NiCd or NiMH?

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Can someone educate on which would better for different flashlight purposes? Thanks.
 
Hello there,

NiMH cells hold more charge so that means whatever you
are using will run longer on NiMH cells then on NiCd
cells. That usually means you'll want NiMH's.

If you need to leave the device alone for months at
a time neither NiMH or NiCd's will be that great as
there is some self discharge. NiMH's are a little worse
then NiCd's but i dont think there is enough difference
to really worry that much about.

Take care,
Al
 
Hi there,

Yes nice Kevin. I use Li-ion too (Sony) and i like
them but the place near me wants $8.50 for one so
i started looking into NiMH cells.

Take care,
Al
 
MrAl, for me the cost of Li-ion is no big deal, but the high current capability is less than I want, and the internal resistance is a bit high. I know Li-poly can support higher current draws, but those things SCARE me. I've seem too many posts about people blowing or burning things up while charging their Li-poly batteries.
 
I'm still using NiMH for my AA cells. NiCads sold around here typically have lower mAH ratings, and I don't remember NiCads very fondly. Plus, metal hydride is just that little bit less toxic than cadmium.
 
NiCd's can be abused more when recharging, a smart charger isn't necessary, and they can be trickle charged without as much degradation, IIRC. The superior capacity of NiMH and availability of good smart chargers makes NiCd's niche pretty small these days.
 
[ QUOTE ]
JonSidneyB said:
given those two choices...I would go NiMH every time.

[/ QUOTE ]

While there are generally advantages to NiMH, "every time" won't cut it. There are clear exceptions. Like when you need to leave it in standby in the charger. NiMH will get killed this way, NiCds are cool with it. Likewise, NiCds have the advantage when it comes to high current.

If it was a 'every time' deal you wouldn't see NiCds with the RC bunch, Surefire or Mag or others 'in the know'......

Or put another way, there's a good, solid reason why serious makers use NiCd and don't go for the extra run time......

Aside from the lower capacity (offset by longer lifetime, BTW) there is the disposal problem. However, if you're going to recycle them, NiCds have their place IMO.

Doug Owen
 
Do NiCd cells supply more "ampre" when shorted as compared with NiMH ? be it just for a few seconds... but is it true ?

NiMH have a capacity up to 2200mAh & best known (atleast to me) NiCd cells have capicity up to 700 or 800 mAh ....

After going through (Mr Al's) lessons and a couple of battery review sites, I feel that many of NiMH battery Manufacturers fool people by giving capacity in mAh ... which at times is actually is calculated at C/10 or even C/20 discharges....which i feel is incorrect / decieving...

Best Quote for battery capacity should be in Watt-Hours (X watts for X hours)... isnt it true ? ... will leave this to the Great Guys /ubbthreads/images/graemlins/wink.gif

Thanks & Regards,
ViReN
 
[ QUOTE ]
ViReN said:
Do NiCd cells supply more "ampre" when shorted as compared with NiMH ? be it just for a few seconds... but is it true ?

NiMH have a capacity up to 2200mAh & best known (atleast to me) NiCd cells have capicity up to 700 or 800 mAh ....



[/ QUOTE ]

Yes, it's true that NiCds are better at high currents (and more tollerant of abuse), which is why you see them widely used in cordless power tools. Or my new Sony mini disk player. When major players like tool makers and Sony continue to use them in new gear, I suggest there's sound reasons.

Yes, they have lower capacity, the AAs I'm using are 1000 mAh, but they also have longer service life (more cycles) if treated properly, *far* more if abused (like flashlights are likely to do).

While power densities are rated in watts per cubic inch, batteries are traditionally rated by current, not power. It's not just NiMH makers, *all* the makers (primary or rechargable) do it.

Doug Owen
 
Hi Doug Owen,

Thanks for a great reply.

So a Good battery should supply higher mAh & Power isnt it ? and relying on just the Current rating is not sufficient i guess... especially when we are designing a flashlight, we must take in to consideration the power density, power capacity, Ampre Hours & Chargability (in terms of charging time & number of charge Cycles in a lifetime) .... all these qualities are not obtainable form a single brand / battery ... and often we have to settle down for a compromise... and may be in that compromise... for a short term gains .. NiMH wins over NiCad ... li-ion is again a alltogether a different story ... (with explosive dangers involved & Saftey concerns as compared to NiCad & NiMH)

Thanks & Regards,
ViReN
 
Personally, I find NiCd a bad choice for flashlights simply because I don't use them daily to run them down very far. I end up with the dreaded 'memory' effect. They end up working great but won't run very long. According to Panasonic, you can get a lot more charge cycles on NiMH if you don't discharge them very far most of the time. This is what the Toyota Htbrids do to get an estimated 7-10 years life from their 277 volt NiMH battery pack.

If I was going to discharge a light frequently (as police do) I'd definitely look towards Li-Ion or NiCd.

Daniel
 
Hello again,

Doug Owen:
Some good points! Im used to flashlights that are running
500ma and less as the norm, so i automatically respond
with that in mind...but there certainly are people
out there running lights at 1 amp or more and/or need other
benefits that can only come from NiCd's. NiCd's arent
dead yet :-)
Thankfully the NiMH's seem to be comming down in price
(perhaps in quality too?) so they are affordable even
if they have to be replaced.
I guess if you need the extra current though NiCd's
are still going to have to be the choice even though they
cant hold as much of a charge.

All:
Another comparison point is Gravimetric Energy Density
(commonly expressed in Wh/Kg). The NiMH can be
four times as high as NiCd, meaning they will either
be lighter or hold more energy for the same weight.

What criteria you use to compare cells will depend mostly
on your application. In general, if you are looking for
light weight and moderate current then Li-ion is the way to
go, if high current then NiCd, if moderate weight ok and
moderate current then NiMH.

Take care,
Al
 
Hello Mr Al,

What would be Gravimetric Energy Density for Li-Ion ?

Thanks & Regards,
ViReN
 
Doug Owen, what do you mean by “abuse”?

Ni-MH is highly recommended to Digital Camera which drains the current very fast and Ni-MH last 3 to 4 times longer than alkaline (about 1 time on other devices). Also, Ni-MH doesn’t have a memory effect like Ni-Cd so you don’t have to fully discharge Ni-MH before recharging it.

I don’t quite understand your term of “abuse”, to me, abuse mean drain as much current as you want, recharge it anytime.

Edit: I’m not sure why SureFire keep using Ni-Cd while other company goes with newer technology like Streamlight’s Strion. Same with laptop computers, they all are now uses Li-Ion.
 
[ QUOTE ]
CalgaryGuy said:
Doug Owen, what do you mean by “abuse”?

.....


I don’t quite understand your term of “abuse”, to me, abuse mean drain as much current as you want, recharge it anytime.

[/ QUOTE ]

Actually, that's the very sort of things I was thinking of. "Draining as much as you want" (rather than stopping at 1.0 Volts or so) and "recharge it anytime" is also potentially abuse as well. NiMH don't take overcharging well at all. NiCds are far more robust, they can be discharged to zero volts (not necessarily a good idea all the time), and are OK with overcharging (within reason WRT rate).

The two abuses above (over discharging and over charging) are not issues with NiCd, but will rapidly kill NiMH. And even if not abused, modern NiCds will do twice as many cycles in their lifetimes as NiMH (of course at half the capactity).

Doug Owen
 
Perhaps one factor that has been forgotten when mentioning that manufacturers still use NiCds is the bottom line. NiCds will still do an adequate job compared to NiMH, but they are a fair bit cheaper. After selling your millionth unit, that profit margin starts to look much stronger for that few cents saved.
 
Hello again,

Viren:
The Gravimetric Energy Density (in Wh/Kg) for
various chemistries is roughly:

Lead Acid: around 30
NiCd: around 40
NiMH: around 100
Li-ion: around 160
Compare to gasoline: over 10,000

The ability of the NiMH to deliver pulse power
is supposed to be highest but i've never done any tests
to confirm this.

Take care,
Al
 
Doug Owen, I do respect what you’re saying but I think that Ni-Cd does have memory effect and need to be fully discharge before charging them.

As for over-charged and over-drained, I can not be sure as the devices that I use; there is a circuit breaker on over-charged and something to stop the battery once it goes below a certain voltage.

Steelwolf, there are expansive device like SureFire 10X Dominator which cost $500 and uses Ni-Cd.
 
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