Charging a Ni-cad battery

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I have a beard trimmer that runs on a Ni-cad battery that I recharge about once a month when the battery runs low. Recently, the battery stopped being able to hold a charge. I charged it for ~12 hours, tested the voltage, and got zero. OK, fine, so I soldered in a new ni-cad, and everything works fine now. The trimmer is only a few years old, so I thought the battery died earlier than I would have expected.
Then I got to thinking about the charger, which is just a simple wall wart. The battery is one AA ni-cad, 1.2 V 600 mAh. The wall wart charger is labeled 2.3 V, and I measured 7.5 V DC actual output. The charger is what came with the trimmer, and molded into the trimmer is something about "use only charger # such-and-such", which is also the number on the charger. So I'm sure that the charger is the one that the manufacturer intented to be used with the trimmer.
Did the higher than expected voltage on the charger lead to the early demise of the ni-cad battery? Should I find a new wall wart that has a voltage closer to 1.2 V? If so, what current output should it have? (I save each and every wall wart from every dead appliance that I have ever owned, so I have a wide selection to choose from a box in the attic, although I think most of them are 5V and up.)
Ken
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Ken wrote:

You found that voltages change depending on how you measure them.
The battery is rated at the voltage it can deliver (likely under a specific load).
The charger is rated at the voltage it delivers under a certain load.
The voltage you measured was likely with a modern digital meter that have a very high resistance, resulting in the high voltage recorded.
If you were to measure the voltage when you first put a battery in need of a charge on it and then measure it again when the battery is fully charged you are going to get two more measurements, the last likely near that 2.3V specified for the charger.
Measure the voltage output of that 5V vampire with that same meter and no load and you might get something about 10V.
The moral of the story, stick with the one designed for the use you have.
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Joseph Meehan

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Stick with the recommended unit. The open circuit measurement doesn't mean much.
1.325 is the voltage of a fully charged cell.
For a longer cell life don't leave it in the charger all the time.
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Rich256 wrote:

A fully-charged cell that's in good condition, you mean. As they lose capacity through abuse, the terminal voltage goes up.
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ISTR that it takes 1.55v per cell for charging a NiCd.(loaded V) You need more voltage than what the cell is rated for.
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Jim Yanik
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Jim Yanik wrote:

With the charger attached to the battery, 1.55V isn't a bad estimate for the voltage you'll see at full charge. With the charger detached, 1.325V is a decent estimate for the battery voltage.
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Under charge load it probably is the right charger and voltage of apx 1.36-1.5v. 1.35 is fully charged for a nicad. 1.2v is considered discharged. Likely just a cheap battery as alot of junk is made. Sanyo and Panasonic are tops. Just don`t leave in the charger and overcharge, and over discharging ruins nicads. When it just slows it is dead. 1.2v is discharged
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I've got a Norelco that's doing a similar thing. I carry it in the truck for when I forget to shave at home.
It's only got one cell. I'm really tempted to drill a hole in the side of the shaver, and wire on a single AA battery holder. Put a high capacity NiMH cell in. Then in two years just pop in another cell. Or use an alkaline (I've got lots of those) and change battery when it gets weak.
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for
alkaline
You might want to use at least a C cell.
I wonder if it would happen if it was hooked to 12 volts. DC motors draw very little current unless they stall. The faster they run the more back EMF they create. Still, 12 might be too much for it.
I did something along that line. I had an old rechargeable B&D screwdriver with two sub C cells. They died and the instructions were how to dispose of the whole thing. I opened it up and about three feet of heavy wire out. I found that the charger would charge 4 batteries if left on long enough so I hooked up 4 D cells. It has power now!!
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Get rid of the problematic Ni-cads
Go to Wal-Mart and buy the NiMh rechargeables. They are the same type of battery that digital cameras often use. The have no real memory effect and are cheaper than N-cads. You can usually find the batteries sold with a charging unit. I have found a four AA battery charger with four batteries for as low as $10 at Wal-mart.
You can also browse http://www.thomasdistributing.com /
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snipped-for-privacy@mucks.net wrote:

If I am guessing right, the OP needs a battery that is soldered in the device. He may not be able to find a NiMh with the proper solder strips attached. Really no need for NiMh as the Ni-cads do just fine.
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wrote:

The NiCd battery in his device is probably not a standard AA size,either. It could be a 2/3A,N,or smaller NiCd.("A" cells are slightly larger in diameter than a AA cell.)
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Actually, it really is a standard AA size. I expected to see a sub-C or something when I opened it up. I had some good AA NiCd batteries laying about, so I soldered one in. It didn't have the solder tabs, but I was able to get a blob of solder to stick to each end without cooking the battery with heat.
Ken
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Ken wrote:

Same with mine, but I bought a new NiCd and for 25 they spot welded the tabs.
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Being a cheap basthud I'd check the battery by subjecting it to a quick shot at a higher voltage then check to see if the cell is still dead. I've zapped apperently dead cells back to stretch the life a bit. I hit a cell with the 12v battery charger (i said quick- a touch ) then I checked to see if the battery is still dead. Leave it sit for perhaps 6 hrs and see if it is still holding a charge. About 1/3 of the time , I can manage to get the dead cell to hold the charge for a while, then I go to a complete slow charge (a typical 500-740 aa cell) will be charged at 50mah overnight.If you already have the cel why not give it a shot. I just retired a 500mah aa nicad that had a 1974 manufacter date. Course it was down to mebbe 40% of capacity for the last year, but I did get some work outa the battery. Pat
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wrote:

There are a couple pros to using ni-cd over NiMH if the info I read on the net was actually correct.
Ni-Cd hold a charge for longer when not in use and I believe will endure more charge cycles then NiMH. Also, NiMH is rather nasty if it is heated to above a certain (rather high) temperature.
I usually tape the trigger on when my Ni-Cd tools run low and let it completely drain the battery before I charge it. They hold a good charge for quite a while. I've found the tool wears out before the battery does... but I'm a little rough.
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Olaf,
Good advice, but I don't agree with taping the trigger to fully discharge the cells. That is overkill and all of my electrical engineering buddies have advised me that 100% discharge to avoid memory effects is not the way to go. When you notice that your drill is struggling to operate, then recharge at that time. You'll get much better life from the cells.
Gideon
==============
wrote:

There are a couple pros to using ni-cd over NiMH if the info I read on the net was actually correct.
Ni-Cd hold a charge for longer when not in use and I believe will endure more charge cycles then NiMH. Also, NiMH is rather nasty if it is heated to above a certain (rather high) temperature.
I usually tape the trigger on when my Ni-Cd tools run low and let it completely drain the battery before I charge it. They hold a good charge for quite a while. I've found the tool wears out before the battery does... but I'm a little rough.
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Gideon wrote:

Agreed. You can reverse bias the weaker cells in the pack that way and bugger them up real good.The "memory effect" with nicads is a much overated problem. About the only times it really comes into play and reduces the capacity of the battery is with devices like cordless phones, when they are used in a mode where they get put back on the charger after each short phone call and never really get discharged very much at all.
Jeff
Jeff
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Cool! Thanks. :-)
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I've read this isn't a good idea. Sometimes one cell goes weak before the others, and then you get voltage reversal on the weak cell.
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