Rechargable batteries

Re: Major consideration ... useable voltage !

Dry-cell when placed on load will fall off in voltage to significantly less than the 1.5v nominal it is supposed to be.

A rechargeable cell is able to sustain near its nominal voltage much better.

A dry-cell has a steady drop in voltage as it discharges.

A rechargeable has a near flat voltage line till near discharged where it then falls to zero very fast.

The above makes the rechargeable cell preferable in many cases as it will deliver better performance and also is rechargeable to deliver again.
There is a problem where many items with battery life indicators will be fooled by the apparent voltage of rechargeable cells.

My experience .... Dry-cell drops from 1.5V to 1.1 - 1.3V but with no real oomph behind it .... Rechargeable remains at about 1.1 - 1.2V and will deliver very high currents if called upon ...
 
Re: Rechargeable batteries ... LIon dangerous ..... so what about ?

NiCD ............ Cadmium is particularly unhealthy ... and they are available in single cells ...

I have a feeling the LiIon may be available ... but won't swear to it ...
 
Re: Rechargeable batteries ... LIon dangerous ..... so what about ?

I have a feeling the LiIon may be available ... but won't swear to it ...


They are available (and despite what you say I did not say they were not available - read my post again) but very unlikely to find them from regular supplier. For the reasons I gave I would not recommend use of them unless one is skilled enuff to repack an existing battery pack (but most I have seen are sealed and not easily repackable at home) with the same or design the protection circuitry.

On the NiCds I did not say anything at all about them not being available so think you are dreaming again correcting me that they are - I thought their availability was common knowledge /forums/images/graemlins/confused.gif

John
 
Re: Major consideration ... useable voltage !

[ QUOTE ]
There is a problem where many items with battery life indicators will be fooled by the apparent voltage of rechargeable cells.

[/ QUOTE ]

Agreed, my camera starts flashing when it is minutes away or less using NiMh cells, my wireless mouse is worse, it starts working erratically prior to the warning on windows that the level is low, but within 20 minutes.

Once you get used to that, like my cells in the mag-light on board, the moment I notice I change them. You just have to be prepared.

As for alkaline being better, maybe in clocks etc he has a point, but in my camera they give maybe a quarter of the time before giving up than my now modest 2100 mha cells. I rotate 3 sets which I have now had for about 3 years, slightly cheaper than buying alkaline each time.
 
Re: Major consideration ... useable voltage !

fair point brought up.. Nicads do definitely not hold their charge well, but do have the advantage that they can take quite alot of charging abuse. Ideal for charge and use; not so good for charge and want to use them days (never mind weeks)later. So re a torch and Nicads- perfect if you use it every day; not good if you pick it up after a month and expect much of a glow.
 
A non rechargeable Zinc carbon battery or Alkaline has a voltage range of 1.5 down to about 1 volt with a steady decline. So while you call it 1.5 volts you will find for much of its life it is less than 1.2. On the other hand the Nicad or NiMh will hold 1.2 volts to the very end then drop suddenly. So really the voltage argument is a dud.

However the thing I liek about Duracell or similar iis that they have 5 year shelf life so for emergency gear they are great. Probably last longer than a torch they are fitted to. (by the time corrosion gets in)
Obviously for high usage like a radio, recharge is the only way to go.
re changing cells if it is a torch 6you don't mind fiddling with try soldering wires to tyhe contacts and bring them to contacyts ie small screws that come through the body to allow recharge without removing the cells. If you use a small recharge current you can leave it on charge permanently.
olewilll
 
Re: Major consideration ... useable voltage !

If your NiCd's are discharging that quickly then you have a real problem. Either dud batteries or a care problem. Given the myths about NiCd's which no doubt will be regurgitated here, improper care is the most common cause of problems with them - myths are along the lines of having to always discharge them 'til flat, and any of the others associated with the fear of so called "memory effect".

I use them alot and find that in torches infrequently used the torch will still give full ouput after well over 6 months (never timed it). I use NiCd's in several handheld radios (NiCd's are particularly good in transmitting equipment) which will be charged at the end of the summer and they will transmit at full output 9 months later no prob's at all without recharging.

Obviously the batteries lose some charge in that time, but are still well usable. Manufacturers typically quote around 30% loss of charge after 6 months at 20C, so it would seem you have a problem. But there again, as several forumites will no doubt soon be telling you, I know nothing about the care of batteries /forums/images/graemlins/frown.gif.

John
 
Oh dear ... whos reading out of gear !!

I was commenting about the safety aspect implied by your post - that LiIon are dangerous ....

NiCD's contain Cadmium - a lethal chemical !! But they are sold singly - so why should LiIon be different ? I was not implying you said NiCd's were not available .... blimey had a bad day have we ??

I'm not in tit-for-tat mood - so will leave at that .
 
Again Oh Dear ....

Having spent years modelling and also friends with Engineer / Research guy at Mallory ... I know well why Radio Control Modellers changed from NiCD's to NiMH for most applications and LiIon in some other.
Why ? Because of NiCD's problem of developing less useable capacity over charge recharge cycles if not done correctly. Many times I have had to change out cells in RC gear - despite having proper charger gear with inbuilt dischargers to "bring cells" down to base value before charging.
Repeated partial charging of NiCD's has been proven again and again in modelling world and other to produce a cell that will only eventually deliver that partial charge amount ...

If this was not true - then why has the world of battery's spent so much time and effort producing cahrge - dischargers, page after page of magazine articles on battery care, etc. etc.

About the only area that NiCD's reign supreme in model worl dnow - is the very high Current delivery applications such as race cars / boats etc. - where the engine / battery combinations are called upon to deliver exceptionally high amps.....

Oh - and I'm not interested in an argument - I'm happy that Mallory R&D Engineer informs and I trust him on this. (He also was RC Modeller - that's how I knew him ... )
 
Re: Rechargeable batteries

From a practical point of view I have not yet found any device that will not work fine and last longer on NiMh than on Alkalines. The lower internal resistance of the rechargables seems to outweigh the slightly lower voltage and has been said already you get most of the rated voltage for the whole time. In my camera, rechargeables last four times longer than Duracells. The previous camera had a Lion battery for which a 12v charger was simply not available.

This means I can keep one 12V fast charger on board with a spare set of charged 2500mah AA's for all eventualities. Though the handheld VHF caught me out once (after it had been on at max volume all day for three days with a couple of short transmissions) 'cos it took six of the blighters instead of four, and NiMh rechargables are sold in fours and the chargers take four.

The C and D adapters that our South African friend mentioned I have seen in the shops in the UK. If I needed this size, this is what I would use as a current high capacity AA NiMh stuffed into a C size tube will probably perform better than the Zinc disposables that the equipment was designed for.

I would only use disposables for equipment that might not be used for say six months and must perform with near full life when switched on.

My present problem is identifying a charger that does what I want. Because I often need to have full life available - either for the ones in use or the spares - particularly for the camera when I am going to be away from house, boat and car, - I frequently find that before a trip I am charging batteries that simply may not have been used for a few weeks. So is my fan cooled fast charger (which comes with mains transformer plug top and cigar lighter plug direct 12v input) just topping them up or is it giving them the same time of charge that it gives flat batteries before dropping to float charge? If not, how do I find one that does - or does it matter if they are overcharged?
 
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