18650 vs 2 123's.

[DR_DEUCE]

New guy here. Some units can use 1 18650, some take 2 123's. What would you expect the difference in performance to be.
Situation; one 18650 3.7v, 2600ma/
or
two 123's 3.0v, 1300ma each.
Which would run longer?
I assume the led module can handle both voltage inputs.
PLEASE SHED SOME LED LIGHT ON THIS!!!

 

[EngrPaul]

Typically the 18650 will have longer runtime, but will diminish gradually over time.

The 2xCR123 will function in very good regulation for about half as long, and then you throw them away.

The 18650 will be heavier, but will not rattle as much. There are no primary 18650's, only rechargeable.

Two CR123's could result in an explosion if not used properly or if the brand is crappy.

 

[DR_DEUCE]

Let me clarify this battery type.
BOTH WILL BE RECHARGEABLES, does that make a diff?
AND is one size safer that the other??

 

[EngrPaul]

:welcome: << Almost forgot.

Rechargeable 123's are 750mAh and 3.7V...

If you use protected cells, they both should be "safe".

If you have a two-bay charger, you can charge back up two cells faster than one. That and constant high output is the benefit of RCR-123's

For 18650's, long runtime and not suddenly losing all light is the plusses.

 

[DR_DEUCE]

SO....if charging time and cost was not an issue, would you opt for the 18650?
Just seems that 2400-2600ma is better than 1500ma, and the 123's are at 3.0v which would "cut out" quicker than a 3.7v.
Does this make any sense..
I may be overthinking this.
Does the LED module do any disconnect, or is it the protection circuit in the batteries?

 

[Marduke]

RCR123's are nowhere near 1500, not sure where you are getting that idea from...

 

[EngrPaul]

You can estimate output & runtime values using a total milliwatt*hour figure.

2 CR-123 @ 6.0V * 1500mA*h = 9000 mW*h

2 RCR-123 @ 7.4V * 750mA*h = 5550 mW*h

1 18650 @ 3.7V * 2600mA*h = 9620 mW*h

The mW*h will be directly proportional to the area under the lumens*hour curve of the runtime.

The higher the voltage, the more regulation will come into play. It will be straight horizontal line then a step directly down. Lower voltage runtimes look more like a gradual slope.

Here's a good example:

 

[45/70]

I just thought I'd point out that 2xRCR123's are 8.4 Volts OC and fully charged, or about 7.2-7.4 Volts nominal. An 18650 still has more power, but the mAh of the cells is deceiving when comparing a single cell to two cells in series. A "buck" circuit effectively makes the mAh of two cells in series higher than an individual cell, as the circuit lowers the final voltage to drive the LED.

Dave

EDIT: Ya sorta beat there, EngrPaul.

 

[Max_Power]

Cool, this is saying the same thing as the graph above, which we posted within a couple minutes of each other.

Non-rechargeable primary CR123 cells are rated for 3.0 V and ~1300 mAh, which is 3.9 Watt-hours. A pair of them would give about double that, 7.8 Watt-hours.

I have some AW 18650 cells that are nominally 3.7V and 2600 mAh, the energy in them is 3.7*2.6 = 9.6 Watt-hours.

Since the voltage is lower on a single 18650 than a pair of CR123 cells, a regulated driver driven by an 18650 will have to pull higher current to give the same power, which means you probably won't get 100% of that power out of the cell. So the runtime will be roughly the same as for a pair of 123 cells, assuming a regulated driver.

If the driver drops out of regulation and reduces current draw, runtime could be become longer on the 18650, but with gradually dimming light output.

On my Malkoff M60 lights which use a voltage buck circuit for regulation, I see a slightly higher output with a pair of CR123 or RCR123 cells than on an 18650, but the difference is not very much with fresh batteries. As the batteries discharge, the 18650 will drop out of regulation and get dimmer before dying completely, while the RCR123s will just suddenly go out without warning when the low voltage protection on one of the batteries kicks in. Primary CR123 cells don't have protection and will gradually get dimmer until they die.