appears to kick in when the cells are still at 3.6v, which seems very early to me.. :shrug:

So, basically has anyone else had a similar experience with this driver? Any pointers as to how to sort this out or disable the 'low voltage' mode altogether would be greatly appreciated.

Thanks

 

[John_Galt]

When Li-ion cells are at 3.6v, they are basically depleted. Discharging an unprotected cell further could greatly increase the chances of having an explosive venting. A protected cell's cut off should be tripped at this voltage, preventing the cell from over-discharging.

Li-ions are not fully charged until about 4.2v.

1) Make sure that your charger is fully charging your cells.

2) If you have a dumb "timed" charger, it may be overcharging your cells, and therefore damaging them,reducing capacity, and the runtime before the cut off is tripped.

 

[45/70]

...... Discharging an unprotected cell further could greatly increase the chances of having an explosive venting.

I just wanted to point out that nothing will happen to a Li-Ion cell if you over discharge it, in a single cell application. You can discharge them to zero Volts, you'll kill the cell, but nothing will happen. If you are running cells in series, you may have a problem, if the cells are in drastically different states of charge during discharge. At any rate, it isn't a good idea to discharge any Li-Ion cell below the recommended minimum state of charge. Why push your luck?

Now, if you go to charge a LiCo Li-Ion cell that has been over discharged, you then run the risk of a "venting with flame" incident.

Red, it sounds to me like your cells are simply discharged to the point they won't run the light any longer. As John mentioned, a LiCo Li-Ion cell that reads 3.6 Volts OC, is pretty much dead.

Dave

 

[RedForest UK]

Oh, that seems alright then, i was under the impression that they still had about 40% useable charge at 3.6v and were completely discharged at 3.2v.. The cells i'm using are the Blue trustfire 900mah and have been rated accurately at about 305mah, I am monitoring them coming of my charger at 4.2v to 4.23v every time so that all seems okay.

What was troubling me was the fact that this 'low voltage' mode is now cutting in where before i was getting another 15 minutes out of the cell on the same measured current draw before they cut off at about 3.2v.

 

[jabe1]

If your driving the LED anywhere close to 1000ma, how do you expect a cell with capacity of 305mah to last longer than 20 minutes?
If you are getting 200lumens with a Q5, you must be close to 1amp drive (and the driver specs it as possible).

 

[RedForest UK]

Well it is drawing at 1.1v to 1.2v, and the 200lumen output was just an educated guess really. But whats annoying is that at the same brightness and measured current draw i was getting 36-40 minutes, this has now halved, even though i'm using the exact same cells, i know their capacity could have dropped but surely not both between one charge? :shrug:

 

[RedForest UK]

Sorry to resurrect an old thread but I've looked around, and the batteries in question are in fact rated at 705 mah at 0.3a draw and 560mah at 1amp, which is what my light is pulling.

However, I am now only getting about 10 minutes out of the battery before it goes into a low flashing 'low voltage warning' mode, however after turning it off for a while and removing the cell it reads 3.97v, surely the light shouldnt be cutting off this soon? :thinking:

 

[SilverFox]

Hello RedForest UK,

It sounds like you have simply worn out your cell. While Li-Ion cells are rated for a maximum 2C draw, you don't expect to get much cycle life when you actually use them at that high a current rate.

You may be able to use the cell in something that draws around 250 mA and get some more life from it.

Tom