LIIon v NiMH batteries?

"Pete Biggs" <p@melonbiggs{remove fruit}.tc> wrote in message
news:[email hidden]...

Quoted message said:

Apart from cost, do LiIon batteries have any disadvantages over NiMH
batteries?

How are they when it comes to durability, reliabilty, and dealing with

cold

Quoted message said:

conditions, etc?

Thanks. (Apologies for not Googling on this one but I have limited

internet

Quoted message said:

access & time this week).

~PB

the discharge curve is better for LiIon batteries than Nimh so they will run
slightly longer and they don't suffer from memory effect when re-charging,
they don't have to be totally dead to recharge them.

cheers
Jon_H

Jon_H said:

the discharge curve is better for LiIon batteries than Nimh so they will run
slightly longer and they don't suffer from memory effect when re-charging,
they don't have to be totally dead to recharge them.

cheers
Jon_H

I thought memory effect was limited to NiCad batteries not Nimh?
Also don't you need quite an expensive charger for Lion
batteries to avoid fires?

Vincent Wilcox said:

Jon_H said:

the discharge curve is better for LiIon batteries than Nimh so they will run
slightly longer and they don't suffer from memory effect when re-charging,
they don't have to be totally dead to recharge them.

I thought memory effect was limited to NiCad batteries not Nimh?

The memory effect does not affect NiCad or NiMH. The memory effect
was demonstrated for one type of NiCd cell (sintered, I think,
but I'm not going to bother to check) in one very specific situation
with precisely identical charge/discharge cycles (orbitting
satelites). In any cells you are likely to get your hands on, it
doesn't exist. In any use outside of orbit, it doesn't exist.

That's not to say that other types of abuse might reduce teh apparent
capacity of some cells, and a full discharge / charge cycle might
restore some of it, but it's not 'memory effect' in terms of repeated
regular cycles.

Quoted message said:

Also don't you need quite an expensive charger for Lion
batteries to avoid fires?

You need a specific charger.

You also need to treat them with care - they are noxious and
potentially violently combust when damaged or abused.

They have good energy density, but relatively poor current capacity
(ie instantaneous power). This can be addressed by putting packs in
parrallel, but is probably unecesary for bike lights (I have an
electric model hovercraft that will draw 50 A from teh propulsion
battery, it prefers NiCd to NiMH and Li-Ion really wouldn't like it).

They must not be fully drained.

Personally, I think NiMH are still better for bike-light applications,
largely because they are more rugged and less likely to combust if
slightly abused.

regards, Ian SMith
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Memory is blamed in place of poor charging techniques and hardware. You cannot get memory from a properly designed charger.

Now for the Li-Ions. They have much higher energy density than Ni and offer better low temperature performance than any other type. Unfortunately, they can not be charged as fast as NiCd but this point is not valid unless one has a proper rapid charger for NiCd. For LiIon, maximum rate chargers are common but still take one hour. My Ni charger will fully charge NiCd in under 20 minutes (4C where Li can only be charged at 1C) .

For durability, NOTHING beats NiCd. Even NiMH will not tolerate physical abuse as well as NiCd. NiCd, properly charged, will outlast NiMH by 20% on charge cycles. Ni batteries also have very durable construction and will not burst into flames when damaged. Li Ion also have additional circuitry to protect the cells and this only adds to critical path failures.

Ian Smith said:

The memory effect does not affect NiCad or NiMH. The memory effect
was demonstrated for one type of NiCd cell (sintered, I think,
but I'm not going to bother to check) in one very specific situation
with precisely identical charge/discharge cycles (orbitting
satelites). In any cells you are likely to get your hands on, it
doesn't exist. In any use outside of orbit, it doesn't exist.

That's not to say that other types of abuse might reduce teh apparent
capacity of some cells, and a full discharge / charge cycle might
restore some of it, but it's not 'memory effect' in terms of repeated
regular cycles.

That may be the theory but my experience was NiCd were pretty fussy and
died early and was backed up with all sorts of articles in e.g. video
camera magazines about the black magic of keeping them working. Maybe
it was bad chargers, maybe it was all in my imagination but the reality
was they did not last. NiMH were a lot better but I have to say the Li
ion batteries I have been using over recent years have been a blessed
relief and just work. I use them on my laptop and cellphone and whether
all this stuff about combustion is true or not I don't know but I also
know of nobody who has ever said they've experienced that problem with
Li ion.

So my advice is if you are prepared to get into selecting fancy chargers
and looking after your batteries go for the black art of NiCd but if you
want something thats reliable and works off the shelf get a Li ion.

Tony

Ian Smith <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

Vincent Wilcox said:

Jon_H said:

the discharge curve is better for LiIon batteries than Nimh so they
will run slightly longer and they don't suffer from memory effect
when re-charging, they don't have to be totally dead to recharge
them.

I thought memory effect was limited to NiCad batteries not Nimh?

The memory effect does not affect NiCad or NiMH. The memory effect
was demonstrated for one type of NiCd cell (sintered, I think,
but I'm not going to bother to check) in one very specific situation
with precisely identical charge/discharge cycles (orbitting
satelites). In any cells you are likely to get your hands on, it
doesn't exist. In any use outside of orbit, it doesn't exist.

You obviously know a lot more than I do about the technicalities, but I
can definitively state from experience that when mobile phones had
Nicads, I saw many examples of 'the memory effect' (i.e. unless you
discharge them fully, they won't take a full charge). Mobile phone batts
improved no end with the advent of NiMH batteries.

Like I say, you know what you're on about & I don't, but c.1996 I started
specifying that my then-employers only buy NiMH mobile batteries (which
were more expensive then), because Nicads just weren't up to normal day-
to-day usage. Most people incl. me couldn't be bothered or didn't have
the time to fully discharge Nicads, prior to recharging.

I remember a long time ago during the 'transportable' (car-battery-size)
mobile phone period that some people used to rig up a light bulb with
some wires so they could fully discharge their big Nicad packs. I believe
that some of the (later) Nicad-era mobile charging cradles also had
'discharge' buttons to drain any remaining charge off before recharging.

--
Chris Bardell
[Remove favourite mode of transport from email address]

Vincent Wilcox [email hidden] opined the following...

Quoted message said:

I thought memory effect was limited to NiCad batteries not Nimh?
Also don't you need quite an expensive charger for Lion
batteries to avoid fires?

Memory effect is largely a myth it appears. Try googling for it.

Yes you do need a special charger for Li ion (If you don't want them to
go pop!), but equally you need a special charger for NiMH / NiCad if you
want to charge them quickly / properly.

Jon

Weisse Luft said:

Now for the Li-Ions. They have much higher energy density than Ni

That's the main attraction for me. The particular battery in mind has an
extra cell included to make the lamps even brighter -- practical because the
cells are so light/small, I guess.

Quoted message said:

and
offer better low temperature performance than any other type.

That's good news (for winter cycling!). I didn't know that.

Quoted message said:

Unfortunately, they can not be charged as fast as NiCd but this point
is not valid unless one has a proper rapid charger for NiCd. For
LiIon, maximum rate chargers are common but still take one hour. My
Ni charger will fully charge NiCd in under 20 minutes (4C where Li
can only be charged at 1C) .

Charging overnight will be fine for me.

Quoted message said:

For durability, NOTHING beats NiCd. Even NiMH will not tolerate
physical abuse as well as NiCd. NiCd, properly charged, will outlast
NiMH by 20% on charge cycles.

I'm avoiding the weight of NiCads for this application so they're not on the
menu (unless I decide on something much cheaper altogether).

Quoted message said:

Ni batteries also have very durable
construction and will not burst into flames when damaged.

What kind of damage or abuse causes Li-Ions to combust?

Note: I would use a special charger included with the package. Battery with
charger costs £50 more than the NiMH version (with smart charger) and comes
with 1.2 more volts. At risk of advertising Lumicycle again, it's one of
their cycle light systems I'm considering (very seriously now). I'm
thinking it's worth investing as much as possible in the battery then worry
about the lamps & accessories afterwards as they're relatively cheap to
upgrade/add.

Quoted message said:

Li Ion also
have additional circuitry to protect the cells and this only adds to
critical path failures.

Can you give me an idea of what "critical path failures" are please.

Cheers, and thanks also to Ian and Tony.

~PB

Pete,

In the rare occurrence of a single cell failure, the mode most common to mid-life span Ni cells is a dead short. All the cell's energy is dumped into the short and the cell is taken out of the battery, reducing the voltage by 1.25 V. With a 10 cell pack, this reduces voltage somewhat but for most types of lights, there is still enough to get you home.

With Li-polymer cells, shorting is an even bigger problem because the internal damage will eventually cause the cell to become open, resulting in a broken battery circuit and zero voltage.

Since over current in the Li-poly cell can cause internal shorting, most cells have additional circuitry to guard against this. It can be a simple as a fuse or more complex as in a solid state device. Either way, over current will result in a open circuit. Ni batteries will produce enough current to cook themselves into death but they will not take out the entire battery...well, the heat produced COULD take the entire battery out (and I have had this on one of my flight packs, a cell went short when the pack had a full charge and the KOH electrolyte shorted the rest of the pack as well as cooking the rest but it still held a 1.2 V/cell charge)

Tony Raven [email hidden] opined the following...

Quoted message said:

That may be the theory but my experience was NiCd were pretty fussy and
died early and was backed up with all sorts of articles in e.g. video
camera magazines about the black magic of keeping them working. Maybe
it was bad chargers, maybe it was all in my imagination but the reality
was they did not last. NiMH were a lot better but I have to say the Li
ion batteries I have been using over recent years have been a blessed
relief and just work. I use them on my laptop and cellphone and whether
all this stuff about combustion is true or not I don't know but I also
know of nobody who has ever said they've experienced that problem with
Li ion.

I suspect a lot of that is also to do with battery design. A NiCad now
is not the same as one ten years ago. The engineering technology has
improved and this has been reflected in the performance of the
batteries.

Quoted message said:

So my advice is if you are prepared to get into selecting fancy chargers
and looking after your batteries go for the black art of NiCd but if you
want something thats reliable and works off the shelf get a Li ion.

If you are building your own then the "black art of NiCad" consists of a
constant current device at about 1/10th or less of the battery capacity
and just connect it up. The technology only gets clever when it comes to
rapid charging when change in the rate of voltage change and or /
temperature must be monitored in order to prevent overcharging. The same
is true of Li ion, only the control circuitry is a little more complex.

If you overcharge a NiCad / NiMH you will reduce the capacity by causing
it to vent hydrogen. If you are _really_ unlucky this could catch fire
but you have to seriously whack it to make it happen.

If you overcharge a Li Ion you are "entering a world of pain". :-)

If you are buying off the shelf setups (Charger / battery pack) then a
NiMH will cost significantly less than Li ion and is a more thoroughly
proven technology. If you are building your own chargers then you should
already know which technology you will be working with! ;-)

Jon

Jon Senior said:

...
If you are buying off the shelf setups (Charger / battery pack) then a
NiMH will cost significantly less than Li ion and is a more thoroughly
proven technology. If you are building your own chargers then you should
already know which technology you will be working with! ;-)

Li-Ion cells store you more electricity in less size and weight and work
well at low temperatures, which are all good properties. I believe they
appear to be more robust than NiCd or NiMH cells in 'real world'
applications like phones and bike lights simply because it's not safe to
use them without pretty advanced charge and discharge management, so
they lead a rather cosy existence and last a long time in regular use.
This is of course another good thing, but all that technology costs
money. I believe it's worth it, but then I'm biased!

Chris

Ian Smith said:

Quoted message said:

Quoted message said:

the discharge curve is better for LiIon batteries than Nimh so they
will run slightly longer and they don't suffer from memory effect
when re-charging, they don't have to be totally dead to recharge
them.

I thought memory effect was limited to NiCad batteries not Nimh?

The memory effect does not affect NiCad or NiMH. The memory effect
was demonstrated for one type of NiCd cell (sintered, I think,
but I'm not going to bother to check) in one very specific situation
with precisely identical charge/discharge cycles (orbitting
satelites). In any cells you are likely to get your hands on, it
doesn't exist. In any use outside of orbit, it doesn't exist.

Hmm, every set of NiCD batteries I've had have crapped out within a few
months of heavy use.
That's been in a mobile phone (those were the days), a charger, a walkman,
an MP3 player and a torch.

I'm not disputing what you're saying, I've just never had the same problems
with either Li-Ion or NiMH batteries :|

Pete Biggs <p@melonbiggs{remove fruit}.tc> wrote:

: Note: I would use a special charger included with the package.

Make sure you pay the extra 20 quid or so to get Lumi's smart charger.

You basic idea is good: spend the money on the battery and the charger,
worry about the lights later.

Arthur

--
Arthur Clune PGP/GPG Key: http://www.clune.org/pubkey.txt
"Blogs are neither necessary nor sufficient for evil to triumph.
They're just what we call an enabling technology" - Danny O'Brien

Pete Biggs p@melonbiggs{remove said:

That's the main attraction for me. The particular battery in mind has an
extra cell included to make the lamps even brighter -- practical because the
cells are so light/small, I guess.

No it doesn't. Li-Ion cells have a nominal voltage of 3.6V. 14.4 is
a 4-cell pack - it's as close as you can get to the slightly-over-12
that is desired.

Quoted message said:

What kind of damage or abuse causes Li-Ions to combust?

Shorting it, physical damage, over-charging it, over-discharging it,
looking at it funny, or being disparaging about its mother. If you
ever get a Li-ion battery you're not 100% confident about, if you
decide you must charge it, do it somewhere where you'd be entirely
happy letting off a moderate size roman candle.

Looking for something else, I've just come across this summary of teh
differences between NiCd, NiMh and Li-Ion. It reads like it's a few
years old (mid-late 90s), but the basic gist of it looks about right
to me:

http://www.national.com/appinfo/power/files/f19.pdf

regards, Ian Smith
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"Jon Senior" <jon_AT_restlesslemon_DOTco_DOT_uk> wrote in message
news:[email hidden]...

Quoted message said:

I suspect a lot of that is also to do with battery design. A NiCad now
is not the same as one ten years ago. The engineering technology has
improved and this has been reflected in the performance of the
batteries.

....

Quoted message said:

If you are building your own then the "black art of NiCad" consists of a
constant current device at about 1/10th or less of the battery capacity
and just connect it up.

Er - isn't the main cause of knackering nicads bad charging? With a proper
smart charger (such as is required for liions to avoid pain), they can be as
easy to use.

Not that I'd touch nicads any more since nimh got cheap.

cheers,
clive

In article <[email hidden]>, [email hidden]
says...

Quoted message said:

Er - isn't the main cause of knackering nicads bad charging? With a proper
smart charger (such as is required for liions to avoid pain), they can beas
easy to use.

Most NiCads (according to the link that Ian posted - Thanks) will easily
tolerate C/10 and most NiMHs will happily survive C/40 with no damage.
Basically what happens is you put too much energy in and hydrogen is
released but is reabsorbed at the same rate so there is no damage due to
loss of hydrogen. Push the energy in faster and this is no longer the
case at which point the cells discharge hydrogen and you get a reduced
capacity.

By trickle-charging you remove the risk of this happening, but the
obvious trade-off is that it takes a very long time to charge the
batteries.

The "smart" chargers will allow you to charge at much higher rates
without risk to the battery. The one I bought for my home build battery
pack came from CPC, cost around £10 and will deliver 1A until it detects
a change in dV/dT. Thus my battery pack takes about 4-5hours for a
complete safe charge.

Quoted message said:

Not that I'd touch nicads any more since nimh got cheap.

Good isn't it? My battery pack cost me about £35 to build but had twice
the life-span of the SLA that my original halogen came with and
overvolted the lamp enough to make it significantly brighter. Oh yeah...
and it weighed half as much!

Jon

Tony Raven said:

Ian Smith said:

The memory effect does not affect NiCad or NiMH. The memory effect
was demonstrated for one type of NiCd cell (sintered, I think,
but I'm not going to bother to check) in one very specific situation
with precisely identical charge/discharge cycles (orbitting
satelites). In any cells you are likely to get your hands on, it
doesn't exist. In any use outside of orbit, it doesn't exist.

That's not to say that other types of abuse might reduce teh apparent
capacity of some cells, and a full discharge / charge cycle might
restore some of it, but it's not 'memory effect' in terms of repeated
regular cycles.

That may be the theory but my experience was NiCd were pretty fussy and
died early

I think that's more to do with crappy charger design - NiCd are
tolerant of crappy chargers, so equipment had really crappy chargers.
For example, a bog standard NiCd may handle C/4 many times with no
charge termination, and 4 hr charge is considered acceptable by the
manufacturer's market research droids, so a C/4 charger is what yuou
have.

Allong come NiMH, which die very fast if you give them more than C/10
without termination. Marketeers decide 12 to 14 hr charge is not
acceptable, so they have to provide a semi-smart charger that actually
monitors what the battery is up to and has some sort of termination.
They may still only provide a C/4 charger, but now it terminates when
teh battery is full and switches to maybe C/30. This is much less
abusive, and the NiMH cells so treated last much longer.
(Incidentally, this is what lumi do - a C/4 charger that then
terminates to a trickle when it detyects teh battery is full).

I think NiMH are also somewhat less prone to crystal-growth failuer
mechanisms, but my knowledge of teh chemistry is not so good as to
swear to that.

Quoted message said:

NiMH were a lot better but I have to say the Li ion batteries I have
been using over recent years have been a blessed relief and just
work.

This I think is the same syndrome, only more so. Li-Ion chemsitry is
so delicate that no manufacturer in their right minds lets mr average
consumer loose on them. They ensure this by all having proprietary
battery packaging / contacts etc, and supplying a specific charger
with each appliance. These chargers _are_ smart, and very gently and
tenderly protect the cells against all sorts of things. Many
batteries have built-in protection circuity, and some are fairly smart
in their own right. Li-Ion chargers are smarter than almost any
NiCd/NiMH charger.

Quoted message said:

So my advice is if you are prepared to get into selecting fancy chargers
and looking after your batteries go for the black art of NiCd but if you
want something thats reliable and works off the shelf get a Li ion.

All you're doing there is getting even further into even fancier
chargers, it's just that you don't realise you are.

regards, Ian SMith
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Ian Smith said:

Quoted message said:

That's the main attraction for me. The particular battery in mind
has an extra cell included to make the lamps even brighter --
practical because the cells are so light/small, I guess.

No it doesn't. Li-Ion cells have a nominal voltage of 3.6V. 14.4 is
a 4-cell pack - it's as close as you can get to the slightly-over-12
that is desired.

I don't know where I got "14.4" from. The Lumicycle site says "14.8V".
Thanks for the correction anyway.

/snip

Quoted message said:

Looking for something else, I've just come across this summary of teh
differences between NiCd, NiMh and Li-Ion. It reads like it's a few
years old (mid-late 90s), but the basic gist of it looks about right
to me:

http://www.national.com/appinfo/power/files/f19.pdf

Many thanks for the link.
The article brings up a very important point (that I don't think anyone
has mentioned; sorry if I missed it):
Cell discharge curve of Li-Ion is nothing like as flat as that of NiCd
or NiMh, meaning (I suppose) that the lights will dim significantly during
use unless some voltage regulation is used. I wonder if Lumicycle use any
special circuitry? How does the discharge curve compare to alkalines though
(so I compare to my experience of how alkalines fade in bog standard
lights)?
This could be enough to put me off the Li-Ion 14.8V option. I think I'd
rather have a more constant voltage even if the lamps weren't quite as
bright initially (with NiMh 13.2V). The £50 saving (even accounting for
smart charger) would make the extra weight more palatable*.

* Although £50 to save 175g is pretty good considering what the price/weight
difference between a Record and Chorus bottom bracket is, for example
(components that are functionally identical).

~PB

I said:

Cell discharge curve of Li-Ion is nothing like as flat as that of
NiCd or NiMh, meaning (I suppose) that the lights will dim
significantly during use unless some voltage regulation is used.

Update: Reply from Lumicycle:

"The LiIon battery starts off at 15v, it will drop down to 14v then stay
at 14v for most of the charge, nearer the end it will drop down a bit to 13
then 12v where the protection circuit will shut off the lamps. So
effectively the lights will not go dim at all."

~PB