How does it work? One 18650 or two CR123 batteries. Which is brighter?

[Patsplace]

Howdy folks,
I'm a bit confused on which is the better and in this case I mean the brightest light. A single 18650 when the light is regulated for 18650's or two CR123 batteries when the light will take them?

Regards,
Pat

 

[kramer5150]

noob answer....
The simple way to think of it is that the 2xCR123 configuration should be brighter, since you will always have more than sufficient drive Voltage to push the emitter optimally. HOWEVER... if a particular emitter has a lower forward voltage when used in an 18650, then the single 18650 very EASILY could produce more light than a 2xCR123.

So in other words I dont think its that cut and dry, higher cell voltage does not always mean more Lumens.

 

[MrGman]

Your asking the wrong question. Or you are phrasing the question in the wrong manner.

For LED type lights, the battery itself does not make the light brighter or dimmer. The battery is an energy storage device and in the case of regulated LED type lights, you match the type of battery to what the vendor designed the regulator circuitry to work best with. Certain batteries will give you longer run time without diminishing their energy output as fast, not necessarily because of higher or lower voltage. And using it won't make the lights "brighter" than others, just hold the output constant longer, or not.

The 18650 is a large single cell of stored energy that has a lot out ampere hour rating capacity and low internal resistance to current flow at an optimum 3.7V. The CR123 non rechargeable battery has much less stored energy in ampere hour capacity, higher resistance to the current flow (which means voltage will sag under load) at an optimum 3V. Two of these in series for 6V gives more total stored energy than 1 but not necessarily more energy than a good rechargeable 18650. However, if the LED driver was designed to work with something in the 4 to 13V range and it will convert the batteries voltage and current over time to what the LED wants, Using the 18650 battery may not be optimum for it. And vice versa. Using a pair of CR123's for a driver that was made to be optimized for the 18650 battery at 3.7 to 4.2V won't make it work better or be "brighter".

Its gas in the tank, not the size and horsepower rating of the engine. Mismatching battery types to the regulator circuit for an LED could cause the regulator circuit to burn out and fail and then you have either a very dim light or a dead light. 20 gallons of the best diesel fuel in the world won't make a Corvette engine run.

Use the battery type that the vendor recommends best for the flashlight and its driver.

The 18650 rechargeable has better energy storage capacity and due to that there are flashlights designed around it that draw high current. Those flashlights are bright due to the fact that they are consuming high current at 3.7V for lots of watts across the LED. Such as the Wolf Eyes Sniper with a a P7 chip that draws current in the 2.8 amp range. Two CR123's are not going to deliver the type of current needed for very long regardless of the total of 6V. A single 18650 battery with a 2.8 Ampere hour rating will deliver that type of current without much voltage sag and keep this light going. But put that same battery in an LED with a different driver that was looking for higher voltage and even with all that ampere hour capacity that might be dim from the get go and stay that way for 100 hours of on time.

Some flashlights can go either way and advertise running on 4 CR123 batteries (12V nominal) or two 18650 batteries (same physical size) but only 8.4V nominal but will deliver lots of current and keep the light running well longer.

For non regulated lights with actual filaments simply match the battery voltage to the lamp. If it says its 9V lamp use 3 CR123's or 2 18650 that are very close to 9V without every going over the rated voltage. The 2 18650's will keep it running longer at a constant brightness. That is not really the same as saying the 18650 battery will give "brighter" light in and of itself. Its the wrong terminology.

 

[Patsplace]

Thanks for the response. I now know a great deal more than I did, at least now the floating bits of data are organized and useable.

Thanks for the class on LED's and battery selection.

Regards,
Pat

 

[abarth_1200]

i must say MrGman thats was very educational, i thought i knew what was what but that helped, thanks

 

[Bullzeyebill]

Nice concise explanation MrGman. I will bookmark this thread and refer to your post when this question comes up.

Bill

 

[kramer5150]

Wow that was highly educational... thanks:thumbsup:

 

[Illumination]

Very helpful; thank you!! I collected some of this in my head over time, but had difficulty assembling it.

The CR123 non rechargeable battery has much less stored energy in ampere hour capacity, higher resistance to the current flow (which means voltage will sag under load) at an optimum 3V.

I do have one question...can someone further explain the concept of the higher resistance. Does this mean that the battery effectively creates some sort of resistor?

 

[MrGman]

Although I don't normally subscribe to the watt hours terminology, here is another tidbit.

A 3.7V battery really starts out at about 4.2V. Lets just say its 3.8V for most of its useful life. At a 2.8 Ampere hour rating. 3.8V x 2.8 A/Hours is 10.64 watts for an hour (in theory) as far as capacity. That would also be over 21 watts for a half hour or 5.3 watts for 2 hours (in theory). Letting the batteries get hot from heavy load will shorten its cycle but in general that's how it works.

2 non rechargeable CR123's really start life at 3.2V but because of the internal resistance under any useful loads sag down to 2.7V. Lets say the load current is low and they actually hold at 2.9V. Their ampere hour rating is not better than 1.0 each. In series that would be 5.8V X 1 Amp/hour or 5.8 watts for an hour for the pair. It would not be 3.2 V at 2 ampere hours, nor would it be 6V at 2 ampere hours. Batteries in series add up the voltage only but the ampere hour rating remains the same.

Maybe I am lying and you would get a little more. Lets say 6V and 1.2 ampere hours for the pair in series. Thats still only 7.2 watts for an hour.

Now you see that the 18650 battery appears to be a serious workhorse compared to the CR123's even in pairs. However its limitation is its only 3.7V and not suited to most drivers, and its wider by 1mm so it won't fit in a lot of flashlight tubes designed for the CR123.

This is why some guys bore out their flashlights or go for the ones that specifically take this size battery and put in a sleeve when they want to go with the CR123's.

Just for fun I took a laptop battery pack and split it in half. I have 2 18650s in series and that is in parallel with another set for a total of 8.4V and 5.6 Ampere hour rating (if we assume the batteries were in fact good for 2.8 ampere/hour rating each).

What does that do for me? For an LED that only needed 600mA at 8.4V from the driver thats good for 9.3 plus hours of continuous use (in theory). But where do I put this monster battery pack and do I need it to to run this one light source, not really. For an Incandescent Xenon Lamp that is rated at 320 lumens and draws 1.6 amps without a regulator to keep it constant; that battery combo help keeps the voltage from sagging right away and delivers that 1.6 amps giving me at least 13.4 watts of power for up to 3.5 hours (in theory again). If the batteries get hot the cycle time is shortened. But if I did it in bursts, I could potentially get that much out of it. It would take a hell of a lot more CR123's in a series parallel combination to get 13.4 watts for 3.5 hours than 4 each 18650 batteries. First I would have to stack them in a series of 3 to get to the 9V. if they are 1 ampere hour each. 3 sets in parallel of 3 in series is 9V and 3 ampere hours rating. thats 27 watts for 3 hours, no because the voltage will still sag faster than the lithium rechargeables. Lets say 8V at 3 amp hours so now we got 24 watts-hours The flashlight will still draw somewhere around 1.5 to 1.6 amps off this battery combination (voltage will sag and the current draw will not be a well held 1.6 amps, so basically I have about 2 hours of useful run time, give or take a little off of 9 batteries instead of 4. I would need 12 CR123's to really do the same job and maybe get 3 hours and a little more in run time. In reality the 18650's are probably only good for 2.5 Ampere hours not 2.8 so the disparity would not be all that great, but it is still a big deal.

I am making a battery pack to run this Xenon lamp for a bike light. Its actually the Lumens Factory 320 High Output 9V unit. The battery pack will go in a water bottle in the bottle holder and the flashlight is on the handlebars. And having all that oomph to run for 2.5 to 3 hours real run time isn't bad. Especially since the batteries were free from a dead laptop, and I have 2 packs not one.

The moral of this lesson is. If you are running a flashlight that is truly a 3 watt LED light source with a good driver that is drawing less than 600mA from the batteries, low cost CR123's is not a bad way to go. Low cost RCR123's that can be recharged will also work well but not great runtime. But if you are running a current draw battery hog such as a P7 or multiple CREE LED heads, the preferred battery source is 1 or 2 18650's and not 2 to 4 CR123's. That's why most of the heavy current draw flashlights are designed around this battery even though its not common and not sold as a non rechargeable. As an example Wolf Eyes has a flashlight with 3 Cree R2 LED's in the head and runs off 3 18650 batteries in parallel to keep it bright for at least 3 hours. 840 lumens rated output. That is brighter than a car headlight (its about 1.5 headlights) for more than 3 hours out of something that will fit in your hand.

I have not gotten into all the little details of battery sag, due to internal resistances, how the wasted power kills the battery, but its there.

If you want a good long running high power flashlight, pick the light source around the 18650 battery as the primary consideration.

 

[HKJ]

2 non rechargeable CR123's really start life at 3.2V but because of the internal resistance under any useful loads sag down to 2.7V. Lets say the load current is low and they actually hold at 2.9V. Their ampere hour rating is not better than 1.0 each. In series that would be 5.8V X 1 Amp/hour or 5.8 watts for an hour for the pair. It would not be 3.2 V at 2 ampere hours, nor would it be 6V at 2 ampere hours. Batteries in series add up the voltage only but the ampere hour rating remains the same.

Your Ah rating for CR123 is very low, see this thread for some real numbers:
http://candlepowerforums.com/vb/showthread.php?t=67078

PS: This does not change your conclusion.

 

[MrGman]

Your Ah rating for CR123 is very low, see this thread for some real numbers:
http://candlepowerforums.com/vb/showthread.php?t=67078

PS: This does not change your conclusion.

Yeah, that thread shows higher current rating for the better rated batteries but still relatively low watt hours because of voltage sag. So 2 Surefire CR123's together show about 7.2 watt hours of energy on that chart, which I actually listed in the middle where I said "lets say its actually 7.2 watt hours ". Still much lower than the 18650 for the pair of CR123's. I listed lower numbers because at higher current loads you just don't get all that out of them.

So the disparity is somewhat less but still a great disparity over the 2 cell types. Overall, we still concur. Thanks, G