I’ve recently changed the power supply of my Solarforce M9 from two 18650 rechargeable batteries to 3 cr123 non rechargeable ones to get the the maximum 9 V that the LED-bulb vill tolerate.
I’ve filled the space for the 4:th battery with a metallic bolt with the length of a battery and it’s head resting in the tail cap.
Why?
Most drivers will have exactly the same brightness on 7V and 9V.
Anyway, your CR123 will probably give lower voltage to the driver than the 18650 batteries for a lot of the runtime.
Maximum throw in Solarforce m9 will be obtained by 9 V, not by 7.4 (two 18650 batteries)
I did not know Solarforce used a cheap unstabilized driver, anyway you 3xCR123 will only give your about 7.5 volt and that is optimistic. With LiIon you will get longer runtime and higher voltage.
In these curve you have to follow the blue or probably somewhere between the blue and cyan curve.
For 3 CR123 multiply the voltage by 3.
For two LiIon multiply the voltage by 2.
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3x 3 V adds to 9,
A CR123 battery only has 3 volt when unloaded, if you turn the light on the voltage will drop to about 2.5 volt (See above curves for more precise values).
The resistance in loaded batteries is negliable and the difference in throw is even more marked when I compare one 18650 to two cr123 in the shortened version of the flashlight.
However, i agree that runtime is longer with 18650 batteries.
Regards
No, it is not. Try doing some actual measurements.
I do have a curve where I compare two LiIon batteries to 3 CR123 batteries.
The LiIon batteries are smaller than 18650 and can only run the light for about the same time as CR123, but with higher voltage all the way, except the first few seconds. This curve is only at 1A, LiIon will have a large advantage at higher current drain.
But I am still surprised that Solarforce is not using a stabilized driver and it must be really bad to have a visible difference on this small voltage difference.
This is very common, most buck drivers requires slightly above 4 volt, before they can drive the led at full power. Two CR123 is about 5 volt.
Here is a curve of that configuration:
The curves are from here: http://lygte-info.dk/info/CR123A%20and%20rechargeable%20substitutes%20UK.html
for Your insightful comments. I normally use my M9 only in the shortened version, the long version being too cumbersome in the dog walk and I will continue to use two cr123 since runtime is not an issue.
Regards
Bosse
That was not what your wrote in the first post.
A single 18650 cell is often a compromise between runtime and brightness (Except for light with buck/boost drivers).
If you only need a short runtime, you could also look at two 16340 LiIon cells, that might save you some money in the long run and might give you some extra brightness in high mode.
To Quite another topic.
I’ve recently ordered a 1300 lm Cree drop in bulb to my Surefire 6p, driven by two Cr123’s
What do You think of that combination?
Regards
Bossr
Sounds like someone trying to argue with yoda over the ‘force’.
:-)))
If you get a difference in brightness based of the voltage, solarforce has some work to do on their end.
Two Cr123’s ill not provide near enough power to drive any LED anywhere near 1300 lumen.
Which batteries will be able to power a 1300 lm LED-bulb?
Is there a cut off point in voltage for maximum light for LED- bulbs, the rest of the battery power only dictating runtime
I doubt it is 1300 lumen.
To get anywhere near 1300 lumen you need a current of about 3A, this is about twice the current that a CR123 can deliver, i.e. you need two CR123 in parallel and two CR123 in series to get enough voltage. That mean 4 CR123 to get near 1300 lumen.