I’m just getting into this fun, and I have a basic battery question. I understand sizes, protected vs. unprotected and capacity, but I’m having a hard time with Max Discharge Current. Some flashlights seem to require a high discharge current, others specify a low current (stating that high discharge will damage them) and the bulk don’t say anything about it. Is there a way to tell what type of battery a specific light will be happy with? If the manufacturer does not specify, can I use a high or low discharge with no issues? Is their a benefit to one type over the other? Thanks!
You can generally tell by looking at the emitter and type of driver:
Some emitters work well at high currents (such as XPL HI). Others have problems (Oslon White Flat).
If you’re using an emitter that has problems at high current the next thing to do is check the driver. Is it one that limits current (such as a 4x or 8x 7135) or does it have a FET? If it has a FET it can probably deliver very high current to the emitter. If you couple that with emitters which can’t handle the current then you should not run low resistance high-ouput cells in it.
High discharge cells are usually IMR. They are sometimes referred to as low-resistance cells.
Some lights, like the FW3A can handle very high current in their stock form (FET with 3x XPL HI), but lack the heatsinking to take it for long. In the FW3A low discharge high capacity cells are recommended, but not required. Low discharge cells will run longer at turbo before the light gets too hot, but turbo on a fresh cell will be dimmer. In the FW3A, the light should function fine on low or high discharge cells, but the temp sensor will ramp output down faster if you use low resistance cells.
Okay, that makes sense to me. Let’s talk a specific. I have ordered a Thrunite Newtron 2C V3. It has a XP-L V6 Led and no mention of the driver. It comes with a protected “High Drain” cell, but I don’t see an actual number for it (I don’t have the light yet). So, do I use the same type of cell as a backup, or will unprotected cells work as well?
According to this review: Review: ThruNite Neutron 2C V3 with Ramping Firmware , this light can only pull about 3A, so pretty much any name brand cell should work. You don’t really need a high drain cell for it, but you can use a high drain cell if you want to - it just won’t benefit this light.
Unprotected cells are fine since this light has LVP. However, it looks like the head end has no spring, so you may need a button-top cell.
Higher drain cells generally have lower internal resistance, and v/v.
With higher resistance, as you pull more current, two things happen.
First, I²R losses generate heat inside the cell itself. More current means more heat (squared).
Second, IR losses cause voltage sag. Less voltage available to the goodies it’s powering.
Higher drain cells can then deliver more current with less heat (like using bigger-gauge wire), and also minimise voltage sag (uhh, like using bigger-gauge wire).
Internal resistance will cause voltage-sag, so yeah, top current will be more limited vs a higher-drain cell, but that’d also heat up the cell’s innards more.
2A vs 3A wouldn’t be too much to worry about, though.
