Rechargeable Battery Voltages

davidpbo

davidpbo

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Boatless in Cheshire. Formerly 23ft Jeanneau Tonic
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Hi Folks,

Does anyone know why rechargable Ni Cads, NiMh batteries of the AA, AAA, C & D Cell sizes seem to always quote voltages less than the equivalent dry/alkaline cell equivalent?

e.g. AA NiMh 1.2V not 1.5V

Surely something can be designed with 1.5V even at the expense of capacity. Or is it to do with the discharge characteristic ?

David :
 
The voltage is determined by the chemical composition of the cell. That's why 12v lead/acid batteries have 6 cells, each with a voltage of 2v, and 9v PP3 batteries have 6 cells of 1.5v. NiMh and such like (recharchable) have chemistry that yields 1.2v per cell. So strictly speaking, you need 10 of these to replace 8 alkaline AA cells.
 
You can buy alkaline 1.5v rechargeable AAs and AAAs.

They are not as long lasting but some electronics just will not work on 1.2v.

Maplin electronics sell Alkaline rechargeable.
 
I had a set of PMR radios that would not work on 1.2v so I bought a set of alkaline AAA's and the charger.

I no longer have the PMRs , I will sell you the charger (as new) and brand new unopened set of 4x AAA for 1/2 price, if you are interested please send me a pm.

You can also have the used sets of AA and AAA's.
 
[ QUOTE ]
You can buy alkaline 1.5v rechargeable AAs and AAAs.

They are not as long lasting but some electronics just will not work on 1.2v.

Maplin electronics sell Alkaline rechargeable.

[/ QUOTE ]

Can you?? where are they on their site, i'd be intrested in a few of those.

Brian
 
I'm not a battery expert .... but years of model flying with expensive models and radio kit hanging on the rechargeables ...... it is safe to ignore the 0.3v nominal difference because under load conditions on average the rechargeable will hold up its voltage but the dry-cell will not and dip lower.

In fact it was common in battery packs before that one cell would be a blank in a recharge pack when replacing a dry-cell pack.

You will also find that rechargeables will deliver higher ampage if called onand also will maintain voltage till right just before being flat. A dry cell will not supply high ampage and will reduce steadily in voltage during use .... this is why many electronics with battery monitors will fail to show correctly bat state remaining with rechargeables - they see full voltage ...

The above is what I've seen and in lay-mans terms .... before the experts get all upset ....

/forums/images/graemlins/tongue.gif
 
Rechargeable alkaline ....

I remember when Tandy used to sell so-called chargers for dry-cells - they had to remove them from shelves .... people were blowing dry-cells and getting into trouble.

I also would love to see rechargeable "normal" techn batterys ...
 
Re: Rechargeable alkaline ....

My father used a home-made rig to recharge disposable cells for his bicycle lights, must be over 25 years ago now. The theory and circuit was published in Wireless World if I remember right. I think the cells only lasted a couple of recharges, but it was done for fun really. Stretching my memory, wasn't the trick to pulse the recharge current allowing pauses for the battery to recover? None blew up, anyway.

Tony S
 
Pulsed .............

Now we are onto another realm ...

With model flying and cars etc. - the glow-plug and chargers / fuel fill pumps etc. are run of 12v batterys ... most use sealed or gel - but I used a small lead acid wet job. If you measured the voltages of any output on the panel - I used a MFA Flight panel with Glow, fuel and Starter provision - ALL showed 12v..... but - Glow-plug was 1.5v, fuel was 6v, starter was 12v. How did it do it ? It was pulsed 12v ... the glow connector in fact could be used in emergency to charge the flight pack of 4.8v in the plane.....

But anyway - we are now getting of subject !! I still haven't seen - except for that short period when Tandy offered them - chargers or anything for recharging dry-cells ... I've always been told as well that it is dangerous to even try ...

So your dad was more clever than you took him for !! /forums/images/graemlins/tongue.gif
 
Re: Pulsed .............

CPC do a charger that will charge dry cells. Current one only does AA and AAA (They may sell another), mine did C and D cells as well, it also had a 9V external power supply so could have been adapted for on boat use I am sure. It ran a test on the battery prior to charging and would reject some alkaline batteries. I think it pulse charges them.

cpc.co.uk Product code BT02702.

David
 
This is a purpose made 1.5v alkaline rechargeable set not like the part recycle ones.

Maplin




product code
vm83e 14.99 charger
vm84f 5.10 4x aa
mc40t 5.95 4xaaa

2005 cat

Mine is still available if you want it.


As I sais some gear will not power up on 1.2 vts.

each cell is 1.5 volts and 1400 to 1600 mah
 
Interesting ....... how many charge cycles ?

I'm interested ... honest.
 
I have found if you look after them and recharge while 20% or 30% left in then they last indefinitely.*

If you exhaust then they are exhausted which is why I guess they have failed to take off.

The best bit is their shelf life, they do not self discharge*

I last used them a year ago and like normal alkaline I can use them today and they will be full.

They are not expensive.
B & Q marketed them at the checkouts a few years back
Rayvac ???????????????????????????

Mine is a Pure Energy made in Canada.

I have been very pleased with the performance.




* for practical purposes.
 
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