Hi, i just want to ask which 18650 battery is better for my convoy flashlight with 105c driver, i added two 7135 so that’s max of 3.5A. i am considering the samsung 25R but is that overkill for this because i will only be using 3.5A maximum? How about the panasonic 18650pf 2900mah 10A. I want a battery that will be able to maintain the 3.5A even at low voltage let’s say at 3.5v, or is that even possible with any battery? I looked at this graph but i don’t know how to read that. http://lygte-info.dk/review/batteries2012/Common18650comparator.php
The question you need to ask is which battery has less voltage sag under a 3.5A load as it discharges. The amount of current an LED can pass is directly linked to the amount of voltage you can supply it.
The only reason we use the higher discharge batteries isn't because we need their peak discharge capability, but instead because they generally have a lower internal resistance, which means that they will have less voltage sag under heavy loads.
If you want to maintain 3.5A throughout the discharge curve as long as possible, I recommend the LG D1 or LG E1 4.35v batteries.
Nope, no possible to do 3.5A at 3.5v with a linear driver like 105c. The led itself needs more voltage than 3.5v to reach 3.5A. This is why RMM is pointing out that you need to look for batteries that can keep the voltage up longer.
4.35v batteries like the LG D1 or LG E1 will need 4.35v charger in order to get the benefit.
Which battery (18650) can maintain 3.6V at 3A loan the longest? I wish i could overlay every battery HKJ has reviewed to figure it out instead of doing it one by one with his comparator.
I find below 3.6V it falls out of regulation.
Bort, you mean including 4.35v cells or only 4.2?
I haven't found anything that is as good as the LG D1 at 3 amps with HKJ's comparitor.
i guess both, 4.2V chargers/batteries are more common but 4.35 may offer more runtime/brightness
Thanks for the input guys. I don’t have charger for 4.35v batteries. Will the lg d1 work ok even if i charge it at only 4.2v?
I read that the LG D1 has an internal resistance of 0.08ohms while the panasonic PF has 0.035ohms. I thought that the lower the IR the better or am i wrong?
Lower internal resistance means less voltage drop under load but high drain cells often go hand in hand with lower mAhr capacity. With the new higher Vf LEDs were probably all going to want(need) 4.35V cells and chargers.
I had compared the LG D1 to the LG HE2 IMR,but at 5 amps,and there,all of the IMR’s beat the 4.35v cells hands down.For the EE X6 however,at 3-3.5 amps they sound perfect.I’ve got a pair of D1’s plus a pair of protected Samsung SDI 30Bs,soon to be unprotected and an Xtar VP2 with 4.35v switch.
It would work, but it would be worse than if you used a good 4.2v cell. You need a 4.35v charger to get any of the 4.35v benefit. You would be better off with something like a Panasonic PF/BD, Samsung 25R, LG HE2, or other good 4.2v cell than trying to use a 4.35v cell with a 4.2v charger.
[quote] I read that the LG D1 has an internal resistance of 0.08ohms while the panasonic PF has 0.035ohms. I thought that the lower the IR the better or am i wrong? [/quote]
You are right, the lower the IR the less voltage sag under load, but you are forgetting that the 4.35v cells start with a 0.15v advantage, so unless the load is heavy the 4.35v cell with higher resistance can still maintain a higher voltage than the 4.2v cell with lower resistance. At a certain amp draw, that will no longer hold true.
The following calculations are purely theoretical and in real life I would expect slightly different results, and the discharge chart seems to give different results. I don't think that static resistance measurements in these cells are the end of the story. When you look at the following calculations, it would appear that at 3.5A the Pana PF would kill the LG D1 at 3.5A...and it might initially, but it doesn't over the entire discharge curve.
V=IR
VDrop = Amps * Resistance
0.1225v = 3.5 * 0.035. 4.2v-0.1225v=4.0775v (Pana PF)
0.28v = 3.5 * 0.08. 4.35v-0.28v=4.07v (LG D1)
How about a constant current driver?
Linear regulator IS a CC driver