Measurements of high drain vs high capacity batteries in 3A lights?

[Aggressor]

I am trying to understand which battery will perform better in typical 3A lights (like stock Convoy S2+, M1, C8, etc.). High capacity battery like Sanyo NCR18650GA (3500mAh 10A) or high drain battery like Sony US18650VTC6 (3000mAh 30A). It is possible the additional capacity of Sanyo is only available at low voltages which the light can not use anyway, while Sony will definitely stay in regulation (providing brighter light) longer.

Did someone actually run such tests?

[stephenk]

The differences in performance will depend upon the type of driver used. I’m sure others can elaborate in more detail.

[Flashy_Mike]

If you are referring to lights with typical 8x 7135 driver I would use high capacity cells. High drain cells deliver more current to the LEDs in direct drive (since they are able to keep the voltage higher), but with current regulators like 7135 you only burn more power through the regulators.

[mdeni]

The higher the drain the bigger the voltage drop:

As you can see when voltage drops below ~4V or the Vf of the LED lets say 3.7V

From the Samsung 30Q you are getting 800mah before it drops below 3.7 under load on *5*A.
The panasonic 18650GA has 1100mah before it drops below 3.7 under *3*A load.
The 18650B has only 750mah before it starts loosing the ability to power the led to the needed voltage of 3.7V @ *3*A.

I think you get the idea of what you need to check. How much of the battery power can be used above 3.7V under load before the led starts dimming.

If you want to drive the led hard for the real capacity of the battery (ex 3000mah) you will need a buck driver to deliver the needed voltage.

[everydaysurvivalgear]

Hey mate the only way to tell would be to try your self. Or read reviews usually people discharge cells at different rates and you can see how they drain at what amperage under load. Also manufactures will rate a certain MAH rating at a certain discharge. Also keep in mind internal resistance once you get to a certain point it will work out better to use a higher draining cell if you want more power.

HKJ review here.
http://lygte-info.dk/review/batteries2012/Sanyo%20NCR18650GA%203500mAh%20(Red)%20UK.html

[DavidEF]

I’m not as ‘experienced’ with different cells as most of the guys on BLF. But, AFAIK, there aren’t any quality brand 18650s that can’t deliver a solid 3A current. In fact, for a cell with 3500mAH, that’s less than a 1C delivery. So, there’s no need for a high drain cell in any 3A light.

[Aggressor]

@mdeni

From the Samsung 30Q you are getting 800mah before it drops below 3.7 under load on *5*A.
The panasonic 18650GA has 1100mah before it drops below 3.7 under *3*A load.
The 18650B has only 750mah before it starts loosing the ability to power the led to the needed voltage of 3.7V @ *3*A.

I think you get the idea of what you need to check. How much of the battery power can be used above 3.7V under load before the led starts dimming.

Yes, that’s the numbers I am after, thank you. They explain quite nicely when the light will fall out of regulation in high mode. But when will it actually turn off? And what about lower modes? These lights use PWM, so they actually always draw 2.8A in any mode, just doing it in pulses when in lower modes. Is there a way to tell from these graphs when such a light will fall out of regulation in, say, mid (30%) mode? I was hoping someone would point me in the direction of actual flashlight tests with different batteries.

[mdeni]

@Aggressor

@mdeni

From the Samsung 30Q you are getting 800mah before it drops below 3.7 under load on *5*A.
The panasonic 18650GA has 1100mah before it drops below 3.7 under *3*A load.
The 18650B has only 750mah before it starts loosing the ability to power the led to the needed voltage of 3.7V @ *3*A.

I think you get the idea of what you need to check. How much of the battery power can be used above 3.7V under load before the led starts dimming.

Yes, that’s the numbers I am after, thank you. They explain quite nicely when the light will fall out of regulation in high mode. But when will it actually turn off? And what about lower modes? These lights use PWM, so they actually always draw 2.8A in any mode, just doing it in pulses when in lower modes. Is there a way to tell from these graphs when such a light will fall out of regulation in, say, mid (30%) mode? I was hoping someone would point me in the direction of actual flashlight tests with different batteries.

When they will stop depends on the driver protection or the battery protection. It is the same as the led Vf but you will look for the 2.8V or 3.0V or 3.6V depending on the cutoff voltage of the protection. Or it will overdrain the battery and never stop.

PWM is very short, and in a battery it averages out the same as lower current. So 3A 50% PWM is arguably the same as drawing 1,5A. As near as makes no difference.

The battery with the bigger capacity will last longer obviously. If it is run within normal conditions. Because it has more capacity. And 3A is very normal conditions for a 18650 cell. So it will be most dependent on the mah of the battery in case you want absolute maximum run-time. There is no replacement for displacement.

[sidecross]

Relativity trumps an absolute answer.

As for “There is no replacement for displacement” any one who follows motor sports should know that engine displacement is only a single factor.

The battery, driver, and LED of a flashlight are an array of complexity.

[Aggressor]

For driver used in stock Convoy lights (Nanjg 105c), this is the estimation I was able to come up with using data from here and here:

		Regulator thermal throttling above 4.0 V	Regulation 4.0 V - 3.5 V (full brightness)	Direct drive 3.5 V - 2.85 V (dimming)
3A	NCR18650GA		35 min	45 min
US18650VTC6	3 min	35 min	33 min
1A	NCR18650GA		135 min	90 min
US18650VTC6		125 min	80 min

Does that sound about right?
Would be nice to have actual test results.