Hi, I was wondering if there is a way to make a single LED only come on when my voltage is low enough, letting me know I need to charge the battery, so I don't damage it.. I plan on making a box mod, and I don't have a lot of room to work with it; I don't really want to add a volt display, or even the ones for rc, where I have to keep an eye on the levels. Is there anything simple?
LED low volt indicator
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Well that is definately close to what I was thinking of, but it is for a higher volt system, do you know what I should change on that in order to get it to the right voltages for my use?
The simplest method would be to use an LED that has a forward voltage the same or about the same voltage as what you want your batt's cut off voltage to be.
Except the LED would light at full batt voltage, dim as the batt's voltage drops, then cut off completely when the batt's voltage gets at or below the forward voltage of the LED.
The wiring would be: + batt > 150 or 220 ohm resistor > + LED leg > - LED leg to - batt. You could also use a small tact switch to turn on and off the LED to check batt status instead of having it on all the time.
You can find LEDs that have a forward voltage of around 3.2v - 3.5v which should work for a low voltage cut off with a single 3.7v batt.
Here's an example of LEDs with their rated forward voltage...
Except the LED would light at full batt voltage, dim as the batt's voltage drops, then cut off completely when the batt's voltage gets at or below the forward voltage of the LED.
The wiring would be: + batt > 150 or 220 ohm resistor > + LED leg > - LED leg to - batt. You could also use a small tact switch to turn on and off the LED to check batt status instead of having it on all the time.
You can find LEDs that have a forward voltage of around 3.2v - 3.5v which should work for a low voltage cut off with a single 3.7v batt.
Here's an example of LEDs with their rated forward voltage...
That definitely sounds better, where can I find those UV led's? The only thing I could find in google are bulk 1000 led's. Or any other color for that matter..
Also I plan on making a box mod similar to http://www.ecigadvanced.com/community/how-to-easily-build-a-variable-voltage-dual-18650-wood-mod/ if I had 1 led in there wouldn't it destroy the led if it is over the max forward voltage even with a resistor? (I have 2 3.7v batteries, I am going to use UCC383T-5 regulator to bring it to 5v) Should I use a different resistor? Sorry if I have silly or common sense questions, I am learning.
Also I plan on making a box mod similar to http://www.ecigadvanced.com/community/how-to-easily-build-a-variable-voltage-dual-18650-wood-mod/ if I had 1 led in there wouldn't it destroy the led if it is over the max forward voltage even with a resistor? (I have 2 3.7v batteries, I am going to use UCC383T-5 regulator to bring it to 5v) Should I use a different resistor? Sorry if I have silly or common sense questions, I am learning.
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You can use 2 or more LEDs in series, or LED + Zener diode to up the total forward voltage.
With a few mods, I used a 220 ohm resister + 5.6v zener diode + LED as a batt status indicator.
Or you can use an LM431 shunt regulator like I used my my flip-top mod. Check my thread here for the pdf step-by-step how-to: Double 18650 VV Regulated Flip-Top Mod
With a few mods, I used a 220 ohm resister + 5.6v zener diode + LED as a batt status indicator.
Or you can use an LM431 shunt regulator like I used my my flip-top mod. Check my thread here for the pdf step-by-step how-to: Double 18650 VV Regulated Flip-Top Mod
Alright that seems to make sense, I wouldn't mind 2 leds. Thank you for that 
I have one other question, instead of using the UCC383T-5 regulator, I am thinking about LDO 5 volt, 3.0 amp Regulator with Control Pin because it is cheaper.. well it has 4 pins instead of the 3 used in http://www.e-cigarette-forum.com/forum/battery-mods/97743-what-ti-voltage-regulator-use-5v-mod-3.html so how would I wire the pins to make it work in this mod?
I have one other question, instead of using the UCC383T-5 regulator, I am thinking about LDO 5 volt, 3.0 amp Regulator with Control Pin because it is cheaper.. well it has 4 pins instead of the 3 used in http://www.e-cigarette-forum.com/forum/battery-mods/97743-what-ti-voltage-regulator-use-5v-mod-3.html so how would I wire the pins to make it work in this mod?
Hey, would there be any easy way to make the LED come on only when it reaches that certain voltage? Say I have 2 x 3.7v running in series, the lowest I want each one to get to is 3.2v each, so I want the LED to come on at 6.4v. Or even making a cut off at that voltage, I would much prefer that over an LED.
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