Why NiCads over NiMHs?

The "memory problem" is so overblown, hyped, misunderstood, etc that you'd be better off ignoring it. Just follow manufacturer's recommandations and ignore 99.44% of what you hear/read about it.

Why would you use NiCd's instead of NiMh's? Because you have a bunch of NiCd's on hand. Because your charger is for NiCd's, not NiMh's. Because NiCd's will take more charges than NiMh's. Because ______ (fill in the blank with your own reason.)

Personally, I prefer NiMh even though their lifetime is supposedly shorter (ie fewer charges) than NiCd. But if my DeWalt drill battery dies I'll replace with NiCd (assuming I can rebuild the pack, which is doubtful), as that is what the charger is designed for, and there is a second battery. Don't want to rebuild

Exactly. This has to be #1 on the urban legend hit parade.

Because NMH have a crap self-discharge rate (at least 2X that of NiCd).

I looked into this when I bought my last drill. The consensus was that NiCds survived about twice the number of charge/discharge cycles, so I went with the Porter Cable and NiCds. The difference (except for toxicity) isn't all that great anymore. NiCd has come along a long way.

That's a thought. I just had a Makita 9V pack die. Maybe I should try to open it. ...can't have too many batteries.

Well one difference that still exists is that NiMH hold more of a charge then NiCd. A typical 'C' cell NiMH holds 2500 mAh while the NiCd 'C' cell holds only 1800 mAh. That's almost 40% more charge.

But to each their own...

daestrom

You can get NiCds with a much higher capacity than this. Sanyo makes 'C' cells at 3000mAh (N-3000CR) and 3600mAh (CP-3600CR). They don't seem to make many 'C' MiMH batteries but their 'AA' cells seem go up to about 1100/1000mAh (NiMH/NiCd), or about 10% difference.

Sanyo battery info:

As I said, NiCd cell chemistry hasn't stood still. I think this is why they're still here. NiMH is clearly better environmentally, and NiCd life cycle costs higher as a result (recycled rather than dumped).

I don't think you have the best of breed cells there. Clearly high- performance NiCds do better than these.

(To the original poster)

NiCds can tolerate higher discharge currents. They can tolerate heat better than NiMH which are destroyed by heat. They also tend to last longer regardless of usage because NiMH have a limited life. NiCds have more charge/discharge cycles but a lower capacity. NiCds are also more tolerant to incorrect charging, whereas NiMH need a special charger and can be damaged by incorrect charging, epecially overcharging. I think that NiCds are better for rough applications like drills and anything involving frequent recharging, high current drain, motors where high startup currents are typical. NiMH are better for mobile phones where long operation time and low power are involved.

Sig: Work saves us from three great evils: boredom, vice and need. -Voltaire, philosopher (1694-1778)

I agree. It's a common mistake to compare the current version of a new technology with yesterdays version of the old technology. For some applications, standard NiMH cells just aren't up to the task. Electric RC airplanes comes to mind. That said, the 40% capacity advantage previously mentioned for NiMH doesn't seem unrealistic. There are some

C cells have to hold more than that. I have AA cells that hold 1.8 amp hours and I have D cells which hold over 5 amp hours.

For c cells I use an AA cell in a C cell carriage.

You really can not be sure of what a NiCad C cell holds as most of those I have seen are really AA cells in a C size casing. In fact most of my NiCad AA cells held more than my Nicad C cells.

The memory effect in NiCad is due to impurities in the cells. My fried Joe Schulman who is or was, (He is probly to old now to be working) developed a NiCad that had almost infinite life by making them very pure and eliminating impuritiess from them. His application for them was in heart pacers where it is quite a job to replace batteries.

I developed a system to recharge pacer batteries while sleeping with special wires on the the bed. TRW agreed to let me patent the idea as it was out side of their sphere of interest, but it was much to expensive to get a patent, at least $15,000 (My lost chance at being a millionair.) Now Teledyne and others use my unpatented teqnique to charge their tooth brushes.

It has been my experiance that nicads have a much higher self discharge current and are almost useless for emergency items that may sit on a shelf for a period of time. I guess Alkaline batteries are best for that. I used to sell batteries and have some still packaged batteries that have been sitting there for over 15 years and when I open the packages, they do not appear to have lost much life. At least they work just fine.

While nimh bats also lose charge over time, in my experiance they do not seem to lose as much as nicads.

Radio shack sells 2 packs of 5 amp hour nicds for about 10 bucks which is a lot cheaper than those they advertise at 18 bucks.

nicads are somewhat cheaper.

OTOH, they self discharge much faster than NiMH and are more susceptable to problems with being trickle charged.

I think NiMH batteries have a little more power density as well.

Not higher than NiMH. You're right, NiCds are not a good choice for long shelf-life applications.

Of course. A primary battery will always have the advantage for long

Try testing their charge. My bet is that they're on the low side.

It's exactly the opposite. NiMH cells have more than twice (some ten times) the self discharge as NiCds.

I guess the lights around here go out often enough and my kids playing with flashlights don't give my batteries a chance to self discharge ;-)

Kids are good at burning batteries. ;-)

Apparently by altering the chemistry one can optimize for capacity or self-discharge. TANSTAAFL, as usual.

Try:

Thanks Keith That site answered a lot of my questions. Evidently there is no clear better battery. They each have their good and bad points. I think the best point of the hydride batteries is that they are not toxic and I think we will see less and less of the NIcad batteries being sold.

Costco no longer carries them and now carries hydride batteries in their place.

Last night the S*it hit the fan. We had to go out and dig my car out of the snow. The sun set and we had to put chains on the car and had to do it by the light from flashlights. We drove into town to get the mail and comming back we could not even get up the street I live on because of the Ice and snow, and the chains would not even cut it. I had to zig zag from one side of the street to the other to reduce the grade to get up the hill and the tires were slipping even then with the chains and four wheel drive. I have seen times when even the snow plows could not get up my street. We live on a mountain ridge just a few feet below the peak. Perhaps now they will learn the importance of a set of charged batteries in the flash lights.

By the way, we are switching over to LED flashlights as fast as we can. I have one with 7 LED's which light up a room, well enough to read by and a set of 4 AA batteries last about 166 hours in it.

The flash light was a little expensive at $20 in costco, but worth the money in the batteries it will save. I have some more multi LED flashlights on order that are a little chaper.

I even have one that you wear on your head with 5 LED's that only cost $10. Again well worth the money when going down snow covered stairs at night or putting out the garbage at night.

They do not throw as good a far away beam as a regular bulb and reflector, but they put out a lot of local light. But then again I am a lot more interested in not tripping over a log or boulder up close than seeing what is 100 feet down the road. It takes a little getting used to but they sure work good when you use them as they are meant to be used.

We even have a dimmable LED lantern with 12 LED's in it and it did not cost more than my Florescent bulb lantern (About 12 to 15 dollars ) which gets about 8 hours on a set of 4 D cells.

Are you familiar with this new breed of flash lights?

Of course not. If there were, there would only be one.

I thought that ten years ago, but it didn't hold then, and I don't see that much has changed. What gets me is the lack of SLAC batteries. They're far better for most things people use secondary cells for.

Likely because they don't want the expense/bother of the mandatory collection/recycling.

I use primary cells for flashlights. The shelf life is years rather than months and when they gotta work, they gotta work. It's simply not worth the cost of the batteries to scrimp here.

Neat. I bought LED keyfobs for my wife and self. Sometimes it's dark when we got home (anytime after about 16:30 this time of year) and it's better than fumbling for the house keys in the dark. I don't know how long the batteries last, but it's just a watch battery, so is light and small.

If they last that many hours, I'll have to invest in them too, though I only go though a set of batteries every couple of years now. I gust bought a 16pack of 'D's and a 36pack of 'AA' alkalines at Home Despot for $10-11 each.

??? not a good reflector? Omnidirectional? Strange, LEDs usually have the opposite problem.

Sure. I've not used ones as big as you're talking about. Mine are single LED keyfobs.

What is a SLAC battery?

Where I live, when there is a storm, they often cut the power, even if no lines are down. They do that to prevent forest fires. That is why the batteries do not have a chance to go flat sitting there. We use flash lights and lanterns quite a bit and I have about a dozen of them of one sort or the other.

They will last supprisingly long, you will find.

Their light is on the surface of the bulb and thus the reflectors do not do much good in concentrating the light. You would have to mount them backwards (the bulbs) for the reflectors to work. The LED surface is fairly large and they do not put out a beam light, but thier light really spreads out for close work. Their light is also a whitish blue and the bulbs are very intense. It can blind you to look at the bulbs on my 7 led flashlight. But they do throw out some beam, just not as much or as far as a good regular well focused flashlight.

I saw them at thrifty today for about $4.95. They seem like a good investment. We have no lock on our front door, just a bunch of very large doors so we never have to fumble for keys. The car has a radio controlled lock.

HOw do those things work. I never have had to change batteries in mine in 5 years. Does pressing the button create the power with a crystal?

Sealed Lead Acid Cell, sorta like a gell-cell, but different. ;-) They're "starved-electrolyte" cells and don't outgas like standard lead-acids. The patents were (they're expired) held by Gates Energy, which apparently has been sold to Hawker.

Then SLACs are perfect for your application. They are very happy being trickle charged and will last eight to ten years (if treated right) with 80% capacity.

Which is what I'd expect. That or no reflector at all.

"White" LEDs are really blue LEDs with a phosphor to make the light appear more white. When I bough the keyfobs both versions were available. I went for the white. ...really don't know why.

Many around here have no locks on their doors. My insurance company seems to think that's a bad idea. My policy states that I have to have dead-bolts.

Sure. Aren't they all these days? Even my '93 Vision Tsi had the keyfob. My wiles Sable also has a 5/5 combination lock buttons on the door. It comes in handy.

No, just turns on the power to the transmitter. There is a watch battery inside. The passive anti-theft keys are more interesting. No batteries.