Bob Engelhardt wrote:

We have a 9.6v Dustbuster that lost it's NiCd batteries rather quickly,
at least compared to the previous, lower voltage, Dustbuster. I have
ordered new cells to replace these, but I'm wondering about the
"charger" that the Dustbuster has. It's just a wall wart and a diode.
I.e., a trickle charger.

I seem to recall that trickle charging is not the best for NiCd's.
Right?

If not, I'm wondering whether I can use the "smart" charger that came
with my 9.6v Makita cordless drill. I'll need an adapter, clearly, but
is the Makita charger somehow specific to the Makita batteries, or will
it smart-ly charge any 9.6v NiCd?

Bob


IMHO continously trickling a nicad at less than 1/10th of it's
milliampere hour rating (i.e. less than 70 ma for a 700 milliamp hour
cell) does them no harm. You might want to measure the charging current
from that wall wart (after the cells are charged up) and if it is higher
than what I just stated, for the cell size in your Dustbuster, reduce
the current by inserting an appropriate sized resistor in series with
the charging circuit.

"Smart chargers" are used to speed up the charging of things like
portable power tool batteries to keep things moving on the job. They
charge at a much higher current initially and have the ability to
measure the voltage rise of the battery pack (and sometimes its
temperature too) and cut the charging current way back when the
circuitry decides the battery is charged.

Smart charging is an overkill for a Dustbuster unless you're an awfully
sloppy family and have to keep using it every five minutes throughout
the day. (Ducking...)

I have to change out the nicads in our two Dustbusters about once every
2 or three years. I buy the tabbed nicad cells from Rat Shack and solder
them in.

You may have been the unfortunate purchaser of a unit with some poorly
made cells in it. Plus, I'd bet the cells in your 9.6 volt unit are tiny
compared to the 3 sub-C cells in my 3.6 volt Dustbsters. Generally, the
smaller the cell (of a given battery type) the less the ratio of active
materials to cell casing, meaning less storage capacity in a similar
volume. Hence the move towards using a single cell combined with a
highly efficient dc to dc converter in many types of portable eqipment.

Methinks that the manufacturer putting a 9.6 volt battery in a
Dustbuster is mainly a "spec race" thing, like the 3 hp (peak of course)
vacuum cleaners which run on a standard wall outlet.

Just my .02,

Jeff

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

"My luck is so bad that if I bought a cemetery, people would stop dying."