well i did that
got the graph
i used a resistor as i did not have a flashlight bulb to use..
it was a strange looking curve though..
i will try to transport it onto this machine to show yall ..

 

NiMh should be similar to NiCd and Alkaline, with a gradual drop off followed by a very quick fall at the end.

I did my tests years ago, but using a torch bulb as a load, this is far more representative than a simple resistor - as it's a common application for the batteries (which was why I used it!). Plus it also gives a nice visual indication of the state of charge :lol:

BTW, what value resistor did you use?.

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I think i used three 10 Ohm resistors in parallel

 

Unlike your tests with a continuous load, a battery's charge lasts longer when used intermittently, with a rest period between uses, which is how they are actually used:
1) I'm in the dark at the top of a ladder and my flashlight's Ni-Cad's fade to nothing. If I wait with it off for a couple of minutes, it gives enough light to see my way down.
2) I left the lights turned-on on my car overnight. The next morning the lights are dim and the engine won't start. If I leave it with everything turned-off for about a half-hour, then it starts fine.

I suppose the battery needs time to recombine gasses that build up.

 

How they are actually used obviously varies from application to application, continuous use of a torch is a quite likely application.

But as far as doing battery tests goes, you simply need to use a standard system to compare between different batteries. Intermittent tests will make batteries last considerably longer, but you would need to accurately specify the time intervals, and it would probably give advantages to one specific battery. Not to mention the time involved?, loading the battery for 10 minutes every day would take weeks (months?) to complete the test, and not really achieve a great deal.

As I see it, using a perfectly normal application (like a torch bulb) gives a fairly short time for the tests, and a true comparison of their capacity. Obviously other 'normal' loads could be used, but you need something reliable and consistant (so a radio, with it's varying current demands, wouldn't be suitable) - and also something that gives a fairly high current drain, to make the time taken for the test reasonably short. AA batteries are commonly used in clocks, and it's a good consistent current drain - but the time taken for the tests would be a little excessive :lol:

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I have noticed that flashlight (torch?) bulbs have a limited operational life of only about 2 to 5 hours and their glass gets blackened internally.
Is it possible that a bulb's resistance increases when its filament evaporates and is deposited onto the glass? Then your battery test results would be biased in favour of the last one tested.

I would use a stable resistor instead!

 

Certainly the specs on some torch bulbs quote extremely short life times, but my bulb completed all the battery tests I performed (many more than once, only a limited number are on my website) without blackening at all, and was still working fine the last time I saw it.

I was trying to find it today actually, I found my old A2D converter from the original tests, but couldn't find the bulb (not yet anyway!).

It's certainly possible, but I didn't perform the tests just once, and later tests (with earlier type batteries) still performed in a similar fashion.

The problems with resistors are that the current reduces as the voltage drops (simple ohms law), and it's a totally artificial test. A bulb's resistance drops as the voltage reduces, so tends to keep the current more constant.

I'd certainly be more interested in how long my torch will keep alight as I try and escape from a deep cave (been there, done that!) than how long it will keep a little resistor slightly warm :lol:

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Hi Nigel,
You have a good point about the "constant current " effect of the filament's temperature.

Have you noticed that a two-cell, 3V flashlight (torch?) uses a bulb with only a 2.4V rating? Surely excellent cells with a low internal resistance would light it much brighter at first, using more current and therefore would get exhausted sooner than would be expected by their mA/hr rating.

 

That's because you want a torch to be bright, and presumably is why they have such a short life?.

The mA hour rating of a battery is pretty useless, it's not done under any useful conditions - simply done to make the battery look as good as possible. Under most uses you won't approach the rated mA hour specification - it's generally measured with low current over a long time. There's obviously going to be an optimum point, where you get the maximum mA/Hr value, and that's what they tend to use.

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yes, stick with alkaline. they are the best. only dummies use heavy duty!!! lol


techno god

 

Most all sealed bulds filament will increase resistance as it heats up as most are made with tungsten, when off the bulb is a short. Positive coefficient. This is why tungsten is used for some oscillators.

Accurate measure can only be determined at the batteries max current drain capability, sometime this can be in the range of 10's of amps with good nicads C size or a few amps for AA size, a several hundered mA for alkalines AA size like close to 1amp but not practical since the hotter alkalines get the less current that it can drive same way if they get to cold, alkalines are very temp sensitive, and can blow up if driven like a nicad. However tests using a low power load would yield capacity to low level loads and most times this would yield a high MaH rating simply because less of the batteries chemistery is being wasted to heat.

Quality batteries have been made in such a way that they can drive heavy loads (20-30 amps C2sce, scrc sub C class and 5 amps AAi sub AAsae, sarc class typical) and are tested to perform against these loads to show the MaH rating in the end, in fact a battery in a high current sub class can perform low level loads and actually increase propotionally to MaH produced.

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Rubbish!.

Accurate measurements can only be determined under the CONDITIONS YOU ARE GOING TO USE IT. If you're not going to use the battery under it's maximum current capability (and it's probably not advisable to do so?), then testing it like that is going to be grossly inaccurate!.

I seem to remember mentioning earlier that high currents will drastically reduce battery life, this is a very well known effect.

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Rubish what is that?

I didn't say high current increase life, I didn't even say anything about battery life.

It is also well known fact that the hotter a battery gets the more of the energy is wasted to heat this is a primary reason why they (alkalids or nicads) die faster, alklids of no life cycle once dead they are dead, sure heavy currents on alklids will make them die quicker this is common sence, this has nothing to do with its life as they only can be used once.

Batteries (nicads) made for heavy loads last as long as batteries made for medium or light loads, and the heavy load (nicads) batteries will last even longer driving small currents.

What I am trying to say is; if you use a rated 5amp 1000mah AA to drive a 100Ma light bulb that battery will last longer than one rated at 1A at 1000mah.

I have tesed alot of nicads, alkalids, and nimh over the years as a RC'er.

Not have I once stated anything about Heavy duty akalids, but I will now they are junk. And I am not reffering to heavy duty alkalids when I say batteries made for heavy duty high drain capacity.

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Hi Juglenaut,
We were talking about old-fashioned garbage carbon-zinc "heavy-duty" battery cells, not premium-priced alkaline cells such as "Ultra", "Titanium" or "e2" which cost much more than "ordinary" alkaline battery cells but have exactly the same spec's. Alkaline batteries are way better than carbon-zinc.

Today's Ni-MH cells have a higher capacity per charge than the best alkaline cells, but they self-discharge in a month or two.

 

A few things I already knew about alkalines vs the "carbon-zinc" heavy duty ones is that alkalines last longer in colder weather and that they last longer while not in use as well as when in use, so if you store batteries or something similar they will last longer. They also last much longer in general because they have a greater weight density to the heavy duty ones. I don't even know why people still buy those old carbon zinc or heavy duty ones anymore. Alkalines are better in every way. They might cost slightly more but they are a much better by because they last like 4 times longer. Sorry if any of this has already been gone over. I've leared a bit more reading some of this thread.