NiCd and NiMh batteries

AA + AAA cells ...

In the old days AA etc. were based on 600mAh and were subject to short life before needing recharge. But nearly all Radio Control stuff ........ and we talk proper expensive stuff was using NiCD's - later NiMH and LiIon .... even though this limit in capacity.

Not so long ago the higher capacity stuff came on general market - based on Industrial cells.

Near all my NiMH's are now 2000 or 2100 mAh jobs ...... giving excellent life and very good charge times. They are clearly marked as such. I have seen in a few places even the 2500 appear - but not often .....

Dry-cells - even Duracells - only use them when they are supplied with the item new !! or when Wife buys them !!

Technology marches on ...................... /forums/images/graemlins/laugh.gif
 
Memory and Voltage ...

Memory is a fact ... I know it from my many years of Radio Control Gear .... AND an engineer from Duracell in Crawley Factory I knew confirmed it from his lab ...

Voltage of a rechargeable against a Dry-Cell. The initial voltage is slightly lower yes ........ but against load it is superior or same. The Dry-cell cannot sustain a 1.5V against a high load and drops significantly - but a rechargeable is able to maintain a higher V against same load ... basically in practical terms balancing out initial difference.
 
Re: AA + AAA cells ...

I would agree with your thoughts on Duracells. A few years back we had problems with the (then new) mercury free cells. It boiled down to the not quite overcoming the problem that the mercury had been put in there to cure in the first place (anode wetting). Because they refused to acknowledge that there was a problem I now refuse to specify them where reliability is an issue.

Until recently Ray-O-Vac were the cell of choice, but they have recently merged with Varta who are not nearly so reliable and you can get either cell without knowing its origin. Buying batteries is a real headache if you want the best, consistently.

We have largely bypassed NiMH technology, it is no good for long term deployments, and I am now engaged in trying to get Li-Ion (polymer) cells to work for us. If you want real capacity, longevity and reliability from a primary cell you have to use Lithiums; LiMnO2 are a good approximation of 2 alkalines, with similar characteristics. Otherwise non-Duracell manganese alkalines are reliable and long-lived.
 
Re: Memory and Voltage ...

"Memory" is often a term misapplied to any effect of which the symptom is reduced capacity of the battery due to poor maintenance (usually through deep discharging or sitting partially discharged). So, in that sense only, "memory" effect can apply to most (all?) batteries. For example, we all know that lead/acid batteries suffer from this effect - there is capacity loss both as part of their normal deterioration through their life and permanent loss of capacity due to deep discharge or other abuse.

"Memory" in its original meaning, and which was specifically coined for association with NiCd's, being loss of capacity due to repeated discharge to a common point of not full discharge, is indeed a myth insofar as the widespread fear of it is concerned. It is very unlikely to be encountered and according to people who were involved in researching the claimed effect in earlier days could only be replicated under quite limited circumstances. This early day research that I am familiar with was driven by the use at that time of NiCd's for energy storage on spacecraft where, obviously, requiring complete discharge before charge cycles is not that easy to obtain nor is it desirable (one reason comes to mind is as it increases the likelihood of a dead platform).

One is far more likely to damage NiCd's through complete discharge (and this seems to be common across most -all?- battery types) than through any charge/discharge cycling to a part charged state. On top of that, managing a near complete discharge before charge cycle is extremely inconvenient so I am unsure why some people persist in believing in it.

John
 
Oh DEar ....

Having spent years modelling alongside guys from Marconi Aerospace and other ..... and run model cars, boats, planes etc. etc. I can honestly say that >

a) Memory situation created by partial discharge DOES occur in NiCd's and is brought on by repeated partial discharge over time. I've seen it, others have seen it, had it happen to various cells I've had as power for cars, RC units etc. etc.
b) Recharge / Discharge packs are common in RC circles for this very reason .... and espcially when it came to RC cars where we were fast charging 9.6V C-size race packs in situ.Anyone stupid enough to NOT discharge his pack before charging very soon found duff cells in his pack and lost races ... And the duff cells were not 'burnt out by fast charge'.

The Model world - despite its 'Toy' appearance to those not involved in it .... had investigated heavily and thouroughly all this issue ..... not only because it needed to be known - but to understand how not to lose thousands of pounds of gear in crashes etc.
The knowledge built up over years was invaluable in saving many a beautiful prepared model from being lost ....

Sorry but Memory is a known and observed fact ..... NiCD's do have it if not dis / re-charged properly .... it is that bad if not looked after - that I for one am glad that NiMH / LiION have appeared so that I can stop worrying about it.

In fact - I will not buy an item that is supplied with NiCD's now ... preferring to choose the one with NiMH or LiION instead.

/forums/images/graemlins/smile.gif
 
My understanding

is similar to Nigel Luther's and, I'd go far to say, the majority of experts.

All batteries are subject to the hysterisis effect, Nickel Cadmium more so then others.

Most re-chargeable batteries are good for 250 charge/discharge cycles (>90% charge) and nearly all are useless after 1000 (<10% charge).

I would suggest however that NiCd have been improved dramatically and to eschew anything powered by them is, perhaps, cutting off one's nose...?

eg 1990 AA size batteries 800mah, 2004 2100mah.
 
Higher capacity Rechargeables ...

Ok - I'm no expert ... but all I've seen literally on shop counters now in higher cap's are NiMH ........... rarely do I see NiCD's now ....

Still I'm sure that techno. has moved on and they improved ...
 
Re: Oh DEar ....

OK, big can of worms here. Memory Effect was a term coined in the early days of NiCd's to describe a particular phenomenon. That is that it was sometimes observed that if they were repeatedly cycled to the same discharge point the battery tended to "remember" that and "lost" capacity. Unfortunately the term is now often applied to any capacity problem whatsoever encountered with NiCd's - why specifically to NiCd's I do not know because it is not commonly applied to similar problems with most (all?) other battery types. It is not just a "NiCd" thing.

The bad news is that NiMH and NiCd's have a very similar problems arising out of their charging regimes so throwing NiCd's away in favor of NiMH is not a good move. Why NiMH batteries are not so often found to suffer from such problems though is because their lifetime in charge cycles is usually considerably less than for NiCd's so they often die of natural causes before the problem has time to appear.

What happens in NiCds (and again it is not memory effect, in its correct use), is that there can be crystallisation of the Ni electrode which effectively reduces its area. But NiMH batteries have nickel electrodes also and so suffer from exactly the same problem - but as said, is not so often encountered as NiMH's usually have a shorter life in terms of charge/discharge cycles. In both cases it is normally caused by incorrect charging, usually overcharging,

However, for both NiCd's and NiMH's the crystallisation can always be reversed (assuming the battery is not reaching the end of its life) by a deep discharge (sometimes several are needed and should never be to zero as many believe) and recharge. This is the reason for an occasional deep discharge which people often think is required because of memory effect (ie loss of capacity due to cycling to a common discharge point).

If these batteries are cycled through random depths of discharge and charged properly (I suspect, but do not know, that many problems with NiCds are from overcharging on fast chargers - it takes a very intelligent charger to not overcharge in that regime) it is unlikely that any problems will ever be encountered. If they are then unless the battery is reaching the end of its life, a deep discharge (but never a complete discharge) and charge will fix it.

The original use of the term memory effect was (and still is its correct use) applied to an effect where a battery (NiCd is where it is used) suffers from reduced capacity through constant cycling to a common discharge point. All the information that I have ever come across states that it is very difficult to replicate this problem in a lab, let alone in the field. And in the end, if one just discharges/charges one's batteries randomly it is obvious that the effect is even less likely to be encountered.

I am sure that will not be accepted by many, but maybe some will give consideration to it as to how they manage their own batteries. Yes, people do have problems with NiCd's. People commonly think that it is "memory effect" and is commonly called that. People commonly think NiMH's are immune from the same difficulties (whatever name you give to the difficulty) but they are not. Most (all?) battery types suffer from similar effects and symtoms (eg sulphation of lead/acid plates through discharge and partial charging causes reduced capacity, but in their case is not completely reversible).

The recommendations that I see for use of both NiCd's and NiMH's is to use them in a normal random fashion as far as depth of discharge is concerned, never completely discharge them, and never overcharge them. If there is a loss of capacity, due to overcharging (usually), then a deep discharge and charge will reverse the crystallisation on the Ni electrode. The deep discharge should never be complete and so should be closely monitored (the voltage drop off from approaching complete discharge to being completely discharged is very fast and is no doubt the cause of the early demise of many batteries always following a regime of deep discharge and are driven into cell reversal or similar). This advice is not new, it has been that from professional users for at least 15 years as far as I can remember.

In a way it is unfortunate that inappropriate prejudices arise against NiCd's because they are better suited to high current demand situations (eg radio transmitters) than NiMH's. I have used them widely for many years and have never had a problem with them. I have never come across reduced capacity except when the battery has reached what I would consider a quite ripe old age in terms of cycles or I have knowingly abused it (this often happens with cordless drills, running them to a complete stop and dead battery).

But now we have Li-ion to keep us happy /forums/images/graemlins/smile.gif. So note, I am not saying that NiCd's are the BEST batteries, the progression of NiCd->NiMH->Li-ion in the batteries available to us is an advance in technology.

I've had enuff say for a decade on this, so take it or leave it, I am off /forums/images/graemlins/smile.gif.

John
 
It\'s strange that majority ...

of what you write agrees with others posts on the subject ... it's just that you seem to take another road that then tries to nail it so tight ... that is unnecessary.

Onto crystalization .... I have somewhere a leaflet sent to me by a Battery Manufacturer describing method to 'reset' a NiCD ....

For example a AA NiCD has gone "Zero" and fails to recharge ...

Charge up a good NiCD of same size and designation. Take two wires and then +ve to +ve, -ve to -ve good cell to bad cell ... momentarily ....

Then take bad cell and recharge / discharge a number of times till cell resumes working. It also warns that a bad cell 'reset' will most likley never be reliable and often give less output (capacity will be reduced).

Sounds horrendous - but I've done it and by golly it works !!!
 
Has anyone mentioned yet that NiMh are no where near as harmful to the environment as any other type of cell.....

Surely this is as good a reason as any to use them!
 
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