i need help understanding this!

Capolini

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If a single cell torch is driven to 4.1-4.4A at the LED and you use an NCR18650BD[10A max continuous discharging current] battery wouldn't that be sufficient enough to get maximum performance from the torch?

Or,,,,,,,would an Efest IMR 18650 30A [20 max continuous discharge current] be better and WHY?

It is confusing to me what the direct correlation is between current boost[amps @ LED],in this case 4.1-4.4A and the Maximum continuous discharge current that a battery provides and sustains.

My logic tells me if a torch is pushed to a max of 4.4A then a battery that sustains 10A continuously should be more than suffice?

I have a feeling there are other factors like the driver, ect.?!

I need to "EASE" my analyzing brain!! :whistle:

:wave: THANKS,,,,,,,,,,,,,,,,,,,,,,,,,,,



 

RetroTechie

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A battery is a power source, and one way to look at a power source, is as a combination of an ideal power source (output voltage stays the same no matter what current you draw) + a series resistance. For clarity: that series resistance 'sits' inside the battery, its power dissipation will cause heating of the battery itself. Or more accurately put: that internal resistance is an inseparable part of the battery.

Now a real battery (obviously) behaves more complex than that, but the above model is a reasonable simplification to understand what's going on.

When you draw current from a battery, that current causes a voltage drop across the 'internal resistor'. Imagine a 'perfect battery' that holds its voltage regardless how heavy it's loaded, with that resistance in series glued to the side. The voltage drop across that resistance will cause power losses, and will also lower the voltage you get at the output. Duhh... battery voltage drops as you load it. :)

Back to your 2 batteries: one that's rated for 30A continuous will have a lower internal resistance than one rated for 10A continuous. And thus for that 30A continuous battery, both the internal losses (self-heating) and voltage sag will be less than for the 10A rated battery. Meaning: with that 30A continuous battery you can effectively use a (slightly? much?) higher % of the battery's capacity.

For light loads this wouldn't make much difference, so you're just looking at mAh figure up till useable end voltage. For a load like 4A+ it most likely would make a difference.

So obviously a 30A continuous battery would seem preferable over a 10A continuous one. But now the fun part: the very design changes required to make a battery support higher loads, usually cause it to have (slightly? much?) reduced capacity. Or in other words: with such a battery and a heavy load, you can eat a bigger % of a smaller pie. :green: For example see mAh differences for IMR vs. LiCo cells. Yeah life gets complicated sometimes!

For the nitpickers: normally this internal resistance is referred to as "impedance", which means effective resistance as a function of frequency. But since we're talking DC here, resistance is both correct & simpler.

I have a feeling there are other factors like the driver, ect.?!
No, they just complicate things further. :D
 
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Capolini

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^^^^^^ Thanks......Its clearer now........I knew the part of IMR having lower internal resistance. Your explanation helped my aging brain comprehend it better!:faint:

The Two modded lights that I have in mind that prompted my inquiry are both Single Mode Direct Drive!! I do not think they have, or at least utilize a driver!

They are: M2Xvn and TX25C2vn V3T. Both direct drive Single mode for most power and least resistance!
 

Chicken Drumstick

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HKJ a member here has a brilliant site about batteries and such. And a very useful comparator.

http://lygte-info.dk/review/batteries2012/Common18650comparator.php


I personally find it easier to understand this with a chart.

This is the 3200 NCR18650BF, I couldn't see the BD listed. Against the 2500 purple Efest.

What you want is for the line to remain as high as possible if you are after performance. This is a 5amp plot, which is likely fair for a direct driven XM-L2 light. Note as the capacity drops, so does the voltage. A high performance battery will hold a higher voltage, but usually have a lower capacity.


(ignore the red jagged line, one of the test batteries must have given odd readings or something)

And that's exactly what happens here, the Efest is always a higher voltage, so will be brighter at any given time. But it doesn't last anywhere near as long.


To see what 'load' does to a battery, here is a chart showing the Panasonic BF at 3 and 7 amps. It's the same battery, but note that from the very beginning under higher load there is much more voltage sag. IMR cells and those rated to higher discharge currents will tend to sag less.


This all means on low output levels or lesser flashlights, many batteries will perform brilliantly compared to others and maybe even the longest runtimes due to their mAh. But up the current and these same batteries may soon not perform anywhere near as well.

Take another look at the first chart, it's the first 3 or 4 columns on the chart that really make the difference. On a fresh charged battery there is a big performance difference.


As a compromise however, it might be worth looking at things like the high capacity IMR's. Efest do a purple 3100mah as well as the 2500mah. Not quite so 'punchy'. But will still offer a performance hike over most ICR's and give you very good runtimes. Also being non protected they tend to fit better as they are shorter.

 

Grijon

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Thanks for asking, Capolini; thanks for answering, RetroTechie! Thanks for the visual examples, Chicken Drumstick!
 
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Capolini

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lovecpf
Thanks for asking, Capolini; thanks for answering, RetroTechie! Thanks for the visual examples, Chicken Drumstick!


+1 Minus me!!! lol!


HKJ's comparator is definitely helpful. One night I spent two hours comparing voltage sag b/w different IMR/ICR batteries! The visual graphs are very helpful and easy to understand. I was struggling with mostly comprehending the amps needed combined with internal resistence in order to get the MOST output!

I have the Efest IMR Purple, 10A[3100mAh] and 30A[2500mAh]. Also the Keeppower IMR 2500 mAh which is another great battery[LG-HE2]

Thanks again,the visual[graphs] and the written explanations have given me a clearer understanding. ;)
 
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