Syd Curtis wrote:
>
> Batteries! We all need 'em.
Yep, and it seems to be getting worse.
> 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 i=
t
> 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 pac=
k
> 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, an=
d 6
> V, and a couple of times I've accidentally bumped the switch to 4 1/2V - =
and
> 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, =
and
> 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 individua=
l
> batteries can vary, and I've just been lucky in getting a particularly go=
od
> one.
The batteries can vary, particularly from different manufacturers. They
are actually pretty tough, but it's still something of a lottery.
Treating a battery "nice" is just trying to improve your odds. A lot of
the nice treatment is to keep the battery producing the same total
output levels. Less nice treatment may not necessarily shorten the life
as much as lower the battery capacity.
> 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 sta=
ys
> permanently on charge apparently without the battery being adversely
> affected.
Some batteries, particularly in NiCads can be designed for this kind of
usage. Part of the trick is that usually the charger is a pretty weak
one, so though the battery is always on charge, it's actually receiving
little current when fully charged. Typically the things designed to be
permanently on charge will have charging instructions that begin "charge
for 14 hours..." which is a tipoff of a slow charger. All these
batteries have a lower limit of charging current below which no damage
will occur no matter how long charged.
With NIMH the lower limit is tighter.
> "Arlec; voltage limited; 12V GEL-Cell; Input 240V 50 Hz; Output 12VDC 500=
mA"
>
> 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 charg=
er
> 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 an=
y
> interest. But no doubt Walter (and many others) who understand these
> things, would know - and know if it's a desirable safeguard.
The device your friend made simply insures that the charger will not
exceed it's rating if it's connected to a battery that could draw more
current. Of course limiting the current does increase the charge time.
As far as what's in it, it could be as simple as a variable resistor,
all the way up to a pretty complex control circuit.
Back in 1979, for a trip to Australia, I built such a box. Mine was more
elaborate as it was a complete charger, it would take for input:
110-120-220volts AC at either 50 or 60 cycle, or any DC voltage at least
a few volts above the battery you wanted to charge. In particular car
voltages. The input was polarity protected. It had both a volt and
ammeter built into it and dial adjustments. I also encrusted the case
with a bunch of different battery holders. And these were wired to a
series of banana plug jacks. By setting the adjustments and linking
jacks with jumpers I could charge as many as 8 AAA through D cell size
nicads, or the 9 volt nicads according to the instructions on it. Inside
was a multitap transformer for the AC, a full wave rectifier for it's
output, a power transistor and a few other odds and ends. The entire
unit was 6" x 6" and 2" high. I used it for quite a few years, it's
probably still here somewhere. It's only disadvantage was it was
entirely manual you provided the settings and timing. Back then nearly
all rechargables had in addition to rating, a charge instruction printed
on them to follow.
I'd hate to think about trying to get that charger through airport
security now. As it was on that trip, the small screwdrivers, pliers and
such like in my camera bag are what they balked at. I was taking that as
carry on.
> 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 an=
y
> way of doing this with a battery that is used inside the recorder, as wit=
h
> the Tascam?
The trick about measuring under load is that it should be rated load.
Typically 1/5 of the battery mah capacity would give you a good load
figure. The main reason for doing it under load is this avoids the
recovery effect.
> 5. When I bought the Tascam, I was told by a technician in the shop that=
it
> 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.
The technician is more or less right. It takes a number of partial
charge cycles to initiate the memory effect. And it can be mitigated by
cycling the battery several times like in the new battery conditioning.
Depending on the particular battery design there could still be some
damage. So, I always discharge NiCad's before charging. In my case it's
just pushing a button when I put the batteries in the charger and it
takes care of the rest.
> My recording is largely confined to the lyrebird season - a few months ea=
ch
> year. It seems to me that batteries left unused and uncharged for severa=
l
> 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 recha=
rge
> each battery a few times. Sensible or not?
Sensible and often recommended. If the battery has lost all charge over
time you run it through the regular new battery initiation. The best way
for this is to discharge at a rate equal to 1/5 or so the mah rating of
the battery, and use a slow charge for each round of that part of the
cycle. For NIMH the recommended repeat is three times. I'm not sure on
NiCad, I always give them at least two.
I've also noted that manufacturers don't seem too concerned if the
battery is allowed to go to zero through self discharge. Whereas if we
are discharging them they want us to stop at 1 volt. So you don't really
have to keep charging batteries in storage.
Note lead acid batteries are different and must never be left discharged.
> 6. (The last. Sorry for this length.) The hobby shop chap said I shoul=
d
> not connect the charger to the the cigarette lighter socket , only direct=
ly
> to the car battery. I accepted this in good faith. But I note that Walt=
er
> is using multiple cig. lighter sockets. Can anyone see any way that ther=
e
> could be a charger that should not be so connected.
A few reasons. If the charger draws more than the current the cig.
lighter socket can handle. It's got a fuse somewhere that can tell you
something about what the socket is designed to handle.
Or, if the wiring running to the cig. lighter socket is not well
connected, or the wire too small, or the socket itself is badly corroded
(like if you actually use the lighter). In this case you could see a
voltage drop under load.
Or if the car has particularly bad voltage regulation. The battery will
act as a sink to regulate voltage, so connecting direct may keep the
voltage slightly more stable.
For the most part this is just a myth as far as the sort of current
draw's we are talking about here.
I not only connect chargers, but a power inverter to put out power at
regular 110AC for things that I've not got a car power supply for. Like
the charger for the lion batteries that my digital camera uses. Or
charging the Portadisc using it's own AC charger. I used to hook my
powerbook up via the inverter, but now have a car power supply with the
usual cig. lighter plug. The trick is to total up all the current draw
and check that against how much the lighter plug can stand. Remember
heating a small heating element red hot in a short time is a pretty
large current draw.
Walt
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