# battery efficiency, increased runtime mod?



## 5S8Zh5 (Dec 27, 2014)

Are there any mods that increase the runtime of rechargeable or throw away batteries?




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## 5S8Zh5 (Dec 28, 2014)

I kind of figured, but I didn't know. ..








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## gofastman (Jan 11, 2015)

Better cooling will increase led efficiency. That's about all I can think of.
is there a particular light you are working with?


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## mcnair55 (Jan 11, 2015)

Are you in need of a few cents towards some batteries?:shakehead


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## darkknightlight (Jan 12, 2015)

Decreasing total system resistance will help, but I'm not really sure by how much. Maybe you can give us some specifics about your light? Or is this just more of a general question?

Edit: I need to qualify my statement. Decreasing total system resistance should allow you to use marginally more of your battery's capacity in many applications, which in turn should increase your runtime in regulated applications. It does not actually alter the battery at all.


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## more_vampires (Jan 12, 2015)

5S8Zh5 said:


> Are there any mods that increase the runtime of rechargeable or throw away batteries?_



Cheapest and easiest? Start with a non-regulated light... you know, one that just has a limiting resistor and such does not give flat output runtime? Perhaps those cheap led 6v lantern-cell lights at Wally's for like $4 (with a free battery.) So cheap if you wreck it, so what?

It'll do for a proof of concept and there's lots of space in there to mess around and you can substitute an AAx4 battery holder to power the light and leave even MORE room... for a stash or whatever. More spare batteries!  It'll also make the thing more likely to float.

Anyway, make the limiting resistor a bigger value by swapping or simply adding another one to the circuit. 1 cut, 2 solder joints or crimps. Done. Less light comes out, but now you can play the moonlight game. There is no driver to get confused in the kind of light I'm talking about and it'll most likely be quite cheap.

If you've not got resistors to play with, a quick trip to the Rat Shack for a sampler should be all you need to get started. Might pick up a switch or three so you can do stuff like cut the extra resistor in and out of the circuit for your "high mode."

Off the shelf, there are a great many options for very well-made lights with very low modes that streeeeeeeeetch that runtime way out! You can also do it yourself on a shoestring budget.

Many choices. Good luck!


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## more_vampires (Jan 12, 2015)

darkknightlight said:


> Decreasing total system resistance will help, but I'm not really sure by how much. Maybe you can give us some specifics about your light? Or is this just more of a general question?
> 
> Edit: I need to qualify my statement. Decreasing total system resistance should allow you to use marginally more of your battery's capacity in many applications, which in turn should increase your runtime in regulated applications. It does not actually alter the battery at all.



To clarify, decreasing resistance should help if it is regulated with a driver as there'd be less waste heat. The mod I mentioned with increasing resistance applies to driver-less lights, as in just a simple limiting resistor. Burn less juice in the led, less output = more runtime.

...unless you want to call the limiting resistor a driver. Muddy waters! Oh no!


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## darkknightlight (Jan 12, 2015)

I'll be first to say I have a lot to learn in this area  so please explain to me when I'm wrong! If something I say is wrong, it's because I don't realize it 
More_vampires (nice handle by the way) when you add a limiting resistor to the circuit, don't you create a source of waste heat? 

Here's my best quick analogy for what I said earlier: by limiting total system resistance, don't you effectively create a marginally larger "fuel tank? "


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## more_vampires (Jan 12, 2015)

darkknightlight said:


> I'll be first to say I have a lot to learn in this area  so please explain to me when I'm wrong! If something I say is wrong, it's because I don't realize it
> More_vampires (nice handle by the way) when you add a limiting resistor to the circuit, don't you create a source of waste heat? "



Thanks, and hey, friendly flashlight conversation is how we learn!  I'm the first to admit that I never know enough. Any CPF'er who can chime in, please do so. If we screw up badly enough, someone will correct us. 

Anyway, here goes:

A real driver is basically a "reactive device." You could think of it as a miniature computer. It has to figure out how to react to let through based on trying to keep the current constant. Inefficient drivers give off lots of waste heat because the designer cut costs wherever possible. Thus, reducing system resistance as far as the driver helps battery life by going to a better driver. ...a more efficient one.

A limiting resistor is a "non reactive device." It doesn't care. It's more like a lever. When the battery pushes so hard, it does it's thing according to Ohm's law and the reactivity of the main diode. It's the same Ohm value every day of the week. Reactive components like the real driver circuit mentioned above do different things based on waveforms and such. Complicated, the math involves "imaginary numbers." Anyway, For the most part, if you hook the LED directly to battery (direct drive,) it tends to fry the LED in short order (depending on how much juice you had on tap.) That said, there are custom makers here at CPF that make short duration blasters with the direct drive method. 

The limiting resistor setup is about the simplest method of "regulation" (though it's not actually regulating,) therefore cheap, therefore widely used on cheap lights.

The limit resistor DOES create waste heat, but this is offset by the LED being under driven (so it lasts nearly forever.) It isn't quite like "any energy not burned by the led is burned by the resistor." Perhaps more like "a larger voltage drop across the resistor leaves less for the LED." Think of a plumbing pipe; the larger pipe moves more water faster, the narrower pipe provides less flow. Adding the limit resistor puts a narrow section in the plumbing line, thus reducing flow. The key to limit resistors is that they're simple, easy to fiddle with, and a lot of fun for some low-skill modding. You could literally lead a science lab of school children doing this. You don't even have to be particularly good at soldering.

What are the other sources of system resistance? You've got the battery, the LED, the switch, and any method used to complete the circuit. A fine tweak is to increase surface area of the contacts touching the battery. A common method used here is to use braided copper "solder wick" and soak it with hot solder on the end of the spring contact (or whatever) in your circuit. Decreasing losses anywhere in the system will help battery life, but you've got to watch out for diminishing returns for your effort. ...unless you're just having fun! :thumbsup:

Switching to more conductive materials will reduce waste heat, but there's diminishing returns. I'm not saying your flashlight is junk unless you're running on 24k gold wire.



darkknightlight said:


> Here's my best quick analogy for this: by limiting total system resistance, don't you effectively create a marginally larger "fuel tank?



My take on that would be limiting system resistance is like swapping your car's engine for one that has less internal friction and higher efficiency. You're on the same batteries, so the "gas tank" would be exactly the same. You're burning less gas with a smaller 4 cylinder, not a larger 6 cylinder engine. There is less lost in friction between the rings and cylinders.

You can't just feed the LED however much power it'll take. The "vF" value of an LED changes non-linearly. That is, it acts differently depending on what's going on in the circuit. It's a class of discrete components called "reactive components." Any diode, coil, or capacitor does this and it isn't a simple ratio like Ohm's law. Voltage is equal to current times (resistance and reactivity.) The limit resistor design tries to play more like Ohm's law (and it's not perfect.) The complete driver circuit is more like the thermostat on your HVAC system in your house.

Reactivity is like Resistance's crazy brother.


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## more_vampires (Jan 12, 2015)

One more thing:

Limit-resistor-only setups cause output to fall off as the battery drains. You're not getting constant output with this setup. It's exactly like an incandescent flashlight dying. If you can put up with barely any light output, you can get massive runtimes this way.

Proper drivers can "suck harder" (muahahaha :laughing as the battery dies to keep output more or less the same until the voltage falls below some critical number.

You've got two ways to fly. Neither is wrong, each has advantages.


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## darkknightlight (Jan 12, 2015)

Thanks for your input! I love friendly flashlight discussions; it's how those of us less technically-minded folk learn 

So i guess I have a couple questions now. Why introduce a limiting resistor into a direct drive setup if the light source can survive the voltage/current? Like I said, it (intuitively) seems like a source of wasted energy. Incan or otherwise, if you introduce system resistance in a direct drive light, some source energy must be lost/burned-off before it makes it to the light source, right? The reason to introduce a limiting resistor in a direct drive setup would be to protect the light source from destruction. For example, a copper-mounted XML2 with adequate heatsinking can survive direct drive from an 18650 while an XPE2 in the same circumstances cannot. So introduce resistance (limiting resistor) in the XPE2 system to keep the led from burning out. But why introduce resistance in the XML2 circuit?

On the other side, why place a limiting resistor prior to the driver? If you have a "regulating" driver, decreasing total system resistance only serves to keep the driver in regulation longer, right?

I feel like I'm missing something really important, so I'm sorry if I'm pulling this thread way off. Like I said, I have more of an "intuitive" understanding rather than a technical one.



more_vampires said:


> One more thing:
> 
> Limit-resistor-only setups cause output to fall off as the battery drains. You're not getting constant output with this setup. It's exactly like an incandescent flashlight dying. If you can put up with barely any light output, you can get massive runtimes this way.
> 
> ...


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## 5S8Zh5 (Jan 12, 2015)

Good stuff guys. I'm trying to soak it in. ..


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## more_vampires (Jan 13, 2015)

darkknightlight said:


> Thanks for your input! I love friendly flashlight discussions; it's how those of us less technically-minded folk learn



Anytime, friend. Way better than a "train wreck" thread! 



darkknightlight said:


> Why introduce a limiting resistor into a direct drive setup if the light source can survive the voltage/current?


Good question. If you want a max blaster with a runtime of 2-6 minutes, this is exactly what you do. A small value (higher wattage rated) resistor can "tone it down" slightly if your battery is too hot. Also to consider is that different battery chemistries can handle different max amp draw. A resistorless direct drive build may work with one chemistry and then  burn when you put a battery in that handles a higher draw.



darkknightlight said:


> Like I said, it (intuitively) seems like a source of wasted energy. Incan or otherwise, if you introduce system resistance in a direct drive light, some source energy must be lost/burned-off before it makes it to the light source, right? The reason to introduce a limiting resistor in a direct drive setup would be to protect the light source from destruction. For example, a copper-mounted XML2 with adequate heatsinking can survive direct drive from an 18650 while an XPE2 in the same circumstances cannot. So introduce resistance (limiting resistor) in the XPE2 system to keep the led from burning out. But why introduce resistance in the XML2 circuit?



It sounds like you've got it exactly! Just don't forget different battery chemistries. It kinda throws a wildcard in the mix.



darkknightlight said:


> On the other side, why place a limiting resistor prior to the driver? If you have a "regulating" driver, decreasing total system resistance only serves to keep the driver in regulation longer, right?



I think you've got it. You wouldn't throw a limit resistor in there in that case. It would likely "confuse" the driver and make it act strangely. Don't forget that the regulating driver changes its resistance (reactivity actually) such that it has different values under different conditions. If across the board you reduced the driver resistance then the LED gets brighter and amp draw on the battery increases as the driver is now letting more juice through. (See also: "current boost mod.")



darkknightlight said:


> I feel like I'm missing something really important, so I'm sorry if I'm pulling this thread way off. Like I said, I have more of an "intuitive" understanding rather than a technical one.


Not at all, sounds like you've got a pretty good handle on it. That is, assuming I have any clue what I'm talking about at all. 

Not derailing the thread at all, title is "battery efficiency, increased runtime mod?" We're all good!


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## more_vampires (Jan 13, 2015)

I love this thread!


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## darkknightlight (Jan 13, 2015)

Sorry, I think I gave the impression that I know little about direct drive led set ups. I know enough about them not to totally destroy whatever light source I'm powering  my questions about introducing resistance were one-sided. I was looking at it from the efficiency standpoint, and not the runtime perspective. My bad! I owe everyone here an apology for not being clear. One of my personal faults is that I don't realize until after the fact that I haven't communicated everything banging around in my head 
More_vampires, I love this thread too!

As an aside, direct drive lights are probably my favorite way to do things. I grew up on incan Maglites, and I appreciate the diminishing output curve.


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## more_vampires (Jan 14, 2015)

Friendly flashlight and electronics discussion is why I'm here! Besides, think of the lurker noobs we're inspiring!


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