you know how they have the battery capacity... in mAh... how do they determine that? multimeter? 
i didn't do too well in physics, as you can tell
i didn't do too well in physics, as you can tell
How do they rate batteries?
- Thread starter gopunk
- Start date
well the construction of a batterry determines the theoretical output, then they test them to make sure they do what they are supposed to, and pitch the bad ones or put a generic label on them and sell them for cheaper.
btw a multimeter would do it, but mine doesnt test current, just voltage and resistance. (cheap walmart multimeter)
btw a multimeter would do it, but mine doesnt test current, just voltage and resistance. (cheap walmart multimeter)
mAh is not milliamp per hour.
it's milliamp-hour, as in multiplication, not per unit time
so it's more like the ability to draw 1600 milliamps for one hour.
it's like the difference between a lightyear, and 300million meters per second. One is a finite distance (ie. battery life) and one is simply a rate.
edit: BTW, even if you have an el-cheapo multimeter, using the simple rule V=IR will allow you to measure current using a known resistor.
-patchy
it's milliamp-hour, as in multiplication, not per unit time
so it's more like the ability to draw 1600 milliamps for one hour.
it's like the difference between a lightyear, and 300million meters per second. One is a finite distance (ie. battery life) and one is simply a rate.
edit: BTW, even if you have an el-cheapo multimeter, using the simple rule V=IR will allow you to measure current using a known resistor.
-patchy
<< mAh is not milliamp per hour.
it's milliamp-hour, as in multiplication, not per unit time
so it's more like the ability to draw 1600 milliamps for one hour.
it's like the difference between a lightyear, and 300million meters per second. One is a finite distance (ie. battery life) and one is simply a rate.
edit: BTW, even if you have an el-cheapo multimeter, using the simple rule V=IR will allow you to measure current using a known resistor.
-patchy >>
Of cource the down side of this dtest is it will drain the battery!:Q
I read that the cheaper batteries are basically the same as duracell and energizer. I just buy the cheapest ones for medium drain items like Radios and the like. I buy energizer for my remotes every year weather they need it or not.
maybe i'm just slow, but with a multimeter how would i be able to get the "hour" part? i can understand the current... but not sure how to translate that into mAh. thanks...
the most definitive way to test a battery is to use it!
usually the big name companies like enercell have mAh ratings for all their batteries. however..they dont tell you how well the battery holds up for large drain applications like digital cameras.
the basic comparison for disposable batteries.
standard non-alkaline < standard alkaline < good alkaline < ultra duracell or energizer e^2 < lithium AA
then theres tons of comparisons for rechargable. usually nicad < nimh < lithium
the in nimh range, the usual comparison is mAh rating. the cheapo ones rate at 1200mAh and the expensive ones are 1600+ mAh. many digital camera sites rate nimh batteries for ya.
to measure mAh definitively..you have to use the battery in its standard operating environment. measure current draw in mA and multiply by the amount of hours it lasts. lithium and alkaline have higher mAh than nimh, yet only work well in low current draw devices.
another thing is...batteries in series do not increase their mAh rating. that is..two 1600 mAh batteries in series does not provide 3200mAh.
usually the big name companies like enercell have mAh ratings for all their batteries. however..they dont tell you how well the battery holds up for large drain applications like digital cameras.
the basic comparison for disposable batteries.
standard non-alkaline < standard alkaline < good alkaline < ultra duracell or energizer e^2 < lithium AA
then theres tons of comparisons for rechargable. usually nicad < nimh < lithium
the in nimh range, the usual comparison is mAh rating. the cheapo ones rate at 1200mAh and the expensive ones are 1600+ mAh. many digital camera sites rate nimh batteries for ya.
to measure mAh definitively..you have to use the battery in its standard operating environment. measure current draw in mA and multiply by the amount of hours it lasts. lithium and alkaline have higher mAh than nimh, yet only work well in low current draw devices.
another thing is...batteries in series do not increase their mAh rating. that is..two 1600 mAh batteries in series does not provide 3200mAh.
i see...
anybody know of any battery intensive tests? i would say my cd player, but the batts last for 72 hours on that thing, so that's a no go. my digital camera is also fairly good about batteries... i'm just looking for something that'll drain my batteries fairly quickly without my supervision (like i could use my game gear but then i'd have to play it....)
btw... is it generally assumed then, that current stays current for the span of the battery's life? or do they graph it and take the area under the curve...
anybody know of any battery intensive tests? i would say my cd player, but the batts last for 72 hours on that thing, so that's a no go. my digital camera is also fairly good about batteries... i'm just looking for something that'll drain my batteries fairly quickly without my supervision (like i could use my game gear but then i'd have to play it....)
btw... is it generally assumed then, that current stays current for the span of the battery's life? or do they graph it and take the area under the curve...
This is almost a highly technical forum topic...
mAh ratings are probably black magic to some degree. I'm not sure there is an ISO or ANSI spec or something that tells companies EXACTLY how to rate batteries....
But for NiCd and NiMH batteries... the mAh rating is a measurement of how long the battery will "last" with a certain current draw. Let's say the measurement spec is the following:
1) Charge the battery fully (using some voltage/temp peak detection method... )
2) Apply XX mA of current...
3) Consistantly monitor the battery voltage...
4) Record the elapsed time at which the battery dropped below Y.ZZ Volts.
The mAh rating is likely not the "steadiest" measure... becuase the battery companies probably use a relatively low current, and relatively low voltage to which the batteries can discharge.... but this voltage level may be too low for your application to operate at... and the current may be different.
At a very high current draw, the battery will heat up and cause the capacity to diminish faster (due to heat and chemical changes)... so the mAh rating will probably go down at a high temp.
Just things to think about....
mAh ratings are probably black magic to some degree. I'm not sure there is an ISO or ANSI spec or something that tells companies EXACTLY how to rate batteries....
But for NiCd and NiMH batteries... the mAh rating is a measurement of how long the battery will "last" with a certain current draw. Let's say the measurement spec is the following:
1) Charge the battery fully (using some voltage/temp peak detection method... )
2) Apply XX mA of current...
3) Consistantly monitor the battery voltage...
4) Record the elapsed time at which the battery dropped below Y.ZZ Volts.
The mAh rating is likely not the "steadiest" measure... becuase the battery companies probably use a relatively low current, and relatively low voltage to which the batteries can discharge.... but this voltage level may be too low for your application to operate at... and the current may be different.
At a very high current draw, the battery will heat up and cause the capacity to diminish faster (due to heat and chemical changes)... so the mAh rating will probably go down at a high temp.
Just things to think about....
thanks for the info cooper.
if i'm understanding correctly then, other than the heat factor, the sole factor in discrepancy between ratings is the voltage they choose to cut off at? the way i figure is because the current and time are inversely proportional, so choosing a high or low current (as long as it doesn't heat up like you said) shouldn't really matter, right?
let me know if i'm way off or something...
if i'm understanding correctly then, other than the heat factor, the sole factor in discrepancy between ratings is the voltage they choose to cut off at? the way i figure is because the current and time are inversely proportional, so choosing a high or low current (as long as it doesn't heat up like you said) shouldn't really matter, right?
let me know if i'm way off or something...
ahh..reminds me of circuits from 3 years back.
depending on your battery, you can test it a few different ways. if it is a NIMH or NICAD battery, its easier to test it with a digital camera. the most laymen way to test it would be to see how many pictures you can take with flash, and compare it with another set of batteries that have a known rating (1600mAh) and a known number of pictures you can take before camera doesnt work. now this method isnt highly scientific but it is the easiest way to gauge approximate battery capacity.
for an alkaline battery, you have to sacrifice the battery to run tests on. best is to read up on manufacturers datasheets.comprehensive data on energizer
the more scientific way to do it...would be something like the following.
1) place ammeter (multimeter) in series with battery and electrical device like a bright flashlight or anything that can deplete the battery to low levels in 8 hours or less.
2) measure current draw (in mA) every half hour till device ceases to function acceptably.
3) graph current draw versus time. area under graph is approximate mAh rating.
now..if you chose to 'apply' a current and watch the voltage of the battery, you must do some other things. you can not be sure of what the current is at any given moment in time. current is not constant with a fixed resistance and variable voltage as you know from V = IR. you can however, watch the voltage drop and measure the resistance of the device to calculate the current. you can chose to measure voltage across battery under load or current draw under load depending on your setup.
if you want to know in detail what the graphs may look like..check out the datasheets i linked in this post. they have graphs for all batteries under constant resistance, constant current, or different temperatures.
depending on your battery, you can test it a few different ways. if it is a NIMH or NICAD battery, its easier to test it with a digital camera. the most laymen way to test it would be to see how many pictures you can take with flash, and compare it with another set of batteries that have a known rating (1600mAh) and a known number of pictures you can take before camera doesnt work. now this method isnt highly scientific but it is the easiest way to gauge approximate battery capacity.
for an alkaline battery, you have to sacrifice the battery to run tests on. best is to read up on manufacturers datasheets.comprehensive data on energizer
the more scientific way to do it...would be something like the following.
1) place ammeter (multimeter) in series with battery and electrical device like a bright flashlight or anything that can deplete the battery to low levels in 8 hours or less.
2) measure current draw (in mA) every half hour till device ceases to function acceptably.
3) graph current draw versus time. area under graph is approximate mAh rating.
now..if you chose to 'apply' a current and watch the voltage of the battery, you must do some other things. you can not be sure of what the current is at any given moment in time. current is not constant with a fixed resistance and variable voltage as you know from V = IR. you can however, watch the voltage drop and measure the resistance of the device to calculate the current. you can chose to measure voltage across battery under load or current draw under load depending on your setup.
if you want to know in detail what the graphs may look like..check out the datasheets i linked in this post. they have graphs for all batteries under constant resistance, constant current, or different temperatures.
damn.. I always thought NiMH batteries would have much closer mah ratings compared to alkaline than they do... AA Alkaline: 2850mah.. AA NiMH: 1600mah
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