Difference in NiCad replacement batteries

If it had a good battery, it wouldn't be at the garage sale.

ba-DUM!

cells

That's no longer possible.

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

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?

often

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.

works

"William Sommerwerck"

** Nah - probably Jewish and too terrified to stop.

.... Phil

"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.

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.

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?

"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.

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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

good-quality

charge.

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."

\

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.

"William Sommerwanker"

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

Tim is turning in his grave...

.... Phil

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

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.

--
Jim Yanik
jyanik
at
localnet
dot com

I must admit that I didn't know that either. I had always assumed the NiCd and NiMH cells were interchangeable in chargers. I guess not.

I've been playing with charging individual cells at 5C or higher. Works fine as long as you know exactly how long to charge, condition of the cell, and ambient temp. From experience, the battery does NOT get hot until it's overcharged.

I didn't say trickle charge. According to Motorola, it's a "maintaining" charge, whatever that means. I agree that a trickle charge would be much less. However, my experience is that you cannot charge a NiCd battery with anything less than about 0.05C. It just never comes to full charge. I don't know what causes this effect and don't want to go Googling for references right now.

There's no such thing as NiCd memory effect unless you're talking about space qualified batteries.

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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

My Dustbuster battery died after about 2 years of sitting on permanent charge. I didn't investigate. I installed a home made battery pack about a year ago. Works fine. I think the original batteries may have had a problem.

Never heard of such a thing, but I'll look.

What creates the problem is that many vendor rate their drills, laptops, and devices by how long it will run on battery power. In order to improve their numbers, they try to cram as much charge into the battery as possible. That works well enough with a new battery, but as the battery gets older, the table driven and timer charge controllers start to overcharge. That causes heating, which is an invitation to a premature demise of the battery.

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.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

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.

You might like the MAHA C9000.

"Bob Fool"

** That is a very obvious error.

... Phil

I'm always suspicious of information sites that don't bother to supply any numbers. This looks like a more useful comparison:

If you want authoritative reading, start here:

You decide. It's not so much the chemistry, as it is how it's used. See below.

NiCd can handle more charge cycles. For NiCd, is you do everything right you'll get perhaps 1000 charge cycles before the battery deteriorates to about half capacity. For NiMH, you'll get perhaps 600 charge cycles.

Doing the math for typical batteries, NiCd will deliver: 0.7A-hr * 1000 cycles = 700A-hr while NiMH will deliver: 2.0A-hr * 600 cycles = 1200A-hr So, if you recycle your batteries when they're half dead, you'll get almost twice the lifetime with a NiMH than with NiCd, where you need to charge NiMH about 40% less often.

However, that's at best, under ideal conditions, with a device that favors NiMH (i.e. no self-discharge problems and moderately high peak current). If you do something non-ideal, such as charge the batteries every day at the same time, you'll get 1000 days out of the NiCd and

600 days out of the NiMH which makes the NiCd the winner. NiMH is the superior technology only if you charge the batteries when they're almost fully discharged (at the knee in the discharge curve). If you recharge by the clock, then NiCd is better because you can recharge it more often.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

I don't know about electric tooth brushes, but I've had far too much entertainment from 2way radio handhelds (HT's), pagers, cellphones, and Norelco rechargeable shavers. The various radios and pagers were all originally NiCd's and would tend to kill batteries far earlier than my calculations would suggest. It didn't take long to find out why. All of them overcharged in some manner. Most commonly, the charge cycle was terminated by a timer that was based on the characteristics of a brand new battery. That was fine for a new radio, but would consistently overcharge (and overhead) an older battery. An important clue is that a battery only overheats when over charged. The brand new batteries would rarely get warm. The older batteries would get rather hot.

Keeping my Norelco shaver batteries alive was an adventure. It stated when I bought a used (cheap) cordless shaver at a garage sale. I replace the batteries (Sub-C NiCd with new cells and noticed that the shaver was warm after charging. After about a year, the batteries were dead and I had only charged it perhaps 20 times. Some measurements found that the charge controller was simply a fixed resistor running at about 0.2C. There was no end of charge circuit, and it would just continue overcharging. I later found a 950RX shaver, which I use erratically today, that has an LCD bar graph to indicate state of charge. Surely this shaver has an end of charge detector. Nope. 0.2C at any charge level. I killed a set of batteries after 2 years, which I guess is an improvement.

My experiences with power tools (mostly older Makita) is a mix. I tend to do better with NiCd batteries because I have more of them and because I tend to charge before every use. The greater number of charge cycles of NiCd makes it a winner over NiMH.

If my rapidly failing memory serves me correctly, NiCd was going out of fashion because of concerned over Cadmium in the water supply and that NiMH was the recommended ecologically correct replacement.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Yes

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