Jim Yanik wrote:
Jeff Liebermann wrote in
:

On Sun, 14 Aug 2011 02:18:37 -0700, mike wrote:

This isn't a problem if you're charging at a fairly low rate. A
good-quality cell -- nicad or NiMH -- will tolerate an indefinite
low ("trickle") charge.

I'd like to see a reference that supports that.

http://batteryuniversity.com/learn/a...l_metal_hydrid

"It is difficult, if not impossible, to slow-charge a NiMH
battery. At a C-rate of 0.1 to 0.3C, the voltage and temperature
profiles fail to exhibit defined characteristics to measure the
full-charge state accurately and the charger must depend on a
timer. Harmful overcharge will occur if a fixed timer controls the
charge. This is especially apparent when charging partially or
fully charged batteries."
Not exactly what you wanted, but a good reason why a "trickle" or
"maintaining" charge doesn't really work.

NiCd batteries are very tolerant of trickle charging.

Nope. I've successfully killed NiCd batteries in (Jedi series) radio
chargers that produce a 0.1c "maintaining" charge when fully charged.
After about a year of continuous charging at 0.1c, the batteries were
all dead. That's what happened to the local hospital emergency
network. The county issued MT2000 radios and chargers to all the
hospitals in the county. In case of emergency, they could all
communicate with each other through a repeater or directly. Once a
week, there was a test to make sure things were working. No problems
for 3 years until I decided to check the batteries. I found a mix of
NiCd and NiMH batteries. All that I tested were dead. The radios
would work for about 2 minutes, which was just long enough for the
test but not long enough for useful operation. Since the batteries
were never discharged, I concluded that the 0.1c maintaining charge
was the culprit.


OTOH,the B&D Dustbuster I had was designed to stay on the charger when not
in use,and it lasted 10 years before I had to have another NiCd pack
installed. that new pack lasted almost as long.
I've seen NiCds listed at DigiKey specifically intended for staying on the
trickle charger when not in use.


Never got any long use like that with several I used. My current red devil
extreme, I only charge it once in a while, and is doing great so far. It is
never without some reserve power left? One Dustbusters I converted to NiMH,
and was a disaster.


Greg

In article ,
gregz wrote:

OTOH,the B&D Dustbuster I had was designed to stay on the charger when not
in use,and it lasted 10 years before I had to have another NiCd pack
installed. that new pack lasted almost as long.
I've seen NiCds listed at DigiKey specifically intended for staying on the
trickle charger when not in use.

Never got any long use like that with several I used. My current red devil
extreme, I only charge it once in a while, and is doing great so far. It is
never without some reserve power left? One Dustbusters I converted to NiMH,
and was a disaster.

The DustBusters I have had (which have two removable battery inserts,
which I believe use sub-C cells) have not survived well. A year or
two sitting on the trickle-charger (as designed) and the NiCd
batteries are toast.

I've been thinking seriously about tearing it open, and replacing
whatever simple fixed-resistor slow-charge circuit it has with a
proper faster-charge-and-real-cutoff circuit of some sort. I'd have
to replace the wall wart, most likely, to get a decent charging
current.

Seems like there ought to be a single-IC solution available today...
and if not, something simple with a PIC or other micro to switch from
full-charge to "off most of the time, very brief current burst every
few minutes to cancel out self-discharge" should be able to do it well
enough.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Monday, August 15, 2011 1:19:07 PM UTC-7, Dave Platt wrote:

The DustBusters I have had (which have two removable battery inserts,
which I believe use sub-C cells) have not survived well. A year or
two sitting on the trickle-charger (as designed) and the NiCd
batteries are toast.

Seems like there ought to be a single-IC solution available today...
and if not, something simple with a PIC or other micro to switch from
full-charge to "off most of the time,

It probably suffices to use a ten-hour timer with an AC outlet .
Plug your batteries into the charger, plug the charger into the outlet,
and hit the button. Ten hours later, the battery is charged and
the charger is off.

I've been thinking seriously about tearing it open, and replacing
whatever simple fixed-resistor slow-charge circuit it has with a
proper faster-charge-and-real-cutoff circuit of some sort. I'd have
to replace the wall wart, most likely, to get a decent charging
current.

The simple, no-cost solution (which works for me) is to use the Dust Buster
until it runs down, then charge it overnight and take it off the charger.