Do Foursevens Quarks modes step down as voltage drops?

[reppans]

Just for clarity: The open-circuit voltage on these cells is 1.30V, and with a 10ohm load 1.11V. So the internal resistance is ~1.7 ohms. This is a good demonstration of why testing cells with a load is more accurate, as you say.

[The 1.09V reading was from a cheap-o battery meter (BT-168D) that supposedly draws ~40mA from the cell during testing and shows you the resulting voltage. In the past I used a 10ohm resistor and a voltmeter. Even though I hate having extra stuff, the tester was hard to pass up for <$4. I had never verified the 40mA load from the meter, but I just tested it at 30mA from this nearly depleted alkaline and 43mA on a fresh one]

The product page for this light says it draws 250mA at High. Presuming the internal resistance is constant (?), that would be a 0.425V drop on each of my cells, meaning I have 1.75V total from the 2 cells driving the head of the light. The head claims it can run from as low as 0.9V, but it seems it can't produce the High brightness from that voltage (?). I just tried driving the head from a single one of these cells (~1.09V), and it also seems like it can still do Medium but no higher.

It would be interesting to hook the head up to a bench supply and start dialing down the volts to see if there are specific voltages at which Turbo suddenly starts looking like High and then starts looking like Medium, which is basically what this thread was asking about.


This is precisely why I went with the quark for my first "good" light! Even a single battery from an old TV remote would give me something.

I'd get a 1xAA tube if you want to vampire test batteries in a Quark, esp Alks. In 2xAA config, a Quark moonlight mode WILL pop Alks via reverse charge - don't ask me how I know :D - just watch for the infamous battery fart and ballooned tailcap boot. The 250ma figure is "LED drive current" (47's terminology), NOT battery draw current, and as we know this strictly regulated light will draw increasingly higher currents from the battery as voltage drops, not to mention the normal driver efficiency losses. If you're dealing with any chemistry <1.2v, my guess is that there's simply not enough available wattage to power high and max, even in 2x format. Med and low will cut out soon after, depending upon battery condition, but moonlight will chug down below 1.0V. The light will shut down completely in the 0.8-0.9v (resting) range, but you don't want to go below that anyway - damaging to NiMhs, and higher risk of Alk leaks (even in single cell format).

 

[Etsu]

The product page for this light says it draws 250mA at High.

Which is about double that current on the 2xAA cells, in order to supply the LED 250ma at about 3v, factoring in the lower voltage the battery supplies, and the loss in the boost circuitry.

On maximum, I measure the (2xAA Eneloop) battery current at about 2.5 amps for the XML2 Quark, and about 2 amps for the XPG2 Quark. Easy enough for Eneloops, but alkalines really struggle to provide that for very long.

 

[aberson]

Which is about double that current on the 2xAA cells, in order to supply the LED 250ma at about 3v, factoring in the lower voltage the battery supplies, and the loss in the boost circuitry

Good points - didn't account for the voltage change.

The 250mA to drive the LED is like 400mA from the 2AA's, which at the high internal resistance of nearly dead alkalines will drop my voltage down to something like 1.3V total, or more likely even less as the AA chemistry struggles under that load.

I'd say the light still performs quite admirably :)

 

[Etsu]

Good points - didn't account for the voltage change.

The 250mA to drive the LED is like 400mA from the 2AA's, which at the high internal resistance of nearly dead alkalines will drop my voltage down to something like 1.3V total, or more likely even less as the AA chemistry struggles under that load.

If I understand correctly, you said that there's no difference between medium->high->max modes, which means that your nearly-dead alkalines are operating the light at medium, which is 50ma current to the LED (not 250ma). At 50ma, the voltage across the LED is probably around 2.6v or 2.7v. So, maybe 150ma for the depleted batteries to supply that?

 

[aberson]

If I understand correctly, you said that there's no difference between medium->high->max modes, which means that your nearly-dead alkalines are operating the light at medium, which is 50ma current to the LED (not 250ma). At 50ma, the voltage across the LED is probably around 2.6v or 2.7v. So, maybe 150ma for the depleted batteries to supply that?

Yeah we're on the same page (maybe just opposite sides ;)

What I was trying to figure out is why the light can't do High and therefore has to step down to Medium. So I was trying to see what the effective voltage on my batteries was at High - I presume the light briefly attempts High and then steps down to Medium when it decides the batteries are too low. It might not really measure voltage at all bit maybe just realizes the available current is not sustainable.

 

[Etsu]

I presume the light briefly attempts High and then steps down to Medium when it decides the batteries are too low. It might not really measure voltage at all bit maybe just realizes the available current is not sustainable.

That would be my guess, too. I doubt there's any circuitry to measure voltage, because you can actually use the Quarks from 0.9v to 4.2v. So it probably doesn't know what kind of battery you have installed, or how many batteries you're using. I can run the Quarks successfully on a single AA cell, which probably produces a voltage close to 1.1v when on high.