NiMH Chargers that I May Have Missed

Discussion in 'Digital Photography' started by SMS, Jul 2, 2007.

  1. SMS

    SMS Guest

    It's actually a trade-off, according to Buchman. The faster charge takes
    better advantage of the available capacity, while reducing service life.

    "NiMH batteries which use the NDV method or the thermal cut-off control
    tend to deliver higher capacities than those charged by less aggressive
    methods. The gain is approximately 6 percent on a good battery. This
    capacity increase is due to the brief overcharge to which the battery is
    exposed. The negative aspect is a shorter cycle life. Rather than
    expecting 350 to 400 service cycles, this pack may be exhausted with 300
    cycles."

    Buchman's book was written before the advent of higher capacity AA
    cells. In the past, higher capacity cells meant larger cells, which
    could dissipate more heat. Now, the fast chargers have to have fans to
    prevent excessive temperature from destroying the cells. Also, now even
    the slower chargers are incorporating the more sophisticated
    end-of-charge detection, where he assumed in his book that the slower
    chargers were strictly based on time.

    Given the relatively low cost of NiMH batteries, perhaps it's a
    reasonable trade-off for fewer cycles in exchange for the higher capacity.
     
    SMS, Jul 5, 2007
    #21
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  2. SMS

    SMS Guest

    While they can't make the manual too complicated, it's also the case
    that the reason for the termination problem at the lower charge rate,
    was probably in the lower capacity cells where 0.33C would be way too
    low for the batteries to heat up enough for the temperature sensor to
    pick it up. The temperature rise is not linear with capacity, it's
    related to both capacity _and_ to the amount of heat that the battery
    can dissipate to the outside, which is relatively constant no matter
    what the capacity is.

    I've seen several recommendations for a minimum charge current of 0.5C,
    and it's always so that the end-of-charge can be detected via
    temperature. They picked the worst case in terms of being able to
    reliably detect end-of-charge, and went with it.
     
    SMS, Jul 5, 2007
    #22
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  3. SMS

    Wayne Guest


    I think you are making up conclusions which are not real.

    The Maha C-9000 does have a temperature sensor, and has a few means to
    terminate the charge, like say the 4000 mah total, but I really think its
    temperature sensor is a safeguard for much more extreme cases, and is not a
    factor at ordinary charge rates, which uses delta V, or least did initially.

    It will take some hours to go through it, but with regard to the C-9000, I
    would strongly suggest reading the several months at
    http://www.candlepowerforums.com/vb/showthread.php?t=140144
     
    Wayne, Jul 5, 2007
    #23
  4. I am referring to the statement; "a little high in terms of maximizing battery
    life, but not as bad as 2000mA"

    I am wondering what support you have for the value of 1350mA being a little
    high.

    It has been indicated in a lot of literature that the higher the charge rate
    the fewer life cycles one might expect, but what in particular indicates that
    1350mA is a little high? At 0.5C it may not be too high at all [and then, it
    may be].
     
    Thomas T. Veldhouse, Jul 5, 2007
    #24
  5. 3000 mAh charging capacity or 3000 mAh battery capacity? I say the latter.
    To charge a battery, you need more charging capacity than there is battery
    capacity due to heat losses. I believe those losses are in excess of 30%.
    Assuming such, it is therefor not going to be possible to charge a battery
    with greater than about 3000 mAh with a single charge cycle due to the fact
    that it cuts off at 4000 mAh charging capacity.

    I bought this charger as a future proof charger and since there are already
    batteries at 2900mAh available [granted, they are a real stretch on capacity]
    that threshold may be quickly exceeded.

    I see it as too low. Perhaps a better solution is something like 1.5x
    capacity and have the user select capacity. I can assure you that if there
    are ever 3200mAh NiMH batteries available and the charger hits the 4000mAh
    charge limit ... this baby will be going back to Maha ... even three years
    from now.
    I noticed that. The two hours were a surprise to me that prompted an email to
    Thomas Distributing, but it isn't a real issue so I never followed up with
    Maha.
     
    Thomas T. Veldhouse, Jul 5, 2007
    #25
  6. SMS

    SMS Guest

    The ΔV method would not have required the change from 0.33C to 0.5C.

    If you read the application notes from the various battery
    manufacturers, they often mention 0.5C in the context of the charge rate
    being high enough to raise the temperature of the batteries enough for
    the temperature sensor to detect the temperature change, both in dT/dt
    and absolute terms.
     
    SMS, Jul 5, 2007
    #26
  7. NiMH has a notoriously weak dV/dt. That is why they use both dV/dt and dT/dt.
    Even then certain cases may not be enough to trigger an obvious end of charge
    state, so most charges seem to use a time constraint. I think that since this
    charger has programmable charging current, setting a time constraint wasn't
    good enough, so they chose a capacity ceiling. However, 4000mAh at 2A in a
    1000mAh capacity AA battery is not likely a good idea, so I don't think this
    stop gap measure is a good one. Much better in my view is to allow the user
    to enter the battery capacity and and limit to 1.5x charging capacity.
     
    Thomas T. Veldhouse, Jul 5, 2007
    #27
  8. SMS

    ASAAR Guest

    How silly can you get. Not only silly but unbelievable. With
    your quest to find any possible AA drawback, inability to produce
    reliable chargers would have to be placed at the top of your list of
    AA negatives if you thought that it was even a remote possibility.
    I'm also certain that if someone had made the identical statement
    about having a drawer-full of Li-Ion chargers that don't work you
    wouldn't have given it any credibility at all.

    FWIW, I have well over a dozen chargers, many NiCd, some for NiCd
    and NiMH and they all still work perfectly. I once had a complex
    "smart" NiCd charger that one day started to only partially charge
    NiCd cells, but excessive heat wouldn't have been a cause. If one
    of today's 2,700mAh NiMH batteries could be charged in it, the
    charger would need about 16 hours to completely charge them.

    I also had a couple of RayOVac chargers that wouldn't reliably
    terminate charging, but that was only when used to charge their own
    "renewal" alkaline batteries. They were completely reliable
    charging NiCD AA and AAA cells, and they were low power, slow
    chargers, so heat was responsible for their problems. We also
    haven't heard innumerable reports of 15 and 30 minute NiMH chargers
    failing, but have had reports from several happy owners (I'm one)
    and they'd have the capacity to produce some really intense,
    destructive heat, so again, it's unlikely for heat to be responsible
    for being what "destroys chargers". All devices have their own
    failure rates, and it would be just as easy to say that Li-Ion
    chargers, or Nikon SLRs, or Canon DSLRs or GE air conditioners"seem
    to definitely be something that don't last forever" because you'll
    always be able to find a few owners of failed devices, some that
    even had multiple devices fail. As is usual for you, you wildly
    speculate but offer no evidence to back up such ludicrous guesses.
    We recognize your naive credulity and are eagerly awaiting the next
    of your fanciful "Tales From The Beyond".
     
    ASAAR, Jul 5, 2007
    #28
  9. SMS

    Guest Guest

    what's the best way to get it replaced - contact maha or thomas
    distributing?
     
    Guest, Jul 5, 2007
    #29
  10. SMS

    Wayne Guest

    I dont know, I have not done it, I only have the 0G0B01. But I'd guess Maha.
    Call each and ask them the procedure I guess, I dont think there are any
    issues. People discussing it have said they phoned Maha who then sent a
    replacement with a return mailer. However I'd guess that way may need a
    credit card number? Again, I have no experience with returns, but Maha
    really seems top notch.
     
    Wayne, Jul 5, 2007
    #30
  11. SMS

    Wayne Guest

    It is not a requirement, it will still charge as low as 200 ma, same as
    before.

    But the termination method is revised, and now it does say "Charging at a rate
    below 0.5C and above 1.0C is not recommended."
     
    Wayne, Jul 5, 2007
    #31
  12. SMS

    Wayne Guest

    dT/dt.


    Yes, it does, and sensing it at low charge current is the issue. And yes,
    the charger does have a temperature sensor and limit (and a total current
    sensor and limit), however it is still my opinion that this is only a
    fail-safe, and that temperature is not a factor in the delta V sensing
    problem. The design goal is to NOT heat the battery.

    We may be arguing chicken and egg.

    This page is not updated to the new G01B01 0.5C numbers:

    http://www.mahaenergy.com/store/mhc9000faq.asp

    but I read it to say that temperature sensing is only a factor when the delta
    V sensing was missed:


    Why is it not recommended to charge battery below 0.33C?

    When charging below 0.33C (except in BREAK-IN) mode, the batteries may not
    produce a sufficient end-of-charge signal for the charger to terminate
    correctly. Although the temperature sensors will safeguard battery
    overheating, lower charging rate might not cause enough heating in the
    batteries to trip the sensors.

    If low charging rate is desired, you should use the BREAK-IN mode. Charging in
    that mode is terminated by only time (1.6 times battery capacity) and
    temperature.
     
    Wayne, Jul 5, 2007
    #32
  13. SMS

    SMS Guest

    So it sounds like the dT/dt sensing _does_ determine end-of-charge
    (along with dV/dt), or they wouldn't have raised the minimum recommended
    current from 0.33C to 0.5C in order for the batteries to get warm enough
    to detect dT/dt. The fail-safe is the absolute temperature, not dT/dt.

    The design goal appears to be to produce enough heat to enable dT/dt
    sensing, but not enough heat to shorten the life of the battery. I guess
    they have a temperature sensor for each cell in the charger.

    It's not all that hard to use zero dV/dt for termination of charge, as
    you sense the voltage plateau that NiMH batteries achieve at the end of
    charge. When dV/dt=0 then you're done (on NiCad batteries it's negative
    dV/dt detection).

    Look at the data sheets for some of the charging chips, i.e. the BQ2003:

    "Primary Charge Termination Method (-)dV, dT/dt"

    But the MAX712 is:

    "Charge Termination Method: 0 deltaV, Max Temp, Max Time, Max V" but no
    dT/dt.

    Has anyone looked to see what chip is used in the Maha MH-C9000? I saw
    the pictures of it disassembled, but I didn't see which controller
    they're using.
     
    SMS, Jul 6, 2007
    #33
  14. SMS

    SMS Guest

    Here is the response:

    This is an automatically generated Delivery Status Notification

    Delivery to the following recipient failed permanently:



    Technical details of permanent failure:
    TEMP_FAILURE: Could not initiate SMTP conversation with any hosts:
    [maha-comm.com (1): Connection timed out]

    Too bad, but I think we got the answer and the reason anyway, it's the
    0.5C that's now the recommendation, and the 0.33C is no longer applicable.

    It's still the best charger out there for the battery hobbyist. There
    seem to be a large number of complaints about the La Crosse BC-900 in
    the various forums.

    It's nice to have a three year warranty, though it begs the question as
    to why they feel comfortable with a lifetime warranty on the MH-C401FS
    but not on the MH-C9000. I was never a big worrier about warranties, but
    there seem to be a lot of crappy, short-life chargers out there.
     
    SMS, Jul 7, 2007
    #34
  15. SMS

    John Turco Guest


    Hello, RJ:

    Personally, I have a Kodak K6100-C+A 1-hour charger, which included four
    AA Ni-MM cells (2500 mAh). Is your "K6000" truly a different model, or
    merely, a typo? <g>


    Cordially,
    John Turco <>
     
    John Turco, Jul 7, 2007
    #35
  16. SMS

    John Turco Guest

    ASAAR wrote:

    <edited>

    Hello, ASAAR:

    Hey, now, don't go knockin' GE's AC units! :p My AG_08 (8000BTU) has
    been going strong, with nary a hiccup, since 2000.

    Although, the summer of '04 was so cool, here in Omaha, that all of our
    house's air conditioners remained off, the entire year.

    Just turned them on, today (Friday, 7-6-07), for the first time in '07,
    alas.


    Cordially,
    John Turco <>
     
    John Turco, Jul 7, 2007
    #36
  17. SMS

    SMS Guest

    The K6000 had a switch for NiMH versus NiCad, while the K6100 did not.

    Neither is very good.
     
    SMS, Jul 7, 2007
    #37
  18. SMS

    Guest Guest

    Your results may vary.

    The KODAK is the first charger I've owned
    that fully charges NiMh batts within an hour.
    No fuss, no over-heating..... ( it turns itself off when it's done )

    On the other hand, I was sorely dissapointed with an
    "ENERGIZER" brand charger. You'd think that
    battery people would know how to do these things......
    <rj>
     
    Guest, Jul 7, 2007
    #38
  19. I suspect the reason they don't offer a lifetime warrentee on the C9000 as
    well is because of the discharge capability. The resister is probably more
    likely to fail than other components.
     
    Thomas T. Veldhouse, Jul 9, 2007
    #39
  20. SMS

    John Turco Guest


    Hello, RJ:

    I agree; my Kodak K6100 has been superb, thus far.


    Cordially,
    John Turco <>
     
    John Turco, Jul 9, 2007
    #40
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