Lets talk about NiMh... Stop all the hating.

[Lastlokean]

The average person here seems to bash on / slam on NiMh AA/AAA batteries. I've seen all kinds of crazy claims from they just don't work (no legitimate explanation given) to using them is dangerous.

So what matters about batteries?

-Power output over life of a charge.
-Internal resistance.
-Safety
-Cost

1xAAA NiMh have no issues up to 8 amps.

NiMh:

Pro's
-Safe Chemistry
-Cheaper
-Consumer available.
-Consistent output over life.
-Can fully charge in 15 minutes.

Con's
-30% less energy density.

Li-Ion

Pro's:
- 30% greater energy density.
- Higher starting voltage
- Variety of sizes available.
(10440 to 18650)

Con's:
-Serious voltage swing over charge
-Fire/explosion hazard
-Not readily available to consumers
-More Expensive
-Requires protection circuitry for over/under charging.
-Takes hours to charge.


The only real advantage of a lithium ion cell is increased storage capacity. Not increased instantaneous output. No magical forces. They have nearly identical internal resistance.



Now lets analyze the power density claim a little bit more closely shall we? Extra power is only good if it is useful for our particular application...

3xAAA and an 18500 are nearly identical in size. The 18500 is slightly longer (5mm) and slightly thinner (5mm)


3xAAA = 1,000 Mah @ 3.6 volts. A nimh goes from 1.25 at fully charged to 1.1 discharged.


1x18500 = 1,4000 Mah @ 4.25 - 2.5 volts.


So the power density statement is kind of flawed. What atomizer will work good over that huge voltage range? Not really any of them.


Say you are using a 2 ohm atomizer.

Fully Charged 50% Cutoff Voltage
Li-Ion (4.2v) 8.82 W (3.35v) 5.69 W (2.5v) 3.125 W


3xNiMh (3.75v) 7 W (3.6v)6.48 W (3.3v) 5.45 W


It is not so simple as to just compare mah ratings and declare one battery superior to another for a specific application.

 

[Vapor Vinny]

I agree with your sentiment. I mod exclusively with AAA batts. Cheaper, safer, last longer or just as long, easier to find. The big downside is the limitations you have by the size of using 3 or 4 AAAs. Although, I can work around that quite a bit with circular and stacked battery holders. I'm speaking cosmetically of course.

I haven't noticed any "hate" of Nimh batts, just that people ignore them.

 

[dr g]

No one in this forum "hates" on Nimh, however most of us are well aware of their limitations and in most mod scenarios, you are fighting for every last mAh you can get. If space and streamlined design is not a priority, NiMH is a fine solution, but it's hard for many people to feel quite "happy" with that solution knowing there is better out there.

You also have self-discharge concerns.

As for your crusade, do some discharge curves, that might open some eyes. Looking at the high current discharge curves for AA NiMH, I think you will hit board cutoffs sooner than you would like and far sooner than a 1S li-ion cell with a 3x NiMH configuration. Have not seen much with AAA but I expect even worse results.

 

[Vapor Vinny]

No one in this forum "hates" on Nimh, however most of us are well aware of their limitations and in most mod scenarios, you are fighting for every last mAh you can get. If space and streamlined design is not a priority, NiMH is a fine solution, but it's hard for many people to feel quite "happy" with that solution knowing there is better out there.

You also have self-discharge concerns.

As for your crusade, do some discharge curves, that might open some eyes. Looking at the high current discharge curves for AA NiMH, I think you will hit board cutoffs sooner than you would like and far sooner than a 1S li-ion cell with a 3x NiMH configuration. Have not seen much with AAA but I expect even worse results.

All that is above my head, admittedly. All I can tell you is that I vape more than a day using 4 AAA Nimh batts, in a 3 x 2 x 1 box mod (fairly small). And it performs very well at about 5 volts, with a 3.2 single coil carto tank. I've managed to fit 3 AAA into a Dollar Tree Flashlight and it vapes good for about half a day.

Using AAAs does have some disadvantages. But I have my reasons for liking them. I'm by no means claiming they're superior.

 

[DrMA]

IMHO, the biggest problem with NiMH batteries is that you need 3 of them to get the same voltage as a single LiPo. That alone will take up valuable space, add a lot of weight and/or limit the capacity you carry around. The energy density comparison gets much more favorable to LiPo's if you think of the flat cells rather than the round/hard case ones.

 

[Lastlokean]

Well maybe 'hate' was too strong of wording... But Dr G, your argument is based on the pretense assumption that lithium ions are better than aaa nimh. You conveniently ignored the key points I brought up. Also self-discharge is only an issue if you want to fully charge a battery and then store it for days...

I think people are missing the key point of my argument... I accidentally formatted my discharge chart very poorly in the first post.

Mah doesn't mean a lot if it is over the huge voltage range like lithium ions are...

Say you are using a 2 ohm atomizer.

Li-Ion:
Fully charged: (4.2v) 8.82 W
50% charged: (3.35v) 5.69 W
Cutoff voltage: (2.5v) 3.125 W

3xNiMh:
Fully charged: (3.75v) 7 W
50% charged: (3.6v) 6.48 W
Cutoff voltage: (3.3v) 5.45 W

This clearly implies that the lithium ion is really only providing a 'good' vape over the first 50% of its capacity. (They discharge pretty darn linearly...) While a NiMh will keep you over 3.3 volts for the entire mah rating.

So if you add the clause usable power to be defined as over 3.3 volts, suddenly 3xAAA NiMh hold more power than a 18500. (They are pretty close to the same size.)

I personally used to go through 2 fully charged 18650's in a day. It wasn't that the first one would 'stop' producing vapor... But by the time the battery was half dead performance would cut down by ~50%. No more awesome clouds or throat hit.

I currently use a modded flashlight using 3xAAA batteries. I use a 1.5 ohm atomizer and have had no issue getting through a 12 hour day of chain vaping... ~ 8 ml of juice. Performance doesn't noticeably drop off for me until the last tank of the day.

 

[Relayer1974]

What I see a lot of on ECF is "NiMH batteries aren't high drain capable" which is absolutely false. I can buy a cheap pack of 1400mAh Energizer NiMH AA cells from Walmart and get 2C out of them all day long. There's a completely legitimate place for NiMH batteries in vaping, one that is underutilized, IMO.

 

[bapgood]

The type of vaping and mod that is intended to be used in this comparison should also be stated. Because any battery used in an application over its max rating is dangerous....like boosted mods or low ohm high amp configs....far more dangerous than using a lithium battery with in its specs.

 

[Thrasher]

What I see a lot of on ECF is "NiMH batteries aren't high drain capable" which is absolutely false. I can buy a cheap pack of 1400mAh Energizer NiMH AA cells from Walmart and get 2C out of them all day long. There's a completely legitimate place for NiMH batteries in vaping, one that is underutilized, IMO.

and 2 amps is considered high drain?

Mah doesn't mean a lot if it is over the huge voltage range like lithium ions are...

this is why VV mods have voltage regulation so Mah will ultimately matter. not so much in a mech

The significant disadvantage of NiMH batteries is the high rate of self-discharge; NiMH batteries lose up to 20% of their charge on the first day and up to 4% per day of storage after that. In 2005, a low self-discharge (...) variant was developed. ... NiMH batteries significantly lower self-discharge, but at the cost of lowering capacity by about 20%.

There is an inherent risk with NiMH chemistry that overcharging will cause a buildup of hydrogen, causing the cell to rupture. Therefore, cells have a vent. Hydrogen will be emitted from the vent in the event of serious overcharging

A complete discharge of a battery can result in one or more cells going into polarity reversal, which can cause permanent damage to those cells. This situation can occur in the common arrangement of four AA cells in series in a digital camera, where one will be completely discharged before the others due to small differences in capacity among the cells. When this happens, the good cells will start to drive the discharged cell in reverse, which can cause permanent damage to that cell

while they may have a place and i welcome any and all advances in vaping, now we are talking about a whole new set of rules and electronics. in most cases a drop from 1.4 to 1v is not enough to interest people into using these whereas 4.2 to 3.2 is much more time.

unless they can come up with a single cell with superior Mah i do not see adoption by the masses, noone in this day and age (outside of the few modders and such) are ready to start carrying packs of batteries again and have a tube mode the width of a 4d maglight.

then you get into the newer subohm vapors well into the 20+ watt range and they arent going to want a battery that runs 2 hours.

while Li may not be perfect it is more stable and suitable and chemestry developments are now seeing batteries with 18 amp peaks and now one with a 30amp discharge. with all the scares going on noone will want to hear that a cell in a pack, no matter how small the actual risk, may go into a venting situation from simply being overdischarged.

 

[WattWick]

Don't think those charts imply much by themselves. We would need to know how long the different batteries can give off an acceptable vape. None of us vape our LiIons down to 2.something volts. Mine are usually at 3.5-3.7 when I'm done with them.

Some lithium cells, like quality LiPos, can be charged in less than 15 minutes. Charging any lithium cell (afaik) for hours is doing it wrong.

Discharge curves on lithium cells (I know of at least) are not linear. You're not at 3.35v after spending half your mAhs. At least with lipos, by pulling out 70-80%, you're at about 3.7v. At least that's what my charger tells me. Usually start charge at 3.75v, then put back an amount of mAh equal to about 80% of total capacity.

2C is not high drain. 2C on a 1400mah battery is 2.8amps. At 4.8v, that's good for 13.44watts. And that's after stacking 4 of them to up the voltage. A Sony 30a lithium battery could put out nearly 10 times that at max charge.

Sorry for all the negativity! There are tons of lithium chemistries. We'd need the numbers for each of them to do a proper comparison.

Guess I am hating on the NiMHs!

 

[dr g]

Well maybe 'hate' was too strong of wording... But Dr G, your argument is based on the pretense assumption that lithium ions are better than aaa nimh. You conveniently ignored the key points I brought up. Also self-discharge is only an issue if you want to fully charge a battery and then store it for days...

I think people are missing the key point of my argument... I accidentally formatted my discharge chart very poorly in the first post.

Mah doesn't mean a lot if it is over the huge voltage range like lithium ions are...

Say you are using a 2 ohm atomizer.

Li-Ion:
Fully charged: (4.2v) 8.82 W
50% charged: (3.35v) 5.69 W
Cutoff voltage: (2.5v) 3.125 W

3xNiMh:
Fully charged: (3.75v) 7 W
50% charged: (3.6v) 6.48 W
Cutoff voltage: (3.3v) 5.45 W

This clearly implies that the lithium ion is really only providing a 'good' vape over the first 50% of its capacity. (They discharge pretty darn linearly...) While a NiMh will keep you over 3.3 volts for the entire mah rating.

So if you add the clause usable power to be defined as over 3.3 volts, suddenly 3xAAA NiMh hold more power than a 18500. (They are pretty close to the same size.)

Part of the problem with the numbers you are quoting is they are static charge numbers, under load the voltage sag will cause a different situation. With such a small range of charge voltage, you don't get much wiggle room. The discharge charts I've seen show AA sized NiMH's dropping to about 1.0v each under a 5a load; that will drop a 3xNiMH configuration to about 3.0v which would cut off almost any ecig board, let alone produce vapor worth much. Even under a lesser load, the voltage sag will likely cause reduced runtime vs li ion even beyond the lower nameplate capacity. You really need to look at actual discharge curves.

I believe relayer has a VAMO pcb, maybe he can tell us how far it can be pushed with 3x NiMH.

I personally used to go through 2 fully charged 18650's in a day. It wasn't that the first one would 'stop' producing vapor... But by the time the battery was half dead performance would cut down by ~50%. No more awesome clouds or throat hit.

I currently use a modded flashlight using 3xAAA batteries. I use a 1.5 ohm atomizer and have had no issue getting through a 12 hour day of chain vaping... ~ 8 ml of juice. Performance doesn't noticeably drop off for me until the last tank of the day.

I am going to have to call shens on this, typical NiMH AAAs carry about 1000mah of juice, even if you are getting 100% of that capacity in runtime, which would only happen at a miliamp-level discharge rate, there are 18650s these days capable of over twice that at 2A+.

 

[Relayer1974]

2C is not high drain. 2C on a 1400mah battery is 2.8amps. At 4.8v, that's good for 13.44watts. And that's after stacking 4 of them to up the voltage.

I used 2C as an example for two reasons. First, I seen the argument made that NiMH batteries aren't reliable, safe, useful, etc. at even that discharge rate. Second, it's where I actually vape at with some of my stuff. I'm really not trying to proselytize NiMH batteries or condemn lithium chemistry. I'm sharing my experience.

A Sony 30a lithium battery could put out nearly 10 times that at max charge.

There are NiMH packs that are capable of that discharge rate as well. I don't have a use for them. Like I said, for me it isn't "X vs Y". It's about debunking myths that lead people to think that NiMH cells aren't suitable for vaping.

 

[WattWick]

Point taken! Guess me having been in the presence of the almighty LiPo chemistry gives me a top-down perspective on other kinds of chemistries.

(Not to be taken all too serious )

 

[cmacclel]

Charging any lithium cell (afaik) for hours is doing it wrong.

I don't know what chargers you use but I have come across and charged more Li-Ion cells that most people on this board. I have been building them into my Product for almost 10 years. To fully charge any regular Lithium cell to full capacity take a minimum of 2-3 hours. You can reach approximately 80% charge in under an hour but the last 20% or so take 4x as long as all Lithium cells are charged with voltage regulation.

 

[WattWick]

I thought that was down to how and which CC/CV algorithm worked. I may be mistaken. Haven't done any "serious" charging of IMR batteries with a serious charger, but I can't imagine it being very different.

Have to admit there's so many lithium chemistries out there that I'm not familiar with even a fraction of them by hands-on experience.

However, for Lipos I use a Revolectrix PowerLab 6. It has no problem charging my lipos to 100% in less than 15 minutes if I'm in a hurry. I usually charge at 1-2C for sake of battery health tho. Up until you hit 4.2v, it uses constant current, then switch to constant voltage (CC/CV). And back and forth while lowering current until it stays at 4.2v with no more current being applied. Apply this process while keeping the individual cells balanced, and it takes some time depending on how exact you want them to be.

I'll be the first to admit I'm threading water here as you introduced a concept I'm unfamiliar with. Consider this information, not argumentation... and take it for what it's worth. Which is exactly how much you paid for it

 

[dr g]

There are NiMH packs that are capable of that discharge rate as well. I don't have a use for them. Like I said, for me it isn't "X vs Y". It's about debunking myths that lead people to think that NiMH cells aren't suitable for vaping.

That's a single cell. How heavy have you drawn on your NiMHs, and what were the results?

 

[WattWick]

@cmacclel and as a thought on my previous post,

Can our different experiences boil down to computerized chargers, and not lithium cells? That's a question because I don't know, not because I'm trying to make lithium cells seem better than they may be. You're the professional here, and I'm just a hobbyist

 

[bapgood]

Charging time for a lithium battery boils down to several factors. The biggest being the charging capacity of the battery, charging algorithm, and charger capacity.

There are some RC lipo cells that are capable of a 5c charge rate (~15min charge time), I'm not sure about IMR round cells.

As always it's best to know and understand the specs of the batteries your using and then operate within them.

 

[cmacclel]

I thought that was down to how and which CC/CV algorithm worked. I may be mistaken. Haven't done any "serious" charging of IMR batteries with a serious charger, but I can't imagine it being very different.

Have to admit there's so many lithium chemistries out there that I'm not familiar with even a fraction of them by hands-on experience.

However, for Lipos I use a Revolectrix PowerLab 6. It has no problem charging my lipos to 100% in less than 15 minutes if I'm in a hurry. I usually charge at 1-2C for sake of battery health tho. Up until you hit 4.2v, it uses constant current, then switch to constant voltage (CC/CV). And back and forth while lowering current until it stays at 4.2v with no more current being applied. Apply this process while keeping the individual cells balanced, and it takes some time depending on how exact you want them to be.

I'll be the first to admit I'm threading water here as you introduced a concept I'm unfamiliar with. Consider this information, not argumentation... and take it for what it's worth. Which is exactly how much you paid for it

Sorry there is no way you charged a standard lithium cell to 100% in 15 minutes. I charge my high power cells on a 1000watt $1k+ Dollar Xantrex variable power supply. Once it comes out of constant current mode you still have at minimum an hour.

A fully charged Lithium cell should be 4.2v off the charger. Like I said you can charge to around 80% fairly quickly.

 

[WattWick]

Think we might be comparing apples to oranges.

Not sure what a standard lithium cell is, but I'm thinking they're not lithium ion polymer? If you really want, I can cycle a lipo a couple times and post the data so you can figure if it's fully charged in 15 minutes or less. Just a friendly offer if you're curious. You have me questioning my beliefs anyway They do come out at 4.208v, to be exact. That I know.

Don't think any of the chemistries we use qualify as standard either. At least I had never heard of IMR batteries before vaping. On the other hand, I had never heard of anyone charging NiMHs in 15 minutes either.