Digital battery meter on your flashlight?

[skyline_man]

Just came up with this idea today and was wondering if anyone has done it before. I am thinking of installing a small permanent digital voltmeter on one of my 18650 flashlight so that i can tell how much volts i have left before the flashlight conks out.
The LED display will only turn on when im using my light and it will be mounted in the centre of the light where the manufacturers label is. The only problem is finding an LED display small enough to fit. I know that i can get one out of those gold plated car battery terminals that they sell.

It would look real cool i reckon!

 

[moon lander]

if its possible that would be excellent, ive already ruined 3 14500 cells in my jetbeam mk2x by running them for too long.

 

[JB01245]

I have looking for something similar. Stumbled across this, what do you think?

Battery Monitor
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXLMR1&P=7

 

[skyline_man]

cant see what the other side looks like. It Certainly is narrow enough.

 

[Cydonia]

I think it is a good idea. (Even an analog dial meter the size of a watch face would be cool. Can pick em up surplus real cheap at some places.)
Not knowing the state of your battery charge or how much run time is left is pathetic really when you think about it. Really stone age primitive isn't it?

 

[LED Cool]

not really a meter but the LiteFlux LF2 has a battery voltage indicator feature and a battery over discharge protection feature.

khoo

 

[skyline_man]

I reckon it's the next big step for manufacturers of high end flashlights. If they can somehow incorporate a digital LED meter into their flashlights - waterproof and shockproof of course, that tells you how much power u have left and flashes when u have 10 or so minutes left or even a count down timer to tell you how much time is left.

Way of the future.

Anyway, found a small red LED panel off of one of my old digital car amp fuse holder. Im going to mount it on one of my cheapy lights first. Have to either drill two holes through the anodizing or rub it down so that there is electrical contact between the body and the LED connectors.
The only problem i can see is that being a 12volt LED voltmeter, it might chew up a bit of power from the flashlight battery just to run it....il see...

 

[chris_m]

Some high end bikelights have a gas gauge in the form of an LED bar graph. This has to be a much better way of providing the information you need than a voltmeter!

I have a slightly different approach with my homemade high powered lights. Capacity remaining is shown by the duty cycle of a 1/2 Hz flashing LED - ie when it is steady the battery is fully charged, flashing on and off for equal periods means it is half empty, very brief flashes means it is almost dead. Field use suggests this also works well. You could certainly incorporate something like this into your flashlight, as you only need space for 1 LED. If there is interest in this sort of thing I could probably throw together a stand-alone circuit for it (mine is integrated into the multi-level controller).

The advantage of either approach over a simple voltmeter is that you can model the discharge curve in the uC and so have a linear meter (though temperature variation does affect this a bit).

 

[jumpstat]

not really a meter but the LiteFlux LF2 has a battery voltage indicator feature and a battery over discharge protection feature.

khoo

:twothumbs very useful indeed! Should have this in all flashlights..

 

[flashlite]

Could you use 3 or 4 small red LED's, each with a different size resistor to indicate battery strength? All lit means full strength, 1 lit means almost dead.

The Nite Ize 3 LED Mini Mag upgrade has a red LED in with the white LED cluster that lights when power is low.

 

[skyline_man]

I have a slightly different approach with my homemade high powered lights. Capacity remaining is shown by the duty cycle of a 1/2 Hz flashing LED - ie when it is steady the battery is fully charged, flashing on and off for equal periods means it is half empty, very brief flashes means it is almost dead. Field use suggests this also works well. You could certainly incorporate something like this into your flashlight, as you only need space for 1 LED

Interesting, yes - a single LED would be a better alternative - less current draw from the battery. Where can i get this circuit?

 

[TORCH_BOY]

Thats a great idea

 

[Kilovolt]

I believe the Pila Codex is something really similar to what you're after

http://edcreviews.blogspot.com/2007/05/pila-codex.html

and more here

http://www.pilatorch.com/codex.htm

 

[kromeke]

The old Tekna lite 2D had a battery meter in the form of 3 LEDs. It had a red, yellow and green LEDs near the switch which was supposed to tell you the status of the batteries.

See photo: http://www.tek-tite.com/src/images/tekna_flashlights.jpg

 

[HenryE]

Almost exactly two years ago I invented a BATTERY RUNTIME METER, which counts down from some user-preset number of minutes while the flashlight is ON. When the light is OFF the countdown stops, and one can glance at the always-on display (like a digital watch) to see how many minutes remain on the charge.

I filed a patent application that protects the REMAINING RUNTIME IN MINUTES concept, as it applies to flashlights, power tools, medical instruments, and any other device powered by lithium or nickel metal hydride cells.

Three months ago I was advised by the USPTO that my application for patent was approved. I've paid the fees and am awaiting issuance.

My partner and I are looking for potential licensees. I think that as a feature in high-end flashlights this invention will add an important competitive advantage.

Cost of implementation in a large-volume flashlight is amortized tooling plus less than $1 per light.

 

[wvaltakis2]

I have looking for something similar. Stumbled across this, what do you think?

Battery Monitor
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXLMR1&P=7

I actually hacked one of those into a lightsaber a couple years ago, alot of work but very cool in the end. I replaced the gold panel you can see in the pic.

~Chip

 

[ringzero]

The old Tekna lite 2D had a battery meter in the form of 3 LEDs. It had a red, yellow and green LEDs near the switch which was supposed to tell you the status of the batteries.

See photo: http://www.tek-tite.com/src/images/tekna_flashlights.jpg

Yes, I remember those.

Tekna also made some 2AA dive-rated lights with Green-Yellow-Red LEDs for a while back in the 1980s.

As I recall their 3-LED system worked fairly well as a warning when to change the cells. It also gave the user some idea of remaining cell life when the light was first picked up and turned on.

Very useful system. I've often wondered why no other manufacuter has done something similar in the 20 years since Tekna did it. The power to run the little LED indicator is tiny compared to the power to the emitter.

.

 

[Stereodude]

A battery meter on a light that uses NiMH cells won't do much good because they don't really drop in voltage over their usage until they finally die.

 

[fangle]

Plain volt meters or runtime timers can give misleading results from different discharge currents or non-linear discharge voltage curves from your batteries.

Google on "battery gas gauge" and you will find a number of manufacturers making ICs that measure the battery as it charges and as it discharges, telling you how much capacity is left. TI's bq27500 is one, I believe they have a bunch of others as well. Linear Technology makes them, as do others like Maxim. Maxim can be very friendly with their free engineering samples IIRC. Hint, Hint. I see there are some with Li-ion protection built in as well.

Alternately, here's a little circuit that claims to linearize the NiMH discharge curve. I haven't used it but it looks interesting. Anyone to do it in surface mount to save space? http://www.hagtech.com/pdf/fuel.pdf

 

[N162E]

I filed a patent application that protects the REMAINING RUNTIME IN MINUTES concept, as it applies to flashlights, power tools, medical instruments, and any other device powered by lithium or nickel metal hydride cells.

Three months ago I was advised by the USPTO that my application for patent was approved. I've paid the fees and am awaiting issuance.

You can start out by filing a lawsuit against Sony. Your patent exactly describes their Infolithium technology present in all of their video cameras for the last 7 years.