NiMH AAAs all are 1.2 V? Effect of LED V/I regulation?

Hey, I wasn't able to find discussion of this anywhere else, at least not easily in any thread on CPF, but all of the NiMH AAA batteries I have found have a stated voltage of 1.2 VDC, which is markedly less than the 1.5 V of the typical alkaline and lithium AAA and AA (and C and D) batteries. On such lights as the Fenix L0P and Arc-AAA-P which use voltage/current amplifiers/regulators is the deficient starting voltage (since they were probably designed to expect 1.5 V from a fresh cell, going to cause their output to suffer from the outset? I wasn't able to detect much (if any) difference with my L0P with an Energizer E2 alkaline AAA vs. and Energizer (newer model 750 mAh, other new 1000 mAh cells on their way in the mail now) NiMH AAA, but I didn't do a very comprehensive test. It seems to me if a voltage amp is designed for a particular gain, say 100% voltage boost, for simplicity's sake, then a standard AAA would give 3V out and the NiMH cells would give 2.4 V, quite a big difference when you're talking about lower than desirable voltage to an LED. Also if it's boosted 300%, say, to have a target voltage of 6V, the NiMH, on a linear amp at least, would be all the way down to 4.8 V, way less than desirable for a nominal 6V circuit.

Just curious, and if Peter G wants to respond I would really like to know how the ARC, at least, would handle this. I have read enough to get a notion that the Arc's regulator/amp is much more sophisticated than that of the L0P, but any info is well appreciated.

Thanks!

proFeign/kelly

at medium to high current draw, alkaline batteries droop to ~1.2v, which NiMH batts can easily do at higher currents. i'm not sure about lithiums, though.

i dont know about the DC-DC converters in flashlights, but most have a minimum voltage threshold that must be maintained for desired voltage. just because recommended input is 3v doesn't mean the chip can't step up ~2.0v to the same levels.

Current regulators provide the same current to the LED as long as the input voltage is within reasonable range ie, using 1.2V cells wouldn't make a difference in the output. The circuit just draws more current from the cells to provide the same power to the LED.

Voltage regulators however, provide an output which is somewhat dependent on the input and using lower voltage cells will reduce the current to the LED though not as much as an unregulated light.

Am I wrong to assume that current regulators are found in fully regulated lights while voltage regulators are found in semi-regulated lights?

eebowler said:

Current regulators provide the same current to the LED as long as the input voltage is within reasonable range ie, using 1.2V cells wouldn't make a difference in the output. The circuit just draws more current from the cells to provide the same power to the LED.

Voltage regulators however, provide an output which is somewhat dependent on the input and using lower voltage cells will reduce the current to the LED though not as much as an unregulated light.

Am I wrong to assume that current regulators are found in fully regulated lights while voltage regulators are found in semi-regulated lights?

Click to expand...

Thanks for the info!

I don't know that "fully regulated" and "semi-regulated" have precise universal definitions but I don't bother using NiMH cells in the Arc-P because the battery life is so long. I'm getting some Lithium AAAs in the mail on Monday because they have a more consistent voltage output over their life, and I expect my Arc's batteries to last for six months plus, but the Fenix L0P is a different story, and I'm pretty sure it's just got voltage amplification (no regulation at all), which means that lower voltage in probably results in a nonideal situation since it's not "regulated", simply amplified.

Anybody know for sure about voltage amplifiers?

Actually nimh are typically hot off the charger at about 1.4v or so and under light loads they get most of their usage from 1.2-1.35v. Under heavier loads (.5amp+) they hold voltage better than alkaline AA and AAAs, and under even heavier loads (1 amp+) they actually excell at holding voltage and supplying current better than all but the lithium energizers. The disadvantage of slightly lower starting voltage accompanied by brightness is made up for by rock solid voltage throughout most of the useful life of the battery charge vs constantly declining charge on all but the lithium 1.5v cells.
Of course the additional bonus of *free* batteries after you recharge them a dozen times vs continued payment on disposable cells is nice on the wallet...

A voltage amplifier as you put it, is a simple boost circuit. It does nothing other than raise the voltage of the battery to something which the LED can use. In this case, output voltage should be directly proportional to the input voltage.

Perfect examples of graphs showing Full regulation, Semi-regulation and No regulation have been done by Quickbeam at flashlightreviews.com

proFeigh, you said: "I don't bother using NiMH cells in the Arc-P because the battery life is so long." Do you mean battery life is so short? lol

I recommend against using regular alkaline batts in high power flash lights.

An Energizer e2 Alkaline's useful capactiy is rated for ~2.9Ah@25mAh (C/116) draw, [email protected] and ~1.6Ah@1A, all at 70F temperature according to their engineering datasheet.

You can assume most high power AA and AAA powered flash lights to be in 0.5 to 1.0A range.

The highest capacity NiMH AA available from Energizer is 2.5Ah and the capacity is rated for C/5 (meaning amp draw = 1/5 x (rated Ah) ) and amazing 2Ah @1.25A (C/2) draw. I recommend the Energizer brand, because Ah isn't the ruler of performance and they make their engineering datasheet available. While you maybe able to find 2700mAh cells, you never know what current draw they're rated for and how they'll behave under heavy load. If the manufacture can't provide engr datasht, don't buy 'em.

Definitely avoid alkaline for AAA high power flashlights. Rated for 1350mAh at 0.025A, it is only rated for 450mAh at 1A.

In a regulated output high power flashlight, a set of freshly charged NiMH will outlast a set of new alkalines. Alkaline seems to last way longer in unregulated flashlights, because voltage drops gradually reducing power draw at the expense of dimming down. NiMH and NiCd holds their voltage at ~1.25v for a long time, but by the you notice dimming, they're basically almost discharged. The disadvantage is that you can't monitor battery charge status by voltage and you get no warning that battery is going to die. Unfortunately, they're like helium balloons. You lose about 10% within a day or two after leaving the charger no matter what, then you continue to lose about one percent a day at room temperature, quite a bit less if refrigerated, more at higher temperature.

At room temperature, you lose around 20-30% at room temperature after 30 days. at 32F, you lose 10% within the first few days, but not much thereafter. At 100F, you lose 50-60% after 30 days.

here's a temperature/self-discharge chart from Sanyo Twicell engineering datasheet

image courtesy of Sanyo.

If you use your flash light a lot, I would go with AA NiMHs and store charged cells in the refrigerator to reduce self discharge or use a trickle charger.

Lithium AA should give a usage hour exceeding NiMH and practical storage life of 10 years at room temperature. Use them for emergency kits. The downside is they're expensive. About $2 per battery, almost approaching that of NiMH.

Hello Handlobraesing,

The chemistry used for NiMh seems to have been improving with regards to self discharge rates. We are seeing less impact from this with the newer cells. Sanyo has just come out with their Eneloop cells that claim reduced self discharge rates. I ran a test and found that after 31 days of room temperature storage, they had around 93% of their initial capacity left.

Tom

SilverFox said:

The chemistry used for NiMh seems to have been improving with regards to self discharge rates. We are seeing less impact from this with the newer cells. Sanyo has just come out with their Eneloop cells that claim reduced self discharge rates. I ran a test and found that after 31 days of room temperature storage, they had around 93% of their initial capacity left.

Click to expand...

Hi guys,
I've been using cheap Powerizer NiMH cells for a couple years now. While I have not done any comprehensive tests to determine the actual self discharge rate of them I'm sure that it is lower than it is represented in the charts I've seen by a significant margin. On a couple of occasions I've been stunned by the runtime of NiMH cells that have been sitting around for 3 months at 80 degrees F.

A couple Holloweens ago I took the optic off my EL Hyper-Blaster and used it to light a pumpkin. Imagelink below. (In hot weather a candle inside a pumpkin wipes it out pretty quickly.)


BOO!

The 9500 mAh Powerizer Ds ran it brightly for six hours, which surprised me as they hadn't been charged or topped off in three months.

Go figure.

A lot of information has been covered here but just to throw out my experience with NiMH vs Alkalines...

In medium to high-ish drain applications (ie most Luxeon-based lights driven reasonably hard) with voltage boosters or 'regulators' you'll never see the difference in initial brightness. With very low drain applications such as 3 or 4 AA cells direct driving (or driving with a resistor) a single 5mm LED, the alkalines will be a bit brighter initially and while it will certainly be a noticable difference, it's not likely to change the usability of the light... That is to say, if the Princeton Tec Impact Impact on alkalines will suffice in a given application, then so will the same light with NiMHs.

Now, when lithiums come into play, different things can happen. Using the Fenix lights as examples, the difference between alkalines and NiMHs are basically non-existant while the difference between Lithiums and alkalines are obvious.

Further, I've compared my L1P on a fresh NiMH (which is my currently ALWAYS with me light) to my new L0P on a fresh Lithium cell and to my eyes and my camera, the L0P looks brighter. I don't know if I have an exceptional L0P or a poor L1P or if these are expected results, but they aren't the results I expected.

L1P with a fresh Energizer NiMH on the left, L0P with fresh Energizer Lithium on the right.