Hi
I have been told some where that you can charge a battery from a higher voltage then the battery its self
is this true and if so I want to charge some mobile phone batteries up from a 12V car battery direct

Thanks
Batista230

 

You need to learn about charging batteries before you cause a Ni-Cad or Ni-MH battery to explode or a Lithium battery to catch on fire.

Use a battery charger IC.

 

Some batteries can't be recharged, and for the ones that can, charging follows different parameters. The site at the link has good information - http://www.batteryuniversity.com/

 

For 12v the simplest way would be to get a voltage regulator such as an LM31T and choose the resistor to make it output exactly what's required.

easiest way, but certainly not the best way, cheap and easy to build is about all it's got going for it... the downside is that the current will not be regulated and if it's a flat battery you could easily be supplying 5 - 6 amps when the battery really only requires 250ma or less, this would cause it to heat up and explode, the simplest solution is to stick a decent resistor on the end to limit the current, again, as the voltage rises, you could be waiting for like 3 days for it to fully charge, 80% of it will be charged in just a few hours though, not really good idea either.

best way would be a CV/CC, but then you'd need IC chips to regulate and monitor the voltage of the battery too cutting off when it hits however many volts you want.

see, the LM31T is perfect for mobile phones because the phone has all the built IC components to check battery volts and perform all the checks, all you have to do is set it to around 5v, simple as, $3 of components and you're cooking.

Bottom line, buy a charger to do it for you unless you're not really bothered about either blowing batteries up or not charging them to their capacity.... batteries work on amps not volts, so providing the voltage is higher, it will draw the current, stop charging you'll see the battery voltage drop back quickly, if it hits say 1.5v for a nimh, it's time to stop. 4.20v for lithium... really depends on what you have in mind.

 

He does not want to charge the battery in the phone. Instead he wants to blow up batteries that are separate from the charger and protection circuit in the phone.
So he needs a charger and protection circuit for whatever kind of batteries he has.