Advertise on Bikeforums.net



User Tag List

Results 1 to 11 of 11
  1. #1
    Senior Member
    Join Date
    Apr 2005
    Posts
    447
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Why and when to discharge Nimh AA's??

    Just received my high zoot charger from Tiger Direct and see it has a one touch discharge feature to use when batteries "have a small amount of electricity left in them".

    Do I need to drain my Duracell 2650's before recharging? I suspect the answer is "no", but a high degree of ignorance in all things electrical means I must ask the question.

    Thx

    Nomo

  2. #2
    Terri's Captain RickinFl's Avatar
    Join Date
    Jan 2007
    Posts
    101
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Supposedly, cycling a rechargeable occasionally (completely discharging it before charging) will prevent the development of "memory", which is a condition in which a battery may be fully charged, but will not discharge beyond a certain level, the result being that it doesn't last as long as you would expect.

    This was an issue with NiCads, but I'm not too sure about NiMhs- some makers claim "no memory problems" for their NiMhs, but as I say, I'm not sure. Here's a link to a page that discusses battery memory, and if you google, you can find plenty of info:

    http://www.dansdata.com/gz011.htm

    My charger has the capability of cycling the batteries, but I usually forget how many times I've charged a set (it's suggested to cycle them every 10 charges), and just don't do it. I guess you could keep a log, but that seems like a lot of trouble.

    Rick

  3. #3
    Scott n4zou's Avatar
    Join Date
    Jun 2006
    My Bikes
    Too Many
    Posts
    2,393
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by nomo4me View Post

    Do I need to drain my Duracell 2650's before recharging? I suspect the answer is "no", but a high degree of ignorance in all things electrical means I must ask the question.
    You are correct; Ni-MH batteries do not develop a memory so you never need to completely discharge them before recharging. Your Ni-MH battery life will be extended by never allowing them to become completely discharged.

  4. #4
    World's slowest cyclist.
    Join Date
    Oct 2007
    Location
    Londonderry, NH
    My Bikes
    Cannondale CAAD5 and Cannondale Rush
    Posts
    1,353
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    My quick research on the subject shows there's no need to discharge NiMH batteries.

  5. #5
    Mad bike riding scientist cyccommute's Avatar
    Join Date
    Nov 2004
    Location
    Denver, CO
    My Bikes
    Some silver ones, a black one, a red one, an orange one and a couple of titanium ones
    Posts
    15,466
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by n4zou View Post
    You are correct; Ni-MH batteries do not develop a memory so you never need to completely discharge them before recharging. Your Ni-MH battery life will be extended by never allowing them to become completely discharged.
    All Ni chemistry batteries can develop crystallites that are the cause of the 'memory' problem for NiCd and, to a lesser extent, NiMH. It just takes longer for the NiMH to do so. According to Buchmann, regular full discharge is still required but less frequently. I have chargers that have a discharge function and I use it about once a month, especially during summer storage (or I run them in an RC car which is a lot more fun).
    Stuart Black
    Solo Without Pie. The search for pie in the Midwest.
    Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
    Days of Wineless Roads. Bed and Breakfasting along the KATY
    Twisting Down the Alley. Misadventures in tornado alley.
    An Good Ol' Fashion Appalachian Butt Whoopin'.

  6. #6
    cab horn
    Join Date
    Jun 2004
    Location
    Toronto
    My Bikes
    1987 Bianchi Campione
    Posts
    28,295
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by Chris_F View Post
    My quick research on the subject shows there's no need to discharge NiMH batteries.
    My additional research says that completely discharging the NIMH is very bad.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  7. #7
    Mad bike riding scientist cyccommute's Avatar
    Join Date
    Nov 2004
    Location
    Denver, CO
    My Bikes
    Some silver ones, a black one, a red one, an orange one and a couple of titanium ones
    Posts
    15,466
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by operator View Post
    My additional research says that completely discharging the NIMH is very bad.
    You don't want to discharge the battery completely but discharging to a controlled voltage...I use a Maha C777 plus II...doesn't harm the battery and does help keep crystallite growth to a minimum. Like I said before, I do it about once a month.
    Stuart Black
    Solo Without Pie. The search for pie in the Midwest.
    Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
    Days of Wineless Roads. Bed and Breakfasting along the KATY
    Twisting Down the Alley. Misadventures in tornado alley.
    An Good Ol' Fashion Appalachian Butt Whoopin'.

  8. #8
    Senior Member
    Join Date
    Jul 2006
    Posts
    2,417
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    If I am reading the Battery University website correctly, nicads should be discharged once per month based upon a GTE Government Systems study commissioned by the Navy and though no study has been done on nimh's an educated guess is every 3 months.
    What is better than getting your heart rate up and saddle time?

  9. #9
    Mad bike riding scientist cyccommute's Avatar
    Join Date
    Nov 2004
    Location
    Denver, CO
    My Bikes
    Some silver ones, a black one, a red one, an orange one and a couple of titanium ones
    Posts
    15,466
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by dekindy View Post
    If I am reading the Battery University website correctly, nicads should be discharged once per month based upon a GTE Government Systems study commissioned by the Navy and though no study has been done on nimh's an educated guess is every 3 months.
    I find that a monthly discharge is just easier to remember. I do it on the first Saturday of each month.
    Stuart Black
    Solo Without Pie. The search for pie in the Midwest.
    Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
    Days of Wineless Roads. Bed and Breakfasting along the KATY
    Twisting Down the Alley. Misadventures in tornado alley.
    An Good Ol' Fashion Appalachian Butt Whoopin'.

  10. #10
    ROM 6:23 flipped4bikes's Avatar
    Join Date
    Feb 2006
    Location
    Coastal Maine
    My Bikes
    Specialized Tricross Comp, Lemond Tourmalet, Bridgestone MB-5
    Posts
    1,713
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Whenever you think the performance of your NIMHs have degraded. I'd go with cyclocommutes advice. Once a month, whenever you remember or whichever comes first.
    Every time we let a vehicle pass there is a little bit of compromise. But compromise allows the city to function and allows cyclists to function in the city. The trick is not to eliminate compromise but to learn how to work safely within it.

    --Robert Hurst

  11. #11
    urban biker
    Join Date
    Feb 2006
    Location
    Twin Cities, MN
    My Bikes
    Haro MTB for commuting and a LHT for everything else.
    Posts
    207
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by n4zou View Post
    completely discharge them before recharging
    I'll stay away from the to discharge or not discharge debate, but want to clarify "completely discharging".

    Nimh, Lead-acid, LiIon and LiPoly cells can get damaged quite easily by discharging them beyond a certain voltage. For Nimh, that voltage is 1 volt/cell.

    The only time I've correctly used the discharge feature of a charger is when I was storing a battery as most types of batteries do not like to be stored fully charged. <----- The key word in that statement is correctly as I've destroyed many batteries over the years

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •