14500 LiFePO4 battery

Calina

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I have a 10 year old L1D Fenix light that I would like to power with a LiFePO4 battery and I have a few questions :

Did anybody try that? Is there a risk of frying the LED? And lastly, what is the highest capacity available for these batteries (I've seen what seems like crazy numbers on AliExpress)?

Thank you.

 
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Calina

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According to Fenix, the L1D shouldn't be used with a 3.2 volt LiFePo4 battery. I find this curious since the L1D uses the same head as the L2D that works with 2 AA batteries.

What is the highest capacity 14500
LiFePo4 battery
currently available ?
 

Timothybil

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According to Fenix, the L1D shouldn't be used with a 3.2 volt LiFePo4 battery. I find this curious since the L1D uses the same head as the L2D that works with 2 AA batteries.
That's not really surprising, since two AA cells in series gives six volts, while a fresh 14500 LiFePO4 just off the charger will put out 3.7 volts for a while. Also, while the L1D head may work on an L2D, are you sure that they are the same. It's the same thing when someone says they are running a 10440 cell in a single AAA light. It will probably work, be insanely bright for a while, but at best you are shortening the life of the LED due to overheating, and at worst the overheating will extend to the driver circuitry and prematurely wear those components out as well. It boils down to risk, and how much you are willing to take. Are you willing to risk premature if not immediate death of your light just to get more output. It can't be just the rechargeability, since one can get that with a NiMH cell.
Probably the quickest way to determine the highest capacity good 14500 would be to look at the reviews HKJ has done. He is very exhaustive in this tests, and lays it all out for us.
 

vicv

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Um.... 2xAA in series gives 3 volts initially. Will drop almost immediately to 2.4v. So a single LifePO4 will be 3.2v under load for the majority of its discharge which is quite a bit higher
 

Calina

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That's not really surprising, since two AA cells in series gives six volts, while a fresh 14500 LiFePO4 just off the charger will put out 3.7 volts for a while. Also, while the L1D head may work on an L2D, are you sure that they are the same.
Probably the quickest way to determine the highest capacity good 14500 would be to look at the reviews HKJ has done. He is very exhaustive in this tests, and lays it all out for us.

Two AA give 3 volts , LiFePO4 has a nominal voltage of 3.2 volts. When I bought my lights, Fenix was offering a kit (that is what I actually got) which included, a diffuser, the L2D and the tube of the L1D, so yes, the L2D and the L1D both use the same head.
Thanks the HKJ reference, I'll check it out. :thumbsup:
 

Timothybil

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Two AA give 3 volts , LiFePO4 has a nominal voltage of 3.2 volts. When I bought my lights, Fenix was offering a kit (that is what I actually got) which included, a diffuser, the L2D and the tube of the L1D, so yes, the L2D and the L1D both use the same head.
Thanks the HKJ reference, I'll check it out. :thumbsup:
You are right, two AA in series gives three volts. I guess I got mixed up with two CR123 in series.

So what you are saying is that the kit you got contained an L2D body, an L1D body, and a head that could be used on either. In that case, I would say that you probably will be safe using a 14500 in the L1d. Fresh off the charge the 14500 LiFePO4 cell will be 3.7v, but I would expect it to drop rather rapidly down to around 3.4 or so, which is not that great of a difference from three volts. As WalkIntoTheLight says, the only way to be sure is to try it. And even then you won't know if you are prematurely aging any components. You are the one who has to decide if the extra output while using the L1D body is worth the possible expense of having to replace the light sooner than otherwise.
 

vicv

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A LifePO4 cell will be 3.6v fully charged. The instant a load is put on it it'll drop to 3.2-3.3v(depending on load and ir) so the light will never see 3.6v. It's not like a lithium ion that steadily drops. That is the same as two fresh lithium iron disulfide cells so it'll be just fine
 

vicv

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Yes usually it drops to 3.35v or so within a couple hours. My point was the light will never see 3.7v even fresh off the charger as the voltage drops instantly under load
 

chillinn

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A LifePO4 cell will be 3.6v fully charged.The instant a load is put on it it'll drop to 3.2-3.3v(depending on load and ir) so the light will never see 3.6v. It's not like a lithium ion that steadily drops. That is the same as two fresh lithium iron disulfide cells so it'll be just fine


Apologies for sticking my nose in here, but not quite, vivc; I know you know the knitty gritty, but accuracy may be important. LiFePO4 cylindrical cell termination voltage is 3.65v, but many smart chargers don't show more than one significant digit, and will display a 3.7v termination voltage when charging is complete, presumably the termination voltage is still 3.65v, but the display will round it. I only mention because manufacturers and retailers are now using voltage specs to identify cells of different chemistry, "a 3.6v cell, a 3.7v cell" etc. Generally speaking, an advertised "3.6v cell" will either be a primary lithium cell that has about that voltage fresh, or a secondary Li-ion chemistry that terminates at 4.2v fully charged but rides 3.6v under load for most of its discharge profile, or averages about 3.6v for the same. A 3.7v cell will be a secondary Li-ion chemistry cell that terminates at 4.35v fully charged, but rides close to 3.7v under load for most of its discharge profile,or averages about 3.7v for the same. Hope you see why I posted. LiFePO4 secondary cells are advertised as 3.2v cells, not because the charge dips to that under load (whether it does or not I have no idea), but because after a LiFePO4 cell reaches charge termination of 3.65v, and then fully rests, it will rest around 3.34v–3.42v, but for most of its dischage it will hover around 3.2v no matter what the charge at rest is. /pedant


edit: slow route, HKJ beat me to it, and you already replied... I'm still talking about stuff from a half hour ago... \o/
 
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HKJ

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presumably the termination voltage is still 3.65v, but the display will round it.

The termination voltage varies between 3.6V and 3.7V, depending on charger, you can easily see that on the curves in my charger reviews.

And I would not assume a cell marked 3.7V need 4.35V charge termination.
 

vicv

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Exactly. But unlike other lithium chemistry rechargables where the 3.6v is nominal; kind of like an average; a LifePO4 cell instantly drops to 3.1-3.3v (depending on load) and stays there almost like regulation until it's dead. Putting a light load on a normal lithium cell the load could see 4.2v at turn on before the voltage steadily drops and the cell discharges. Whereas the LifePO4 cell will instantly drop to it's working voltage
 

chillinn

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The termination voltage varies between 3.6V and 3.7V, depending on charger, you can easily see that on the curves in my charger reviews.

And I would not assume a cell marked 3.7V need 4.35V charge termination.

Wise words, which highlights why I posted. Advertisers are using nominal voltages to define and identify cells, and that doesn't really work, because a "nominal" voltage says absolutely nothing about the state of charge of the cell nor clearly reveals what the chemistry is, which is why I specified "in general." Must never assume anything.


Exactly. But unlike other lithium chemistry rechargables where the 3.6v is nominal; kind of like an average; a LifePO4 cell instantly drops to 3.1-3.3v (depending on load) and stays there almost like regulation until it's dead. Putting a light load on a normal lithium cell the load could see 4.2v at turn on before the voltage steadily drops and the cell discharges. Whereas the LifePO4 cell will instantly drop to it's working voltage

Ok, but just to be clear, nominal means "in name only" and has no other meaning (in this context). So talking about nominal voltages is kind of silly, though everyone does it.


FWIW IMO it would be a lot less ambiguous and less confusing for advertisers and manufacturers to call 3.6v cells 4.2v cells; 3.7v cells 4.35v cells; 3.2v cells 3.7v cells; and 3v primaries 3.4v cells. IOW, if they chose the termination voltage as the nominal voltage instead of what must instead be something like an average voltage over the dischage time. YMMV
 
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