NiMH vs. NiCAD

[RebelRAM]

I have used NiCAD batteries for years in various things, and they are pretty much the rechargable battery type I have had the most experience with.

However, over the past few years I have noticed more things using NiMH batteries. I'm assuming there must be some advantage.

So what are the major differences (advantages and disadvantages) between the two types. I am most wondering about runtimes, how long they can be stored and still hold a mostly full charge.

--Jason

 

[BatteryCharger]

There really aren't any disadvantages with NiMh. They are better, period. They hold more power, and don't have any sort of memory problems. Nicads can have a higher maximum discharge, but we're talking 20c here. Nothing you would ever need in a flashlight or a power tool.

 

[SilverFox]

Hello Jason,

NiCd cells can handle overcharging situations better than NiMh.

NiMh cells have more capacity than NiCd.

NiCd cell work best when completely discharged (to a safe level).

NiMh cells are tolerant of partial discharges.

The chemistry of NiMh cells is supposed to be less damaging to the environment.

I think that covers some of the differences.

Tom

 

[Sub_Umbra]

I think NiMh cells are better than NiCd in high discharge applications also.

 

[shiftd]

i believe NiCd is better in high drain application, but like batterycharger said, the difference does not apply in our common flashlight usage.

 

[Wingerr]

Main disadvantage may be the higher self-discharge rate of NiMH when left sitting around in storage mode.

 

[gwbaltzell]

After I did a little refresher on the subject because of some other threads. I've come to the following conclusions:

NiMh must absoulutly be charged in a smart charger made for them.
NiCd will do better in a smart charger made for NiCd.

NiMh can have a much larger capacity.

Both will suffer voltage depression if overcharged.

Neither should be discharged just to prevent so-called "memory".

NiCd have lower internal resistance and may be the better choice for very heavy loads.

Both may be recharged even if not fully discharged.

After a rapid charge both charger should switch to a trickle charge of 1/20 to 1/30 C, however on NiMh the total charge time must be limited to 10 to 20 hrs. NiCd can be left on trickle or dropped to a lower 1/30 to 1/50 C rate. Leaving NiMh on trickle will reduce its life.

Discharge on both should likely be stopped at 1 V to 0.9 V per cell

Packs (batteries) should never be allowed to go below 0.8 V per cell for two reason. 1. Less likely to reverse charge a cell in the battery. (NiMh are even less tolerant of this.) 2. Poorly designed smart charges may not properly change a battery that is drained lower.

NiMh self-discharge is higher (near twice).

Both should be stored for long term in a partial discharge state.

NiCd that are well treated should be good for 500 - 1000 full cycles.
NiMh that are well treated should be good for 300 - 600 full cycles.

Cadmium is toxic for the environment.

edit: This crystals that form in NiCd from overcharging and can lead to rapid self discharge or a full short, so far, have not shown up in NiMh. Don't know if this is the chemistry or just better charging practices.

 

[shiftd]

thanks for the compilation, Gwbalt.
I agree to most except this

"NiMh can have a much larger capacity."

define "much larger" /ubbthreads/images/graemlins/wink.gif
I have only seen NiMH goes as high as twice the capacity of NiCd, maybe slightly more than twice, but still around that. If you mean much larger is twice, then i agree. But if it goes to like 3 times or more, i have to disagree.

 

[gwbaltzell]

I was talking up to twice! Maybe a hair beyond. /ubbthreads/images/graemlins/grin.gif

 

[shiftd]

/ubbthreads/images/graemlins/blush.gif

LOL

define "a hair" !!! /ubbthreads/images/graemlins/tongue.gif

just kidding /ubbthreads/images/graemlins/grin.gif

 

[Sub_Umbra]

Wow, good info.

I think that when I made my post, in my head I was comparing NiMh to alkalines. Sorry.

 

[BentHeadTX]

Interesting,
As far as discharging NiCAD batteries, I used to discharge them down to nothing, then run them through a amp meter and resistor bank... then a direct short (pos to neg) and let it sit for 24 hours that way. That was the way we conditioned those 144VDC giant battery packs that powered portable X-Ray units back in the day.

****WARNING! Doing the below can lead to NiCAD battery explosion! Don't play around with NiCAD battery shorting bars if it is not 100% clear what you are doing. Find an "old school" person with the knowledge and experience to train you.****

For entertainment, I grabbed a few defibrillator NiCAD batteries that had been stored dead for 6 years and tried something. Hammered the 12VDC packs with 30VDC at around an amp for a fraction of a second and viola! they would then charge. They made it past 100% capacity after going through the conditioner.

I had an electric shaver that the NiCADs lasted 11 years. Just ran it down to nothing before charging it and slapped it on a conditioner every couple of years. As far as longevity goes, NiCADs beat NiMH, Lithium Ion and Gell Cells (Lead Acid) If the machine function is critical, give me NiCAD.

I am buying a NiMH charger and batteries next week, I prefer the lightness and capacity of them over NiCAD. Maybe a AA NiCAD or two would be nice for storage reasons.

 

[kitelights]

The higher capacity NiMH cells are heavier than their lower capacity NiCad counterparts.

 

[Sub_Umbra]

[ QUOTE ]
BentHeadTX:
I had an electric shaver that the NiCADs lasted 11 years. Just ran it down to nothing before charging it and slapped it on a conditioner every couple of years.

[/ QUOTE ]

Emphasis mine

Could you give a rough idea what the conditioning process involved with the razor?

Thanks

 

[PeLu]

Just a few things to add to this very good list...

[ QUOTE ]
gwbaltzell said:
NiMh can have a much larger capacity.


[/ QUOTE ]
NimH cells have 'only' about 30-50% more capacity as NiCd cells with the same kind of electrodes.
When you compare SubC cells, which all have sinter electrodes, the highest NiCd have 2.4Ah, the highest NiMH 3.3 or 3.5Ah.

[ QUOTE ]
NiCd that are well treated should be good for 500 - 1000 full cycles.

[/ QUOTE ]

Actually NiCd cells have an (theoretically) infinite live, as there is no materia moved when cahrging/discharging.
Prof. Wiesspeiner (the inventor of the CCS charging sytem) was able to get to 5000 cycles with no problems. People quotetd him that he could get 'up to 5000 cycles', which is not true, they just stopped after that because time was over.
Older cells suffer from worn out seperators and things like that.
[ QUOTE ]
This crystals that form in NiCd from overcharging and can lead to rapid self discharge or a full short

[/ QUOTE ]
Yes, the dendrites. People used to zap them....

I just had a rotary hammer battery (NiCd) which was forgotten for some ~15 years and was charged first this year. It performed well (BTW, much better than the newer batteries).


Some years ago there were well setup recycling facilities for NiCd cells, but none for NiMH. So when you gave the sued cells back, they were actual less environmental unfriendly than NiMH.
In a few years, NiCd cells will be illegal in the EU anyway (and it will turn out that nobody cares).

 

[snakebite]

i just looked at some nicd d cells i got at mendelsons 10+ years ago and the oldest has a 10/79 date.
they are rated at 4 ah
a pack of 10 put on the maha shows around 4650 mah.
they have been in and out of stuff so many times the jackets are ragged.
these were old when i got them and have been used heavily.
not one cell out of 70 or so has failed.
btw these were made in yugoslavia.
the cheap china nimh cells i got a while back have more capacity but half of them have failed by shorting or leaking.

 

[RebelRAM]

Some really good info here. Much more response than I expected over that little question.

I reason I asked was because I purchased some FRS/GMRS 2-way radios last week and they came with NiMH cells. Honestly I wasn't even looking for a recharable unit, alkalines were going to be fine with me for what I was going to use these radios for. But since I have limited experience with NiMHs I wanted to know if there were any major difference I should look out for. Yall have definitely given me plenty of info on this subject.

As a side note, it should be ok to use Alkalines in these radios if I need to right? These are what look to be AAA NiMH cells, or that's what they are marked as anyways.

Thanks,
--Jason

 

[gwbaltzell]

They should be marked as either. I doubt if they are NiMh only. Look close at the manual because many of these have the charger built in and only need the proper wall-wart.

 

[RebelRAM]

These are Cobra PR-955 radios that I bought at Wal-Mart. I'll check tonight and see if they say "NiMH only" on them. I would still think it would work with alkalines as long as I don't try to charge them.

--Jason

 

[Ray_of_Light]

NiCD have a different behavior at end of charge with respect to NiMH. The latter shows a voltage drop while the former keeps a constant voltage plateau.
If the charger is not able to detect the different voltage curve, it would kill NiCd cells.

Regards

Anthony