I have a question about power to a shuffle.

Hi,

I have a FM transmitter that opperates on 12V @ 500mA. Does anyone how how I can "steal" or combine the power from that device to my shuffle. The shuffle opperates 5V @ 500 mA. I want to be able to just plug the transmitter in and then not have to worry about the battery running out on the shuffle or using 2 DC adpters. Does this make since? Can you help?

Thomas AShworth

You will need to build a DC - DC power inverter that will turn 5 volts into 12 volts.

To turn 12 Volt DC to 5 Volt DC, you simply put two resistors in series. This is called a voltage divider. The voltage drop on the first resistor is 7 Volts, and on the second it is 5 Volts.

The formula is E (Voltage) = I (Current) * R (Resistance)

12 Volts divided by 1/2 Amp( 500mV) = 24 Ohms resistance.

5 Volts divided by 1/2 Amp = 10 Ohms. 7 Volts divided by 1/2 Amp = 14 Ohm. The total of 10+14 = 24 Ohms resistance.

.

o---------
|
R1=14 Ohms
|
12 Volts ----------------o
|
R2=10 Ohms 5 Volts
|
o------------------------o

However, if the FM transmitter needs 500mA and the Shuffle needs 500mA, then something might be starved for power. The is a good chance that it will work. You would have to try it.

Ignore the above post about DC-DC power inverters. That would be better suited to stepping up voltage from 5 Volts to 12 Volts--much more difficult; and it would be a converter not an inverter. An inverter is for making AC from DC.