Why do rechargeable produce more light?

[Helstar]

I did a search but did not find what I was looking for.
Basically I want to know why Eneloops and Rayovac Hybrids produce brighter light then an off the shelf Duracell or other use and lose battery?

I am sure it is something super simple I looked at the volts and the fact that they are 2100 2200 milli. But, I always thought use and lose had higher ratings?

 

[h2xblive]

I believe many rechargeables produce more light (than disposables) despite lower voltages because of their lower internal resistance.

 

[Battery Guy]

I did a search but did not find what I was looking for.
Basically I want to know why Eneloops and Rayovac Hybrids produce brighter light then an off the shelf Duracell or other use and lose battery?

I am sure it is something super simple I looked at the volts and the fact that they are 2100 2200 milli. But, I always thought use and lose had higher ratings?

The short answer to your question is that primary (non-rechargeable) cells tend to have a higher internal resistance than non-rechargeable cells.

Longer answer: primary cells are manufactured in the charged state, and are expected to maintain their charge for long periods of time during storage. In addition, the "horse power" wars between primary battery companies have pushed energy/capacity over power for primary batteries. For rechargeable batteries, you typically want to be able to charge them quickly, which also means that they can be discharged quickly.

In general, if you want to design a cell with low self discharge and high energy, you want to have a low electrode surface area. The opposite is true if you want to design a high power/high drain cell.

So, in general, primary cells have high energy and low power, whereas secondary cells have high power and low energy. You can see this clear in the Ragone plots here, where the primary cells are shown as dashed curves and the secondary cells are shown as solid lines.

Hope this helps.

Cheers,
Battery Guy

 

[was.lost.but.now.found]

Alkalines are generally well suited for low drain devices, like some types of TV remotes, wall clocks, certain children's toys, etc. However, NiMH is not only more energy dense, but also has lower internal resistance. This is why they are prone to self discharge when alkalines can sit for a few years at nearly full charge. But it also speaks to why NiMH handle high current rates better - they can dump all that current much more efficiently than alkaline.

What this all means is both battery types still have a place in most households, just not for the same job.

 

[Battery Guy]

However, NiMH is not only more energy dense, but also has lower internal resistance. This is why they are prone to self discharge when alkalines can sit for a few years at nearly full charge.

Not quite right. NiMH cells actually have lower energy than alkaline cells. For example, a typical alkaline cell has a capacity of 3Ah and energy of 3.7Wh, compared to typical NiMH cells that have capacities in the 2-2.7Ah range and energies in the 2.2-3.1Wh range.

Higher self-discharge of NiMH cells has more to do with differences in the cell chemistry and construction than it does with the total cell energy.

Cheers,
Battery Guy

 

[was.lost.but.now.found]

Not quite right. NiMH cells actually have lower energy than alkaline cells. For example, a typical alkaline cell has a capacity of 3Ah and energy of 3.7Wh, compared to typical NiMH cells that have capacities in the 2-2.7Ah range and energies in the 2.2-3.1Wh range.

Higher self-discharge of NiMH cells has more to do with differences in the cell chemistry and construction than it does with the total cell energy.

Cheers,
Battery Guy

It's all based on your discharge rates. Poor Energizer, I always pick on them because their data sheets are so readily available and I know how to find them, but they state a max of 3000mAh (like you say) when the drain is at 10mA; capacity immediately drops to approximately 2850mAh at a discharge rate as 'high' as 25mA.

So to ascertain a 3000mAh capacity would require you to figure a discharge rate of .0033C; I always understood the standard industry discharge rate to be .05C. If .05C were used, Energizer's discharge graph puts us spot on to an 80mA discharge, which yields a 1600mAh capacity.

 

[Mr Happy]

What's the discharge rate in a clock? Or a TV remote?

Or the average discharge rate in a light switched on for ten minutes every week?

 

[Battery Guy]

It's all based on your discharge rates. Poor Energizer, I always pick on them because their data sheets are so readily available and I know how to find them, but they state a max of 3000mAh (like you say) when the drain is at 10mA; capacity immediately drops to approximately 2850mAh at a discharge rate as 'high' as 25mA.

So to ascertain a 3000mAh capacity would require you to figure a discharge rate of .0033C; I always understood the standard industry discharge rate to be .05C. If .05C were used, Energizer's discharge graph puts us spot on to an 80mA discharge, which yields a 1600mAh capacity.

You are correct. I just wanted to point out that technically, the alkaline has a higher energy density, while the NiMH has a higher power density. Your previous post implied that the NiMH cell self-discharges faster because it had a higher energy density.

Not sure about the 0.05C industry standard rate. I had not heard that before. But there is no question that you need to discharge an alkaline battery over ~1 week to get all of the capacity.

Cheers,
Battery Guy

 

[was.lost.but.now.found]

Energy density was probably a poor choice of words on my part. They are just different batteries, containing different chemistries, for different purposes. Each has its pros and cons. You probably did a better job actually answering the OP's original question than I did.

Battery University makes mention about discharge rate for SLA being measured at .05C, but unfortunately it doesn't answer the question for other chemistry types. I know I've heard it used before, maybe SilverFox or someone else can chime in and site a reference. At any rate, primary and secondary batteries will always be on separate playing fields, so comparisons will always be difficult.

 

[alpg88]

I did a search but did not find what I was looking for.
Basically I want to know why Eneloops and Rayovac Hybrids produce brighter light then an off the shelf Duracell or other use and lose battery?

I am sure it is something super simple I looked at the volts and the fact that they are 2100 2200 milli. But, I always thought use and lose had higher ratings?

for the same reason that a power washer works better than a garden hose.
power.

 

[uk_caver]

It's all based on your discharge rates. Poor Energizer, I always pick on them because their data sheets are so readily available and I know how to find them...

Duracell do have their datasheets online
http://www1.duracell.com/Procell/productdata/

 

[45/70]

Some good and accurate explanations have been presented. The simple answer is that most NiMH cells perform better at medium and high current loads than alkaline primary cells, because they can maintain a higher voltage under these conditions for reasons already explained in more detail.

In a direct driven light, this will always yield higher output. In most regulated lights with a boost circuit, the same is true to some extent, as the boost circuit doesn't have to boost as much, and the circuit runs more efficiently, again often yielding a bit higher output. In lights which use a buck circuit, usually there is no difference in output between alkaline and nickel based cells. The only real difference in these lights, is that NiMH cells will generally yield longer runtime than alkaline cells, under higher current conditions.

Dave

 

[Ray_of_Light]

The document you are looking for is:

IEC 60086-1 - Primary batteries – Part 1; General.

Good luck in finding it on the Web...

Anthony