OT: Batteries

[Nel]

Is there any reason why a portbable DAB player would work OK with Duracell batteries and not rechargeables? I have tried 3 different sets of fully charged batteries but get nothing! TIA

[s--p--o--n--i--x]

Yes. Typically rechargeable batteries give a lower output voltage than non-rechargeables.

sponix

[Dave]

Rechargeable cells are 1.2V, non-rechargeables are 1.5V. How many does it take?

Dave

[Christian McArdle]

OTOH, the discharge of an alkaline is slow and relentless, dropping to about

1V by the time it is spent. A rechargeable generally stays spot on 1.2V for the vast majority of its useful charge. A device that couldn't cope with 1.2V would be unable to use more than the initial flush of youth of an alkaline cell.

Christian.

[Dave Plowman (News)]

Yes. Duracell are nominally 1.5 volts per cell. Re-chargeables 1.2 volts a cell - so about the same as a very flat dry cell. To get the same voltage you need to use more rechargeable cells. So instead of 8 dry cells for 12 volts you'd need 10. Etc.

[Nel]

3 - I'm going to check the manual tonight, but the unit itself only specifies 3xAA 4.5vDC.......4.5?....that's 3 x 1.5!! Shit! Can you get 1.5v recharcheables??

[usenet]

Apart from the voltage question (which I too think is unlikely) the problem may well be the shape of the batteries. I've often found that the little pimples etc. on Duracell and similar batteries mean that rechargeable cells in the same place simply don't connect.

[Rob Morley]

You can get rechargeable alkalines (need a special charger) but I don't know if they're any good.

[mungoh]

Yup, the 0.3 volt difference can be significant, especially if you multiply it by umpteen cells.

Related story (probably repeating myself here so apologies to the regular readers) We were shopping for a new carpet and I had measured the room using feet and inches. A 17-year-old spotty kid approached us as we entered the carpet emporium. I gave the kid the room sizes and was told that "nowadays sir we have gone metric". I debated internally whether to punch the arrogant little sod, mainly because I had to do Imperial and Metric units whilst at school! :-)

Kid takes the Feet dimension and multiplies by twelve to get to inches, then adds the extra inches I had measured. Kid then (still using calculator) multiplies by 2.5 to turn inches into centimetres.

I asked him how he was converting the inches to centimetres and got the "2.5" reply. I pointed out that the conversion should be "2.54" at least, only to be told "Sir, 0.4 of one millimetre is too small to bother with."

Yes, 0.4mm is negligible for most DIY purposes, but add enough of them together and you may get something too short!

So don't dismiss the (substantial) 0.3v difference between standard cells and rechargeables.

Mungo :-)

[Dave Plowman (News)]

Not according to the last Which test. They're a bit like a lead acid - run it flat and it's bu****d. Better if recharged when only slightly discharged, but still not good.

[Rusty]

What make of DAB radio ? I have a cheapo Goodmans DAB that works fine on MNH rechargeables, but they're either C or D cell's as I remember, rather than AA. Though that doesn't affect the volts argument.

If the alkalines were a bit overlong they may have distorted the Battery holder such that rechargeables don't n make contact any more.

rusty

[Ian Stirling]

However, the amount of energy extracted by discharging an alkaline cell to (say) 1.3V (if it won't work with rechargables) is quite small - IIRC about 30%. Return it as unfit for purpose IMO.

[Sam Nelson]

My kitchen is 21'x16'. That missing 0.4mm in the conversion of each dimension results in a difference of very nearly a m^2 in the floor area. Well, if I can still do sums, it is.

Mind, I'm still trying to work out, for the moment, why anyone would want to bother putting batteries in a DAB radio.

[Dave Plowman (News)]

Anyone using a battery operated portable radio is hardly looking for Hi-Fi. And DAB works pretty well for portable use - no multi-path etc you'll invariably get with an FM portable which sounds much worse than reduced bit rate DAB.

[Christian McArdle]

Except that for most of the life of an alkaline, it gets nowhere near 1.5V a voltage that is only available to low current applications using brand new batteries.

The actual terminal voltage drops fairly linearly over its life. It also drops considerably if anything other than trickle power is taken from it. Indeed, its capacity is measured right down to 0.8V, where it is determined that no useful power remains. A NiMH will drop rapidly to 1.2V and just stay there until a few seconds before conking out. It will also supply considerably more power, due to a much lower internal resistance. It is much more efficient in applications requiring high power outputs. At the 1A mark, an alkaline loses about 90% of its potential capacity, much of its terminal voltage and is practically unusable for the application even when new. A NiMH would eat the application for breakfast.

Christian.

[Ian Stirling]

.4 in 25 is 1.6%. So, 3.2% in area. Or for a 7*5, 35m^2 area, about indeed a m^2.

[Christian McArdle]

Possibly to listen to it when not plugged into the mains?

Christian.

[Sam Nelson]

One path would be nice.

[Ian Stirling]

If you use them like NiCd cells, and recharge when the NiCd cell would have needed recharged, you get maybe 3 or 4 cycles.

The only real 'good' place for them is in low drain appliances, where they are recharged when they reach about 90% capacity, and in that circumstance, you can get maybe a few hundred cycles. Comparing with NiMH, and the only two areas in which they are good is lower weight, and better charge retention if left idle.

[Sam Nelson]

Well, obviously, but if there is mains around, there can be better-quality sound than can be had from DAB, and if there isn't, there has to be DAB coverage---which map currently looks like mobile-phone-coverage maps circa

1988 or so.