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Thread: What's the Best Battery Charger?

  1. #46
    Senior Member DougPaul's Avatar
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    Quote Originally Posted by LivesToHike View Post
    Regardless, both these chargers appeared to have overheated cells. The cells are still very warm when the charger has finished, giving me the impression that the charger hasn't really shutdown charging, or that the trickle charge really isn't a trickle. I've never measured the current draw, but that would be easy to do if I wanted to know.
    In general, the cells get quite warm in the last bit of charging.

    In the early part of charging, most of the charging energy is absorbed in chemical changes in the cell (ie the charging). Once the chemical changes have completed (ie the cell is fully charged), most of the charging energy goes into heating the cell. The resulting increase in temp can be used to terminate charging if the charger has a temp sensor. It also causes the voltage across the cell to drop slightly which is also used as a cue to terminate charging. (Most smart chargers switch to a slow trickle rate (typ <= ~50mA) rather than completely stop charging.)

    So a certain amount of heating is normal, but too much is not.

    The above is why you want a smart charger--it knows when to stop charging. If it does not stop the cell will ultimately overheat. (This is why timer-based chargers are bad--the user has no way of knowing the proper charging time and eventually the cells will be damaged by overcharging and overheating after the user has overestimated the time.)

    BTW, charging too slow is also not the best for NiMH cells--the reactants develop a poor crystal structure and do not work as well as they should. A charging rate of ~.2C to ~.5C is best, but it must be stopped before the cell becomes overcharged.


    The MH-C401fs charger has a switch for fast (1000mA ~ .5C ~ 2hr) or slow (300mA ~.2C ~ 5hr) charge rates--a nice feature, IMO. I normally use slow to be more gentle to the cells unless I am in a hurry. (I've seen no evidence that the fast setting has damaged any of my cells.) A number of other chargers also have selectable charging rates.

    If you have the Ray-o-Vac PS-4 charger, just use it on the NiCad setting for NiMH cells (900mA ~ 2hr rate) and it should be fine. (The NiMH setting is a 1800mA ~ 1hr rate.)

    BTW, for typical NiMH AA cells (2000mAh--2700mAh):
    2hr rate ~ .5C ~ 1000mA
    4hr rate ~ .25C ~ 500mA
    trickle <= ~.02C ~ 50mA

    A nice reference on charging NiMH and NiCad batteries is http://www.batteryuniversity.com/partone-11.htm

    Doug
    Last edited by DougPaul; 03-10-2010 at 05:05 PM.

  2. #47
    Senior Member LivesToHike's Avatar
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    Quote Originally Posted by DougPaul View Post
    In general, the cells get quite warm in the last bit of charging.

    In the early part of charging, most of the charging energy is absorbed in chemical changes in the cell (ie the charging). Once the chemical changes have completed (ie the cell is fully charged), most of the charging energy goes into heating the cell. The resulting increase in temp can be used to terminate charging if the charger has a temp sensor. It also causes the voltage across the cell to drop slightly which is also used as a cue to terminate charging. (Most smart chargers switch to a slow trickle rate (typ <= ~50mA) rather than completely stop charging.)

    So a certain amount of heating is normal, but too much is not.

    The above is why you want a smart charger--it knows when to stop charging. If it does not stop the cell will ultimately overheat. (This is why timer-based chargers are bad--the user has no way of knowing the proper charging time and eventually the cells will be damaged by overcharging and overheating after the user has overestimated the time.)

    BTW, charging too slow is also not the best for NiMH cells--the reactants develop a poor crystal structure and do not work as well as they should. A charging rate of ~.2C to ~.5C is best, but it must be stopped before the cell becomes overcharged.


    The MH-C401fs charger has a switch for fast (1000mA ~ .5C ~ 2hr) or slow (300mA ~.2C ~ 5hr) charge rates--a nice feature, IMO. I normally use slow to be more gentle to the cells unless I am in a hurry. (I've seen no evidence that the fast setting has damaged any of my cells.) A number of other chargers also have selectable charging rates.

    If you have the Ray-o-Vac PS-4 charger, just use it on the NiCad setting for NiMH cells (900mA ~ 2hr rate) and it should be fine. (The NiMH setting is a 1800mA ~ 1hr rate.)

    BTW, for typical NiMH AA cells (2000mAh--2700mAh):
    2hr rate ~ .5C ~ 1000mA
    4hr rate ~ .25C ~ 500mA
    trickle <= ~.02C ~ 50mA

    A nice reference on charging NiMH and NiCad batteries is http://www.batteryuniversity.com/partone-11.htm

    Doug
    Doug, Thanks for your follow-up message - esp about the short charging for NiMH cells.

    I'm fairly certain my Ray-o-Vac is not the PS-4 model, I think what I have instead is a fairly dumbed-down NiCad/NiMH battery charger.

    Great reference article! The most telling quote in the article you referenced was: "The battery should cool to room temperature when on trickle charge. If the temperature remains above room temperature after a few hours in ready mode, the charger is performing incorrectly."

    I'm fairly certain my batteries are very warm to the touch after they've 'finished' charging and are on trickle charge. I'm convinced that my existing charger is doing the wrong thing.

    --Mike
    --- Help stamp out entropy!

  3. #48
    Senior Member DougPaul's Avatar
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    Quote Originally Posted by LivesToHike View Post
    I'm fairly certain my Ray-o-Vac is not the PS-4 model, I think what I have instead is a fairly dumbed-down NiCad/NiMH battery charger.
    My PS-4 says "PS4" on the bottom.

    Great reference article! The most telling quote in the article you referenced was: "The battery should cool to room temperature when on trickle charge. If the temperature remains above room temperature after a few hours in ready mode, the charger is performing incorrectly."

    I'm fairly certain my batteries are very warm to the touch after they've 'finished' charging and are on trickle charge. I'm convinced that my existing charger is doing the wrong thing.
    That sounds like the "trickle" is too high a current or the charger has not detected a full cell and is continuing to supply a full charging current. Either can damage NiMH cells. As noted in one of my earlier posts, a NiCads can take a higher trickle current than NiMH so a possible cause of a high trickle current is mis-auto-cell-type determination or just bad design of the charger.

    FWIW, I generally remove the cells from the charger as soon as I notice that the charger is indicating "full charge".

    Doug

  4. #49
    Senior Member DougPaul's Avatar
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    I have seen reports that a number of LaCrosse BC-900/BC-9009 chargers have overheated both the charger and the cells including melting some of the plastic, often described as a meltdown. There is some evidence that the problem was fixed in firmware versions v35 and v36. (The version number is visible on the right at turn-on.) As such, I am rescinding my recommendation of the BC-900 charger.

    FWIW, I have had no problem with mine so far (v35 firmware). However, I always run a fan on mine when using them because some of the cells used to get a bit hot during charging. I have no idea whether the fan will prevent the problem, should it occur.

    For more info, see http://www.candlepowerforums.com/vb/...d.php?t=253907. This link is a survey and shows reports for a variety of models and firmware versions.

    A search brings up lots of reports: http://www.google.com/search?as_q=la...owerforums.com

    I'm still researching the issue.

    Doug

  5. #50
    Senior Member psmart's Avatar
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    Quote Originally Posted by DougPaul View Post
    I have seen reports that a number of LaCrosse BC-900/BC-9009 chargers have overheated both the charger and the cells including melting some of the plastic, often described as a meltdown. There is some evidence that the problem was fixed in firmware versions v35 and v36.
    Doug
    FWIW, my BC-9009 has been trouble free with v35. There was a power supply recall and replacement due to overvoltage problems - sounds like this could be related to the overheating.

  6. #51
    Senior Member TomK's Avatar
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    Any update on this subject?

    Thinking about getting a decent set of rechargable batteries and a charger for them.

    Mostly for a Garmin GPSmap 62S - I use it about 6 hours a week. Been using 2500 mAh NiMh AA's charged using a Radio Shack charger that charges either 2 or 4 at a time, feeds each pair 170 mA and turns itself off after 13.5 hours. So, per the instructions, I charge for 4 hours, reset it, and run it the remaining 13.5 hours until it turns itself off to get the 17.5 hours of charging that the instructions tell me these batteries need.

    But the batteries are at least 5 years old now, have gone through a fair number of charge/discharge cycles. Today I went through 3 (!) pairs in about 2 hours, which tells me that they aren't holding a charge well anymore, and I really need to replace them. The cold temps today may also have something to do with that.

    Thinking I ought to spring for one of those fancy chargers that charge each cell independantly, can charge/discharge, analyse etc. Would rather buy quality and cry once. Prefer a charger that is gentle on the cells, and won't harm them. Don't really need to charge quickly, happy to let the charger take it's time if that is better for the batteries. Don't need to charge more than 4 cells at a time.

    The info in this thread is close to 10 years old - any developments folks ought to know about?

    Besides a charger recomendation, suggestions for the batteries themselves?

    Also, where might I actually go to see/purchase - I'd rather make the purchase in person than over the internet (I'm weird that way). Lowes/Home Depot? Best Buy? Someplace I hadn't thought of? Was thinking of a road trip to U Do It in Needham, but thier web site doesn't seem to show much in this area...

    Thanks in advance...

    TomK
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    High on my hills of dream, dear hills that know me/And then how fair will seem the lands below me
    How pure at vesper time, the far bells chiming/God, give me strength to climb, and hills for climbing. "Hills" - Arthur Guiterman

  7. #52
    Senior Member DougPaul's Avatar
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    The advice in this thread is still basically sound. A smart charger that charges the cells individually at a moderate rate is best for the cells. (Low charging rates may seem to be gentler but are not best for the cells. Too high a charging rate will overheat them.)

    FWIW, I have standardized on the lower capacity (2000 mAh for AA, 800 mAh for AAA) Eneloop low-discharge cells. They have a longer lifetime (more cycles) and are more (electrically) rugged than the higher capacity models. I use these cells in both my headlamps and GPSes. (My spares are more of the same and/or lithium non-rechargables.)

    My main workhorse charger is still the Maha MH-C401FS. Recently bought another one...


    BTW, there are temp limits for charging both NiMH and lithium-ion rechargables--they should be kept between 32F (0C) and 113F (45C) when charging. The discharge range is larger. https://batteryuniversity.com/index....w_temperatures

    Doug
    Last edited by DougPaul; 11-09-2019 at 11:21 AM.

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