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'[EE:] First Project Finished! But... it used up al'
2004\06\06@193931 by Jinx

face picon face
> Nope ;-) But trickle charge through 1Kohm is a little low imho. If Jinx
> says it works, then it works.
>
> Peter

I think I've got it reasonably right, after looking at the copious facts and
opinions on both battery chemistry and chargers, for example

http://www.mhpower.com.au/Batteries/FAQ's%20-%20Battery%20Charging.html

The most commonly agreed figure for trickle (not float, as I mistakenly
called it the other day) charging is that it should be < 0.1C. AFAICT
"trickle charging" is a maintenance procedure rather than for replenish-
ment after battery usage, and simply to balance the battery's small
self-discharge. The batteries are just 1.3Ah, and need to supply only a
few mAh on rare occasions. Assuming at worst 10 hours/year that's only
0.1% cycle. The 1k could be reduced, but for this application it probably
would make no difference. To all intents and purposes the battery is
simply sitting around for a few years, ready for action, until it gets
replaced. For applications with more active cycling I'd use a battery
monitor

I'm glad the topic came up - it's reminded me that I never did get an
answer to emails to Panasonic and Hitachi. The question was what
lifetime I could expect from an SLA in a situation like this. SLAs are
often quoted with a lifetime measured in charging cycles, but what
happens if you have no cycling ? If anyone has an opinion..........

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2004\06\07@051337 by hilip Stortz

picon face
sounds like an excellent application for a "super cap", i.e. the very
high capacitance capacitors designed for memory backup power etc.  the
advantage being that you avoid all of the wear out and aging issues of
batteries.  in fact i plan to convert several of my computers to using
supercaps rather than batteries for pram maintenance, particularly
considering the high cost of some batteries (some being more than most
super caps).

Jinx wrote:
--------
. The batteries are just 1.3Ah, and need to supply only a
> few mAh on rare occasions. Assuming at worst 10 hours/year that's only
> 0.1% cycle. The 1k could be reduced, but for this application it probably
> would make no difference. To all intents and purposes the battery is
> simply sitting around for a few years, ready for action, until it gets
> replaced. For applications with more active cycling I'd use a battery
> monitor
--------------

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2004\06\07@055358 by Jinx

face picon face
> sounds like an excellent application for a "super cap", i.e. the very
> high capacitance capacitors designed for memory backup power

I do use super caps for a couple of memory circuits and find them
invaluable, but they wouldn't do in this case. Powering the circuitry
is not a problem, but operating the solenoid (4R load for 1/2s every
30 seconds) would quickly drain it. An SLA is not too expensive on
a cost/year basis

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2004\06\07@062423 by Russell McMahon

face
flavicon
face
> I do use super caps for a couple of memory circuits and find them
> invaluable, but they wouldn't do in this case. Powering the circuitry
> is not a problem, but operating the solenoid (4R load for 1/2s every
> 30 seconds) would quickly drain it. An SLA is not too expensive on
> a cost/year basis

This started as a simple suggestion, but has got me thinking about Alkaline
battery shelf life:

Alkaline batteries sound like a possible solution here!

Shelf life unused is 4 to 6 years shelf life

5-7 according to http://www.zbattery.com/zbattery/chemistry101.html).

Panasonic say "up to 7 years"
<www.panasonic.com.au/catalogue/details.cfm?pcode=LR03T%2F2B&pdiv=BAT
ALK&cat=46_3>

Kodak state 80% capacity at 7 years for their AA & AAA Alkalines
!!!!!!!!!!!!!!!!!!!!!!!
http://www.techadvice.com/info/pil.asp?pid=1295&old=0&SortColumn=company_name


Even lithium at 10 years shelf life may be attractive.

It would be interesting to  see how standard Alkaline batteries lasted under
a minute trickle charge.

Maybe a small Peltier effect cooler in a thermally insulated battery pack
would give a far longer shelf life (reactions tend to halve in rate per 10C
drop). Maybe a 10C target. Runs only when mains power available.



       RM

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2004\06\07@070703 by Jinx

face picon face
> Alkaline batteries sound like a possible solution here!

The first thing to do would be to estimate the energy needed to
pull in the solenoid. 4 ohms for > 0.25s @ > 9V. Assuming an
overnight power failure, 8 hours x 120 operations/hr. To get reliable
operation I use 0.5s with a 470uF cap charged to 13V. 0.25s will
work, and voltage can be down to 8V, but pull-in starts to get a bit
weedy. At 13V the initial pull-in is strong. As the capacitor voltage
decays there's enough to hold it until around 4-5V, at which point
the solenoid releases and the ratchet moves the clock's hand

I'm not an EE so have no idea what calcs to use. Joules ? CV ?

> It would be interesting to  see how standard Alkaline batteries
> lasted under a minute trickle charge

Although you're "not supposed to", I do throw mine in the NiCd
charger and use them over and over in the VCR remote. They
came with it - Digitor non-rechargeable alkalines. Lasted for nigh
on 4 years now and they do freshen up in the charger. I tried it at
first JFTHOI but it seemed to work so I kept on doing it. Not looked
into so-called green chargers

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