Re: Φορουμ για φακους!!
18650 battery h 2*CR123 ποια απο της δυο ειναι καλυτερη?ελλαδα δεν υπαρχουν?
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I have a question regarding batteries and my LED light.
I have a Q5 CREE LED light from ultrafire.
What is the difference between using one 18650 3.7 volt battery and using two CR123A's 3.6 volts?
Isn't two 3.6 volt batteries actually 7.2 volts?
So would I get more power/length from the 2 batteries?
The LED's operating voltage is 3.6 to 9 volts.
It really depends...
In the case of the cheap electronics from the ultafire it's hard to say exactly what will happen but let's go thru a basic comparison between the two power sources.
An RCR123 runs average 3.7V and has a capacity of around 700 mAh (a generous estimate imho) therefore we have (volts x amps = watts) ~2.6 watt hours per cell. 2 of them are therefore around 5.2 watt hours.
An 18650 also using the same chemistry runs an aerage 3.7V and has a capacity of about 2200 mAh. So we have 8.1 watt hours.
The 18650 is clearly superior on paper.
LED lights don't get brighter from more voltage like incandescant lights do. LEDs have a very specific voltage required to make the LED light up. So driver ciruits are often put into lights which allow use of a range of voltages and cell configurations.
Now depending on the driver circuit the 18650 may or may not run the LED at full power. In the case of your ultrafire I'd bet it only stays in regulation for half of the battery life on an 18650. Then after that it will start to dim slowly as the simple circuit no longer controls the voltage to the LED. However this will just give you even more runtime on an 18650 for a negledgeable drop in output.
So in almost every case I'd go with the 18650.
One other thing to point out is that lithium batteries don't like to be driven at more than 1C or so. So for a CR-123 battery you're looking at an optimistic 800 ma draw before voltage sags and you start losing more power in the batteries internal resistance, and cell chemistry limits. So you effectively have a battery that can't output as much as it's rated for. But if you must absolutely have flat regulation go for CR-123's as they'll output voltage higher than the vF of the led. The disadvatage is that you'll go from full power to no light with practically no warning since all of a sudden a cell will go into protection, or worse if you're using unmatched primaries is you're light will go
I personally don't mind my 18650's dimming, gives me warning that I need to change the batteries with freshly charged ones. And though I only get half the battery time with regulation on the light, that half is actually longer than the total runtime on 2 RCR-123's.
I think too many people were indoctrinated by Surefire and Inova to think CR-123 is the ideal power source, I mean Surfire even has a light that uses 20 CR-123 batteries called The Beast II that's just inviting trouble to try and power it with that many individual primaries, think of it as a bomb in your hand with about a 2 hour fuse before a bunch of cells start reverse charging and BOOM goes the dynamite.
mAH alone does not translate to runtime, total WattHour energy storage at the load in question does.
A CR123 primary delivers an average ~2.5V during a discharge, while lithium cobalt rechargeable cells deliver about 3.7V on average into a load. Both voltage and capacity must be factored in to describe the total energy stored in a cell.
There are also variations in the way that these cells perform at different loads. Generally speaking, the li-ion rechargeable cell starts to pull ahead of 2 CR123s when the load gets a little higher, while a pair of CR123s will have more available stored energy when discharged slowly.
In the end, a 1x18650 light and a 2xCR123 light are going to be in the same ballpark of total runtime, as both configurations have similar stored energy.
After factoring in the fact that the 18650 is rechargeable, comparing it to a primary configuration is less meaningful, it should instead be compared to other rechargeable options as the recharge-ability is a major feature that sets it apart. To get the same output/runtime from competing battery configurations would require 4 RCR123s or 3AA NIMH or 3 14500 li-ion cells. All of which would be far more space consuming.
If your ultimate goal is runtime, your best bet is going to be to run a single larger Li-Ion cell to drive the module, this will reduce your output some, but will give you a very efficient use of the cell through the discharge, with a steady but barely noticeable drop in output through the discharge.
The stock 6P does not have room for an 18650 (you could run a single 17670 if you want), but if runtime and recharge-ability in that platform are the goal, then you'll want to pick up an 18650 compatible body for the light. CPF member Nite is selling some FM brand bodies that are really decent over in the custom-mod/BST section of this forum.
As far as rechargeable vs primary runtime comparisons, this is a comparison that is not really fair to make, but I will try to summarize some of the important points:
A pair of CR123s packs slightly more stored energy than a single 18650 cell when the 2 configurations are compared at a LOW drain rate (like an LED module).
A single 18650 packs slightly more stored energy than a pair of CR123s when the 2 configurations are compared at a higher drain rate (like an incandescent module).
A Single 18650, with its lower voltage than a pair of CR123s, will operate most buck regulated LED modules at a lower (read "direct drive or less") output than would be the case on a pair of CR123s. This results in less output, but much more runtime because less energy gets used over time.
So... the answer to most of your questions will always depend on the specific configurations being compared.
If your main goal is to get really good runtime, then I suggest you take the following things under consideration:
1. RCR123s are the worst option for maximizing your stored energy.
2. Something with multiple modes will allow you to run for extended periods of time with less power consumption.
3. Just because a pair of CR123s technically has more stored energy than an 18650 at low drain rates, does not mean that you will always be leaving the house with a fresh set of CR123s loaded. With Li-Ion cells, you can "top off" your cells whenever you feel like it. This means that you are always starting "fresh" and never have to play the guessing game of how much of the batteries you have used up and whether you need to bring along spares.
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