Ni-MH or Ni-CD
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SRV

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I was looking for a set of rechargable batterys to use and i noticed that my charger will accept Ni-CD or N-iMH batterys. I noticed that the Ni-CD batteries where less expensive than the Ni-MH is there a reason for this? Basically i was just wondering what the differences where and wether or not i should just go for the cheap ones.
 
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martioz

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Go for NI-MH!
no memory effect, higher capacity that is why you need to pay extra.
Voltage is 1.2V for both types.
Differences in a price can be not significant when you consider all cons and prons.
Many think NI-CD can deliver higher peak current, I don't agree.
Anyway majority of the PCDP use nimh.
 
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}{azard

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On the one hand, nimh do not have a cell memory (apparently, though I think it is still there, though not as present as in nicads) so charging them is easier, but they are more sensitive to overcharging, you have to watch them a bit more closely.

Nicads must be dumped before re-charging them, due to their cell memory, however they are not as sensitive to overcharing as nimh.

The voltage curve on a nicad will typically be steeper than that of a nimh battery because nimh batteries tend to have higher capacities. Although the batteries used in PCDP's are not sophisticated enough, so the nicads will probably have a higher peak voltage.

IMO, for PCDP's, nimh are the way to go, voltage not being all that important, you shouldn't worry about discharging before charging (maybe only do this once every 5 charges) and you will get more capacity.

I race remote control cars, in which a battery pack runs about 80 dollars...I think I have around 8 batteries currently, mostly mimh though i had all nicads before nimh was introduced. Due to this I think I am pretty well versed on each.

Josh
 
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recephasan

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Depends...
If you have a low power application where your batteries sit inside the instrument for weeks before the next recharge, NiCds are better. They retain charge longer than NiMHs.

I use NiMHs when I know I'll need a recharge within the week, in my portable CDP, for instance.
 
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purk

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Hi,
Definitely go for Ni-Mh. They are great and should be available everywhere.

Purk
 
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blr

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There are several missconceptions about the NiMH vs NiCd issue.

First and foremost, it's the memory effect. Contrary to what everyone is saying the true memory effect (first discovered in aerospace applications) is next to impossible to obtain in normal use. Even careful lab tests often fail to reproduce the memory. There is an effect called "voltage depression"ofren mistaken for memory effect. It is caused by overcharging NiCd cells. As a result the voltage drops to close to 1.00 V in the begining of discharge cycle, which fools your gear to belive that the cells are drained. In fact you can extraxct full capacity albeit at lower voltage.
The truth is:
YOU CAN PARTIALLY DISCHARGE BOTH NiCd and NiMH CELLS MANY TIMES (10-50) WITHOUT LOSS OF PERFORMANCE PROVIDING THAT THE CELLS ARE CHARGED PROPERLY.
I have a set of 700mAh NiCds that haven't been drained flat in a couple of months and is still going at the same capacity. How did I do it? I have a good charger.
This is just to clear the issue.
Now, SRV if you tell me a bit more about the charger you have and the PCDP I I may think about recommending something. Most probably, you'll be servd quite well by NiMH.
 
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}{azard

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blr...you are wrong. I have several 2400mah nicad packs that I use in my RC Cars. If I do not fully discharge them, when I re-charge them they will not feel as punchy.

The charger I use for the cells (Competition Electronics Turbo 35BL) has the ability to cyle packs (peak charge, then discharge at constant amperage up to 35A) it measures IR, AIR, Peak Voltage, Average voltage, mah, discharge time, and you can graph the discharge curve.

I tell you with confidence, that if you do not discharge nicad cells fully before you recharge them, they will not perform as well.

Josh
 
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fredpb

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Head for...........


http://www.thomas-distributing.com/


Do your shopping there. They are experts.

A good charger is essential. Most chargers are NOT good.

Get the Maha charger, and you can get the batteries at Thomas Distributing or Wal-Mart.

Radio Shack, does have one good charger, costs about $35 and does up to 8 AA/AAA batteries.
 
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Quote:

Originally posted by }{azard
blr...you are wrong. I have several 2400mah nicad packs that I use in my RC Cars. If I do not fully discharge them, when I re-charge them they will not feel as punchy.

The charger I use for the cells (Competition Electronics Turbo 35BL) has the ability to cyle packs (peak charge, then discharge at constant amperage up to 35A) it measures IR, AIR, Peak Voltage, Average voltage, mah, discharge time, and you can graph the discharge curve.

I tell you with confidence, that if you do not discharge nicad cells fully before you recharge them, they will not perform as well.

Josh


The problem with packs most often is bad cell matching. Your charger measures all these values for the whole pack. At the same time one (or more) individual cells may be weaker than the rest and thus not perform properly. The probability for this increases with increasing the number of cells in the pack. It is not that much of a problem with only two separate cells used for portables. After all you can (and should from time to time) cycle them separately.
Draining any rechargeable cell fully before recharging only shortens the number of cycles, i.e. your packs will not last as long.
 
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Joe Bloggs

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Take a look at Dan's Quick Guide to Memory Effect, You Idiots


In short discharging your packs before recharging DOES make them punchier, but not because of memory effect; you have to be very careful not to reverse the polarity of any of the cells inside your pack when discharging; and despite all precautions, your packs are not going to last as many cycles as if you don't discharge them.

While you're there, take a look at the rest of the site, it's wacky
 
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This is exactly what I said in my first response Joe. Read further up. Memory effect and voltage depression are physico-chemically different phenomena and are often confused because the outcome is quite similar. I am too lazy to explain what exactly happens, but mind that the above mentioned physico-chemical changes occur at the Ni electrode. Since this electrode is nearly identical on both NiCd and NiMH there is no reason why NiMH batteries should be voltage depression free (which they are not).
In a word, neighter chemistry has memory effect in practise, and the amount of voltage depression is just a BIT better on NiMH. The rest is a advertisment hype, NiMH cells are more expensive.

For PCDP use you don't need to worry about cell reversal because you can cycle you cells separately. Also, good chargers (such as Ansmann PowerLine4) have 4 independant circuits and monitor every cell individually. This is very helpfull in preventing univen charge/discharge.
 
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Joe Bloggs

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Just allow me to quote the first few paragraphs of Dan's Quick Guide to Memory Effect, You Idiots:


Quote:

I have, upon occasion, heard people explain that the nickel metal hydride (NiMH) battery of cordless drill X is superior to the nickel cadmium (NiCd) battery of cordless drill Y, because NiMH has no "memory effect", but NiCd does.
I have heard other people talk about how the lithium ion battery in their laptop's better than NiMH because lithium ion has no memory effect, but NiMH does.

I have not yet heard anybody extolling the virtues of running your cordless drill from a truck battery, because lead acid batteries don't have memory effect but everything else does, but I'm sure someone has. Probably someone with an impressive collection of trusses.

People have all kinds of strange religious beliefs about the rituals that must be performed to exorcise the Memory Monster. If they were just dancing around their laptop, MP3 player or cordless drill waving incense sticks then I wouldn't care. But they're usually doing unnecessary charge/discharge cycles. Which is bad.


Golden Comedy
 
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Yeah, funny, but guy is actually correct.
Most of it is pure myth fed basically by rechargeable batteries retailers that want to sell more expensive batteries that will last shorter.

IMO, for very low current draw applications (modern PCDP) NiCd may be even better than NiMH. Sounds insane?
If your PCDP can be powered by a pair of AA NiMH cells for say 25 hours and you use it on average an hour per day, how much capacity do you loose in self discharge?- roughly about 50% at room temperature and much more at elevated temperature. Thats a waiste. With NiCds the self discharge is about half of that plus it will run two times shorter, i.e. you waiste 3 to 4 times less on self discharge-makes some sense.
 
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Joe Bloggs

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It makes sense if the electricity you use to charge your batteries costs $100/mAH


Really--NiMH give you longer life, waste or no waste--what's not to like?


And BTW, it's not a good idea to put batteries into storage after they've run flat, right? Charged batteries last much longer in storage than flat batteries right?
 
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