Difference in NiCad replacement batteries

[William Sommerwerck]

You're letting your desire to be right overshadow your analysis.
How many battery powered drills does the average family need?
When every other garage sale has one, two or even three dead
drills, the statistics are hard to ignore.
The drills are rarely dead. It's almost always the batteries.

Take a design that was intended to be the cheapest initial
purchase cost based on the crappiest batteries available at the time.
Replace the cells with ones having 5x the capacity.
Now, even if the charger design was proper, fast charge termination
is unlikely to be anywhere near correct...as in "never terminates".

Sure, it often works. You feeling lucky?

"Well, do ya, punk?"

Not that many years ago I bought a Ryobi drill at Home Despot. It had a
conventional, non-rapid-charging charger. The battery died (in my view)
prematurely, and (violating Federal law) Ryobi could not supply a
replacement pack. So I bought a new drill (a Ryobi with a modular pack). Had
a replacement been available, I'd probably still be using the original.

Your correct observation about the average family rarely needing more than
one cordless drill only confirms my point.

You missed the point I was making -- rapid chargers almost always have some
form of auto cutoff. The kind of charging I was talking about (which I made
perfectly clear) was the "resistor-in-series-with-the-power-supply" type.
This is not a rapid-charge -- though it does charge faster than when the
cell voltage is lower. Such a system works fairly well -- eg, a Dust Buster.
I've gotten a good 200 recharges on my Model 5000, because I let the cells
run down before recharging, and I don't leave the unit on the charger all
the time.

NiMH "behavior" is "close-enough" to nicad that replacement
[often] works well.

I'm in complete agreement. The only thing we seem to differ on is the
consequences of when it DOESN'T work and if those consequences
are acceptable.

I completely agree with your complete agreement. The confusion occurred
because you misread me. I do not advocate rapid charging of any kind of cell
without a "fool-proof" shutoff system. I'm surprised at how far my MAHA
C9000 pushes NiMH cells. I keep an eye on it, and sometimes terminate the
charge cycle manually, because the cell has gotten warmer than I like, even
though the cell voltage is above 1.4 volts. I'm so cautious, I rarely charge
faster than 0.3C, though MAHA and other NiMH manufacturers recommend as high
as 0.5C.

 

[Steve Stone]

I have had good luck with LSD NiMH, like the Sanyo Eneloop for use in
cameras and two way radio gear.

 

[William Sommerwerck]

I have had good luck with LSD NiMH, like the Sanyo Eneloop
for use in cameras and two-way-radio gear.

Do you use them when you go on trips?

 

[William Sommerwerck]

<http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride>
"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.

If that's true (and I assume it is), it's the first really significant
difference between nicads and NiMHs I've heard of.

It also explains why my C9000 charger doesn't shut off when I charge at
"only" 0.3. Guess I'll have to change the way I charge."

\

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.

I stand corrected. HOWEVER... No one would consider 0.1C a trickle charge,
as it has traditionally been the "standard" charge for regular nicad cells.

It's also possible this might have been a memory effect.

 

[Phil Allison]

"William Sommerwanker"

"Steve Stone"


Do you use them when you go on trips?

** Let him who is without sin cast the first Stone ...

Tim is turning in his grave...




..... Phil

 

[William Sommerwerck]

I have yet to see data, numbers, and reproduceable tests that
demonstrate memory effect. What I have seen are problems with
electrolyte loss, caused by overcharging and subsequent venting, that
mimick the problem. Incidentally, I found this by carefully weighing
the better before and after overcharging. It's not much loss, but
it's always present.

Reports on "memory effect" go back almost 50 years to the introduction of
cordless toothbrushes, which were commonly used briefly before being
recharged. They would (supposedly) lose capacity.

Then people whose toothbrushes were accidentally activated in their luggage
and thoroughly run down recovered most of their capacity (the toothbrushes,
not the people). GE supposedly discovered the cause of memory effect
(electrode crystallization), but no cells that addressed the problem were
ever manufactured, that I know of.

 

[William Sommerwerck]

In my never humble opinion, there's only one correct way to charge
batteries, and that's with a "coulomb counting" charge controller. It
measures the current in, runs tests on battery capacity, and adjust
the charge current and timing as necessary. They can programmed for
almost any desired attribute (long battery life, fast charging,
conservative capacity, etc), and will compensate for battery aging.
Many of the charge controller chips made for LiIon will work for NiMH.

You might like the MAHA C9000.

 

[Bob F]

Hmmmmmmm. I peruse
http://www.streetdirectory.com/travel_guide/159640/technology/nimh_vs_nicad_vs_li_ion.html
and it sez longer (than NiMh) life cycles for NiCd.

If true, I'd likely be better off with NiCd. No?

It says NiMH has larger capacity, but NiCd has longer run time. You say what?

 

[Phil Allison]

"Bob Fool"

It says NiMH has larger capacity, but NiCd has longer run time.

** That is a very obvious error.



.... Phil

 

[Steve Stone]

Do you use them when you go on trips?

Yes