Gary123
Enlightened
Which provides longer runtime, two rechargeable 123's or one 17670?
Thanks
Thanks
Last edited:
17670 vs 2x123
- Thread starter Gary123
- Start date
Help Support Candle Power Flashlight Forum
2xTrinity
Flashlight Enthusiast
A lot of this will probably depend on what you're doing, but I'd suspect the 17670 in most applications because it should have slightly more energy content as not as much internal space is taken up with contacts and packaging, which there is more of with two smaller cells.
In lights that run on either 2 123s, or a single cell (17670, or even 18650), the 17670 is almost always longer running by a large margin, though occasionally the output is higher from two cells (Lumapower M1). This is because those drivers are less efficient the further away the input voltage (from the batteries) is from the ouput voltage (3.7V or so at the LED). In the case of the 17670, the two voltages are close, to the convertor doesn't have to do as much "converting" and thus is more efficient.
Even comparing two separate lights powering 3.7V LEDs with the same ouptut, one designed to run only on 123s, another only on 17670s, I'd expect the latter to have a slightly more efficient driver, and have an advantage due the extra energy capacity. However, the situtaion might be reversed if you are driving something that requires ~8 volts, in that case, the 17670 would have to be stepped up a lot, and the 2 CR123s would be closer.
In lights that run on either 2 123s, or a single cell (17670, or even 18650), the 17670 is almost always longer running by a large margin, though occasionally the output is higher from two cells (Lumapower M1). This is because those drivers are less efficient the further away the input voltage (from the batteries) is from the ouput voltage (3.7V or so at the LED). In the case of the 17670, the two voltages are close, to the convertor doesn't have to do as much "converting" and thus is more efficient.
Even comparing two separate lights powering 3.7V LEDs with the same ouptut, one designed to run only on 123s, another only on 17670s, I'd expect the latter to have a slightly more efficient driver, and have an advantage due the extra energy capacity. However, the situtaion might be reversed if you are driving something that requires ~8 volts, in that case, the 17670 would have to be stepped up a lot, and the 2 CR123s would be closer.
Last edited:
Depends on the driver type and efficiency. For a linear regulator, the 17670 will be more efficient and most likely provide longer runtime. Depends though also on the efficiency of the linear regulator and it's drop-out voltage and ability to sustain output voltage at what range of input voltage. For a SMPS, same thing...depends on the efficiency of the SMPS at those specific voltages and the capability of the SMPS to vary it's PWM or PFM control. Some may not be able to go low enough pulse width or frequency to make full use of the higher voltage and end up supplying more current than when using a 3.7V supply resulting in lower runtimes.
This isn't a simple A or B question...depends on the driver design. Many lights use linear regulators because they're low priced to design and mfr, low part count, and take up less board real-estate. Some lights use SMPSs, but not all are very good resulting in poor efficiency when running at higher (6V) voltages due to lack of ability to reduce control signal appropriately to maintain the proper Vo.
This isn't a simple A or B question...depends on the driver design. Many lights use linear regulators because they're low priced to design and mfr, low part count, and take up less board real-estate. Some lights use SMPSs, but not all are very good resulting in poor efficiency when running at higher (6V) voltages due to lack of ability to reduce control signal appropriately to maintain the proper Vo.
kakster
Flashlight Enthusiast
17650 is 4.2v x 1600ma = 6.72 watt hours
2 SF123 is 6.4v x 1300ma = 8.32 watt hours
So going on published specs alone, the 2 lithium primaries hold the advantage when it comes to pure energy density.
However, as the previous posters have said, Lithium Ion rechargables do have a few characteristics that are desirable. The main one is the ability to hold its voltage under heavy loads, so this makes li ions the cell of choice when it comes to high drain applications.
Of course, they also work out cheaper in the long run due to the fact that they can be recharged and re-used.
2 SF123 is 6.4v x 1300ma = 8.32 watt hours
So going on published specs alone, the 2 lithium primaries hold the advantage when it comes to pure energy density.
However, as the previous posters have said, Lithium Ion rechargables do have a few characteristics that are desirable. The main one is the ability to hold its voltage under heavy loads, so this makes li ions the cell of choice when it comes to high drain applications.
Of course, they also work out cheaper in the long run due to the fact that they can be recharged and re-used.
2xTrinity
Flashlight Enthusiast
Rechargeable CR123s (what the OP asked about) have lower energy density than the primaries unfortunately. I think around 700-800mAh @ 3.7V nominal, rather than 1300mAh at 3V nominal. So there, the 17670 clearly has an advantage. Primaries have the advantage of higher energy density, and shelf-life, so having a light that can take both primary CR123s, and single-cell LiIon rechargeables is nice.
kakster
Flashlight Enthusiast
D'oh, didn't see "rechargable" CR123s, you're quite right.
Unless you specifically need a high voltage (Lux 3, cree or seoul using a buck circuit), the single larger cell wins hands down.
Unless you specifically need a high voltage (Lux 3, cree or seoul using a buck circuit), the single larger cell wins hands down.
