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Old Jan 08, 2010, 02:41 PM
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United States, WI, Evansville
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NICd and NiMh charging and discharging rate

Ok first of all I am sorry if this question sounds too primitive. But I searched a lot in forum and could not get satisfactory answer. Someone pl tell me the charge / discharge for following typeof batteries:-

NiCd 4.8V, 600 mah

NiMh 7.2 , 900 mah

LiPo 2200/3S/20C

What is memory effect and which type of battery is more effected. How do I get over memory effect? Is the cycle function of charger used for this. In that case what charge and discharge rate do I select for each of the above batteries

Are there any thumb rules for charge and discharge rate?

I am using MaxPro charger.

Thanks
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Old Jan 08, 2010, 02:53 PM
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Letchworth, Great Britain (UK)
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NiCd is the one with memory effect. That means that if, for instance, you keep recharging it when you've only used 10% of its capacity, it'll eventually "refuse" to go down below 90%. To get over this, you should from time to time (I used to do it every charge when I had NiCds) discharge it down to nominally empty, which in practice is generally regarded as being 0.9v per cell (i.e. 3.6v for a 4-cell NiCd).

For a battery that small I would always charge it at about 1/10C (i.e. 60mA in your example) for 14 hours or so. I'm not sure what discharge rate I use -- my cycler sets it for me -- but I think about twice the charge rate is usually recommended.

NiMh doesn't have a memory effect, so cycling is not required so often, but I believe an occasional cycle can help keep the cells in balance. I charge my small NiMh receiver and transmitter packs (1200mAh capacity) at somewhere around 1/10C overnight. You may be able to charge at up to 1C rate (i.e. 900mA charge rate for your example), depending on its physical size and type.

LiPo also doesn't have a memory effect, and I would charge them at 1C rate (2.2A for your example) which should take about 75 minutes if they're fully discharged. Some newer LiPos can be charged at a higher rate, but their life may be shortened if you do that. If the label doesn't say so, charge them at 1C.
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Old Jan 08, 2010, 03:19 PM
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Florida
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I have to dissagree with abenn in part. Here is some very good and factual data on all types of batteries. It may take you a few minutes to read them but they give a good factual outlook on the batteries.
Battery Information
http://www.hangtimes.com/redsbatteryclinic.html

http://www.camlight.com/techinfo/techtips.html

http://www.whenshtf.com/showthread.php?t=2153

http://www.srbatteries.com/nimh.htm

http://dansdata.com/gz011.htm

http://users.frii.com/dlc/battery.htm
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Old Jan 08, 2010, 08:00 PM
CamLight Systems
New York City, USA
Joined Oct 2003
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There is no "memory" in any cells or application you'll ever come across. However, several things can the internal chemical structure of a cell to form fewer, larger crystals. Since there are fewer crystals, there's less active surface area and higher internal resistance. This higher internal resistance causes a voltage drop inside the cell. This causes the voltage you measure at the cell terminals to be lower (when being used) and makes the cell seem to be discharged before it actually is. This is called "voltage depression" and is commonly attributed to "memory", but actually isn't.

Discharging a cell completely (not to zero volts!) and recharging causes all of crystals to be reformed at their normal smaller size, increasing their surface area and lowering the internal resistance of the cell. This helps to restore the cell to close to its rated capacity and voltage (when being used).

Both NiCd and NiMh cells are susceptible to voltage depression, but NiCd more so. I have some info on my site at http://www.camlight.com. See the Tech Tips and Why Discharge? sections.

[Edit: Oops, just saw Rodney's link to CamLight ]
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Old Jan 08, 2010, 08:03 PM
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United States, NJ, Frenchtown
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Bigger problem with NICAD is sitting an a shelf and slowly discharging inside of itself.
1 month is a weak battery.

Rich
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Old Jan 08, 2010, 08:06 PM
CamLight Systems
New York City, USA
Joined Oct 2003
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I agree, self-discharge is a big problem with NiCd/NiMH cells (compared to Li cells, let's say). I highly recommend a monthly cycling of all NiCd/NiMH packs.
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Old Jan 08, 2010, 09:03 PM
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United States, NJ, Frenchtown
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I can see the LIGHT !!

I removed ALL nicads from cordless tools & put in LIFEPO4s..........
A drill dropped less than 10% AFTER a year...MOOOOO HA HA.

Rich
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Old Jan 08, 2010, 09:26 PM
CamLight Systems
New York City, USA
Joined Oct 2003
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Umm...OK.
"Mooooo"?
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Old Jan 09, 2010, 03:36 AM
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Letchworth, Great Britain (UK)
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Quote:
Originally Posted by Rodney View Post
I have to dissagree with abenn in part. Here is some very good and factual data on all types of batteries. It may take you a few minutes to read them but they give a good factual outlook on the batteries. ...
Some good info in your links, Rodney. I'm presuming that your disagreement is on the matter of "memory effect"? If it's something else, please let me know, as I'm learning all the time
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Old Jan 09, 2010, 09:02 AM
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Florida
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Quote:
Originally Posted by abenn View Post
Some good info in your links, Rodney. I'm presuming that your disagreement is on the matter of "memory effect"? If it's something else, please let me know, as I'm learning all the time
Your presumption is correct. That and that both NiCad and NiMh suffer from the voltage depression effect.
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Old Jan 09, 2010, 03:38 PM
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Ireland
Joined Apr 2001
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to aswer the original question as simple as posible ; it depends on if the batteries are made for fast charging or not.
Generic nicad and nimh used to be best charged at 1/10 c for 14 hours ; so called slow or overnight charging.
So that would be 60 and 90 mAh for your packs.
This is a save charging rate even if your batteries are designed to handle higer charging rates.

If you want to charge faster the performance cells could be charged in about 30 min so that would be 2c ( 1.2 amp and 1.8 amp)
This gives you a impression of range ; what you can do is charge at 1/2 c and feel if the packs get warm during charging wich is a indicator if the energy you put into the pack is used to charge or heat the pack; warm would be hotter then what is confortable to hold for longer time.
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Old Jan 11, 2010, 10:02 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,140 Posts
Here is a great document as far as the NiCad/NiMH part of the question, it really covers it all:

http://www.camlight.com/techinfo/camlight_techtips.pdf

The CamLight web site is a great place for accessories and info on the classic battery systems.

Jack
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Old Jan 11, 2010, 10:14 AM
m25
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There's lots of info in these older batteries just by checking on wikipedia, but with current prices, IMO you'd better use nothing but LiPos and I hope Zinc-air ones make it for midyear.
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