Two newbie questions

timothydavidson1

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Feb 18, 2015
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Hey guys! I have two question that i have searched for but can't find the answer too. I apologize if the answers have been said, but just i just need some clarification.

1. I just bought a Fenix PD22ue and LOVE it so far. I'm running it with a CR123a battery (until my 16340 gets in!) And recently there is no difference between the high and turbo mode. I just put in a new battery last Friday and haven't used it THAT much, i don't think. First off the difference was very noticeable, but is it just by battery going down? Is this normal?

2. I have a Surefire 6P that I want to get a new drop in for. I would to use a 18650 or 17670 battery in it, or two CR123a batteries in it. I see many drop ins with a voltage of 3 to 9 volts or something like that with X amount of lumens. the two rechargeable batteries run at 3.7 volts and two CR123a batteries run at 6 volt. Using these, does that mean i won't get the full lumen out from the drop in, or will my run time just be less with same lumen out?

Sorry for the beginner questions but thanks for the help!
 

GeoBruin

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Sep 20, 2010
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Hello and welcome to CPF!

First let's talk about your PD22ue. Your light is regulated. That means it has a circuit that will deliver a constant amout of current to the LED regardless of the state of charge of battery (to a certain extent). As such, you shouldn't notice your light just slowly getting dimmer. It will put out the same amount of light up until the point where it can't maintain that output any longer. Lights can do a couple different things when their batteries reach that point. A single mode light may just shut off until you replace the battery. Some lights may drop out of their regulated mode and behave like an old school direct drive light where they do just start getting dimmer. In your case, I think something different is going on. Your light knows the battery doesn't have enough voltage to run the turbo mode without having to draw an unsafe amount of current from the battery. It does have enough voltage however to run at it's next highest mode safely. As such, when you switch to turbo, it's only giving you the highest mode it can run given the state of charge of the battery. We refer to this as "step down". Step down can be based on battery voltage, temperature, or even just a timer. In your case, it sounds like you have drained the battery far enough that turbo won't run anymore but high will still function. I can't promise you this is what's happening, but it's my guess based on what you've described. Also note that because of the way our eyes work, you would need to increase the output by a factor of 4 for you to be able to perceive just double the output. Since you're only getting about double the high output on turbo, you're only perceiving .5 times the increase in output on turbo. In the right conditions, that may make it tough to discern between high and turbo. My guess is, you could plug a fresh battery in there (or your new 16340) and you'd be back in business.

As for your 6P, it's a very similar discussion. Almost every drop in available today is regulated. That means that whether you supply 3, or 5, or 9 volts, you're going to get the same output. Now let's talk about batteries for a second. Lithium Cobalt Oxide (LiCo02) is likely the chemistry of lithium ion battery you're talking about. It's the most common cell used in our hobby. You are correct that it has a nominal voltage of 3.7 volts, although when you pull one fresh off your charger, you will actually measure closer to 4.2 volts. A lithium ion battery that registers 3.0 volts is basically dead. In practice, you will likely won't discharge your cells that far before they're back on the charger. All this to say that a drop in rated from 3 - 9 volts will happily accept 1 - 2 lithium ion cells, or 2 - 3 lithium primary cells. Here's the tricky part. You're actually likely to get MORE runtime from a single lithium ion 18650 (or even 17670) than two lithium primary cells. This is because you're running the primaries in series, meaning the capacity is halved (though the voltage is doubled). That means you're only going to get the capacity of a single cell (~1500 mAh) whereas a single 18540 can be rated in excess of 3,000 mAh.

Hope this helps.

Cheers!

-G
 
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timothydavidson1

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Feb 18, 2015
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GeoBruin: Thank you so much for taking the time to respond to my questions!! That all makes sense and i understand it now! On the PD22ue, that's what i was thinking was happening, but just wanted to make sure something wasn't wrong with my light.

Also thanks for the help with the 6P drop in! That too makes sense and I'll now know what that means!

Thanks again!
 

reppans

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Mar 25, 2007
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I agree with most of GB said above, but I think the following could use some clarification.

Here's the tricky part. You're actually likely to get MORE output from a single lithium ion 18650 (or even 17670) than two lithium primary cells. This is because you're running the primaries in series, meaning the capacity is halved (though the voltage is doubled). That means you're only going to get the capacity of a single cell (~1500 mAh) whereas a single 18540 can be rated in excess of 3,000 mAh.

I think GB meant to say more "runtime" as opposed to "output". Also there is an implication that an 18650 will have twice the run time of 2xCr123s, but regulated drivers actually need a given number of watts (Volts x Amps) to achieve a fixed output. So the 6V of 2xCR123 will require a lower amp current to achieve the same output as single 18650. Runtime is determine by Watt-Hours or VxAH, so it's ~ 6x1.5=9 WH vs 3.7x3=11.1 WH.
 

GeoBruin

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Wow, yes good catch reppans. I definitely meant more runtime as opposed to output. I have modified it in my original post to prevent confusion for future readers but we'll keep the mistake immortalized here in your reply.

Regarding your other comment, you are correct that in practice, adding an additional cell in series will increase runtime for exactly the reason you state: lower current will be required to deliver the same output when the voltage is higher. Still, for the OP, the best runtime will be achieved in the following descending order: A single high capacity Li Ion -> two primaries in series ->two lithium ion cells in series.

Also, I did not mention but will add it now that some newer, very high current drop ins including some triples and some of the high output monsters such as those Vinh makes will draw way too much current for primaries. They will require a lithium ion and in some cases a high drain lithium ion to run safely.

thanks again

-G
I agree with most of GB said above, but I think the following could use some clarification.



I think GB meant to say more "runtime" as opposed to "output". Also there is an implication that an 18650 will have twice the run time of 2xCr123s, but regulated drivers actually need a given number of watts (Volts x Amps) to achieve a fixed output. So the 6V of 2xCR123 will require a lower amp current to achieve the same output as single 18650. Runtime is determine by Watt-Hours or VxAH, so it's ~ 6x1.5=9 WH vs 3.7x3=11.1 WH.
 

reppans

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Still, for the OP, the best runtime will be achieved in the following descending order: A single high capacity Li Ion -> two primaries in series ->two lithium ion cells in series.

Yes agreed, not to mention, and perhaps even more importantly, a single lithium config (rechargeable or primary) is far safer than dual cells in series, due to risk of imbalance and reverse charge :).
 

more_vampires

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Nov 20, 2014
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Well, darn! I showed up to help and the questions are already killed! :)

Oh well, maybe next thread. :)
 

KosmoC

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Jan 1, 2015
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Northern IL, USA
I see your questions have already been answered, but I would like to add that I own the PD22UE, and the turbo mode only works while using a 16340 cell. You may get what looks like turbo with a cr123a, but only briefly. This is covered in the owners manual and on the website.

Darn fine light for sure. Mine lives in my pocket all day, every day. Just wait till you try the 16340 cells in it, and you'll see what I mean..:D
 
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