Anything that will replace NiMH soon?

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nquinn
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Anything that will replace NiMH soon?

So, NiMH batteries are around a decade old now, and while there have been improvements in # of recharge cycles, capacity has been pretty much flat.

All the modern stuff seems to be lithium, but this operates at voltages that don’t play nicely with most 1.2-1.5 electronics.

What technology (if any) is close to replacing NiMH?

DavidEF
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NiMH is much older than a decade by now. In fact, it’s older than me! I think NiZn was probably supposed to be the successor, but it failed. Some people even tried rechargeable Alkaline, but that isn’t so great either. Both of those chemistries are still around btw, but not useful to replace NiMH. I’m not a battery guru, but I’ve not heard of anything coming close to replacing NiMH.

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Yes, Eneloops were the last innovation of NiMH, and I think they made them pretty-much an ideal replacement for alkalines. It doesn’t appear capacity is going to improve much, so I think we’ve reached the best NiMH are going to get. Maybe a bit more power (wattage), but that’s really not needed given the current capacity.

There’s Energizer lithium primaries if you want more capacity. Better in almost everything, except power, compared to NiMH Eneloops. Well, they’re disposable, so maybe not better in that regard either.

In rechargeables, the next step-up is lithium-ion cells. It’s not really a direct comparable, as you note, given the difference in voltages. But if you want more power and higher energy density, lithium-ion is the next step up.

In ~1.5v cells, I don’t think there’s any huge improvements on the horizon. Good news for Duracell and Energizer shareholders.

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I wonder if there could be a hybrid or a sort of in-between cell chemistry that has the higher voltage of NiZn and the higher capacity and low self-discharge of NiMH. Maybe there’s something they haven’t tried because Li-Ion made it not worth their while to push Nickel battery technology.

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NimH is a very mature technology now, and an excellent, safe and inexpensive one.

The major technical improvement was ultra-low self discharge, (Eneloop and others.) making them a “fit and forget” cell

Capacity is comparable with Liion, e.g. compare an AA 2500 mAh 1.2V cell with a 14500 700 mAh 3.8V cell, The AA NimH has more capacity (3 Wh c.f. 2.66)

And substitutable with e.g. alkaline primary cells, or lithium primaries (no, they don’t have any more capacity, just better behaved for things that take peak currents, like digicams, otherwise much the same, see HKJ for facts and data).

At really low temperatures Li primary rule, NimH second, Liion and alkaline fail badly, and I do use torches in these conditions and speak from experience. My headtorch has an external battery pack which is tucked inside my jacket to keep it warm, and this matters.

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Ya I can remember over 20 years ago getting my first nihm battery charger for my aa cells as a kid. Much older then a decade.
About a decade ago in 2009 in the barracks. I had a CD player and bought a energizer fast charger and 4 cells that came with it. To listen to music because there was nothing else to do. It literally caught on fire after there 3rd use. The batteries didn’t but the something inside the unit did. The batteries ended up being fine. I was in my rack and smelt burning plastic. Luckily the floors are solid concrete. Nothing around that could catch fire. I’ve never had anything energizer that plugs into a wall again. It was one of those 20 minute chargers or whatever. Before I knew anything about batteries.

Crazy thing was I use to recharge alkaline cells in it as well. I was like 9 years old. Sometimes they would leak out and other times they would recharge and work.

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I still have an ancient charger that can re-charge alkalines, using a subtle pulsing mode. It still works, as long as the cells aren’t fully discharged, but hardly worth the effort these days.

Their chemistry is simple and amenable to re-charging, but realities mean things can go wrong (leaks, drying up etc.) so don’t bother trying. NimH changed all that.

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Tom Tom wrote:
NimH is a very mature technology now, and an excellent, safe and inexpensive one.

The major technical improvement was ultra-low self discharge, (Eneloop and others.) making them a “fit and forget” cell

Capacity is comparable with Liion, e.g. compare an AA 2500 mAh 1.2V cell with a 14500 700 mAh 3.8V cell, The AA NimH has more capacity (3 Wh c.f. 2.66)

And substitutable with e.g. alkaline primary cells, or lithium primaries (no, they don’t have any more capacity, just better behaved for things that take peak currents, like digicams, otherwise much the same, see HKJ for facts and data).

At really low temperatures Li primary rule, NimH second, Liion and alkaline fail badly, and I do use torches in these conditions and speak from experience. My headtorch has an external battery pack which is tucked inside my jacket to keep it warm, and this matters.

It’s crazy to me that modern Li-ion batteries, at least at the 14500 size don’t have much more capacity than the NiMH batteries.

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Tom Tom wrote:
I still have an ancient charger that can re-charge alkalines, using a subtle pulsing mode. It still works, as long as the cells aren’t fully discharged, but hardly worth the effort these days.

Their chemistry is simple and amenable to re-charging, but realities mean things can go wrong (leaks, drying up etc.) so don’t bother trying.

I’ve experimented with recharging alkalines, and it’s definitely not worth it. They will leak badly within a few days after charging. You can top them up with about a 20% charge, as long as you do it while they’re half-full or higher. And you can do it a few times, but they’ll leak before you do it more than 4 or 5 times.

You have to keep the charge rate low, 200mA is okay. Otherwise, they won’t take the charge. Stop at 1.6v. For safety, do it somewhere that can take a mess in case they rupture during charging. I’ve never had that happen, though.

It’s fun to experiment. But it’s definitely not worth it economically, or for safety reasons.

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nquinn wrote:

It’s crazy to me that modern Li-ion batteries, at least at the 14500 size don’t have much more capacity than the NiMH batteries.


Well, exceptions abound, but comparing good quality NiMH cells against similar quality Li-Ion cells, it seems that NiMH has twice the capacity in mAh, but Li-Ion has three times the voltage, so Li-Ion comes out just slightly ahead.

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DavidEF wrote:
nquinn wrote:

It’s crazy to me that modern Li-ion batteries, at least at the 14500 size don’t have much more capacity than the NiMH batteries.


Well, exceptions abound, but comparing good quality NiMH cells against similar quality Li-Ion cells, it seems that NiMH has twice the capacity in mAh, but Li-Ion has three times the voltage, so Li-Ion comes out just slightly ahead.

There aren’t any really good 14500 cells. 18650 (and maybe 21700) is where the sweet spot is now.

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WalkIntoTheLight wrote:
DavidEF wrote:
nquinn wrote:

It’s crazy to me that modern Li-ion batteries, at least at the 14500 size don’t have much more capacity than the NiMH batteries.


Well, exceptions abound, but comparing good quality NiMH cells against similar quality Li-Ion cells, it seems that NiMH has twice the capacity in mAh, but Li-Ion has three times the voltage, so Li-Ion comes out just slightly ahead.

There aren’t any really good 14500 cells. 18650 (and maybe 21700) is where the sweet spot is now.

I wish a major company would develop the 26650 format. It seems plb and others are now. We can get 5500 and close to 6000mah with a low discharge rate. And it can do 20 amps+ Like the new shockli battery. But they don’t have access to the patents and technology like the big giants. I guess they could try to reverse engineer it. Like run a mass spectrum on the electrolytes to see the exact ratios and such. And the anode and cathode materials to see their make ups

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nquinn wrote:
It’s crazy to me that modern Li-ion batteries, at least at the 14500 size don’t have much more capacity than the NiMH batteries.

Isn’t it just. For example you can buy a D cell in NimH with 10,000 mAh capacity, which is maybe equivalent to a decent 18650 Li ion. But far larger and heavier, and more expensive. Though you could strap x4 2500 mAh AAs together into the same diameter and shorter, for less money.

In the AA/14500 size though, which covers a lot of useful devices, they are comparable. It seems nobody is interested in developing 14500, I think it is a lost cause. But the AA NimH will continue to be the best, though I doubt much more improvement will come, it is very mature. (Watch out for “fat” AAs though, some won’t fit devices built to spec.)

Summary: in AA/14500, NimH has the advantage except for the highest currents, and is an affordable, safe and readily available cell, in alkaline or even lithium primary versions. A torch that can only work with the voltage from a 14500 is a bit of a dead-end (though I have two).

I have a lot of use for AA torches.

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Coupled with the versatility and performance characteristics of the simple AA NimH, AA torches IMO are the most underrated of flashlight platforms.

What they can do plus all the advantages of their compactness still kinda astonishes me to this day. I mean we’re talking about something with only 1.2V behind it pushing over 200 lumens in some cases for a good duration.

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Improvements in the NiMH chemistry are just icing on the cake and not really required when we already have those glorious eneloops.  <img src= " />

 

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Maybe part of the reason that NiMH (along with alkaline, NiZn, etc) is not seeing much development is because they aren't a very optimal voltage.

LEDs require, what? 3 volts or so? If you use Li-Ion, its not too hard to make drivers with around 90% efficiency. And lots of other electronics runs around 2-5v.

But sub 2 volt chemistries require boost drivers, which are not as efficient, and if you want to avoid them, you need to use multiple cells in parallel. Both of these options can be less appealing than using a single Li-Ion cell.

 

Please tell me if I'm wildly off track or something here. Smile

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I think the problem just comes from size. Each battery chemistry has an optimal cell size for max energy density and small cells just aren’t as optimal. Pretty sure that’s why 21700 was picked up by Tesla because the energy density is more optimal vs 18650s.

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I thought the 21700 was for “packing” density, along with energy density to match.

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nquinn
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Pablo de Llama wrote:

Maybe part of the reason that NiMH (along with alkaline, NiZn, etc) is not seeing much development is because they aren’t a very optimal voltage.


LEDs require, what? 3 volts or so? If you use Li-Ion, its not too hard to make drivers with around 90% efficiency. And lots of other electronics runs around 2-5v.


But sub 2 volt chemistries require boost drivers, which are not as efficient, and if you want to avoid them, you need to use multiple cells in parallel. Both of these options can be less appealing than using a single Li-Ion cell.


 


Please tell me if I’m wildly off track or something here. Smile

Not everyone uses batteries for flashlights Smile Obviously plenty of 1.5v applications out there right now.

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flydiver wrote:
I thought the 21700 was for “packing” density, along with energy density to match.

I suspect economy of manufacture as well, i.e. much of the cost of making a cell must be in the casing materials and processing to assemble it, which is probably little different between 18650 and the “21-70” as Tesla name it. So the larger capacity cell should inherently be cheaper, per Watt-hour of capacity.

Just as e.g. AAAs cost nearly as much as AAs, per unit, despite having 1/3 the capacity.

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Pablo de Llama wrote:

Maybe part of the reason that NiMH (along with alkaline, NiZn, etc) is not seeing much development is because they aren’t a very optimal voltage.


LEDs require, what? 3 volts or so? If you use Li-Ion, its not too hard to make drivers with around 90% efficiency. And lots of other electronics runs around 2-5v.


But sub 2 volt chemistries require boost drivers, which are not as efficient, and if you want to avoid them, you need to use multiple cells in parallel. Both of these options can be less appealing than using a single Li-Ion cell.


 


Please tell me if I’m wildly off track or something here. Smile

I’m not sure what sort of simple LED driver gives 90% efficiency from a single Liion cell, far from it. FET direct drive is the worst, linear better, but you need a buck driver for best efficiency.

FET or linear simply burn off the excess voltage from the cell (compared with Vf of the LED) as heat. In the case of the FET, most of the heat ends up in the over-driven LED, operating itself at a less efficient current level, even when PWMed to lower brightness. In the linear it is dumped in the driver.

A boost driver for e.g. NimH is no more complicated or less efficient than a buck (they are almost the same circuit design).

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Tom Tom wrote:
Pablo de Llama wrote:

Maybe part of the reason that NiMH (along with alkaline, NiZn, etc) is not seeing much development is because they aren't a very optimal voltage.

LEDs require, what? 3 volts or so? If you use Li-Ion, its not too hard to make drivers with around 90% efficiency. And lots of other electronics runs around 2-5v.

But sub 2 volt chemistries require boost drivers, which are not as efficient, and if you want to avoid them, you need to use multiple cells in parallel. Both of these options can be less appealing than using a single Li-Ion cell.

 

Please tell me if I'm wildly off track or something here. Smile

I'm not sure what sort of simple LED driver gives 90% efficiency from a single Liion cell, far from it. FET direct drive is the worst, linear better, but you need a buck driver for best efficiency. FET or linear simply burn off the excess voltage from the cell (compared with Vf of the LED) as heat. In the case of the FET, most of the heat ends up in the over-driven LED, operating itself at a less efficient current level, even when PWMed to lower brightness. In the linear it is dumped in the driver. A boost driver for e.g. NimH is no more complicated or less efficient than a buck (they are almost the same circuit design).

Thanks for enlightening me. Smile

I had gotten the impression that boost drivers were the most inefficient somewhere on this website, and that Li-Ion drivers are more efficient due to the higher voltages involved.

Do you have any suggestions for interesting topics about boost driver efficiency I can read, to learn more?

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Tom Tom wrote:

I’m not sure what sort of simple LED driver gives 90% efficiency from a single Liion cell, far from it. FET direct drive is the worst, linear better, but you need a buck driver for best efficiency.

FET or linear simply burn off the excess voltage from the cell (compared with Vf of the LED) as heat. In the case of the FET, most of the heat ends up in the over-driven LED, operating itself at a less efficient current level, even when PWMed to lower brightness. In the linear it is dumped in the driver.

A boost driver for e.g. NimH is no more complicated or less efficient than a buck (they are almost the same circuit design).


Direct drive is 100% efficient.
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Enderman wrote:
Direct drive is 100% efficient.

Not really, there is resistance everywhere and adding pwm will reduce the efficiency more for direct drive than for other ways.

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Enderman wrote:
Direct drive is 100% efficient.

Sure, no heat dissipated in the driver, but with e.g. a cell at 4.2V, an LED that needs say 3.5V for the desired brightness you are hammering the LED into an operating region way beyond peak efficiency.

PWMing it to lower brightness doesn’t change these facts.

There may be no wasted power dissipated in the driver, it’s instead dissipated in the LED, and the internal resistance of the cell, and other bits of the torch, springs etc.

Direct drive is the crudest and least efficient way of powering an LED, until the cell is discharged to the same voltage as the LED Vf., by which point it is pretty well empty.

It is not obvious how inefficient direct drive is. Looking at my example you might think the system is (3.5/4.2) = 83% efficient, but far from it, you also need to factor in the much higher current taken by the LED at the higher voltage, which you can estimate using e.g. djozz’s measurements of LED transfer characteristics.

The most efficient system is to power the LED with direct current, at the level needed to achieve the desired brightness. LED efficiency drops dramatically when over-driven by direct drive. In the limit you can easily reach the point where e.g. 50% more power gives only 10% more light.

Once you start modding with e.g. spring bypasses, better FETs, in pursuit of headline lumens figures in turbo for brief blasts, you are also further reducing efficiency in normal operation.

Don’t kid yourself, a FET driver is always pushing and stressing the LED at full turbo level (least efficient), and hammering the cell at higher instantaneous current leading to increased loss from internal resistance, even when it is PWMed back to much lower light output.

A linear driver can do this by burning off the excess voltage as heat, whilst operating the LED at an efficient point (generally the lower the current the more efficiently the LED performs). A buck (or boost) driver can do this more elegantly by dropping the voltage without wasting the excess as heat.

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Tom Tom wrote:

Sure, no heat dissipated in the driver, but with e.g. a cell at 4.2V, an LED that needs say 3.5V for the desired brightness you are hammering the LED into an operating region way beyond peak efficiency.

PWMing it to lower brightness doesn’t change these facts.

There may be no wasted power dissipated in the driver, it’s instead dissipated in the LED, and the internal resistance of the cell, and other bits of the torch, springs etc.

Direct drive is the crudest and least efficient way of powering an LED, until the cell is discharged to the same voltage as the LED Vf., by which point it is pretty well empty.

It is not obvious how inefficient direct drive is. Looking at my example you might think the system is (3.5/4.2) = 83% efficient, but far from it, you also need to factor in the much higher current taken by the LED at the higher voltage, which you can estimate using e.g. djozz’s measurements of LED transfer characteristics.

The most efficient system is to power the LED with direct current, at the level needed to achieve the desired brightness. LED efficiency drops dramatically when over-driven by direct drive. In the limit you can easily reach the point where e.g. 50% more power gives only 10% more light.

Once you start modding with e.g. spring bypasses, better FETs, in pursuit of headline lumens figures in turbo for brief blasts, you are also further reducing efficiency in normal operation.

Don’t kid yourself, a FET driver is always pushing and stressing the LED at full turbo level (least efficient), and hammering the cell at higher instantaneous current leading to increased loss from internal resistance, even when it is PWMed back to much lower light output.

A linear driver can do this by burning off the excess voltage as heat, whilst operating the LED at an efficient point (generally the lower the current the more efficiently the LED performs). A buck (or boost) driver can do this more elegantly by dropping the voltage without wasting the excess as heat.

HKJ wrote:
Not really, there is resistance everywhere and adding pwm will reduce the efficiency more for direct drive than for other ways.

If you want to be pedantic, yes there is some resistance which causes losses.
So technically it is more like 99.9% efficient instead of 100%.
Other than that, direct drive is literally just like a wire.
The power going into the driver is the same as the power coming out.

Driver efficiency has nothing to do with how much current or voltage your LED is using, it is simply power out from the driver divided by power in to the driver.

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Enderman wrote:
Driver efficiency has nothing to do with how much current or voltage your LED is using, it is simply power out from the driver divided by power in to the driver.

Nonsense. The driver is essentially an impedance matching network, matching the characteristics of the cell, with those of the LED. It has to be looked at as a system.

A FET driver isn’t really a driver at-all, just an on-off switch, performing no useful matching function, leaving the cell+LED system mis-matched and mostly operating at it’s least efficient point.

Fortunately it mostly works quite well, but there are much better (more efficient) ways of doing it instead.

Watt-hours in, lumen-hours out, (Edit: integrated over the cell duration) is to my mind the best measure of efficiency, but not easy to characterise. That’s why HKJ’s cell measurements and djozz’s LED measurements are so useful for those curious to get a grasp of what’s really going on.

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Enderman wrote:

If you want to be pedantic, yes there is some resistance which causes losses.
So technically it is more like 99.9% efficient instead of 100%.
Other than that, direct drive is literally just like a wire.
The power going into the driver is the same as the power coming out.

Driver efficiency has nothing to do with how much current or voltage your LED is using, it is simply power out from the driver divided by power in to the driver.

That depends on what efficiency you look at, I like the lumen/watt definition and mostly direct drive is fairly bad at that, because it either overdrives the led or looses a lot of power in series resistance (And it is way worse than 99.9%). Overdriving a led may get slightly more brightness, but the price is much more heat and much lower efficiency. Some may believe that it is a good trade off, I prefer much longer runtime and a bit lower brightness. Reducing brightness with pwm do not improve the efficiency!

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HKJ wrote:

That depends on what efficiency you look at, I like the lumen/watt definition and mostly direct drive is fairly bad at that, because it either overdrives the led or looses a lot of power in series resistance (And it is way worse than 99.9%). Overdriving a led may get slightly more brightness, but the price is much more heat and much lower efficiency. Some may believe that it is a good trade off, I prefer much longer runtime and a bit lower brightness. Reducing brightness with pwm do not improve the efficiency!

I didn’t say anything about PWM. Read the post.

Tom Tom wrote:

Nonsense. The driver is essentially an impedance matching network, matching the characteristics of the cell, with those of the LED. It has to be looked at as a system.

A FET driver isn’t really a driver at-all, just an on-off switch, performing no useful matching function, leaving the cell+LED system mis-matched and mostly operating at it’s least efficient point.

Fortunately it mostly works quite well, but there are much better (more efficient) ways of doing it instead.

Watt-hours in, lumen-hours out, is to my mind the best measure of efficiency, but not easy to characterise. That’s why HKJ’s cell measurements and djozz’s LED measurements are so useful for those curious to get a grasp of what’s really going on.

Nobody was talking about luminous efficacy, only driver efficiency.
If you’re going to mix both the LED and driver efficiency into one then you’re never going to have anything that makes sense, because LEDs aren’t even 50% efficient.
So it would make 0 sense for you to say 90% efficiency a few posts up.

Direct drive is literally just a wire with an on/off switch on it.
That’s why it has 99.9% efficiency.
There is near 0 resistance.

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Enderman wrote:
I didn’t say anything about PWM. Read the post.

That do not exclude it.

Enderman wrote:
Nobody was talking about luminous efficacy, only driver efficiency.
If you’re going to mix both the LED and driver efficiency into one then you’re never going to have anything that makes sense, because LEDs aren’t even 50% efficient.
So it would make 0 sense for you to say 90% efficiency a few posts up.

Direct drive is literally just a wire with an on/off switch on it.
That’s why it has 99.9% efficiency.
There is near 0 resistance.

Burning a lot of power in the led is not very efficient, you always have to look at the total solution, i.e. from battery to light. Using the led as a heater is usual a very bad idea, only exception is if you are trying to break the record for the brightest light around.

Anyway direct drive is a wire with some resistance, I have not seen any good explanation why it has to be 0.01ohm or 1ohm or 1000ohm or why/why not you can switch the led on/off at a fast pace, before it stops being direct drive.

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FET drivers are certainly not efficient. If I compare my BLF A6 (which uses a FET at high levels) to my ZL SC600w (which uses a boost driver), I can get twice the runtime from my SC600 at about the same brightness as the A6. And the SC600 has the advantage of a regulated constant output, whereas the A6 decreases as the battery drains.

Boost drivers win by a huge margin.

You can argue semantics about where the inefficiency comes from, but as a whole system, FET sucks in every way except the simplicity of the design. Which is why it is so popular for high output budget lights.

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