D-cell Alkaline VS AA nimh

[qwertyydude]

Your multimeter has more resistance than a true dead short. We test cells at 10 milliohm resistance when measuring flash amps. I have stacks of data showing D cells putting out 20 to 25 flash amps, while AA cells typically fall between 8 and 12 amps into the same load.

Even if it did have more resistance than a dead short, that still doesn't explain why the AA would basically outperform the D battery in an equal resistance test. Same multimeter, essentially the same state of charge, the .007v difference shouldn't lower the D cell current by 3 amps if the D-cell truly had lower internal resistance. And I do use very low resistance short length 16 gauge wires on my multimeter, it's about as close to a dead short as you're really going to get and considering the high resistance of the batteries it's a gives a good representation of the discharge capability of alkalines. Nimh not at all because AA can go up to 20 amps, D-cell forget it, it can smoke 16 gauge wire on a dead short. I know my high performance 5300 mah sub-c RC cells can put out 75 amps peak on a dead short.

 

[MorePower]

Even if it did have more resistance than a dead short, that still doesn't explain why the AA would basically outperform the D battery in an equal resistance test. Same multimeter, essentially the same state of charge, the .007v difference shouldn't lower the D cell current by 3 amps if the D-cell truly had lower internal resistance. And I do use very low resistance short length 16 gauge wires on my multimeter, it's about as close to a dead short as you're really going to get and considering the high resistance of the batteries it's a gives a good representation of the discharge capability of alkalines. Nimh not at all because AA can go up to 20 amps, D-cell forget it, it can smoke 16 gauge wire on a dead short. I know my high performance 5300 mah sub-c RC cells can put out 75 amps peak on a dead short.

No, as close to a dead short you're going to get is the method we use, day in and day out. 10 milliohms read at 20 milliseconds. I'm not saying NiMH cells can't output higher current than alkaline cells; they certainly are more than capable of doing so. What I am saying is that you are wrong in your comparison of the discharge capability of alkaline AA and D cells.

Since no one ever wins an argument on the internet, I'm going to stop now.

 

[lightseeker2009]

No, as close to a dead short you're going to get is the method we use, day in and day out. 10 milliohms read at 20 milliseconds. I'm not saying NiMH cells can't output higher current than alkaline cells; they certainly are more than capable of doing so. What I am saying is that you are wrong in your comparison of the discharge capability of alkaline AA and D cells.

Since no one ever wins an argument on the internet, I'm going to stop now.

Wise words

We've gone a bit off the path here. Thanks for all the responces. I got the answer I was looking for, part of it anyway.
Regarding the AA VS D-Cell Alkalines dilema. It should be easy to prove which cell can provide the most current for a specific task, without the need for any of us to have to battle it out over the web

I just feel that too short out a cell only means so much. If it can provide 7 Amps why can't it sufficiently power a less than 1 Amp led? It struggles to do so. I'm glad I gutted the spotlight and will never buy alkalines again, exept in an emergency of course. I don't see the point if you can use rechargebles. Its far cheaper in the long run and you charge them again when you've used just 20%. With alkalines you will go on a trip with 80% full batteries under the same circumstances.

I've done my last test in this regard. I've measured the voltages under load.
With the alkalines I got 2.85V unloaded for the two. The moment the flashlight is turned on the reading drops to only 0.68V! But as can be seen the batteries are not fresh anymore, and no, I won't be buying some anytime soon
With the Nimh's, and they are over 3 year old 2000mah Energizers, I bought them before I knew about Eneloops The unloaded voltage was 2.68V for two, the loaded voltage was 2.41V. ( Sorry, its a mistake, it was 2.21V )
Not bad hey?

 

[Lynx_Arc]

Testing batteries using a dead short gets you nowhere because it doesn't tell you what voltage you can expect at what current levels which is key to battery choice. Knowing internal resistance does tell you which batteries can supply large currents with minimal voltage depression and alkalines are not them. For currents under an amp alkaline D cells do well enough with currents 500ma and under yielding long runtimes that make them worth using if it were not for the risk of leakage.
The biggest issue today is more and more lights and electronics are gobbling up more power which is problematic for both alkaline D cells and AAs of any type as both have capacity issues when it comes to high power usage runtime. Many people are opting for AA to D adapters (2AA versions becoming more popular) so they do not have to pay for the alkaline D cells issues with larger current loads.
I think the biggest question is at what current level does an alkaline D cell have identical runtime to 1 or 2 eneloop AAs (that have been sitting off the charger for a week or two). If we knew this we could know when it would make sense to use adapters and forget using alkaline D cells altogether.

 

[45/70]

I think the biggest question is at what current level does an alkaline D cell have identical runtime to 1 or 2 eneloop AAs (that have been sitting off the charger for a week or two). If we knew this we could know when it would make sense to use adapters and forget using alkaline D cells altogether.

In my years and years of experience (well OK, not that many, only about 30) with both alkaline cells, and NiCd/NiMh cells, my general conclusion has been that the break even point as to which chemistry is preferable, is ~500mA for D cells, and ~300mA for AA cells. This does not take into consideration cost, ease of use, having to make a special trip to the store to get replacement cells and so on, only a head to head comparison as to which chemistry will work for the longest from fully charged, to empty.

Dave

 

[45/70]

dbl post

 

[Battery Guy]

Greetings Everyone,

I thought that the following discharge curves might be useful for this discussion:

This plot shows 1 A discharge curves for a standard Eneloop and new Energizer and Duracell D cells. I think that what these curves show is that unless you have brand new, out of the package, alkaline D cells, a fully charged Eneloop (and any other good quality NiMH AA) is going to have a higher voltage compared to the alkaline D. And even with a brand new alkaline D, there is still a significant length of time where the NiMH has a higher voltage (at least until the NiMH is depleted, of course).

btw: please don't make the conclusion that the Duracell is better than the Energizer. I have found that D alkaline cells are highly variable in their performance at discharge currents of 0.5 A and higher. As has been pointed out already, a 1 A discharge is really at the upper limit of what these cells are designed to perform at.

Cheers,
BG

 

[Mr Happy]

I thought that the following discharge curves might be useful for this discussion...

That's an interesting graph. Now if you stretched the black curve across to the right by a scale factor of 5x I imagine that would be a fair approximation of a 10,000 mAh D size NiMH cell. And that would be a stunning indication of what D size NiMH cells are capable of...