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More on batteries

Subject: More on batteries
From: Syd Curtis <>
Date: Sat, 08 Jun 2002 04:47:22 +1000
Batteries!  We all need 'em.

Not many of us have Walter's detailed understanding of them nor Paul's
specialised knowledge.  Still fewer would be as ignorant of such
electrical/electronic matters, as I.

Some observations for possible comment:

1.  Vicki wrote:

> It's a bit of a trap to think that all batteries should be fully discharg=
ed
> before recharging.  My Sony TCD D10 DAT takes a rechargeable 6V 1800 ah
> NP-22H.  Nowhere in the documentation can I find the words "Ni-cad" but I
> suppose it is? (John Campbell confirmed: "That supposition is correct.  I=
t is
a nickel-cadmium battery.")

(Snip)
>
> So I measured what the battery voltage was "when the tape stopped running=
" -
> it was 5.5V.  Now when I'm discharging a part-used battery, I am careful =
to
> take it down ONLY to 5.5V, before recharging.  I've had no battery proble=
ms
> since then.=20
>

I have a Sony Walkman analogue cassette recorder WM-D6C.  Not sure when I
bought it, but many years ago. (The Sony manual is dated 1983.  It has a
rechargeable battery pack with this iformation:

    Fast charge BP-23
    Nickel Cadmium Batt : 12VX4
    Capacity : 450 mAh  (Nominal)

(Notwithstanding the "12VX4" it supplies 6V to the recorder.)

Having "killed" a very expensive Uher nicad in a few months by treating it
like a lead/acid and always topping up the charge (early '70s and no-one
told me of the memory effect) I have always fully discharged the Sony pack
with a torch (flash-light) bulb before recharging.  On more than one
occasion I've forgotten about it and left it connected to the bulb
overnight.  The Arlec charger (240V input) offers outputs of 3, 4 1/2, and =
6
V, and a couple of times I've accidentally bumped the switch to 4 1/2V - an=
d
of course on checking some hours later, the 6V pack is still flat!

Despite that sort of abuse, that original battery pack still works fine.  I
now use a Tascam DAT for field recording and keep the Sony as a back-up,
but it gets quite a bit of use in editing and archiving cassettes to CD, an=
d
I use the battery pack (or four ordinary AAs) for that to avoid the
possibility of hum from the mains supply.

So I wonder whether with a particular type of rechargeable, the individual
batteries can vary, and I've just been lucky in getting a particularly good
one.

2.  I also note, and am mildly intrigued by the fact that we have a small
battery operated household vacuum-cleaner and when not being used, it stays
permanently on charge apparently without the battery being adversely
affected.

3.  Walter wrote:

> You are generally always safe slow charging if the charger has the right
> voltage rating, but fast charge requires the whole system be designed for=
 it.
> So if the hobby shop charger has a slow charge that should definitely be =
safe.

My hobby shop charger, operated from the car battery, does have a slow
charge as well as fast charge, so that's fine.

For charging the hobby shop nicads (7.2V 1600 mAh) from a mains supply, I
use an Arlec charger which I already had.   It has this information printed
on it:

"Arlec; voltage limited; 12V GEL-Cell; Input 240V 50 Hz; Output 12VDC 500mA=
"

A friend who does understand matters electrical (ran a launch around the
Solomon Islands for years, so had to be self-sufficient) said the charger
would be fine provided I limited the rate of charge.  Using quite cheap
items from a Tandy Shop, he made me a "black box" to go between the charger
and the battery and which externally has a 1A ammeter and a knob to turn,
and carries my friend's instruction:

    "To protect the charger, limit charge rate to 400 mA or less."

I don't know what's inside the box, but could ask my friend if it's of any
interest.  But no doubt Walter (and many others) who understand these
things, would know - and know if it's a desirable safeguard.

4.  Someone, and I thought it was Walter but I can't find the posting now,
wrote that simply measuring the voltage of a battery is only an imperfect
guide, that measuring its voltage under load is much better.  Is there any
way of doing this with a battery that is used inside the recorder, as with
the Tascam?

5.  When I bought the Tascam, I was told by a technician in the shop that i=
t
wasn't necessary to fully discharge the rechargeable before charging, but
that if the time it operated after a charge dropped appreciably, then to
completely discharge it and fully charge it a few times would restore it.
After the Uher experience, I still discharge it each time, but I have
another situation of concern to me.

My recording is largely confined to the lyrebird season - a few months each
year.  It seems to me that batteries left unused and uncharged for several
months lose some of their capacity but I've not critically tested this.
Before going to the field after months of inaction, I discharge and recharg=
e
each battery a few times.  Sensible or not?

6.  (The last.  Sorry for this length.)  The hobby shop chap said I should
not connect the charger to the the cigarette lighter socket , only directly
to the car battery.  I accepted this in good faith.  But I note that Walter
is using multiple cig. lighter sockets.  Can anyone see any way that there
could be a charger that should not be so connected.

Syd



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