aribert wrote:

snip

You sound almost as anal compulsive as me when it comes to keeping old stuff
running just for the sheer joy of proving you can do it, even if it means my
time is worth less than a buck an hour while I'm doing it. (One of the many
blessings of being semi-retired.)

Less than two weeks ago I replaced the four Sub-C nicads in our kitchen B&D
dustbuster for the second time in it's 18 year life! I sprang about $18 for
those four cells (the kind with solderable tabs welded on) at Radio Shack
just because it was more convenient to pop in there than to find and order
them from a web store and wait...

I also replaced to pair of C-sized nicads in my bird feeder which were about
three years old and are trickle charged by a little solar panel I added to
the feeder. (Never seen an electric bird feeder? Go to

http://www.yankeeflipper.com/droll/index.cfm

The batteries in my old pack are labeled: N-1300SC. THe ones in the
Sears 18v pack are labeled: N-1900SCR. I assume the N is for Ni-cad.
Does the 1900 imply a higher battery capacity, what are the units? If
so, could the extra 1900 battery capacity overtax the old 12v charger
that was intended for the 1300 batteries?

The units are milliamp-hours. Anyway, you are correct that the larger number
indicates more capacity, and that shouldn't bother your charger one bit,
it'll just take a little longer for them to charge.


I'll have 5 c-size Ni-cads
batteries left over - can I buy 5 additional batteries and upgrade
another battery pack - I assume that I will need Ni-cads that are rated
at 1900?

Yes on the 1900, and you should be able to do that transplant *if* the
batteries from that old "returned" pack weren't returned as "unused" after
someone had really had the pack for several months and cycled them lots of
times.

The leads between the batteries are metal strips that appear to
be resistance welded between the batteries. I assume that I can solder
wires onto the ends of the batteries - correct?

It ain't easy to solder directly to the batteries without damaging them from
the heat. That's because they have such high thermal conductivity that you
get their guts pretty hot by the time you get the part you're trying to
solder to hot enough to wet with solder. That's why the tabs are spot
welded, with one quick pulse of heat right where it's needed for fusing the
two tiny welds. They ain't like the old "LeClanche" dry cells with zinc
cases and a brass cap on the central carbon rod. Those were routinely soft
soldered to by both battery manufacturers and hacks like me.

Those tabs should be easy to soft solder to, because they're thin, and the
right material. That's why I sprang the few extra bucks at Rat Shack when
replacing the Dustbuster batteries. Just cut 'em in the right places to
leave a bit to solder to.

You can also use conductive epoxy to connect wires to Nicads. That stuff is
a bit pricey, but a little goes a long way. And, if you keep the unused
stuff in the freezer, it'll still be good years later.

Is there a way to test
each Ni-cad in a pack - I have one old battery pack that shorts out the
fuse in my charger if I plug it in?

Generally, by the time one or two Nicad cells in a pack short out, the
others aren't worth using save for emergencies. And, it isn't good practice
to mix new cells with old, it can get you into the wonderful world of
"reverse charging" the older cells during discharge, which sure don't help
their remaining capacity one bit.

But, assuming you've got multimeter with a voltage scale on it (HF is now
selling their cheepos for less than $5!) you can "test'" them by charging up
the cells one by one and see whether the voltage across them starts rising
and comes up to about 1.3 volts after a few minutes of about 100 ma of
charging current flowing through them.

You can get close enough to 100 milliamps just by picking up a 100 ohm 5
watt wirewound resistor at Rat Shack or elsewhere and putting it and the
cell in series across either your charger's output terminals or even a 12
volt car or motorcycle battery. If the cell you're trying to charge has an
internal short, the voltage will not rise above zero much if any. Watch the
polarity, and make sure that if you use a charger it has internal isolation
and doesn't end up with line voltage on either of it's terminals. (Wedging
in a disclaimer.)

Measuring old cell's storage capacity is quite a bit trickier, and is left
as an excercise for the student.

Thanks for reading this far and I'm
hopeful for answers, directions to links or suggestions.

Jeff

--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can keep smiling when things go wrong, you've thought of someone to
place the blame on."