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Thread: Standard charge of NiMH, IEC 61951-2.

  1. #1

    Default Standard charge of NiMH, IEC 61951-2.

    Hello, no offense to anyone, but I'm calling the aid of the likes of SliverFox, or perhaps HKJ, the ones I've seen plenty of on these forums. :-D Of course, any and all others are more than welcome to chime in. :-D

    The standard charge is, for NiMH, 0.1C for 16 hours. It's stated on all sheets provided with cells you buy, even sometimes printed upon them.

    I'm usually in no big hurry, I have cells to spare, I have my trusted C9000. Is the "standard charge" a "measurement only" type of thing, or is it a true and tested good way of charging if time is not an issue?

    I've read all I've found, but haven't reached a conclusion on this. Is the overcharge something to care about? Is the "smart chargers" just a quick fix to speed up time, or do they also gain something by not over charging and terminating more properly?

    If over charging is not an issue at those small Ampereges, then why don't we all just always do a standard charge, and get the full bucket load of charge into our cells?

    Regards,
    /Dennis, (with all the time in the world. :-D )

  2. #2

    Default Re: Standard charge of NiMH, IEC 61951-2.

    That standard charge is when you have what I refer to as a dummy charger, that is one that will continuously put current into the battery for as long as the battery is plugged in. Obviously the math says that .1 C for 16 hours would be the equivalent of 1.6 times the rated capacity of the battery. The best way to charge those cells would be with a charger that has peak detection. Peak detection will monitor the voltage of the battery as it charges. As the battery charges, the voltage will climb until the battery reaches full charge. Once the battery reaches full charge, the voltage will start to come down, even though the charger is still charging it. The charger is watching for this and it knows that now is the time to shut off the charger. As a general rule, the slower you charge your batteries, the more complete the charge they will take. That standard charge isn't the best way to maintain your batteries. Especially since the idea behind NiMh is that they have no memory and can be charged from a partially discharged state. If the batteries are only half dead, they only need half a charge. Without peak detection, you're just guessing when the batteries are done.

  3. #3
    Enlightened
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    Default Re: Standard charge of NiMH, IEC 61951-2.

    I don't like to leave NiMH batteries charging when no-one is home.

    My Opus BT-C2000 and MH-C9000 chargers apply 115% - 125% of the battery's rated capacity when they are depleted down to about 1.0 volts.

    The attached image has been modified to make it somewhat easier to understand the IEC 61951-2 standardized endurance test procedure.


  4. #4
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    Default Re: Standard charge of NiMH, IEC 61951-2.

    Hello Dennis,

    Let's back up a moment...

    Pretend I am a battery manufacture. I come up with a battery that has higher capacity, but when the RC crowd tests it the performance is not up to what is expected. Now I am trying to figure out what the problem is. I make a few changes and now the flashlight people are complaining about the performance.

    I "discover" that everyone is charging differently and the currents during use vary widely. What is needed is a uniform way to compare. I discuss this with my scientists and we work to develop a standard.

    Capacity is settled on as a measuring metric. The engineers figure out the best way to get the most capacity into the battery and everyone agrees. Now we have a standard for charging.

    Using the charging standard I can do some discharge testing and come up with an estimate for cycle life.

    If you purchase my batteries and use them according to the standard you can expect my declared capacity and number of charge/discharge cycles. You can compare other batteries using the same criteria and see if you can find a deal on the batteries you want to purchase.

    OK, back to the real world.

    The people that use batteries appreciate the standard, but have discovered that different charging methods favor the performance under differing use patterns. In addition many people prefer to stockpile fewer batteries in exchange of rapid charging. Charging a battery in 2 - 3 hours is much easier to attend to than having to attend to a 16 hour charge.

    The price for this convenience is a slight reduction in cycle life. Since the cost of replacement batteries is low, this seems like a worthwhile trade off.

    The caveat to this is that the standard was formulated using conventional batteries. With the introduction of low self discharge chemistry, the extended charge may be damaging them. In the past, chargers were available that would first discharge the battery followed by a standard charge but that adds to the charging time and subjects the battery to a complete charge/discharge cycle with every charge. If you are only partially using the capacity of the battery, why not just partially charge it back up to replace what you used?

    I use the standard charge to check the health of my batteries. When the capacity drops below 80% of its original capacity it is time for replacement. I try to limit the number of standard charges on low self discharge batteries and try to make sure they go through a discharge cycle prior to the standard charge.

    I hope this adds to your perspective.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  5. #5

    Default Re: Standard charge of NiMH, IEC 61951-2.

    Quote Originally Posted by SilverFox View Post
    Hello Dennis,

    Let's back up a moment...

    Pretend I am a battery manufacture. I come up with a battery that has higher capacity, but when the RC crowd tests it the performance is not up to what is expected. Now I am trying to figure out what the problem is. I make a few changes and now the flashlight people are complaining about the performance.

    I "discover" that everyone is charging differently and the currents during use vary widely. What is needed is a uniform way to compare. I discuss this with my scientists and we work to develop a standard.

    Capacity is settled on as a measuring metric. The engineers figure out the best way to get the most capacity into the battery and everyone agrees. Now we have a standard for charging.

    Using the charging standard I can do some discharge testing and come up with an estimate for cycle life.

    If you purchase my batteries and use them according to the standard you can expect my declared capacity and number of charge/discharge cycles. You can compare other batteries using the same criteria and see if you can find a deal on the batteries you want to purchase.

    OK, back to the real world.

    The people that use batteries appreciate the standard, but have discovered that different charging methods favor the performance under differing use patterns. In addition many people prefer to stockpile fewer batteries in exchange of rapid charging. Charging a battery in 2 - 3 hours is much easier to attend to than having to attend to a 16 hour charge.

    The price for this convenience is a slight reduction in cycle life. Since the cost of replacement batteries is low, this seems like a worthwhile trade off.

    The caveat to this is that the standard was formulated using conventional batteries. With the introduction of low self discharge chemistry, the extended charge may be damaging them. In the past, chargers were available that would first discharge the battery followed by a standard charge but that adds to the charging time and subjects the battery to a complete charge/discharge cycle with every charge. If you are only partially using the capacity of the battery, why not just partially charge it back up to replace what you used?

    I use the standard charge to check the health of my batteries. When the capacity drops below 80% of its original capacity it is time for replacement. I try to limit the number of standard charges on low self discharge batteries and try to make sure they go through a discharge cycle prior to the standard charge.

    I hope this adds to your perspective.

    Tom
    Hi Tom, and Yes, this thourough answer is exactly what I was after to add to my perspective.
    I'm all with you in your fine description on why and how the "standard charge" came to be.

    I'm there too, with LSDs, I had a hunch that this is not the way to go, I'm not using Powerex standards anymore, but I'm at the same time curious, so if you say as you do that a standard charge is a measurement only for LSDs then that is what it is for me too now, going forward. I don't care about the price for a single cell, I'm just a bit nerdy that way.

    Right now I'm nurturing a 1300 Duracell cell, its companion in the 2-pack shows a healthy +1300 on a standard charge, but this poor thing gets worse and worse the more I charge it. :-D Still 1200+ but just barely, but a standard charge does not help it, I almost get More out of it with a refresh and analyse on my C9000.

    And yes, I don't standard charge my cells just because I can, but when I do, I always discharge them first.

    Thanks Tom.

    Regards,
    /Dennis
    Last edited by SweD; 01-22-2018 at 06:17 PM.

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