3 x Alkaline or Nimh = 1x Li-ion?

[zulumoose]

Hi All

Sorry for such a noob question, but what are the advantages/disadvantages of running a light that is meant to take 3 AAA batteries in series on one Li-Ion rechargeable, since the voltages should be within range, and the Lithium batteries are meant to take higher current anyway, what is wrong with using two dummies and a (protected) Lithium, or a larger lithium in a holder wired directly to the + and -?

 

[Timothybil]

There is nothing wrong with the idea. That is why I have several dummy cells in AA and AAA. Since alkaline cells rapidly sag their output voltage there should be no problem with the Li-Ion as it works its way down to three volts. I have used one 14500 and a dummy cell in one of my 2xAA lights with no problems.

What are you powering with the 3 AAA cells? An LED or incan bulb will be no problem. Something with more delicate circuitry might have an issue with the starting voltage, but then again, 3 AAA in series produces more voltage than a single Li-Ion cell.

 

[zulumoose]

The main thing I might like to try this in is an LED LENSER H7 headlamp, a few years old now. It takes 3x AAA in a box behind the head and I use it for running at night, making weight a factor, and carrying 3 cells as a backup in running shorts is not practical either. One lithium in each would be great, and a single cell charger is simpler than wondering how to balance the charge in 3 cells when chargers I have at the moment for NiMh only take 2 or 4.

 

[Timothybil]

I'm assuming the three cells are in a series arrangement, or this would never work. Also, all of the four cell chargers that I have had have no problem charging three cells, or one for that matter. Now, they weren't dedicated NiMH chargers, but most of those are not friends to NiMH cells anyway. The ones I have are a Nitecore i4 v2 and an Xtar VC4. Not all that expensive, and have four independent channels so one can mix chemistries and sizes with no problem.

Correction: The i4 only has two independent channels, #1 & #3 is one, and #2 &#4 is the other. As long as they are on separate channels Li-Ion and NiMH cells can be charged at the same time.

 

[eh4]

3 AA batteries should give you roughly half the capacity of an 18650, more or less depending upon the AA and the 18650 in question.
Close enough for estimating anyways.

 

[Kestrel]

Hi ZM,
I'm on my smartphone so my apologies for the brevity.
I'd bet that you will have issues with what you're proposing.
Most of the inexpensive 3xAAA lights rely on the substantial internal resistance of the three alkalines in series to limit the current supplied to the LED(s) - they don't have a driver per se.
A LiIon will not do this, and very probably damage the light.
Maybe not immediately, but will be pretty abusive nonetheless.
Hope this helps,

 

[Timothybil]

That's why I won't even look at any 3x light (excluding Li-Ion) unless I can see the word 'regulated' in the documentation.

Is the high internal resistance why alkalines drop their voltage so fast when first used?

 

[BloodLust]

That's why I won't even look at any 3x light (excluding Li-Ion) unless I can see the word 'regulated' in the documentation.

Is the high internal resistance why alkalines drop their voltage so fast when first used?

Same. No odd number of batteries here.

The 1x AA lights now are more powerful than the 3x AA's of yesteryears. I've streamlined all my emergency gear to run off AA's. I have a portable solar panel as backup charing plus a single bay li-ion/nimh charger is handier than a 4 port one. I do have a Goal Zero Guide 10+ for 4port charging but the Olight UC takes up negligible space. Also. The 1x AA lights are often regulated as well and even a single spare is easier to bring than 3x AAA. Much easier to change batteries in the dark too.
I will consider 2x AAA if it has good offerings. Also 2x and 4x AA. Just not 3.

Single bay li-ion/ni-mh usb chargers really changed the game for me. 1 batt is inherently safer too. Also it's easier to find a bad cell since there's only 1. With multiple cells, usually the whole batch is thrown out. For li-ion, no risk of thermal runaway.

What I personally do is 1xAA light for general use and if I need something stronger, I grab my 18650 light.
An 18650 light is quite versatile too as they can usually take 2x 123A and a number of models RCR123 as well.

 

[zulumoose]

Some interesting points to think about, thanks guys. The LED LENSER website does not seem to have the info on the older products, so I don't know if there is regulation on the input voltage, or if the power adjustment is current or PWM. I have sent them a query. If it is current then I would think it is safe to run it on just below max regardless of voltage regulation, right?

My chargers have 2.8V circuits so no odd numbers of batteries accepted, the light does not come on without a pair inserted. I have a LII 100 and a Nitecore F1 on order from GearBest at the moment, thanks to favourable reviews on this forum, what an incredible source of information it is.

I guess I may be on the market for a new headlamp soon, maybe an 18650 version as that is the way everything seems to be headed (no pun intended) and I like the idea of rotating 18650's through chargers that can be used as power banks for phones as well, and lights that can be removed from the headstrap so the strap can be washed, and maybe replaced.

 

[BloodLust]

My next headlamp might be a Zebralight in neutral flood.
Comes in either AA/14500 or 18650 size and can be a stand alone angle light. I believe it has a clip too.

 

[Timothybil]

Most of the 3 cell lights one finds these days (AA & AAA) don't have any driver at all. They are just direct drive. The way to tell is watch the output. If it starts slowly getting dimmer before finally quitting it is direct drive. Just like the Photon I and II were direct drive.

If you are interested in a nice 2 AAA light, Lumintop makes the IYP365, a very classy penlight that has three modes M-L-H, no memory, and is available with the Nichia 219B emitter. Usually sells for $30, but with some judicious coupon/sale hunting, it can be had for around $20.

 

[Woods Walker]

Oh God. I hate math..

Ok lets see. Making certain assumptions series vs parallel.....

3XAA at 4.5 nominal volts/2.5 is 11.25 watt hours but notice something changed from the last time we did this hack math on your other thread. There I was just comparing 1 AA and adding the energy up but now we have 3 in a light and making certain assumptions voltage goes up but mAh remains. That could be an issue.

1X 14500 Lithium ion at 3.7 nominal volts/.8 ah is 2.96 watt hours. A 18650 at 3.7 nominal volts/3.5 ah is 12.94 watt hours. On a side note a LSD 2500 mAh has a bit more energy than a 14500 800 mAh lithium ion. The pro to the lithium ion is within it's chemist aka higher voltage and draw. Even given my hatred for math which should be assumed to be hack and dubious in nature the bottom line remains. You will be removing 3 batteries each of which has a bit more energy than the one replacing them if it is a 14500 lithium ion 800 mAh. But the real problem might be the voltage. 3.7 is also less than 4.5 for alky primary chemistry but not too far off 3.6 for NiMH for 3 in a series... aw God I hate this part of the hobby. LOL! It's hard to say how the circuit will respond unless we knew the voltage range and a bunch of other things which are beyond a woods bum like myself knowing.

EDIT.

Oh snap. I just noticed we are talking about AAA. Ok then just reduced the mAh within the hack math. I am too mathed out right now so will do so later.

 

[BloodLust]

Most of the 3 cell lights one finds these days (AA & AAA) don't have any driver at all. They are just direct drive. The way to tell is watch the output. If it starts slowly getting dimmer before finally quitting it is direct drive. Just like the Photon I and II were direct drive.

If you are interested in a nice 2 AAA light, Lumintop makes the IYP365, a very classy penlight that has three modes M-L-H, no memory, and is available with the Nichia 219B emitter. Usually sells for $30, but with some judicious coupon/sale hunting, it can be had for around $20.

The last 3-cell light I bought was my Princeton Tec EOS. 3xAAA regulated. They were so proud of that they even have "regulated" printed on the front of the light near the bezel. 50 lumens. 3 L-M-H. I really liked the light. Wasn't bluish white too. Slight shift towards green but only noticeable when you look for it. I guess it's similar to my EDC Fenix LD10 so I don't mind it. It served me well outdoors and in household tasks and it's now my backup headlamp or my loaner. I also frosted the lens a bit with a frosting spray and it warmed up and evened out the beam a bit. Still a pain to change 3 cells instead of 1 though. Also, a spare carrier has 4 slots.