What value of resistor do I need to take 12V to 5v?

Question

I need to charge my iPod in mar car I have some resistors and other parts laying around how can I calculate what resistor I need to use?

Answer 1

Theoretical answer:take the amperage when the iPod is being charged by its own charger,then divide 5 to this amperagr,you get the internal resistance of your iPod.Because you need the same amperage,you divide 12/(Ri+R),calculate R and put it in series with your iPod.

Engineering answer:you SHALL NOT DO IT because you will have waste of energy in terms of heat in your R.

Answer 2

What you really want is a DC to DC converter that is made to take 12VDC and make 5VDC.

digi-key.com lists thousands of these.  search for the one that is the right size for your application.

http://search.digikey.com/scripts/DkSear...

Answer 3

You can't.

Resistors don't produce a fixed drop, it will vary with current.

You need a voltage regulator or a zener diode.

This is over your head, get someone to help. Or buy a charger that runs from 12 volts.

edit, yes, a 7805 will do. Be sure to download the data sheet and study it carefully. Depending on the current, you may need a heat sink, and you will need a few capacitors.

BTW, how did you determine you need 5 volts?

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Answer 4

The value of the resistor needed varies with the current draw of the device.  There is no correct answer.

This is not the way to do it.  The IPOD is probably 5v, so just get an LM7805, an output capacitor (10uf will do nicely) and it will handle 12v just fine and turn it into 5V.  However, it might need 3 volts, so you might have to get a little creative as there is no simple 3V regulator.

But the point is, if you get a resistor to drop the voltage at one volume level, then another will cause a different current to flow and the voltage across the IPOD will no longer be what you need, and you may blow the whole thing up, which will probably improve your grades and your social life.  So for your mother's sake, use a 1 ohm, 2 Watt resistor and get your life back...

Answer 5

Get one voltage regulator 7805, they have 3 legs. Conect (welding) positive 12V on the external left leg (looking from the numbered side), the negative to center leg. You will get 5v between right leg and center leg.

Test tension before conecting!

Good Look