Difference in NiCad replacement batteries

I recently bought a 2-AA-cell pack for this purpose from Mouser... part number 6396-1K-F2 / CM1T-AA1000. It uses 1000 mAh NiCd cells, and cost $5.95 plus shipping.

You could easily get more than twice that capacity by using NiMH cells or a pack thereof, but if the charge-control circuit in the shaver is designed for NiCd it might not work all that well with NiMH (might over- or under-charge the battery, shorten its life, etc.).

$15).

Probably not. The Norelco "charger" is probably little more than a resistor in series with the power supply. A NiMH should have no trouble with that.

Why not get some NiMH cells with tabs from Thomas Distributing? The ones I used in my Polaroid #365 electronic flash work fine, and the #363 rapid charger -- designed for nicads -- shuts off properly.

Hmmmmmmm. I peruse

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

If the life cycle of 1.2v NiCd rechargables is appreciably variable, what is the best NiCd I can buy? Brand or mnfgr or ? with the longest life cycle??

Thx, P

"Law Without Equity Is No Law At All. It Is A Form Of Jungle Rule."

Nicads are obsolescent, if not actually obsolete. If you can find NiMH cells that fit, use them.

I've been listening to my Sony Discman at work. It runs on two AA cells. I use PowerEx (MAHA) 2700mAh NiMH cells. In two weeks, I've gone through 16 disks of Bach organ works, seven of Hermann Baumann playing valveless horn, and I'm well into an Andras Schiff collection -- and they're still running strong.

"Puddin' Man"

The number of cycles quoted by makers is a complete fantasy that has almost nothing to do with any real life application.

Wiki quotes 2000 cycles for NiCd, but gives no source for that mad claim.

IME, treat NiCd or NiMH cells with great care and you can expect a few hundred cycles - do anything careless ( overcharge or overheat) and you can ruin them in one day.

.... Phil

I'm using 1000mAh NiMH AA cells from Poundworld, sold in packs of 2 (everything £1, kinda like a 5 and dime) GPB). I'm very happy with them for TV remotes, wireless keyboard / mice, 80's vintage CBM calculator and even a hair trmmer. 2 AA cells for 1GPB. As almost everything has $1 = £1 exchange rate should be able to find some for about 1$ in USA.

At that price the key issue is how easy it is to rebuild the device you are putting them in.

"Peter Hill"

Wonder if he uses any of his NiMh cells for what they are good at.

.... Phil

As I understand it, the problem with this approach is the question of shutting off the charge when the battery is full. NiMH cells are less tolerant of being overcharged than NiCd, and are best used with a charger that has a somewhat more sensitive full-charge detector (e.g. zero-delta-V and/or direct temperature sense, rather than negative- delta-V as was often used with NiCd cells.

It's slightly more complicated, if you replace NiCad cells in a battery pack with a temperature sensor, you have to replace the sensor too. NiMH cells have a much lower "cook temperature" than NiCads.

The other night I was having trouble sleeping and read a very nice article about modifying Motorola NiCad chargers to properly (and not over) charge NiMH packs. Since it was late at night, I remember the main points and that I read it, but not where. :-)

Geoff.

These simplistic chargers are horrible and will kill any battery fed to it in short order. There are some similar Kenwood chargers with the same problem. They tend to overcharge, even after the battery pack gets over-heated. I've modified a few of these with good results as the author describes.

Depending on current draw, nicads will deliver more current due to lower impedance. For motors that can be a problem.

Greg

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

I've read that charge terminating NiMH by temperature rise is not good or proper,that it has to be done by voltage monitoring. By the time the NiMH cells heat up,the damage has been done.

I believe that they're both aspects of the same phenomenon... that is, the change in the cell's terminal voltage is the result of the rise in temperature, which itself results from the fact that the energy being pumped in is now being converted to heat rather than to electrochemical potential.

In effect, sensing the terminal voltage and shutting down when it ceases to rise is a faster way of detecting the rise in the cell's internal temperature. You don't have to wait for the heat to "soak out" of the cell and warm up the thermistor.

The recommendations I've read suggest that the best shutdown approach for NiMH cells is via zero-delta-V measurement, with a temperature sensor as a secondary, and a timer as a last-ditch shutoff.

The temperature sensor is best used to detect "sudden rise in temperature" rather than "specific temperature threshold". This makes the detection less sensitive to variations in the room temperature, and also to the sort of variation in thermistor values written about in the document Jeff pointed us to. This is probably best done with a microcontroller or a dedicated charge-control IC that can perform time-based measurement analysis.

"gregz"

AA cells in NiCd or NiMH have closely similar impedances and hence max current outputs.

The figure is between 10 and 20 milliohms in both cases.

.... Phil

resistor

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.

If the resistor is chosen to give a 0.1C charge rate when the cell is at about 1V, the charge rate when the cell has "fully" charged will be rather lower ("depending").

It's only in the past decade or so that rapid-charging with auto-cutoff has become commonplace. Prior to that, almost every nicad device was charged with a simple series resistor. And guess what? It worked.

As I said earlier, I have a Polaroid #365 electronic flash with NiMH cells that replaced the original nicads. The #363 rapid charger has no trouble stopping and switching to trickle charge. It was designed almost 45 years ago.

Based on what I learned at Microsoft Hardware, this is not true. "Hitting" the NiMH cell "hard", to the point where it significantly heats the cell, supposedly gives a deeper charge.

I've have NiMHs get quite warm -- even hot -- in chargers. If one such occurrence ruined the cell, then most of my cells would be useless. None is.

cells

horn,

running

Not in a circuit that regulates the current flow to the motor. Which, of course, CD players have.

The only case I know of where what you say is true, is the use of nicads in really cheap electronic flashes. These were designed so that the higher internal resistance of alkaline cells would limit the current flow. With nicads, they can overheat and be damaged.

I had a bunch of NiMH cells laying around for a few years, they just did not work anymore.

From using them in model cars and Dustbusters, etc, the general idea 10 years ago was the nicads had lower impedance, but in reading further, today's NiMH cell are better Z wise.

Still got some 50 year old German nicad packs that still work.

Greg

Ah, German precision...