Half-Height AAA NiMH 1.2v---They seem to exist in size charts and certain websites...

tgm1024 · Nov 9, 2015

Ok, I'm beyond confused now.

I have a wonderful LED flashlight designed for 3 1.5v AAA's. It just doesn't last long. I thought I'd try fitting in 4 NiMH AAA's into the same housing (AAA + AAA + 1/2 AAA + 1/2 AAA with the half heights stacked) for a total of 4.8v.

Yes, I'll be slightly overvolting the SMD.

I've discovered that half-height AAA's seem to be for sale from a (boat) dock lighting company, and are listed in the all-batteries size chart.

1. Will my idea "work"? (I'll charge the two 1/2 heights in two slots by themselves in a 4 slot charger with a home-made extender to have it reach the electrodes.

2. Does a 1/2 height 1.2v NiMH actually exist? I see conflicting views of this online.

THANKS!

Str8stroke · Nov 9, 2015

Kinda lost me on some of that. Series or Parallel or both? What part is what? I am trying to figure out your placement in the holder. Seems dangerous due to not being balanced.

Anyways, depending on the light, what about fitting one 26650 cell or possible a 36650?? BTW: these cells are 3.7 volts, they charge and rest around 4.2 volts.

What is your goal? Longer running? Using rechargeable cells I assume.
What light is it?

more_vampires · Nov 9, 2015

The only thing wrong with what OP is suggesting is mismatched capacity. It's the same as "mixing and matching" hot fully charged and partially depleted batteries. It's pretty much exactly like you don't want to mix 18650 and 18350 in the same circuit, mismatched capacity.

Sub-size batteries all have less capacity than their full size counterparts, a tradeoff for the size.

teacher · Nov 9, 2015

Welcome to CPF 'tgm1024'.

I think you'd be better off to get you some AAA Eneloops and just charge em' when they needed it. What you said above might work but the Eneloop solution would be much simpler and probably less expensive.

more_vampires · Nov 9, 2015

...and safer. Mismatched capacity can pop cells and damage them. Lithium-ions vent with flame when you do this.

Str8stroke · Nov 9, 2015

teacher said:
Welcome to CPF 'tgm1024'.

I think you'd be better off to get you some AAA Eneloops and just charge em' when they needed it. What you said above might work but the Eneloop solution would be much simpler and probably less expensive.

What he said!

more_vampires said:
...and safer. Mismatched capacity can pop cells and damage them. Lithium-ions vent with flame when you do this.

What he said!

apisdorf · Nov 9, 2015

To answer the original question, yes; 1/2 AAA NiMH batteries do exist. I have a couple keychain lights that use them. I have not attempted to find replacements, however.

Jordan

tgm1024 · Nov 9, 2015

I'll try to rephrase to see if this makes any better sense.

In my flashlight, the 3 1.5v AAA batteries are in series (a total of 4.5v).

So what I have left then is two choices:

3 1.2v AAA NiMH in series. A total of 3.6v. This undervolting will dim the light substantially (roughly 20%).

....or....

2 1.2v AAA NiMH + 2 half height 1.2v AAA NiMH all in series. A total of 4.8v. This will overvolt the SMD by .3v total (roughly 6.66%...hopefully not a risk to the SMD).

chillinn · Nov 9, 2015

tgm1024 said:
2. Does a 1/2 height 1.2v NiMH actually exist? I see conflicting views of this online.

Yes

And I'm only a little sure this might belong here instead of where it ended up, tl;dr reread post #3

more_vampires · Nov 10, 2015

tgm1024 said:
I'll try to rephrase to see if this makes any better sense.
In my flashlight, the 3 1.5v AAA batteries are in series (a total of 4.5v).
So what I have left then is two choices:
3 1.2v AAA NiMH in series. A total of 3.6v. This undervolting will dim the light substantially (roughly 20%).
....or....

Maybe so, maybe no. AAAx3 is really common for bottom-of-the-barrel budget lights. A lot of them rely on voltage sag of alkalines to avoid frying, that and the thought that the light is going to have mostly dead alkalines in there 99% of the time.

The main reason for AAAx3 is that the maker can skimp on the driver as this is already about the right voltage to run a light.

There exists lights that FRY on NiMH AAAx3 that would run on alkaline AAAx3. I couldn't believe it when I first found out, but it is so. Even MAGLITE is guilty of non NiMH compatibility! NiMH handles amperage draw far, far, far better than alkaline; this "undervolting" is less of an issue than appears at first blush.

tgm1024 said:
2 1.2v AAA NiMH + 2 half height 1.2v AAA NiMH all in series. A total of 4.8v. This will overvolt the SMD by .3v total (roughly 6.66%...hopefully not a risk to the SMD).

It's all fun and games until the half-height batteries deplete first. What happens next?

Reverse charge scenario. Since these batteries are in series, it's going to DESTROY the half-height batteries WHEN they run out first. Your choices? Watch the half-height batteries like a HAWK (with a multimeter) or just don't do it. This isn't a safe combination, you're going to pop those batteries (the half height ones will DIE) and it won't be the manufacturer's fault.

Reverse charge scenario; this is what will happen when the half-height batteries deplete first. It could get exciting!
http://www.batterystuff.com/blog/battery-myth-can-a-battery-reverse-polarity.html

Remember, a completely discharged battery is nothing more than an empty vessel. In order to gain a negative charge, it would then necessitate being hooked up backwards, and charged that way. So the real question here is: how can a battery reverse polarity after it has been installed? That same previously discharged battery would then be vulnerable to reverse charging, either by connecting the battery charger backwards, or by a charging system that reversed polarity (very rare, but still possible).

So let me restate: The only way for a battery that has a positive charge, to reverse itself, is for the battery to be completely discharged, and then reversed charged. We have seen this happen a couple of times, and it would be considered the more common of these rare situations.
For all intents and purposes, the battery will be ruined.

http://batteryuniversity.com/learn/article/non_correctable_battery_problems

Even with modern manufacturing techniques, the cell capacities cannot be accurately predicted, especially with nickel-based cells. As part of manufacturing, each cell is measured and segregated into categories according to their inherent capacity levels. The high capacity 'A' cells are commonly sold for special applications at premium prices; the mid-range 'B' cells are used for commercial and industrial applications; and the low-end 'C' cells are sold at bargain prices. Cycling will not significantly improve the capacity of the low-end cells. When purchasing rechargeable batteries at a reduced price, the buyer should be prepared to accept lower capacity levels.

The cells in a pack should be matched within +/- 2.5%. Tighter tolerances are required on batteries with high cell count, those delivering high load currents and packs operating at cold temperatures. If only slightly off, the cells in a new pack will adapt to each other after a few charge/discharge cycles. There is a correlation between well-balanced cells and battery longevity.

Why is cell matching so important? A weak cell holds less capacity and is discharged more quickly than the strong one. This imbalance may cause cell reversal on the weak cell if discharged too low. On charge, the weak cell is ready first and goes into heat-generating overcharge while the stronger cell still accepts charge and remains cool. In both cases, the weak cell is at a disadvantage, making it even weaker and contributing to a more acute cell mismatch.

A sub AAA NiMH is guaranteed to have more than 2.5% difference in capacity than a full size NiMH AAA.

Hope that's a bit more clear, plus some added reading info for background and clarity.

teacher · Nov 10, 2015

tgm1024 said:
Ok, I'm beyond confused now.

I have a wonderful LED flashlight designed for 3 1.5v AAA's. It just doesn't last long. I thought I'd try fitting in 4 NiMH AAA's into the same housing (AAA + AAA + 1/2 AAA + 1/2 AAA with the half heights stacked) for a total of 4.8v.

Yes, I'll be slightly overvolting the SMD.

I've discovered that half-height AAA's seem to be for sale from a (boat) dock lighting company, and are listed in the all-batteries size chart.

1. Will my idea "work"? (I'll charge the two 1/2 heights in two slots by themselves in a 4 slot charger with a home-made extender to have it reach the electrodes.

2. Does a 1/2 height 1.2v NiMH actually exist? I see conflicting views of this online.

THANKS!

Hmmmm, looks like we have established the answer to:
#1 is that it 'might' very well "work", but there is a good chance of an ......

...... at which point everything goes....... :poof:

#2 is YES they sure do exist. [I had never heard of them...

]

But going further, if you look at the graph below [posted by SilverFox in this thread http://www.candlepowerforums.com/vb/showthread.php?222784-Why-are-NiMH-1-2v-instead-of-1-5v .... Post #26] ..... you see that the only slight advantage 1.5 Alkalines have is in the first 7 minutes or so.... then the NiMh stand tall. Go with the 3 AAA Eneloops and rest easy at night........

teacher · Nov 10, 2015

more_vampires said:
Maybe so, maybe no. AAAx3 is really common for bottom-of-the-barrel budget lights. A lot of them rely on voltage sag of alkalines to avoid frying, that and the thought that the light is going to have mostly dead alkalines in there 99% of the time.

The main reason for AAAx3 is that the maker can skimp on the driver as this is already about the right voltage to run a light.

There exists lights that FRY on NiMH AAAx3 that would run on alkaline AAAx3. I couldn't believe it when I first found out, but it is so. Even MAGLITE is guilty of non NiMH compatibility! NiMH handles amperage draw far, far, far better than alkaline; this "undervolting" is less of an issue than appears at first blush.

It's all fun and games until the half-height batteries deplete first. What happens next?

Reverse charge scenario. Since these batteries are in series, it's going to DESTROY the half-height batteries WHEN they run out first. Your choices? Watch the half-height batteries like a HAWK (with a multimeter) or just don't do it. This isn't a safe combination, you're going to pop those batteries (the half height ones will DIE) and it won't be the manufacturer's fault.

Reverse charge scenario; this is what will happen when the half-height batteries deplete first. It could get exciting!
http://www.batterystuff.com/blog/battery-myth-can-a-battery-reverse-polarity.html

http://batteryuniversity.com/learn/article/non_correctable_battery_problems

A sub AAA NiMH is guaranteed to have more than 2.5% difference in capacity than a full size NiMH AAA.

Hope that's a bit more clear, plus some added reading info for background and clarity.

Thanks 'm_v', good info & reading. :thumbsup:

more_vampires · Nov 10, 2015

Anytime, friends! Stay safe!

(He says, hoping he didn't make a typo or mental slip.

)

tgm1024 · Nov 12, 2015

teacher said:
But going further, if you look at the graph below [posted by SilverFox in this thread http://www.candlepowerforums.com/vb/showthread.php?222784-Why-are-NiMH-1-2v-instead-of-1-5v .... Post #26] ..... you see that the only slight advantage 1.5 Alkalines have is in the first 7 minutes or so.... then the NiMh stand tall. Go with the 3 AAA Eneloops and rest easy at night........

Can you explain further? I'm not sure I understand where you get 7 minutes from this. That chart is showing a cross-over point at 40 minutes, and for my specific application you would need to know the amp draw the LED pulls. In my case, the flashlight quickly becomes too dim for use after just over an hour of use.

Sounds like I should test the AAA eneloops and be happy.

magellan · Nov 12, 2015

apisdorf said:
To answer the original question, yes; 1/2 AAA NiMH batteries do exist. I have a couple keychain lights that use them. I have not attempted to find replacements, however.

Jordan

I have a custom copper body that takes a 1/3 height AAA NiMH. I just put a Maratac copper head on it and it works great.

Rick NJ · Nov 12, 2015

tgm1024 said:
Ok, I'm beyond confused now.

I have a wonderful LED flashlight designed for 3 1.5v AAA's. It just doesn't last long. I thought I'd try fitting in 4 NiMH AAA's into the same housing (AAA + AAA + 1/2 AAA + 1/2 AAA with the half heights stacked) for a total of 4.8v.

Yes, I'll be slightly overvolting the SMD.

I've discovered that half-height AAA's seem to be for sale from a (boat) dock lighting company, and are listed in the all-batteries size chart.

1. Will my idea "work"? (I'll charge the two 1/2 heights in two slots by themselves in a 4 slot charger with a home-made extender to have it reach the electrodes.

2. Does a 1/2 height 1.2v NiMH actually exist? I see conflicting views of this online.

THANKS!

Eneloops do deliver most of it's power at around 1.2V even by my personal test, so indeed one does not need to worry about loosing out on 3xAAA NiMH @3.6V being less powerful than 3xAAA Alkaline @4.5V. The graphs shown in earlier reply really demonstrated the points well.

What you described made sense but you may over-volting it by more than you think, and getting less back than you think. 1.2V is the nominal but fresh out of a charger, it could be 1.3V to 1.4V and perhaps even higher. 4x1.2V is not as helpful as it seems as you will be clipping that power away as the voltage is clipped down to what the LED should take so all that power is lost. Worst is, the 1/2 size cell often has less current capability and less than 1/2 the mAH capacity.

If you really like it to run longer, perhaps consider the 18650 is your flashlight can take it.

tgm1024 · Nov 14, 2015

Is there a safe place to buy Eneloops? I don't trust eBay (bought black market energizers there before---got to learn just how sneaky those guys can get with appearances), and I'm not even sure that the sold BY amazon ones (not just fulfilled by, or marketplace sellers) are legit.

MidnightDistortions · Nov 15, 2015

tgm1024 said:
Is there a safe place to buy Eneloops? I don't trust eBay (bought black market energizers there before---got to learn just how sneaky those guys can get with appearances), and I'm not even sure that the sold BY amazon ones (not just fulfilled by, or marketplace sellers) are legit.

The ones I have been getting from Amazon have been legit. Just buy them from Amazon itself, not from any 3rd party seller and you should be good.

teacher · Nov 16, 2015

teacher said:
But going further, if you look at the graph below [posted by SilverFox in this thread http://www.candlepowerforums.com/vb/showthread.php?222784-Why-are-NiMH-1-2v-instead-of-1-5v .... Post #26] ..... you see that the only slight advantage 1.5 Alkalines have is in the first 7 minutes or so.... then the NiMh stand tall. Go with the 3 AAA Eneloops and rest easy at night........

tgm1024 said:
Can you explain further? I'm not sure I understand where you get 7 minutes from this. That chart is showing a cross-over point at 40 minutes, and for my specific application you would need to know the amp draw the LED pulls. In my case, the flashlight quickly becomes too dim for use after just over an hour of use.

Sounds like I should test the AAA eneloops and be happy.

Hmmmm........ I wish I could explain where I got that number [7 minutes] but it looks as though I had a total 'brain fart'.... my bad.

The Eneloops will hold a more constant Voltage for a longer time though, as the chart shows. I bet you'll be happy with them.

Again my apologies for the incorrect statement I made.

teacher · Nov 16, 2015

tgm1024 said:
Is there a safe place to buy Eneloops? I don't trust eBay (bought black market energizers there before---got to learn just how sneaky those guys can get with appearances), and I'm not even sure that the sold BY amazon ones (not just fulfilled by, or marketplace sellers) are legit.

I have used both of these places in the fairly recent past with excellent success. With Light Junction you can also get a CPF discount. :thumbsup:
Light Junction
http://lightjunction.com/new-eneloop-2100-cycle-aaa-nimh-800mah-battery-8-pack.html
Thomas Distributing
http://www.thomasdistributing.com/S...0mAh-NIMH-Rechargeable-Batteries-_p_3223.html

Half-Height AAA NiMH 1.2v---They seem to exist in size charts and certain websites...

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