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Thread: dead nicad battery rejuvenation?

  1. #1
    Join Date
    Feb 2002
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    central USA
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    883

    Default dead nicad battery rejuvenation?

    I have a lot of bad rechargeable battery packs and there is a guy on eBay that claims that he has a way to bring them back to life without replacing cells. Has anyone tried this? Did it work? How is it done? thanks--Mike.

  2. #2
    Join Date
    May 2008
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    Charlestown NSW Australia
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    Check these out. I haven't tried any of these myself

    http://www.youtube.com/watch?v=1e8hHLyXAyQ

    http://www.youtube.com/watch?v=PzIlVLOH9XI

    there is a lot of stuff out there if you do a search on "rejuvenating nicad batteries" or similar

    bollie7

  3. #3
    Join Date
    Nov 2007
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    Wenatchee, Washington USA
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    474

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    Mikem,

    There are 3 basic failures in NiCd battery packs. The first is shorted cells. If this is the problem you can sometimes clear the short with a high current pulse. This can be risky as the battery can explode and hurt you. The second failure is simply the battery chemistry is kaput, done, dead ..... A typical NiCd battery is rated for between 400 and 700 charge/discharge cycles before the chemistry is finished. In this case there is really nothing that can be done to "fix" the problem. The third failure is "memory effect". This is where the battery looses capacity due to short discharge cycles. If a NiCd battery is discharged say 25% then recharged and this pattern continues, very soon the battery will only last for that 25% time. If this is the problem the battery can often be rejuvenated quite easily. Without special equipment the procedure is to fully discharge the battery to between .8 and 1 volt per cell (each NiCd cell is 1.25 volts fully charged so do the math to figure out how many cells are in your battery). Next full charge the battery, slow charge is best but the rapid charge is OK. Now repeat the discharge / charge cycle 3 to 5 times. Your battery will now be in better shape than when you started. A NiCd with memory has been damaged and will never be as good as would be with proper care, but you can get a lot more use out of one this way.

    Just a note about measuring battery voltage... After charging a NiCd battery you can measure the voltage and determine if there are any shorted cells. Put a small load on the battery (I often use an automotive test light for the load) and measure the DC voltage. If there are any shorted cells the battery will almost always read low by a multiple of 1.25 volts. You MUST use a load on the battery or the reading will be misleading as a fully charged battery will read high without a load. I have seen 7.5 volt batteries read 9.5+ when fresh out of the charger without a load. Put a load on them and they will drop right down to 7.5-7.7 like expected.

    The above info is only applicable to NiCd batteries as other chemistries have different characteristics.
    Robin

    Happily working on my second million Gave up on the first

  4. #4
    Join Date
    Jul 2002
    Posts
    3,924

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    Mike. I did most everything to rejuvenate the batteries to my two Dewalt 12 volt drills. Including rebuilding the batteries. A new battery is $50.00. A new 18 volt Riobie(?) drill driver with two batteries and a saw is $89.00 an Home depot. In this instance I think I'm going to throw money at the problem.

  5. #5
    Join Date
    Sep 2006
    Location
    DeWinton, Alberta, Canada.
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    I think there is a thread here on rejuvenating batteries using a welder. the battery is hooked with reverse polarity and give a short jolt of power.

    I have looked and can't seem to find it, maybe someone else remembers the thread.

  6. #6
    Join Date
    Feb 2011
    Location
    South Africa
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    I did the welder thing with my Dad's 14,4V Bosch Pro drill battery.
    I used a inverter welder kicking out 58V and set to the lowest current to charge the battery by just touching it with the welder in the correct polarity.
    I gave it 5 short pulses and popped the Battery in the charger and she works.
    Before it just gave a error on the charger and refused to charge.
    What can I say My Dad is one of those guys that leaves the Batt in the charger till he remembers to take it out .... Could be in a hour could be next week.

    Kobus
    If you are using violence and it does not work, You are not using enough.

  7. #7
    Join Date
    Nov 2010
    Location
    South Western Ontario
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    82

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    Mike..
    Have a look at this site.
    http://www.hangtimes.com/redsbatteryclinic.html

    Top notch nicad stuff....

    bert

  8. #8
    Join Date
    Aug 2009
    Location
    Canada, Bc
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    Nicads do not have 'memory' effect that you would ever see outside a satalite that has EXACTLY precise charge/discharge cycles. Nicad chemistry has changed since the story of memory first started, and its now reduced to such a level you'd never experiance it.

    Secondly, I would never use a welder on a nicad.. I have however, successfuly used about 10,000uf capacitors charged to 20v or so, shorted into a single cell, about 10~50 times, with a DMM across the capacitors, with a current limited power supply (about 100mA is all you need really) charging the capacitors

    With thick, short wires, you connect one end of the cap to the cell, and tap the other on its terminal repeatly, then hold it there for a few seconds and watch the DMM, if the DMM rises above 1V, the cell is unshorted. If not, repeat untill unshorted, Generaly once it rised above 1V I would let it charge via the current limited charger for about 20 seconds, and it would hold its charge for long enough for me to do the other cells and get the pack into the charger.

    If your battery pack isent outputing its rated voltage after a very quick charge, its most likey a cell is shorted.

    Capacitors+current limit will signifigantly limit the average energy, while allowing the high peak energy needed to unshort the cells.

    A welder could EASILY put enough average energy into a cell to boil it internaly and cause it to explode in seconds.

    On a subnote, I have PERSONALY had a nicad battery pack last 20 years, and then it only died because of lack of use and me getting tired of unshorting the cells every couple months.

    Nicads LOVE to be used, I highly doubt they have any 'cycle' limit, And I will guarentee you a properly discharged and charged nicad used every day, will outlast one used occasionaly.

    What is properly discharged for a nicad? FULL discharge, Nicads HATE to be recharged before fully discharged, because discharging them actualy removes crystals that form on the plates, without a full discharge, the crystals grow bigger and bigger every discharge cycle.

    Its basicly recommend that nicads get fully discharged at least once a month, Reguardless of use. Studys have shown nicads 'abused' by allowing them to fully discharge (Devices left on overnight by accident, etc), lasted way longer then those that where babied (Recharged before full discharge, never allowed to fully discharge)

    This means use your nicads till they can't even spin the drill anymore! Never charge them up before that... Infact....

    its known that a very slow (1/10c or less, basicly only about 100mA or less) discharge to 0.4v per cell, actualy improves capacity on tired nicads!! (Best to be done on a per cell basis, so you don't apply any reverse current on any cells that discharge fully first, but then thats also why you use a TINY current)

    Also, Any '10hour'+ nicad charger likey trickles them with absolutely no intelligence. NEVER leave your nicads in such a charger, as they will destory them with overcharging. Infact most intelligence chargers have a limited 'float' mode that will also destory nicads over time.

    For the TLDR version:

    1: Never charge Nicads before fully discharged. As in won't even turn the drill over with no load on it discharged.
    2: Never leave Nicad in charger.
    3: Fully discharge your nicads once a month. Don't use your cordless tools enough for that? Buy li-ion instead. They may only last 3~ years, but thats longer then you'll get outta lightly used nicads!

  9. #9
    Join Date
    Aug 2011
    Location
    South Florida
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    Quote Originally Posted by Westline
    What can I say My Dad is one of those guys that leaves the Batt in the charger till he remembers to take it out .... Could be in a hour could be next week.

    Kobus
    Nicads are a royal PTA no matter how they're handled, unless they're used regularly. They don't like sitting idle much better than they like sitting in a charger for prolonged periods. Contractors that use them every day and charge them every night will see much longer longevity than an occasional user. The Engineering dept where I work get about 5 years lifespan on the HT Nicads they carry.

    That said, I've kicked some of them back to a lesser life with capacitive discharge.

  10. #10
    Join Date
    Nov 2007
    Location
    Wenatchee, Washington USA
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    474

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    Black_moons,
    I will not question your having a NiCd last 20 years as I have had them last 10+ years. I will very much dispute your comment about memory effect on NiCd batteries and also the cycle-life of a NiCd. I have sold and disposed of literally thousands of NiCd batteries used on older two-way radios and flashlights. I can almost set a reorder schedule for the radios used by my police customers as the officers all work 5 shifts a week and charge the radios after every shift... 5 cycles per week X 52 week a year = 260 cycles per year X 2 years = 520 cycles = New Battery time.
    Also the chemistry in a NiCd battery is the same now as it was 30 years ago. Please do your homework before misleading others.

    Now NiMh is more like what you describe except it to has a finite cycle life.....
    Robin

    Happily working on my second million Gave up on the first

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