witch resistor for P7
- Thread starter landries
- Start date
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mdocod
Flashaholic
Hi landries,
Based on the information provided, nobody could accurately answer the question.
The only way to answer the question would be to have an LED and 26650 equal to the ones you are using to test. As different 26650s are going to have different behavior, and each P7 will have a slightly different effective Vf...
In some cases, if the Vf of your LED is high enough, and the natural resistance in your design is high enough, you won't need any resistor at all. In other cases, with a low Vf and low resistance cell and host, you may need quite a but of added resistance.
Usually the best way to decide on a final resistor to use is to experiment. Start with a "relatively" high resistance and work your way down. Or use an adjustable resistor and a multi-meter to find an optimal point. Do testing with a freshly charged cell, so that your maximum current desired occurs at that point.
I'm guessing that your final required resistance will be somewhere between 0 and 0.33 ohm.
Hope that helps
-Eric
Based on the information provided, nobody could accurately answer the question.
The only way to answer the question would be to have an LED and 26650 equal to the ones you are using to test. As different 26650s are going to have different behavior, and each P7 will have a slightly different effective Vf...
In some cases, if the Vf of your LED is high enough, and the natural resistance in your design is high enough, you won't need any resistor at all. In other cases, with a low Vf and low resistance cell and host, you may need quite a but of added resistance.
Usually the best way to decide on a final resistor to use is to experiment. Start with a "relatively" high resistance and work your way down. Or use an adjustable resistor and a multi-meter to find an optimal point. Do testing with a freshly charged cell, so that your maximum current desired occurs at that point.
I'm guessing that your final required resistance will be somewhere between 0 and 0.33 ohm.
Hope that helps
-Eric
lolzertank
Enlightened
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What he said. Also, if you're using LiFePO4 cells, it won't work without a boost circuit unless you're fine with a low drive current or if you have a very low vf P7.
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What he said. Also, if you're using LiFePO4 cells, it won't work without a boost circuit unless you're fine with a low drive current or if you have a very low vf P7.
bshanahan14rulz
Flashlight Enthusiast
so there is no way to figure out mathematically what resistor you need, even if you know voltage drop of LED, resistance of cell, etc? Why can't you just do R=V/I where V=Vsource-Vf
You can do exactly that, given accurate knowledge of Vf and Vsource (both for the specific current in question). But we don't know either of those for landries's case...
bshanahan14rulz
Flashlight Enthusiast
Ok, cool. I've been sitting here thinking DD was way more complicated than it was. So those boards like at KD and DX, those are DD, but they pwm to dim, right? so no current regulation save for an onboard resistor somewhere in the circuit? This is so awesome!
