converting ac adapter to battery charger
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converting ac adapter to battery charger
is it possible to convert an ac adapter to a battery charger? if so, how would you do it?
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just hook it up to your battery. (assuming it is outputting DC, which many 'AC' adapters do. if you are getting AC then you need a rectifier)
its voltage needs to be maybe 1 or 2v higher than your battery's, but higher is fine, to a point. the higher the adapter voltage the more current you are going to be pumping into your batteries. some batteries dont like very high currents though. so immediately measure the current.
you should be aiming for 1/3 the battery's mAh rating in current or less. so dont be putting 2A into a 1800mAh rechargeable AA battery, you are probably going to a'splode it. something like 600mA is more acceptable (for fast charging).
if you are fast charging, you have to know the battery capacity as well as the current. do the math (mAh/mA = h) to figure out how long to charge it for. then stop it when its done. if you dont stop it, it will probably asplode. if the batteries are getting hot then they are done. in the previous example it should take about 3 hours.
you could also trickle charge it, which means to give it a very low current, like maybe 60mA (all these numbers are assuming a AA NiMh battery). on trickle charge there is no risk of breaking your batteries, and you could leave them on there even after they are fully charged and still be ok. (but still, its best not to just leave them for a week). im not sure exactly how to accomplish this with minimal parts, but methinks that a resistor in series with the battery should do the trick. typical charge time is on the order of 24 hours. this method is easy on your batteries and might extend their life a bit.
you could also CV (constant voltage) charge it, where you put the DC from your adapter through a voltage regulator like an LM317. the 317 is adjustable, so just set it to 1.3v (for a 1.2v battery, which actually hits about 1.35v on a full charge) and let it do its thing. the current will be high at first, but the last leg of the charge will take excruciating long as the current approaches zero (or some acceptable trickle-charge level)
thats about all you can do for free, if you were expecting some fancy automatic charger than you are out of luck.
i personally havent tried any of these methods except some dabbling with fancy power supplies and lithium batteries. do at your own risk, blah blah blah.
its voltage needs to be maybe 1 or 2v higher than your battery's, but higher is fine, to a point. the higher the adapter voltage the more current you are going to be pumping into your batteries. some batteries dont like very high currents though. so immediately measure the current.
you should be aiming for 1/3 the battery's mAh rating in current or less. so dont be putting 2A into a 1800mAh rechargeable AA battery, you are probably going to a'splode it. something like 600mA is more acceptable (for fast charging).
if you are fast charging, you have to know the battery capacity as well as the current. do the math (mAh/mA = h) to figure out how long to charge it for. then stop it when its done. if you dont stop it, it will probably asplode. if the batteries are getting hot then they are done. in the previous example it should take about 3 hours.
you could also trickle charge it, which means to give it a very low current, like maybe 60mA (all these numbers are assuming a AA NiMh battery). on trickle charge there is no risk of breaking your batteries, and you could leave them on there even after they are fully charged and still be ok. (but still, its best not to just leave them for a week). im not sure exactly how to accomplish this with minimal parts, but methinks that a resistor in series with the battery should do the trick. typical charge time is on the order of 24 hours. this method is easy on your batteries and might extend their life a bit.
you could also CV (constant voltage) charge it, where you put the DC from your adapter through a voltage regulator like an LM317. the 317 is adjustable, so just set it to 1.3v (for a 1.2v battery, which actually hits about 1.35v on a full charge) and let it do its thing. the current will be high at first, but the last leg of the charge will take excruciating long as the current approaches zero (or some acceptable trickle-charge level)
thats about all you can do for free, if you were expecting some fancy automatic charger than you are out of luck.
i personally havent tried any of these methods except some dabbling with fancy power supplies and lithium batteries. do at your own risk, blah blah blah.
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