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Resistors and Batteries help

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chriskid

New Member
hi, ive been starting to do some 'electronic operations' and am confused. i have a 12v battery 9ah and would like to charge something like my nintendo ds or mobile phone which needs an input of 5.2v, what resistor would i need to use in order to get the voltage down to roughly 5.2v from the battery?

thanks from chris
 

tcmtech

Banned
Most Helpful Member
what type of batteries do they have? And do the devices in question have built in charge control systems. Most dont and require a dedicated power pack withthe right charge control system built in.

Give us some battery specs and what ever else you can and we will see what we can come up with!
Even if its way over your head and completely over the top of practical and nessisary!
 

Sceadwian

Banned
Actually TCM, on most modern electronics like cell phone's game boys, and many other gadgets the charge controller is in the unit, the 'charger' is just a voltage supply.

I would most definitely NOT use a resistor to try to drop the voltage, resistors only work to drop the voltage reliably on static loads, the voltage would be all over the place depending on the load of the device. What you need is a simple variable linear regulator and a multi meter or built in meter to adjust the voltage to what you want.
 
Last edited:

Hero999

Banned
Use a regulator IC such as the LM7805.

Or use a 6V 9Ah battery (which is half the size of a 12V 9Ah) and a low drop-out regulator and it'll last just as long as the 12V.

Another option is the wonderful world of switching regulators.

Don't worry about using 5V instead of 5.2V, it will still work.
 

tcmtech

Banned
Most Helpful Member
Was not sure. I am not a game person and I hated having a cell phone. :p

Small battery powered gadgets for me are pretty much my scientific and graphing calculators and my laptop that never works on batteries. :p

Everything else is just something waiting to be lost smashed or cost me a monthly fee that I dont care for. :)
 

Thunderchild

New Member
Was not sure. I am not a game person and I hated having a cell phone. :p

Small battery powered gadgets for me are pretty much my scientific and graphing calculators and my laptop that never works on batteries. :p

Everything else is just something waiting to be lost smashed or cost me a monthly fee that I dont care for. :)
most modern cell phones have a charging regulator in the battery, if you pull one apart there will be 3 flat cells and a tiny SMD controller circuit at the end where the battery contacts are, the battery has 3 terminals: GND, charge and supply (to the divice), phone chargers and the like nowadays are no more than small SMPS
 

Sceadwian

Banned
I get many a nice power supply from people getting rid of out dated cell phone chargers. There's actually a bit of a problem right now cause every phone has their own, so when users upgrade phones a lot of the time they have to get a new charger so there's a lot of e-waste being produced from these supplies. A group of cell phone companies has just recently agree'd to come up with a universal charger format for all their phones, but you won't see them for several years.
 

Andy1845c

Active Member
I get many a nice power supply from people getting rid of out dated cell phone chargers.
The charger from my old phone puts out a surprisingly nice 5v. I have used it to power PICs and a few LEDs on a breadboard with no problems.
 

Sceadwian

Banned
Many cell phones use 5 volts now, cause USB chargers are getting popular and they do great on single cell lithium packs for chargers. I have several very nice fully regulated 5 volt chargers from old cell phones just like you =) They usually can put out a pretty healthy amount of current as well because they're switch mode. I don't even use decoupling caps with them.
 

be80be

Well-Known Member
If you want a good cheap regulator find a cel phone car charger the IC in all most all of them is a real good switching regulator with it you can get 5 volts from 3 volts or more
and from 12volts you can make a good varable supply that will go down to about 3 volts
Most all of them have mc34063 in them here the datasheet
 

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