Battery combination behavior...

[rewdee]

Hi, need some help getting to understand the different pro and cons in using certain battery combination.

Lets say i am using a 2 cell light setup, how will runtime/brightness/depleting behavior differ in these setup:

a. 2x CR123 primaries (3v, ??)
b. 2x RCR123 (3.7v, 750mAh)
c. 1x 18650 (3.7v, 2900mAh)

also, does higher voltage in serial set up result in higher light output in a regulated drive led?

maybe someone kind enough to put all these volatge/mAh/output thing in a bigger picture?

Thanks.

 

[HKJ]

The 18650 contains most energy (voltage*capacity, i.e. 3.7*2.9 -> 10.7 Wh) and will usual have the longest runtime.
But brightness depends on the lights, some lights can keep the same brightness with all 3 battery combination, but other lights will have reduced output with only 3.7 volt.
I usual put a "voltage sweep" graph in my reviews, it looks like this:

The part where green line is flat, it the stabilized part. This light stabilizes down to 4 volt, i.e. a 3.7 volt LiIon will not be stabilized.

This lights stabilize down to 3.1 volt and will be stabilized with a single 18650 LiIon battery.

 

[rewdee]

Hi, thanks for the explaination.

Does it mean that 2 cr123 (1.5Ax6v= 9) last longer than 2 rcr (0.75Ax7.4v=5.55) but rcr produce a brighter output (6v vs. 7.4v x whatever regulated output from the light)?

Or is the max output is the same regardless of the voltage (in a regulated output light, lets say malkoff m61 regulated at 650mA 3.4-9v)?

Thanks

 

[HKJ]

Hi, thanks for the explaination.

Does it mean that 2 cr123 (1.5Ax6v= 9) last longer than 2 rcr (0.75Ax7.4v=5.55) but rcr produce a brighter output (6v vs. 7.4v x whatever regulated output from the light)?

Or is the max output is the same regardless of the voltage (in a regulated output light, lets say malkoff m61 regulated at 650mA 3.4-9v)?

Thanks

CR123 can last considerable longer than RCR123, but not at very high loads (See my review of TN12 for a case where CR123 cannot sustain the power).

On stabilized lights the output will be the same with all types of batteries, as long as they can maintain their voltage. A CR123 battery will slowly drop in voltage and at some point the light will go out of stabilization. Protected RCR123 will shut completely off when empty, i.e. the light goes from directly full power to nothing. This can be seen on the runtime curves.

 

[old4570]

Ok , not sure how many times this question has come up : But never mind !

Lets assume for a moment that the light is 5 Watt Cree LED R2 [ for the heck of it ]

So if we know the emitter is going to take 5 Watts :

Voltage x Amps = Watts

To work out current draw ,

Watts divided by Volts

So 5 watt / 4.2v = 1.19A
5W / 6v = 0.83A
5W / 8.4v = 0.59A

But , there is no accounting for driver behavior or design or function , each one may be unique in itself , but this is the basic math of it \
And as for run time , the variable there is battery capacity ...

 

[45/70]

......And as for run time , the variable there is battery capacity ...

...... and the ability of the cell to hold voltage under load.:)

In any light, either direct drive, or with some sort of regulation, the ability of a cell to hold voltage under load, is just as important.

Take for example, two cells with 2500mAh capacity. One holds an acceptable voltage under load, to run a light at an acceptable output, or stay in regulation, and the other does not. In this case, the cell that is able to hold higher voltage under load, will effectively, run the light longer, even though the capacity of the two cells is the same.

A good example of this is IMR cells vs. ICRs. In many applications where IMR cells are preferred, their capacity may be considerably less, but they will effectively run the light longer.

So anyway, capacity is really only one criteria for cell selection. You really need to know how a cell performs under various current loads, and then evaluate both capacity and voltage performance, in order to select the proper cell for any specific application.

Dave

 

[rewdee]

Thanks. I get it now. By regulated it means that the output(watts) is constant and if when the voltage of he battery drops, it draws more current(volt * amp = watts).