Measurement info on cut-off voltage (Low Voltage protection) of various flashlights

Hi guys.

Decided to find out more about the cut-off voltage (low voltage protection) of various flashlights.

Benckie and I had a nice discussion about termination voltage of discharge tests with hobby chargers. It was mentioned that many guys like to terminate at 3.0V under load. Any lower and it's just only useful "in theory" and not useful in reality.

For me I think we can safely go lower than that and there is use in reality. Not that i'd recommend it, but sometimes you do run into such scenarios of long runtime. My experience is that as long as you recharge immediately and do not let the cells sit there, there is no issue. I have done so many times and the cells more or less can still discharge the same mAh as well and produce good high current.

My measurement is by using a key to complete the circuit of the light, while the + and - DMM probes are constantly touching the + and - as well. So when it cuts, i would take away the key immediately and do a reading. This is the best i can do and is the open circuit voltage figure of the cells (ie not under load). So the under load voltage is even lower.

In between the tests, i'd recharge the cells at 1.0A for 2 minutes.

To determine the extent of drop in output, i am using a lux meter.

1. Crelant 7G5. No low voltage cut-off by the driver. It just let the cells dive to about 4.2V before it starts to dim. Because this is a 2-cell light, there is enough juice supplied so that it does not dim as compared to what a single cell light would have.

2. Fandyfire STL-V6. About 4.7V. That's 2.35V per cell.

3. Balder BD-4. 3.9V! That's below 2.0V per cell. There is a low voltage warning in the form of the light ramping up and down smoothly and continuously <<-- Nice feature of Balder!

4. Sunwayman T40CS. Went to 4.4V and the light went into an erratic flickering randomly between like 15Hz-30Hz.. Sheesh, that's dangerous, thought i would spoil the driver so did not test further. The Sunwayman V10A does a 10Hz strobe when there is not enough juice. This is 2.2V per cell.

5. Shadow TC6+. At 4.6V, the light went into strobe, signalling low voltage. This is 2.3V per cell.

6. Solarforce Masterpiece Pro-1. No low voltage cut off. Still plenty of light at 4.0V and below. (that's expected)

7. Dereelight DBS aspheric. No low voltage cut off. Plenty of light.

8. Dereelight CL1H V4 with 3SM. No low voltage cut off. Plenty of light.

1-cell lights.

1. Jetbeam RRT-2 XM-L . 2.5V cut off. Light output at cut off is 240 lumens OTF.

2. Xpower Thunder XM-L. No low voltage cut off. 2.5V is about 200 plus OTF..

3. Xeno F42. No low voltage cut off.

4. Balder BD-2. Low voltage warning starts at 2.2V.

Great info 2100, much appreciated !

This is what I was saying that it's not ending at 3V, even under 3V you can get good light.

Yeah, it depends on the driver/circuit and most importantly the cell. If it's a good low resistance cell, there is gonna be a heck lot of light even at 2.8V for a XM-L. In a desperate situation, you are gonna be doing at least a good tens of minutes on medium and much longer on low.

Oh yeah, i was just using a lousy Trustfire Flame, the ones at 2200+ mAh aka bottom of the bin. Smile Don't wanna play with my XTAR/Solarforce/Panasonic/Sanyos.

It is possible to find some more cut-off voltage on my website.

I do include this information in all my reviews, in the form of a voltage sweep. There it is possible to see when the light start reducing output and when output is nearly zero, together with the current consumption.

Hi HKJ, it's somewhat difficult to determine the cut-off voltage from some graphs. I was expecting a sudden drop in output like a cliff. This is for the M31.


This one's better for the Catapult V2.


Excellent, 2100!

The graphs follow the lights behaviour, most lights does not turn off abruptly, but reduces brightness slowly

My newer curves has much better resolution: