too much current for alkaline aaa battery?

[rgbbv]

hello

i saw alot of flashlight that uses 3*aaa alkaline(primary cell)batteries in series,for running the led with 1A,1.5A (and even more )current.and i read,also,that this cell doesn't like currents above 0.5C(more that around 600mA,when it's capacity is 1200mAh)so how can this battery can handle 1500mA currents?(cells in series doesn't increase the capacity,and therefore not have the ability to divide the high current between them,still will have 1200mAh)so aren't these current won't kill the battery?is it ok. and normal to use that currents on these 3*aaa bateries when running a flashlight?and if not,why to sell a flashlight with currents that the battery can't handle?
what should be,really,the maximum current that we can load on the 3 alkaline batteries in series to operate a flashlight,and still to have the ability to enjoy from the use of the flashlight,without kill the battery?(what is the maximum current that allowed to consume from them?)

thanks in advance.

 

[jpanhalt]

The higher the current drain, the less capacity such batteries exhibit. The 1200 mAH rating is at a drain such as 50 mA.

Here is a chart from Duracell for its Coppertop battery:



Here are the links. The first is to Duracell technical data. The second is to the AAA Coppertop. There are differences between manufacturers and for products within a single manufacturer. The highest capacity rating was at 50 mA for 4 hours per day.

https://www.duracell.com/en-US/Glob...ets.jspx?icn=AdLob/ProductDataSheets&cc=AdLob

https://www.electro-tech-online.com/custompdfs/2013/02/MN2400_US_CT.pdf

John

 

[rgbbv]

thanks for your reply
i had,already,checked and knew the changes in the capacity of the batteries regarding to the discharge rating,like on duracell and energizer for example,and i had already saw these graphs and understood them.the issue rise after i saw them,saw the flashlights that use 3*aaa battery running with to much current,and i figured that something is weird,and i began to ask questions.
so i will very appreciate if you can help with my several question a bove. like the one:

is it ok. and normal to use that currents on these 3*aaa bateries when running a flashlight?and if not,why to sell a flashlight with currents that the battery can't handle?

and if i'm going to buy a flashlight that uses 3*aaa,what should be the maximum current,that beyond that it is not worthy to buy it?
thank in advance

 

[jpanhalt]

You haven't defined what you mean by OK and normal, nor have you actually said which battery you are using, so your questions can't be answered. It would also have helped, if you had given a link to the claims you made for acceptable discharge rates. That is why I looked up the technical information for a common battery and posted it as a reference point for discussion.

Information from Duracell for the AAA Coppertop battery does not include characterization for a discharge rate of more than 1 A. The charts clearly show that battery capacity is less than maximum at discharge rates considerably less than 0.5C. Since such discharges are characterized, one could assume that such less-than-optimal discharge rates are "OK." The fact that characterization at higher discharge rates is not presented is consistent with, but does not prove unambiguously that they are not "OK." Rather, we can assume that battery life will be dramatically shortened. One might argue that Duracell should say discharge rates above a certain level are not recommended, and we do see such statements in literature for lithium-based, NiCd and NiMH batteries. However, alkaline batteries are substantially less prone to fire from too high discharge rates than other chemistries, such as NiCd and lithium.

Perhaps, you should write Duracell and ask why similar cautions are not given for its alkaline batteries? It does state in red that delivered capacity is dependent on several variables, including load, temperature, and duration.

As for the final question about why a flashlight would be sold that used such high currents, you need to consider that the way you use such lamps may not be how other people use them. Bottom line, however, is caveat emptor. In other words, you knew it was a very intense lamp with a very small battery source. Why did you buy it? There is no free lunch.

John

 

[audioguru]

The voltage of a tiny AAA alkaline cell drops like a rock at 600mA and drops faster with a higher current.

 

[rgbbv]

thanks for your replies.

John,i didn't mentioned a specific type of battery or technical information,because i saw that the graphs of the commom known aaa battery like duracell and energizer are more or less the same.also,as the same one that you gave.but your last reply answer all my questions,and my question,really had to be

...why similar cautions are not given for its alkaline batteries?...

so like you said is ,probably,because they less prone to fire(safer for high discharge rate).and in higher rate than shown on the spec,the capacity,dramatically,shortened.your bottom conclusion is tottaly right"there is no free lunch".the flashlight was really cheap relatively to its high lumen output,with only the uses of 3*aaa alkaline battery,but this comes,unfortunatly, at the expense of usage time.

thanks alot for your replies
best regards

 

[rgbbv]

Hi

i thought to open new thread,but my question is in the same context.
i try to understand the influence of two flashlight on the same 3*aaa alkaline batteries.

1)one cree flashlight has one mode,no regulation,no pwm,and consume from the batteries 300mA.
2)second cree flashlight has 3 mode,no regulation,but uses PWM to to get 300mA on low mode.when in the high mode the flashlight consume 1400mA.
the two flashlights are using 3*aaa alkaline batteries.(like duracell or energizer).
so if i use the second flashlight(the one that uses pwm) with only the lower mode,does it affects different on the batteries compared with the first flashlight?(discharge time?too much load on the batteries?)or the affect on the batteries will be,exactly,the same on both cases?
because at the second flashlight,even that the average current is 300mA(by using pwm to reach this average current from 1400mA by lower the duty cycle rate)the battery,practically,experience,high pulses of 1400mA.(despite of the fact that those high current are not constant,and come as pulses).
so,doesn't the batteries suffer from this high current pulses compare to the batteries that give real constant 300mA on the first flashlight?or it is,exactly the same?

thank in advanced.

 

[audioguru]

The flashlight that uses PWM to reduce the average current to 300mA probably charges a capacitor to provide a lot of the peak current.
Then the average current from the battery is also only 300mA.

 

[rgbbv]

Hi audioguru

the average current is 300mA indeed.but this wasn't my question,this was some of the facts in the question.

 

[audioguru]

If the average battery current is 300mA for the one that is limited to 300mA with a resistor and the average battery current is 300mA with a capacitor and PWM then of course the battery lives will be the same.

But some PWM systems reduce the voltage which increases the available life of a battery because then no current-limiting resistor is needed (it wastes battery power).

 

[jpanhalt]

Hi

so if i use the second flashlight(the one that uses pwm) with only the lower mode,does it affects different on the batteries compared with the first flashlight?(discharge time?too much load on the batteries?)or the affect on the batteries will be,exactly,the same on both cases?

thank in advanced.

I found this an interesting question and spent quite some time searching for the answer with no luck. At least, I found no answers from authoritative sources. There are responses relative to lead-acid batteries as used with photovoltaic and wind turbine generators. They have a similar problem, in that the principal current drain is usually an inverter, which provides a pulsed drain. In brief, there are some effects both good and bad, but I did not feel the results would apply in this example with a semi-paste electrolyte, relatively high internal resistance, alkaline battery. I will also suggest two experiments for you.

First, one could go on and on about the chemical cause of rapid deterioration from too rapid discharge. With lead-acid batteries, stratification of the electrolyte can be shown, and there are experiments that use a continuously flushed electrolyte to mitigate that. In your case, the question becomes whether the local changes caused by high current are averaged out during the no-drain time and end up no worse than what the average drain will produce. Since with heavy use, internal resistance increases. You have something to measure.

Experiment #1: Test the internal resistance of the PWM'd cells and compare that to the internal resistance of the non-PWM's cells after comparable total drain. I suggest current-time discharge of about 30 to 50% of the claimed capacity of the non-PWM cells. Try to keep the cells cool.

Second, one major cause of early deterioration is heat. Heat comes form two sources: 1) the exothermic chemical reaction during discharge; and 2) Ohmic heating by the current (W = I^2R). Obviously, the heat produced by twice the current over half the time will be more than the heat produced by a steady drain. The net effect of both processes may be complex to predict, but you can measure the result.

Experiment#2: Put each flashlight in an identical, separate, and insulated container with the same amount of a liquid (water is probably OK). Be sure to disassemble and dry well afterwards. Measure the temperature of each during equivalent discharge and see whether they are the same.

If you do the experiments, please post your results back here.

John

 

[audioguru]

MANY years ago I had a calculator that used LEDs for a display, not an LCD display. Of course the display was multiplexed which caused the peak current to be too high for the little 9V alkaline battery that powered it and it did not last long.
Then I added a 100uF supply bypass capacitor and the display became brighter and the battery lasted much longer.

 

[jpanhalt]

That may answer the question and provide a work-around. Thanks.

John

 

[rgbbv]

thanks for your replies,but i didn't understood the answer,i didn't understand how the capacitor belongs to whole things?.
maybe i should mention,that i am talking about PWM for brightness control.
on high mode the duty cycle is,let say-100%("on"),so the battery experience drain of steady 1400mA,and in the low mode the duty cycle is being reduced(more"off"times)to the point that the average measure current with ammeter will be 300mA,but the batteries will experience,actually,(even though it for short time)high current of 1400mA,opposed to the batteries in the other flashlight that experience steady 300mA.
so which battery will last longer?will experience less damage?does those high peak current pulses on the alkaline batteries(when the average is 300mA) are bad for them compare to the method of drain from them steady 300mA?

with regard to the experiments,this is too complex for me,and i prefer my flashlight stay dryyour experiment's description gave me some points of view,but didn't gave me an answer.i see that you spent quite some time searching for the answer with no luck,so thanks for your time
i hope that the addition clarifications about my question will help to solve the issue?

 

[audioguru]

A capacitor charges slowly from a fairly low battery current then it can provide the 1400mA pulses when required.
The battery with a capacitor will last longer than if there is no capacitor.

The battery without a capacitor will waste a lot of its power getting hot when it is overloaded by trying to provide 1400mA pulses.

 

[rgbbv]

thanks,audioguru,for the explaination about the capacitor,but the problem is that i try to figure out if the 1400mA pulses(with low duty cycle that give 300mA-average) are going to reduce battery life compare to the battery that discharge only with steady 300mA.after all,1400mA for alkaline battery is too much,if it was steady 1400mA,it was drained the battery very very fast(high voltage drop),cause the battery to heat and maybe cause something bad in the chemistry inside the battery.therefore my question was: if i use 1400mA pulses with low dutycycle(less"on"time)that will give average of 300mA,will it affect the battery the same like with a battery that drained with steady 300mA?

 

[audioguru]

For the duration of each 1400mA pulse with no capacitor, the battery is drained a lot. The battery will not get hot enough to damage itself.
I think that the high pulsed current with a duty cycle creating an average current of 300mA will reduce the life of the battery when compared to continuous 300mA.

Try both and measure the battery voltage vs time.

 

[Nigel Goodwin]

MANY years ago I had a calculator that used LEDs for a display, not an LCD display. Of course the display was multiplexed which caused the peak current to be too high for the little 9V alkaline battery that powered it and it did not last long.
Then I added a 100uF supply bypass capacitor and the display became brighter and the battery lasted much longer.

Unbelievably crap design then

Such a capacitor is a standard part of pretty well every circuit, and absolutely essential on battery powered electronics - notice I said 'electronics', a crude LED torch wouldn't be helped by it.

 

[audioguru]

Unbelievably crap design then

I agree. Almost EVERYTHING made for and sold in RadioShack was crap.
That is one reason that RadioShack is gone from Canada. Ripoff prices is another reason.
I think Maplins in the UK is like RadioShack.

 

[thedoc8]

MANY years ago I had a calculator that used LEDs for a display, not an LCD display. Of course the display was multiplexed which caused the peak current to be too high for the little 9V alkaline battery that powered it and it did not last long.
Then I added a 100uF supply bypass capacitor and the display became brighter and the battery lasted much longer.

How did the cap change the power consumption of the led, if it became brighter wouldn't that mean more power being used?