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Stocking a village hall for emergencies
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emordnilap



Joined: 05 Sep 2007
Posts: 14167
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Thu May 11, 2017 4:18 pm    Post subject: Reply with quote

What are the D cells for? In all my years of cutting back on anything battery powered, I've ended up with all but one item using AAs or AAAs. The odd one that does use Ds is a nuisance from that perspective.

I use eneloops by preference. How long do you expect your Ds to last in storage?
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adam2
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Joined: 02 Jul 2007
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Location: North Somerset

PostPosted: Thu May 11, 2017 4:40 pm    Post subject: Reply with quote

The D cells are for lighting and radio sets.

Two fluorescent lanterns each use 4 D cells for about 24 hours run time.
Two rubber torches each take 2 D cells for about 24 hours runtime.
Six home made LED area lights each use 6 D cells for 100 hours run time.

No affordable rechargeable cell or battery comes close to the capacity of an alkaline D cell, they are nearly 20 AH!

Rechargeables are fine for everyday household use, but quite unsuited for emergencies. Consider the logistics of keeping dozens of cells charged ready for use, but not exposed to loss, waste, or being borrowed whilst times are normal.
And how are they to be recharged without electricity ? No affordable solar powered charger will charge them in less than a week in mid winter.

100 alkaline cells can be simply locked in the bottom of a cupboard, forgotten about for years, unpacked and put to use. Shelf life should be at least 9 years, much longer than rechargeables.
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emordnilap



Joined: 05 Sep 2007
Posts: 14167
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Thu May 11, 2017 5:57 pm    Post subject: Reply with quote

adam2 wrote:
100 alkaline cells can be simply locked in the bottom of a cupboard, forgotten about for years, unpacked and put to use. Shelf life should be at least 9 years, much longer than rechargeables.


Right, I didn't realise they'd keep so long.
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"Buddhists say we come back as animals and they refer to them as lesser beings. Well, animals aren’t lesser beings, they’re just like us. So I say fụck the Buddhists" - Bjork
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emordnilap



Joined: 05 Sep 2007
Posts: 14167
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Thu May 11, 2017 5:59 pm    Post subject: Reply with quote

adam2 wrote:
No affordable solar powered charger will charge them in less than a week in mid winter.


If you take out the word 'affordable', is there at least a decent one you can recommend?

One problem with all the cheap solar chargers is there's never any indication of the state of the battery. Easily checked of course but something built in is more likely to be used.
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adam2
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Location: North Somerset

PostPosted: Thu May 11, 2017 7:22 pm    Post subject: Reply with quote

I have never found a directly solar powered charger that will charge high capacity cells in less than a week in UK winter conditions.
Some of the cheaper solar chargers will NEVER charge in UK winter conditions, the losses in the battery can exceed the winter charging input.

To achieve effective, though rather expensive charging, in UK winter conditions I would proceed as follows.

Purchase one or more chargers for small cells that are intended for car use and therefore designed for 12 volts DC input.

Power from a deep cycle lead acid battery that is charged by a PV module.

For reliable winter use you will need an astonishingly large PV module.

Consider the following worked example as to just how big a PV module is required !
Presume that each day one wishes to charge perhaps 20 rechargeable D cells each of 4 AH capacity. 20 cells a day may sound a lot, but in capacity terms it is only equivalent to between four and six disposable cells a day.

The 20 cells in total contain about 100 watt hours of energy. They are not that efficient and will take about 140 watt hours input to fully charge them all.
Small battery chargers are far from efficient, 50% might be a fairly optimistic estimate. So we need about 280 watt hours input from the 12 volt battery in order to charge 20 D cells a day.
Say about 25 AH to allow a bit for losses in the 12 volt battery.

A PV module to supply 25 AH a day in winter will be large and costly, in the region of 500 watts or very roughly 500.

And remember that the rechargeable D cells and the lead acid battery will need replacing every 5 years at a cost of well over 100, even if never used.

The disposable alkaline cells should last 10 years if unused and cost about 100 to replace.
I would buy new disposables after say 8 years, but not discard the old ones. When the emergency comes use up the old cells first before starting on the newer ones. They would probably work after 20 years, but this is not to be relied upon.
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emordnilap



Joined: 05 Sep 2007
Posts: 14167
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Fri May 12, 2017 10:22 am    Post subject: Reply with quote

Fascinating, thanks Adam.
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