nihm vs. lithium

[vic2367]

ok....AA rechargeable nihm 2600 mah vs. 2600 mah lithiums same size AA,,,,which are better and why ? currently have the aa rechargeable nihms 2600mahs ,,,but am thinking of buying some 2600 mahs lithium rechargeables,,,any difference in performance ?

 

[cratz2]

I was thinking the Lithiums were 2800 or 2900 mAh.

Even if they are both an honest 2600 mAh, the primary Lithiums are 1.7V and the NiMH cells are 1.2V so there is literally more power in the Lithium cell.

In general, higher drain lights will have longer runtimes with Lithiums. Things like the Fenix L1D and L2D, Rex, C-LEs, things like that on high will have noticably better runtimes with Lithiums. Low drain lights like the Infinity Ultra or Fenix E0 will have a bit longer runtime, but not as much of a difference as with the higher drain lights.

Personally, I tend to use more NiMH cells, mostly for environmental and financial reasons as I know I'll be more likely to use a light a lot if it's fed with either NiMH or LiIon cells. I keep Lithiums in rarely used lights and in my EDC if I know I'll be out and about and expecting to use my light quite a bit. I keep a 4 pack of AA Lithiums in my car so I always have them on hand.

 

[vic2367]

are lions and lithiums the same thing ?

 

[vic2367]

the highest mahs ive found for the lithiums were 2600 mahs,,,are there any higher mahs available ? these battery will be for a fenix l2d-ce,,,just reieved it and am looking for a very good battery ,,,

 

[vic2367]

hey arent lithiums rated at 3.6v ?

 

[SilverFox]

Hello Vic,

Lithium AA cells, like the Energizer L91, are rated at 3000 mAh and a nominal voltage of 1.5 volts, even though they start off at around 1.7 volts. These cells are not rechargeable.

NiMh AA cells are around 2700 mAh, and have a mid point voltage of around 1.2 volts. They hold voltage higher under heavy loads, and are rechargeable.

Li-Ion AA cells are listed as 14500 in metric size. They have a nominal voltage of 3.7 volts and a capacity of around 700 mAh. These cells are rechargeable.

If you want to use a Li-Ion AA cell, you need to make sure your application can handle the higher voltage, or it will burn out.

Tom

 

[vic2367]

hey tom,,,that was very informational....thanks,,,

 

[vic2367]

can i use 2 of the 3.7v in the fenic l2d -ce ? am looking at the li-ion...

 

[bridgman]

>>can i use 2 of the 3.7v in the fenic l2d -ce ? am looking at the li-ion...

Nope. Poof !!

The L2D-CE runs normally up to just over 3V, ie 2 Lithium non-rechargeables, 2 NiMH rechargeables, or 2 alkaline non-rechargeable AAs. Some people have run with a single 3.7V cell in the L1D-CE but you lose the lower modes (they're all kinda like Max brightness). Nobody has mentioned a single 3.7V cell hurting the flashlight but certainly more than 1 3.7v cell would be a Bad Thing.

Remember that the L1D and L2D are the same flashlight with a different tube connecting the head and switch assemblies, so the L2D isn't "designed for higher voltages" or anything like that.

 

[vic2367]

thanks everyone ,,,,learned alot tonight,,,am going to stick with my recharegable nihm....

 

[Katdaddy]

Dumb newbie question.
Why the difference in power between the Li-Ions and other batteries of the same size? For those of us who are unenlightened this could be a big problem.

 

[SilverFox]

Hello Katdaddy,

Different chemicals when mixed together produce different voltages.

Tom

 

[Katdaddy]

Hello Katdaddy,

Different chemicals when mixed together produce different voltages.

Tom

That's simple enough! I'm still not sure I understand why not adjust the mixture so all cells of same size have comparable ratings?

 

[mudman cj]

Unfortunately it's not that simple. Each battery chemistry has a different chemical reaction that provides the energy, and this usually means different ions are carrying that energy. If you tried to conduct two different reactions simultaneously in one cell, the higher voltage-yielding reaction would polarize the battery much stronger than the lower voltage-yielding reaction would normally, so the lower voltage-yielding reaction would probably be driven in reverse. And to make things worse, each battery chemistry requires different electrode materials.

Never use cells of different chemistries together in series or in parallel because one will discharge quickly into another and then you could have real trouble.

 

[SilverFox]

Hello Katdaddy,

Sorry for the confusion...

Li-Ion chemistry is naturally higher in voltage. The size of the cell has nothing to do with the voltage. The size of the cell limits the amount of material you can stuff into it. This directly effects the capacity, but the voltage is defined by the chemistry used.

Li-Ion has a nominal voltage of 3.7 volts.
Li-Iron-Sulfite has a nominal voltage of 3.3 volts.
Lithium Manganese Dioxide (used in CR123 cells) has a nominal voltage of 3.0 volts.
Lead Acid has a nominal voltage of 2.0 volts.
Lithium Iron Disulfide (Energizer L91 AA) has a nominal voltage of 1.5 volts.
Alkaline has a nominal voltage of 1.5 volts.
Carbon Zinc has a nominal voltage of 1.5 volts.
NiMh has a nominal voltage of 1.2 volts.
NiCd has a nominal voltage of 1.2 volts.

There are others out there, but that is some of the most common ones.

You can't mix a little lithium along with some nickel to adjust the voltage. Well, at least not yet...

Tom

 

[txmatt]

In general, higher drain lights will have longer runtimes with Lithiums. Things like the Fenix L1D and L2D, Rex, C-LEs, things like that on high will have noticably better runtimes with Lithiums. Low drain lights like the Infinity Ultra or Fenix E0 will have a bit longer runtime, but not as much of a difference as with the higher drain lights.

I have always thought the same thing, but the runtimes of the L2D CE seem to show otherwise.

http://candlepowerforums.com/vb/showthread.php?t=155819

The lithium AA's run ~27% longer on max (140 minutes vs 110 minutes) but they run ~43% longer on low (~5150 minutes vs ~3600 minutes).
I guess the low internal resistance of NiMH makes up for the capacity gap at high current draws. That said, the capacity gap between the 2650 NiMH's and the L91 Lithiums wouldn't indicate a 43% difference, so maybe there's something else going on here, like self-discharge in the NiMH over a 2.5 day run.

Whatever the reason, the Lithiums provide a pretty significant increase in runtimes (more than a day on low). If you wanted to load up an L2D CE with two batteries and not carry any spares/chargers, I think the L91's would be worth the additional cost.

 

[MrAl]

Hi,

I like both types of cells, but with the NiMH 15 minute chargers you can get back
up and running much faster than with the Li-ion cells even if you dont have any
extras laying around already charged.

 

[Power Me Up]

Different chemicals when mixed together produce different voltages.

I know you're probably referring to the electrodes, but for the benefit of those that think you're actually meaning the electrolyte, the voltage is mostly influenced by the different reactivities of the electrodes. The more disimilar the electrodes, the higher the voltage potential. Lithium is highly reactive which is why cells using that material have a relatively high voltage.

 

[SilverFox]

Hello Light Me Up,

Welcome to CPF.

Thanks for that correction. I guess I was going for super simple...

Tom

 

[LiteTheWay]

All very informative. I like the VERY simple expanation that "different chemicals .... produce different voltages". When you combine it with the fact that it is indeed "The more disimilar the electrodes, the higher the voltage potential" you have a pretty good simple and mechanistic expanation that might satisfy a professor who has to deal with beginning students.