Testing the mah rating
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Thread: Testing the mah rating

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    Default Testing the mah rating

    Does anyone know of a way to test the mah rating of a battery ??? Say an EGO battery , say some one tells you it's 1100 mah , and in reality , it's only a 650 mah . Is there a way to test them , to find out ????
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    Well, there's no easy way - that's for sure.

    The rating is an expression of the amount of time it takes to drain a battery by using a known load. It should be do-able but finicky.

    Do a thread search - I seem to recall some time back there was a suggestion that one could get a rough idea by firing an atty of known resistance in 5 second bursts and counting these 'pulses' until the battery worked no more.
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    That is pretty much it, operate it under load over a period of time to see if the math works.

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    Or do it backwards, as if that's possible with the Ego.
    Drain the battery completely and see how long it takes to fully charge.

    Then there's also the obvious, how it looks.
    A 650 mAh battery is shorter then a 1100mAh battery.
    EGO Battery Sizes
    650mAh= 72mm
    900mAh= 87mm
    1000mAh=97mm

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    Quote Originally Posted by Eddie.Willers View Post
    Well, there's no easy way - that's for sure.

    The rating is an expression of the amount of time it takes to drain a battery by using a known load. It should be do-able but finicky.

    Do a thread search - I seem to recall some time back there was a suggestion that one could get a rough idea by firing an atty of known resistance in 5 second bursts and counting these 'pulses' until the battery worked no more.
    Quote Originally Posted by Duekster View Post
    That is pretty much it, operate it under load over a period of time to see if the math works.
    But I thought that was some of the Mystery to mAh.

    What load is it being tested under and does Everyone use the Same Load when they come up with their mAh Rating?

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    Quote Originally Posted by zoiDman View Post
    But I thought that was some of the Mystery to mAh.

    What load is it being tested under and does Everyone use the Same Load when they come up with their mAh Rating?

    Actually, to determine the amp-hour (or in this case, milliamp-hour) rating of a battery all you need to know is how much current the battery supplied (in amps) over what time (in hours). Having a known resistance in this circuit doesn't help you, because the voltage will drop as the battery discharges, thus any calculation you make with ohm's law will not be accurate.

    For determining the ACTUAL mah of your battery, I would reccomend you fire the battery with your meter in dc current mode, leads in series with the circuit over a 2 ohm resistor, and time it. That would get you close.
    For truly accurate capacity measurement a low resistance bar of known resistance per square mm (also called a shunt) is preferred - however this is not advisable with Lithium-Ion batteries, unless you have a very controlled lab set up.

    Hope that helps.

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    To test the mah rating you'd have to put a fully charged battery under a known load until it is completely drained. An eGo battery, or a protected battery of any type will cut off when the voltage drops to a pre-set level. Therefore, you'd have to remove the protection circuit in order to test this type of cell. That wouldn't be adviseable with a li-ion cell.

    As an example, if you start with a 1000 mah battery at full charge and put a 10 mah drain on it, it should take 100 hours to completely discharge. If it takes 80 hours, well you've got an 800 mah battery instead of a 1000 mah.

    That's the theory anyway. Other factors can influence your reading such as temperature, or age of the cell.
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    Quote Originally Posted by DarkAynjil View Post
    ... Having a known resistance in this circuit doesn't help you, because the voltage will drop as the battery discharges, thus any calculation you make with ohm's law will not be accurate. ...

    Hope that helps.
    Thanks, it does.

    Yeah, that’s where those God Awful Differential Equations come in.

    Since the Voltage Rate of Change from say 4.2v ~ 3.3 volts is Non-Linear, the Dif-Eq will probably be Nasty at Best.


    Quote Originally Posted by cskent View Post
    To test the mah rating you'd have to put a fully charged battery under a known load until it is completely drained. An eGo battery, or a protected battery of any type will cut off when the voltage drops to a pre-set level. Therefore, you'd have to remove the protection circuit in order to test this type of cell. That wouldn't be adviseable with a li-ion cell.

    As an example, if you start with a 1000 mah battery at full charge and put a 10 mah drain on it, it should take 100 hours to completely discharge. If it takes 80 hours, well you've got an 800 mah battery instead of a 1000 mah.

    That's the theory anyway. Other factors can influence your reading such as temperature, or age of the cell.
    So If the Same 1,000 mAh Battery was tested at 20 mAh, would the Discharge time be Exactly one half the time of what it was when tested at 10 mAh?

    If it does then I think I'm getting this.

    I guess I should have paid more Attention in those EE classes instead of checking out the Undergrad next to me in the Short Skirts back in the 70’s.

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    There is the aspect of the chemical power source dropping off the E as it discharges but other wise it is straight math with a known load and time.

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    Quote Originally Posted by Duekster View Post
    There is the aspect of the chemical power source dropping off the E as it discharges but other wise it is straight math with a known load and time.
    If I'm understanding this correctly.

    The Straight math part is put a Constant Load on the Battery and then Time how long it takes the Battery to go from Full Charge to Full Discharge.

    Then Multiply the mAh times the number of Hours

    Correct?

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