This is only a preview of the April 1996 issue of Silicon Chip. You can view 26 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
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Mobile phone batteries are way over the odds. You
can buy this NEC Sportz phone for $299 with $1000
worth of free weekend calls but the battery will
set you back anywhere up to $100 or so. The open
battery in this photo has just had its cells replaced
for $25!
DEAD PHONE BATTERY?
Don’t toss it – refill it with standard
AA rechargeable cells
Dead battery in your bat-phone again?
Getting sick of paying out big dollars to
replace it? Well cheer up. In this article,
we show you how to replace the cells
in your mobile phone batteries with
standard AA-size nicad cells and save
heaps of dollars.
By ROSS TESTER
6 Silicon Chip
If you’re one of the million plus
Australians who owns a mobile
phone, chances are you have already
discovered one of the negative aspects:
the price of replacement batteries.
Sure, mobile phones themselves have
dropped in price dramatically in recent years. The phone shown above,
an NEC Sportz, is a classic example.
When purchased two years ago it cost
me the best part of a thousand dollars
– $899 to be precise. Yesterday, I saw
an advertisement for the same phone
for just $299, with a thousand dollar’s
worth of weekend calls thrown in for
nothing! That’s progress, I guess.
Fig.1: reproduced from the August 1994 issue, this Nicad Zapper circuit charges
two 1000µF capacitors to 33V. This charge is then dumped through the dud cell
by Mosfet Q7 when the ZAP button is pressed.
It’s a pity that the same thing hasn’t
happened to mobile phone batteries.
Unfortunately, this is the one “expendable” where they can really get at you.
Or at least they could until now.
Typical replacement mobile phone
batteries will set you back anywhere
from about $50 up to more than $100.
And that’s for the “ordinary” models
which give you minimum talk time. If
you want the “super” batteries which
last a lot longer, be prepared to pay
significantly more. In addition, buying
genuine (ie, branded) phone batteries
will set you back even more.
The service life of mobile phone
batteries leaves a lot to be desired,
mainly due to the way we treat (or
mistreat) them. Manufacturers normally rate their nicad cells for at least
1000 charge/discharge cycles but most
mobile phone users find that their
batteries last a year or less. Last time
we checked, there were less that 1000
days in a year, so it follows we are
doing something wrong!
Nicad problems
Many readers would be aware of the
various problems which befall nickel
cadmium batteries but to briefly recap,
here are just some of them:
(1) Memory effect – the battery
loses capacity by being constant
ly
discharged only partially and then
recharged. For example, you take your
phone out for the day, then you come
home and bung it on the charger so it’s
ready for next day.
The problem, of course, is that the
battery is only partially discharged
and never receives a full charge. Over
time, it “remembers” this amount of
charge, and this becomes its total
capacity.
Memory effect can be cured by a
few cycles of complete discharge and
recharge but you need to know when
your batteries are discharged. Generally, if you wait until your phone starts
beeping with its low battery signal you
can be sure it is discharged but that
brings us to another problem.
(2) Reverse polarity cells – all phone
batteries are composed of a number of
individual cells connected in series. In
a typical 6V phone battery, there will
be five nicad cells, each rated at 1.2V
(5 x 1.2 = 6V). However, not all nicad
cells in a pack are born equal. Some
may discharge further than others,
and the charge/discharge patterns
may actually cause one or more cells
to be discharged “below zero” so that
they become reverse polarity. This is a
prime reason for battery failure.
(3) Dendrites – the ideal battery
would never lose its charge while
waiting to be used. Unfortunately,
this is not the case – all cells discharge over time. Also over time,
crystalline growths may occur inside
the cell which has the effect of in
creasing the internal leakage current
dramatically. These growths, called
dendrites, will eventually short out
a cell and are another major reason
for battery failure.
(4) Overcharging – all batteries have
Fig.2: if you have a
DC power supply
which can deliver
more than 30V, you
can use this circuit
to zap dud nicad
cells.
April 1996 7
The battery on the left, from an Ericsson GH198, was given a new lease of life
by “zapping” bad cells. The battery on the right, from an NEC Sportz, was
completely renewed.
This photo shows the Ericsson and NEC batteries with their cases disassembled.
The Ericsson was delightfully simple, the NEC took a little more work!
a correct charge rate and a correct time
to be charged. Exceed either of these,
and you risk overcharging. Usually,
this means a build-up of heat which
will ultimately cause irreparable
damage inside the cell. Often it will
cause the cell to start leaking fluid
and that leads to corrosion and general
degradation. Occasionally, this heat
build up is so dramatic that it blows
the cell apart.
Many phones have smart chargers
which monitor the state of charge
and adjust automatically. Many do
not –they rely on the user to remove
the battery once it is charged. And that
doesn’t always happen!
(5) Corrosion – surprising though
it may seem, many users fail to
recognise the need to keep battery
contacts (both charging contacts and
8 Silicon Chip
phone contacts) clean. This can lead
to a battery not charging properly,
or not being able to deliver power to
the phone.
Resurrecting a dead battery
There are three steps to breathing
new life into an apparently dead battery. The first is quite simple – clean
the contacts on the battery, the phone
and on the charger. For people living
near the sea or in industrial areas,
this is an all-too-common problem
and one which many people seem
blissfully unaware of. You might find
that after cleaning the contacts, the
battery accepts charge and works quite
satisfactorily.
The second is a little more complex,
involving the opening of the battery
case and checking the individual cells
with a multimeter. You may well find
that one, two or even most cells are
quite OK, each measuring around
1.2V. However, it is quite likely that
at least one cell and maybe a couple
are showing either very low or no
voltage. These cells need to be zapped
or replaced.
We have talked about zapping
nicad cells in past issues of SILICON
CHIP. If cells are low in charge due to
dendrites, you can often fix them by
zapping. This literally blows up the
dendrites by applying a very brief but
powerful charge to the cell. This technique was covered, along with a Nicad
Zapper to build, in the August 1994
issue. This circuit is shown as Fig.1.
Don’t be tempted to apply a high
voltage directly from a power supply
to the cell in the hope that this will
blow the dendrites away. All you
will succeed in doing is permanently
cooking the cell and you might even
damage your power supply in the
process. However, if you have a suitable power supply, you can use the
circuit of Fig.2 to make a cut-down
version of a Nicad Zapper which is
just as effective.
We were able to fully restore an
apparently dead phone battery to
life using the Nicad Zapper. The
technique is to “zap” individual
cells, not the whole battery at once.
To do this, the battery case must be
opened and we will show you how
to do this shortly.
As luck would have it, the battery
concerned (for an Ericsson phone) was
one of the easier ones to disassemble.
Once this was achieved, we had to
zap one particularly difficult cell half
a dozen times but eventually it said “I
give up” and accepted charge.
In this battery, there was only one
cell apparently dead, with only a
couple of hundred millivolts across
it instead of more than 1.1V for each
of the rest. It was the obvious target
for “zapping.”
You don’t need to disconnect the
cell to be zapped from the other cells.
Instead, you simply connect the leads
from the zapper across the cell concerned (taking care of polarity) and
press the button.
It’s easy to check whether your “zapping” has worked, simply by measuring the voltage across the suspect
cell after the whole battery has been
on charge for a few hours. Take the
battery off charge and measure each
Corrosion is a major cause of
rechargeable battery problems. These
contacts clearly show a bad case of
oxidisation – no wonder it wouldn’t
charge properly.
cell. Depending on how long they have
been on the charger, they should all be
somewhere between 1.1V and 1.2V (or
maybe higher if they are almost fully
charged).
If the zapped cell looks OK, put the
battery back on to fully charge it and
then leave it for a day or so. This done,
check all the cells again. If they are all
close to the same voltage (ie, 1.2V),
then you cured it.
On the other hand, if the suspect
cell has dropped to below 1V, you can
assume it still has a few problems! Try
zapping it again – you’ve got nothing
to lose. You may cure it or if the cell
is really dead, you’re not going to do
any more damage by over-zapping it!
Ultimately, nicads do wear out;
the chemical components become
exhausted and will no longer support
the reaction neces
sary to recharge
a cell. Again, cell voltage is a good
check of this.
Cell strategy
So what if you have one or more
dead cells in your battery? Do you just
replace dead cells or replace the lot?
The answer is to replace the lot. This
might seem like overkill but is the only
practical approach.
For a start, if you place one or two
new cells into a battery, the new cells
will almost certainly have more capacity than the old cells, even if their label
ratings are identical. It stands to reason
that a brand new cell will always have
more capacity than an old cell.
If you have cells of different ages in
a battery, its capacity will always be
limited to that of the weakest cell in
the pack – it’s like the weakest link in
the chain. So if you put one or two new
cells in a battery, you will be wasting
your money. Do the job properly and fit
all new cells – you will still be saving
heaps of money over the cost of a new
sealed battery!
Just as importantly, instead of the
measly 700mAh battery which came
with your phone, you will end up with
at least a 1000mAh battery, which will
give you hours more standby and talk
time!
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Nicads or NiMH?
SATELLITE ENTHUSIASTS
STARTER KIT
Throughout this feature, we have
talked about nickel cadmium (nicad)
batteries as if they were the only types
used. One of the more recent batteries
to come onto the consumer market is
the nickel metal hydride, or NiMH,
type. These offer some advantages
over nicads.
For a start, NiMH batteries do not
develop a memory. They are much
more forgiving of the type of charge/
discharge cycles we consumers inflict
on them, and they are much more
environmentally friendly in manufacture and disposal.
Most importantly, size for size
NiMH batteries offer sig
nificantly
better capacity than their nicad counterparts. For example, the AA types we
feature in this article offer a 1000mAh
capacity in nicad form and 1100mAh
capacity in NiMH form.
On the downside, they are more
expensive and they are not suitable
for high discharge applications such
as in battery-powered tools and radiocontrolled toys.
There is also the question of whether
chargers, especially smart chargers,
designed for nicads would be suitable
for NiMH batteries. It’s a question that
we have not been able to get firm answers for. Experience, though, suggests
that every charger we have tried has
no problem whatsoever with NiMH
batteries.
We have used both types in preparing a number of batteries for this
article. All original batteries were
nicads, as would be expected, but
when replaced all have performed
at least as well as the original (and
usually much better), whether fitted
with nicads or NiMH cells.
Note that which ever cell you
choose, make sure it has solder tags.
It is possible to solder to cells but it is
not easy and when they are available
with solder tags already on, why not
take advantage of them? You place
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April 1996 9
This photo shows how to open up the battery. If it is gripped along an edge
as shown and the vise slowly tightened, eventually the weld or glue will give.
Suitable tools (eg, a table knife) can then be used to open up the crack.
To fully open the case, continue working slowly around the edge with the knife.
The screwdriver prevents the case from closing again.
the cells under much less stress by
soldering to tags.
Opening the case
The manufacturers don’t want you
to replace cells. They want you to buy
a new battery! Because of this, they
don’t make it easy to open up the case,
usually welding it or seamlessly gluing
it. But if you know the secret, it’s not
too hard to defeat this.
The technique for opening any
welded plastic battery case is to apply
10 Silicon Chip
just enough pressure in the right place
to make it give. This is most easily
achieved in a bench vise, because the
pressure is very easily controlled.
Sometimes, it is not even necessary
to go to this level. The battery for the
Ericsson, for example, came apart very
easily once we removed the label covering the back of the battery.
Examine the case carefully – it
should be possible to make a reasonable guess as to where the halves of
the case join. Place the battery so that
this seam runs lengthwise from one
jaw to the other in the vise (as shown
in the accompanying photo). The
battery should be positioned so that
it is just gripped along the very edge
to be broken.
Now very slowly tighten the vise so
that pressure is applied to the seam.
If all goes well, before too long you
should hear a reassuring “crack” as
the first seam gives way.
Sometimes, I have found it necessary to give a little extra help by
tapping lightly along the seam with
a small hammer, or even a knife handle. Eventually, you should hear that
“crack” and you’re on your way.
Don’t be too concerned if the seam
doesn’t break completely cleanly –
after all, you are breaking a weld.
Besides, it will be glued together later
anyway. It is also possible that the
plastic may crack in the wrong place
–again, a dab of super glue later will
generally fix this up.
The best tool for expanding the seam
is an ordinary table knife. It doesn’t
need to be sharp (in fact, it’s safer if
it’s blunt) – just as long as it’s thin
enough to work into the seam, and
wide enough to give a little leverage.
Use a second knife or a thin blade
screwdriver to keep working your
way around the seam until you have
lifted it on all four sides. Before
opening up the battery completely,
prise it apart slightly and see how
the cells are assembled inside. You
might find that they have used some
glue, double sided tape, wax or other
gunk to hold the batteries together
or in place.
Just take your time, prising the case
apart slowly until you’re sure you can
see what goes where. Inside the case,
you’re likely to find a polarity protection diode, perhaps a thermistor or
some other components. Make a note
(or drawing) of how and where these
are placed and connected.
Incidentally, we did find one slightly disturbing thing when breaking
apart several batteries for the NEC
Sportz phone. The genuine NEC
battery contained protection components, while the significantly cheaper
non-genuine “equivalent” replaced
these with lengths of wire!
Once you have the case apart, you
might have to carefully remove some
insulation to gain access to the individual cells.
At this point, you can decide wheth-
the replacement cells, keep your solder
joints as thin as possible.
We found that tucking a negative-end tag under the positive-end
tag achieved the minimum bulk. You
might find that some solder tags need
to be trimmed a little shorter if space
is very tight in your battery but so far
we haven’t had to do that.
You might also find it necessary, as
we did in one battery, to solder the
tags at approximately 15° angles to
each other in order to get the cells to
fit. Experiment with your cells before
soldering.
If using the connecting straps from
the original cells leave them until last.
Double and triple check your positive
and negative terminals before soldering the straps into place.
Reassembly
This battery is from the surf club transceiver pictured on the next page. Unlike
mobile phone batteries, this is rated at 7.2V and therefore required six new
cells. As you can see, there is plenty of room inside the case.
er you want to persevere and “zap”
cells, or simply replace the lot. In
many ways, the second option is the
best, because you know you have a
brand new battery when it’s done. It’s
obviously the only route to follow if
you don’t have a zapper.
Removing cells
In all batteries that we have disassembled, the cells themselves are
welded together. This is a pity, because
if at all possible, we want to use the
same connecting straps on the new
cells. These were made to fit the case.
The straps are usually spot-welded to
the first and last cell in the string but
they usually come free with a little
coaxing (ie, with pliers).
In the case of the NEC Sportz battery,
the connecting straps also form the
connection to the charging contacts
as well as the phone power contacts,
so it was imperative to get the straps
off in one piece. Other batteries have
separate contacts moulded onto the
case and are connected by flying leads.
Remember if soldering or unsoldering
to a moulded contact, apply heat for
as short a time as possible.
Any insulation or other material
removed should be kept as intact as
possible for reuse. In some cases, due
to the method of original manufacture,
this may be impossible. However, keep
any broken pieces to make fabrication
of new pieces easier.
Replacing cells
The major difference between original cells and replacement cells is
that, in most cases, the original cells
don’t have a raised “dimple” on top
which marks the positive end; they
may not even have positive or negative
markings on them, so be careful when
identifying which end is which!
That dimple on the replacement
cells could create a space problem but
so far we haven’t found any cases that
can’t accommodate the slightly longer
replacement cells.
Because the cells are connected in
series, it’s simply a matter of soldering positive to negative in the right
position – use the cells which came
out as a guide.
It’s always wise to pre-tin the solder
tags and, contrary to what you might
imagine, a good, hot iron is better than
a lukewarm one. It gets the job done
quicker, before the battery has a chance
to think “Hey, I’m getting hot!”.
Check and double check your solder
connections. Keeping in mind our
comments about the extra length of
Refit any protection diodes, therm
istors, etc, to exactly the same positions and cells as they were originally.
Your charger might rely on certain
connections to sense charge levels
and cell temperature to avoid overcharging.
Be sure also to replace any insulation (preferably the original insulation). In many batteries we have seen,
the con
necting straps are separated
from the battery terminals by a thin
piece of insulation – if this is creased
or bent out of shape, shorts are almost
inevitable.
We have found that in some cases
the replacement cells are smaller in
diameter than the original cells. In
this case, it may be necessary to provide a small amount of packing (eg,
cardboard) inside the case to prevent
cell movement.
Naturally, any packing material that
was used in the original cells should
be re-packed if possible. Where cells
are a tight fit, we found the kitchen
knife a handy tool to help slightly
expand the case as cells were re-inserted.
If possible, you should do a “dummy
run” of the new battery before final
assembly. With it held together as far as
possible, check with a multimeter that
voltage appears at the phone termi
nals. Check that the charging contacts
make contact with the charger (most
chargers have some form of indication)
and that the battery still clips on to
the phone.
If all appears well, reassemble the
case with a tiny drop of super glue at
April 1996 11
each of the four corners. Ensure that
the case is clamped together for five
minutes or so, until the glue dries.
You don’t want to use more glue
that necessary – after all, in a year
or so, you might want to replace the
cells again! It will be so much easier
the next time around because you will
know exactly what to do.
Transceiver batteries
We mentioned before that mobile
phone batteries aren’t the only ones
which can be refurbished. In fact,
The techniques are
not limited to mobile
phone batteries. This
UHF transceiver
belongs to a surf life
saving club and their
batteries are even
more expensive. Six
new NiMH cells and
an hour’s work saved
them more than $80
for a new battery!
while this article was in preparation
we received a call from the local Narrabeen Beach Surf Life Saving Club.
They had just been told that the batteries for their hand-held UHF radio
transceivers had gone up to more than
$100 plus tax (or more than $130). As
volunteers, their finances were already
stretched beyond the limit.
Using the techniques described in
this article, we cracked open two of
their defunct batteries and replaced
the cells – one with NiMH cells and
the other with nicads.
Probably the only real difference
between these batteries and mobile
phone batteries was that they took six
cells (7.2V) and there was still plenty
of room inside the cases. The chargers
used by the Surf Club are very sophisticated models, offering a switched
choice of standard trickle charge or
a 1-hour rapid charge with automatic
switch-over to trickle charge.
Without wanting to delve too much
into the charger electronics, we want
ed to know if there was any difference
between the NiMH and the nicad batteries. As far as we can tell, both new
batteries behave identically. Charging
times appeared similar, switch over to
trickle charge is identical and radio
operation is the same except for the
slightly longer operation of the NiMH
battery.
What about other transceivers, such
as handheld units for the CB or amateur bands? As far as we can tell, the
process described here still applies
and you can save heaps of money.
Special offer from Jaycar
High capacity rechargeable cells
are not normally all that easy to buy,
especially at a reasonable price, but
Jaycar Electronics has made a huge
purchase of them and is offering them
at very good prices.
For example, 1000mAh AA nicad
batteries, with solder tags, are just $5
each and 1100mAh AA NiMH batteries, also with solder tags, are just $6.25
each. But exclusively for SILICON CHIP
readers, Jaycar has agreed to a bargain
offer: buy four cells and get the fifth
one free! And for the vast majority of
readers wishing to refurbish phone
batteries, five cells just happens to be
exactly what they need.
So for AA nicads, you pay just
$20.00 for five (instead of $25) and for
AA NiMH cells you pay $25 (instead
of $31.25). To take advantage of the
offer, fill in the coupon below (or a
photocopy) and take it with you to
your nearest Jaycar Electronics store
(offer also available through Jaycar
mail order). Note: this offer is available for two months only, until 31st
May 1996.
References
For additional reading on the care
of nicad batteries, these articles will
be of use:
(1). An Automatic Nicad Battery
Discharger; SILICON CHIP, November
1992.
(2) Single Nicad Cell Discharger; SILICON CHIP, May 1993.
(3) Nicad Zapper; SILICON CHIP, August 1994.
(4) Automatic Discharger For Nicad
Battery Packs; SILICON CHIP, September 1994.
(5) A Fast Charger For Nicad Batteries;
SILICON CHIP, October 1995.
(6) Reflex (“Burp”) Charging Nicad
Batteries For Long Life; SILICON CHIP,
SC
January 1996.
Jaycar Nicad/NiMH AA Battery Offer
For the months of April & May 1996 only, Jaycar Electronics is making the following
special offer to SILICON CHIP readers: buy four AA 1000mAh nicad cells with solder tags
(Cat. SB-2441) or four AA 1100mAh NiMH cells with solder tags (Cat. SB-2457) and get
a 5th cell for free. That's represents a saving of $5 for the nicad cells and $6.25 for the
NiMH cells. You can take advantage of this offer only by filling in this coupon and taking it
to your nearest Jaycar store; or fax or mail the coupon to Jaycar’s mail order department.
Yes! please supply: ❏ 5 1000mAh nicad cells ($20) ❏ 5 1100mAh NiMH cells ($25)
Name ___________________________________________
Street ___________________________________________
Suburb/town_______________________ Postcode _______
12 Silicon Chip
Note: please include
credit card details for
mail order & add $4
for p&p.
Offer expires 31st May, 1996.
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