Low voltage cutoff or alarm?

Flashlight Modding and DIY Parts
1

I’d like to add some sort of low voltage protection to this

http://www.fasttech.com/products/1602/10002726/1202200-067-cree-xp-g-r5-3w-led-348lm-5-mode-white-headla

I put a cell protection circuit in the battery holder, but that has two problems.

  1. cutoff is too low (I want 3V).
  2. once cutoff occurs, power must be applied to the protection circuit in order to restore normal functioning

If I could find a protection circuit that cutoff at 3V, I could add a momentary switch to the battery holder, so that I could apply power to the circuit from a fresh battery. But…I’d prefer to avoid that extra work.

I’d be ok with an audible low voltage warning.

I could modify the voltage indicators that use colored LEDs to indicate voltage, but I’d have to remove the LED that indicates ~3V, and mount it where it is visible during normal use (again, extra work).

I found this, which is available for less on ebay.
http://dx.com/p/2-in-1-1-8s-lipo-battery-low-voltage-buzzer-alarm-for-rc-helicopter-white-black-180468

3 problems

  1. really loud (could reduce that volume but might ruin them trying)
  2. it is big, so it’d have to be mounted on the outside of the battery holder
  3. depending on parasitic drain, i’d probably add a switch to have the option of disabling it.

Does anybody have better ideas or products I could try?

2

A TaskLED driver is what you want :wink:

3

Actually, I like the driver that is in the light…except for the lack of low voltage protection…

and I definitely do not like taskled prices, especially since I’d like to add low voltage protection to three of these headlamps…

4

the only thing I can think of is using a DrJones driver which has a great low voltage response - current is cut by 50% when 3V is reached, then again and again (as the battery keeps hitting 3V) until it gets down to moonlight mode. The only trouble is that I don’t know how it would work with your current switch and the dual LED set up. He has an e-switch version in the works and he’d probably be able to set up a driver to control 2 different LEDs, but you’d have to ask him about that yourself as I have no idea how :slight_smile:

5

I thought I liked that type at first, but after realizing the danger and also just trying one on (annoying) I went with: “4 Mode 1200 Lumen CREE XML T6 Bulb LED Bicycle bike HeadLight Lamp Flashlight Light Headlamp” for $29 on Amazon. I really dont like having a Li-ion on the back of my head even with voltage cutoffs. The 4 mode has a cable to a 4 battery battery pack that really isnt as bothersome as you might think, and the light is very bright (prob 700 lumen) with great throw (I can even see the spot in my J18 beam on at the same time), low modes last a long time, it wont go into strobe mode unless you hold the switch for 3 seconds so that annoyance is eliminated as well (wish I had that on my other lights). I’ve been on 3.5hr hikes with high mode on and it did not run down, and I think you could go through the entire night in the northern hemisphere with low mode on.

6

may be overconstrained, constrained to such a point that a solution does not exist, unless you build your own comparator circuit.

7

thanks for the suggestions, but I guess I should have been clearer in the OP.

so, I’ll try again.

Does anyone know of

  1. a li-ion cell protection circuit that cuts off at 3.0V instead of 2.75V or 2.5V.
    or
  2. a low voltage warning/alarm that is smaller than this

http://dx.com/p/2-in-1-1-8s-lipo-battery-low-voltage-buzzer-alarm-for-rc-helicopter-white-black-180468

thanks