Direct Drive as a "Mode"

Fird · Jan 31, 2008

This is just a random thought I had yesterday.

Here's what I'm talking about. I'm out in a situation where I really need a light, it might be an emergency. I have my trusty [insert regulated flashlight name here], and everything's good. Suddenly I see the dreaded blinky warning that my precious lithium cell(s) are just about spent. I really need a workable light for whatever reason for a bit longer, and the cost of the lithium cell I might destroy by doing this is something I'm willing to risk. I'd like to be able to click it into 'direct drive' (with a resistor if it's a 2+ cell light) and run that battery right into the ground.

First obvious answer I know I'm going to get: reach for your backup cell(s). Answer: it's dead.

Second obvious answer: Reach for your backup light
Answer: I loaned it out

Third obvious answer: it's a protected cell, it's going to cut out at 2.6v anyway.
Answer: well pretend it's an unprotected cell

.

Just an idea, I don't really know if it would have practical value at all.

Fird

slvoid · Jan 31, 2008

This is taken directly from the Novatac manual.

As the battery becomes depleted, it will not be able to supply enough power to run the light at its selected brightness. It will momentarily turn off, then back on at half of its previous brightness. This step down process repeats as the battery is depleted. When the lowest brightness level is reached, the light will blink continuously until the battery can no longer power the light. The battery should be replaced before the light reaches this point.

If there is continued use of a rechargeable battery after the light has dropped to its lowest brightness level, it is assumed you are in an emergency situation and the light will sacrifice the battery to remain on.

Although I find that when the novatac won't use a cell anymore, my old hds edc b42 will nurse on it for another 1-2 hours on the lowest setting.

I came to the light... · Jan 31, 2008

That sounds like it could be really useful, additionally because you could start it up a bit higher. But I think it shouldn't really be considered unless it can be worked unobtrusively into the UI very well - it could be a huge pain, as sometimes you wouldn't be able to tell that you've switched into it.

LEDninja · Jan 31, 2008

Trying to run lithiums into the ground is NOT a good idea. That is when lithiums are 2nd most likely to explode. (Most likely is improper charging.)

slvoid · Jan 31, 2008

Then you'll end up with a hand grenade with an extremely long unpredictable delay.

Gary123 · Jan 31, 2008

I like the idea of a direct drive mode option because you can prolong runtime with frequent use of direct drive. I know this works best only when started as soon as the battery is installed. You would do it if you need to prolong runtime, because it is an emergency - or you don't have ready access to batteries or a charger.

Lobo · Jan 31, 2008

I would think it's a great idea! Maybe not with explosive materials like lithium and li-ion, but with alkas and NiMH. I've noticed that a lot of the later multilevel lights can shine for a LONG time on low, but it doesnt really matter since the circuit demands more power for turning on than what the LED needs to lit up. In other words, if you turn of the light on low power, it won't turn on again, even though the battery still has plenty of power to lit up the LED.

On a sidenote, does both lithium and rechargable li-ion explode if run too far? I thought they where relatively safe unless you ran 2 unmatched cells in series? Cause there are a LOT of rechargable li-ions out there in cells and laptops, and most users don't have a clue how to threat a battery, so you would assume that the technology would be close to idiotproof.

Lighthouse one · Jan 31, 2008

Ninja Maybe I'm wrong, but it was my understanding that running the li-ions very low will not make them unstable...flame out. Rather, it's the uneven power level...one battery too much stronger than another that will cause an overheat situation.
I have a modified direct drive Seoul led light that I love as an emergency light. It uses an 18650....and will run 12 hours on an unprotected cell.
I've tried it- while checking battery voltage, and current draw as it runs down. What happened was this. Starts around 700ma..real strong light.
after an hour- down to 450ma. Then soon it's at 200ma- and the output is great- no overheat issues. After about 8 hours it's at 50 ma. Amazing, but the light is still very good at this level. Finally at 12 hours I stopped the test. It was drawing 9ma...the level was good enough for a no power situation, and the battery was just a little under 2.75 volts. A protected battery would probably have done as good, but shut off on it's own after 10 hours or so.

Fird · Jan 31, 2008

LEDninja said:
Trying to run lithiums into the ground is NOT a good idea. That is when lithiums are 2nd most likely to explode. (Most likely is improper charging.)

That's one of the concerns I thought about. Maybe not Li-ions, dunno.

For the switch into the "direct drive" mode, I was thinking to have a separate physical internal switch, to basically bypass the driver and leave just the tailswitch and LED (and a resistor if necessary) inline. That way it would be impossible to switch into it by mistake under normal operating conditions, you'd have to remove bezel and reflector and flip a (dip?) switch on the pcb underneath to force it into direct drive mode. Once that's done, clearly label the pcb, and you're in good shape.

I've already spotted a problem as I've been writing this, and that is, how can one flip the switch in a dark emergency situation..

Alternately, it could be a switching sequence during the 'low battery' state, where the light refuses to power up, press and hold... The internal microcontroller would have to function just enough at 2.7v to cause it to switch into direct drive (a latching solid state switch if such a thing is possible.

I dunno, the UI problem seems to be the largest one to me, and I don't have a perfect solution.

I was not aware of the Novatec's behavior with a dying battery, that's COOL that someone has thought about this before! Their method might be the best, just let it go automatically. Problem: what if I forgot my light on in my pocket, I just sacrificed a battery for no reason..

Fird

slvoid · Feb 1, 2008

Fird said:
That's one of the concerns I thought about. Maybe not Li-ions, dunno.

For the switch into the "direct drive" mode, I was thinking to have a separate physical internal switch, to basically bypass the driver and leave just the tailswitch and LED (and a resistor if necessary) inline. That way it would be impossible to switch into it by mistake under normal operating conditions, you'd have to remove bezel and reflector and flip a (dip?) switch on the pcb underneath to force it into direct drive mode. Once that's done, clearly label the pcb, and you're in good shape.

I've already spotted a problem as I've been writing this, and that is, how can one flip the switch in a dark emergency situation..

Alternately, it could be a switching sequence during the 'low battery' state, where the light refuses to power up, press and hold... The internal microcontroller would have to function just enough at 2.7v to cause it to switch into direct drive (a latching solid state switch if such a thing is possible.

I dunno, the UI problem seems to be the largest one to me, and I don't have a perfect solution.

I was not aware of the Novatec's behavior with a dying battery, that's COOL that someone has thought about this before! Their method might be the best, just let it go automatically. Problem: what if I forgot my light on in my pocket, I just sacrificed a battery for no reason..

Fird

Seeing as how the hds/novatac's can run a light for hundreds of hours on the lowest level in your pocket... i think you'll have to be dead and lying in a ditch with the light on in order for it to run down far enough to sacrafice a battery.

precisionworks · Feb 1, 2008

hds/novatac's can run a light for hundreds of hours on the lowest level

0.3 lumens for 240 hours ... with lower settings/longer runtimes available (NovaTac 120P)

Fird · Feb 1, 2008

slvoid said:
Seeing as how the hds/novatac's can run a light for hundreds of hours on the lowest level in your pocket... i think you'll have to be dead and lying in a ditch with the light on in order for it to run down far enough to sacrafice a battery.

LOL! well if that's how long it'll run... I need a Novatec.

So, other uses for direct drive? it's been mentioned that it will increase the runtime if started at 100% battery charge.. I think that's only true if you would be running the regulation at 100%, If I start my light on low, and only need low...

Anyway, other ideas are appreciated!

Fird

MikeSalt · Feb 1, 2008

Fird said:
Second obvious answer: Reach for your backup light
Answer: I loaned it out

Sorry, I just had to say it. In the spirit of CPF:

...

...

...

Reach for your backup to the backup light! :crackup:

But yes, DD would be good for non-lithiums.

Fird · Feb 1, 2008

MikeSalt said:
Sorry, I just had to say it. In the spirit of CPF:

...

...

...

Reach for your backup to the backup light!

But yes, DD would be good for non-lithiums.

HAAAAAAAA haha, yes, and I would if I had one.. my light collection is in progress right now lol. :broke:

Fird

slvoid · Feb 1, 2008

Also, with regards to accidentally turning it on and/or leaving it on.
The novatac's can be programmed to have an auto-off feature (it starts blinking after 5 minutes or something then cycles down and turns itself off) and time delayed automatic button lock (takes a triple click to turn it on for the first time after 5 minutes of inactivity), both features can be independantly activated and deactivated.

Fird said:
LOL! well if that's how long it'll run... I need a Novatec.

So, other uses for direct drive? it's been mentioned that it will increase the runtime if started at 100% battery charge.. I think that's only true if you would be running the regulation at 100%, If I start my light on low, and only need low...

Anyway, other ideas are appreciated!

Fird

tony22r · Feb 1, 2008

slvoid said:
...the light will sacrifice the battery to remain on...

That sounds pretty useful.

I didn't like the way my P2D just quit without warning when batt was "dead".

I started looking at Crenshaw's Battery Vampire Lights thread for a battery eater light.

I assume the Novatac P's can do that without "exloding" the lithium battery, right?

Also, I believe when Surefires drop out of regulation, they go into some kind of "resistored" direct drive mode, right?

I think that would be a nice "mode" to have on multi-mode lights to get the most out of a battery.

jzmtl · Feb 1, 2008

I don't quite get why you want a seperate direct drive mode. Doesn't alot of regulated lights go into direct drive when the circuit cannot supply desired voltage anyway?

greenLED · Feb 1, 2008

jzmtl said:
I don't quite get why you want a seperate direct drive mode. Doesn't alot of regulated lights go into direct drive when the circuit cannot supply desired voltage anyway?

Exactly my thoughts.:shrug:

270winchester · Feb 1, 2008

I thought so too, at least from my experience using Surefires, HDS, Novatac, McGizmo lights, etc.

Although I do remember seeing a few Fenixes abruptly shut down on various levels with no warning due to battery depletion, a price some people are willing to pay for a flatter output curve.:shrug:

greenLED said:
Exactly my thoughts.:shrug:

slvoid · Feb 1, 2008

For some reason, I think the novatac is regulated all the way down to 0.08 lumens. Cause I've had it completely refuse to turn on, like dead dead, popped the battery into my HDS light, and had it going a bit longer on the lowest setting on that light.

Direct Drive as a "Mode"

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