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

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."

Jeff Wisnia wrote:

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. ...

Thanks, that's exactly what I needed to know.


"Smart chargers" are used to speed up the charging ...

Makes sense. I was thinking that I needed their ability to
stop/minimize charging when the battery was "full". But, what you said
above does away with that.

I have to change out the nicads in our two Dustbusters about once every
2 or three years. ...

Oh, OK - that's about what the life of ours was. I guess that we just
got a diamond in our first Dustbuster - those batteries lasted 15 years!

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. ...

Actually, our cells _are_ sub-C.

Methinks that the manufacturer putting a 9.6 volt battery in a
Dustbuster is mainly a "spec race" thing, ...

The 9.6 is much more powerful, but the old one worked just fine, so I'd
agree with you.

Bob

A nicad cell is a nicad cell. Size does matter when it comes to charging
them but the voltage requirements are the same.
The problem you are probably having is that the new charger is putting too
high of a voltage on the batteries and thus they are overcharged.
If you are using the vacuum regularly, leave it off of the charger until it
runs down and then recharge and pick off the charger the next morning.
There are nicad FAQs out there in webland that can provide good info on the
care and feeding of a nicad battery pack.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

I just had Batteries Plus rebuild a 6.5V Dustbuster battery pack. They
said that rebuilding Dustbuster packs just about pays their rent. Their
recommendation was to leave the charger/holder unplugged and only
recharge for 8-10 hours when the battery is stone dead and then unplug it.

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

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Glenn Ashmore wrote:
I just had Batteries Plus rebuild a 6.5V Dustbuster battery pack. They
said that rebuilding Dustbuster packs just about pays their rent. Their
recommendation was to leave the charger/holder unplugged and only
recharge for 8-10 hours when the battery is stone dead and then unplug it.


Stone dead is bad.
IF you discharge the battery below around 1V/cell (8V for a 9.6V pack)
then you run the risk of reverse charging a weaker cell or two.
This can rapidly kill them.

Bob Engelhardt wrote in message ...

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?

Trickle is best if the charger doesn't automatically shut down at full
charge. Dust Busters tend to use a very low current that requires
24-48 hours to fully charge dead cells, and one mistake many people
make the first time they charge new cells (or cells that have been in
storage for at least a few months) is not overcharge them -- leave the
charger on for twice the normal time or you'll likely develop a dead
cell prematurely. But trickle charging is known to give cells lower
capacity than fast charging will because it causes smaller cells to
grow, which have higher capacitance, and the best way to treat nicads
is probably by charging them at a 3-6 hour rate with a charger that
senses voltage or temperature and shuts off completely at full charge.
For information about this, check www.maxim-ic.com , especially the
data sheets and applications notes for chips like the MAX713 (nicads),
MAX712 (NiMHs), and MAX2003A. Maxim will even send you samples, and
you can get the needed MOSFET and inductor from a broken computer
motherboard to build a fast charger.

You can probably use the Makita charger without modification, if it
senses end of charge by voltage, but if it uses temperature for this
it may require the battery to have a built-in thermistor (look for any
third terminal) or that you place at least one cell next to the
charger's thermistor. But if the Makita uses just a bimetal
thermostat, I'd avoid it since those tend to be rough on cells.

The most common problems with batteries is that one cell develops
reverse polarity or shorts, and with an automatic charger this can
make the other cells overcharge. Reverse polarity occurs when the
battery is drained to too low a voltage, and the only fix is finding
the affected cell and trickle charging it alone for a few minutes.
Shorts come mostly from crystal whiskers growing between the plates
because of overcharging, so the advice to charge only when needed is
correct, although 8-10 hours is rarely enough for a Dust Buster.
Vaporizing the shorts with high current and voltage (even 12V is
enough) rarely fixes the cell for more than a few days before the
whisker grows back.

AA NiMH cells are often very cheap, often under $1
(www.mcmelectronics.com often runs specials0 and can usually
substitute for most sub-C nicads, but charge them at an 8-hour or
slower rate, unless you're sure that the charger senses end of charge
properly for them (rate of temperature change is OK but temperature
increase is not; I don't know about voltage or rate of voltage
change).

The Makita charger is probably a heat end for the charge cycle. This has
been the standard for tool batteries for a long time and everybody does it
that way for the fast charging stuff.
Voltage ending is more for the slower charging systems where the batteries
don't get hot at any point.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

On Wed, 04 Feb 2004 11:42:25 -0500, Jeff Wisnia wrote:
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.

Overcharging a NiCd is *never* harmless. Overcharging can cause
voltage depression (often mistakenly called "memory"), and shortens
the life of the cell, even if it is at a "trickle" rate. It *may* not shorten
its life enough to matter if the trickle rate is really low (say 1/100 C),
but any overcharge is bad. You want to avoid it if you can.

"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 chargers work in one of two different ways. Older rapid chargers
sensed temperature rise in the battery pack to signal end of charge
(thermistor built into the pack). Cell temperature does start to rise
rapidly when the pack exceeds full charge. This is a workable, but not
ideal, charging method if all the cells in the pack are well matched. It
will result in a battery pack capable of about 300 to 500 charge/discharge
cycles before problems start to show up.

The second, and better, way that smart chargers work is by sensing
battery voltage and looking for a *droop* in battery voltage of about
5 mV per cell just as it reaches full charge. This is a definite and positive
indication of exactly when the cell reaches full charge. If charging is
stopped there, you'll get maximum life out of the NiCd. Again, the cells
in the pack have to be very well matched for this to work properly, if
you're charging a pack rather than individual cells.

The voltage droop method requires pulse charging with battery voltage
sensed across a load between pulses. The chipmakers have implemented
the "brains" of this sort of charger in single chips, so battery charger
manufacturers have a proven off the shelf system to use. Using this
method, and well matched high quality cells, you can expect up to
about 2,000 full charge/discharge cycles out of a pack before you start
to see problems.

Note that can be equivalent to many more *partial* charge/discharge
cycles. The idea that you should fully cycle your NiCds is bad voodoo,
left over from the days of timed chargers which needed a known starting
point for charging to avoid grossly overcharging a partially discharged
battery. With a proper sensing charger, it just needlessly shortens the
useful life of the batteries.

Now the question at hand is which method of charging Makita uses
in the smart charger you have. If it only senses temperature rise, and
many cheaper tool battery chargers do, it won't know when to stop
rapid charging your battery, which doesn't have a built in thermistor.
So it will very quickly cook your battery. OTOH, if it senses voltage
droop, it'll do a good job of charging your battery.

Some chargers do both, with the temperature rise indication a backup
for the voltage droop sensing, and for cases when the battery is too hot
from use when you plug it into the charger to safely allow rapid charging.
(Milwaukee's latest battery chargers are examples of this.) So the presence
of temperature sensing contacts in the charger isn't a foolproof way to
determine whether it uses the voltage droop method or not. It is cause
to investigate further before risking your battery with it.

Gary

The Makita battery has 3 terminals, so it's very likely that the charger
uses temperature to stop. I'll not be using that for the Dustbuster.

When I get the nee cells, I'll check the current from the Dustbuster's
trickle charger and go from there. Maybe a procedure of not always
having the trickle on, or using a timer.

Thanks to all who replied and excuse me for not tagging this "OT",
Bob

Gary Coffman wrote:
On Wed, 04 Feb 2004 11:42:25 -0500, Jeff Wisnia wrote:
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?

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.

Overcharging a NiCd is *never* harmless. Overcharging can cause
voltage depression (often mistakenly called "memory"), and shortens
the life of the cell, even if it is at a "trickle" rate. It *may* not shorten
its life enough to matter if the trickle rate is really low (say 1/100 C),
but any overcharge is bad. You want to avoid it if you can.

In practice, overcharging at C/10 or so does not matter, if you do
not leave it on charge for weeks at a time.

Are you going to get the old cells back from the refurb? I'd be curious to
see how many gave up the ghost. I've been scrounging cells from dead packs
and have made useful (though not anywhere close to a matched new pack)
batteries for my 2 mak 9.6 drills. The cells from the cheap harbor freight
12 v (drillmaster) work but discharge at a surprisingly quick rate (on the
order of a week). But the packs sometimes are on sale for 5 bucks. Pat

Ian Stirling writes:

In practice, overcharging at C/10 or so does not matter, if you do
not leave it on charge for weeks at a time.

....which is exactly what happens with Dustbusters, of course. :-)
Ours was totally useless after a few years on the wall wart (died
within seconds after turning it on), until I ran the battery pack
through a couple of full discharge and recharge cycles on a proper
charger. Good as new again.

See http://www.rcbatteryclinic.com/ for all the info you could wish
for on the care and feeding of rechargable cells.

-tih
--
Tom Ivar Helbekkmo, Senior System Administrator, EUnet Norway
www.eunet.no T: +47-22092958 M: +47-93013940 F: +47-22092901