How do you convert 3 ohms to amps?

Answer 1

The voltage drop across a resistor is calculated using Ohm's Law. For a DC or direct current circuit then

V=IR where V is voltage in volts, I is current in amperes, and R is resistance in ohms

If this is a DC circuit the voltage drop is 3A*3ohm=9V

Answer 2

I'm assuming you want to know what the current is at a given voltage through a 9 ohm load.

You need to put an ampmeter in series with the 9 ohms. To do this, disconnect one end of the speaker and put one lead on the terminal of the speaker you just disconnected and the other lead connects to where the speaker was connected. Make sure the meter is on the HIGHEST CURRENT setting to start. The reading will be in amps.

I could go into all the math here but I'll just give you the simplified answer on how to determine power which is measured in Watts. Measure the highest voltage across (positive lead of a voltmeter on one end of the 9 ohm load and the negative lead on the other end with the speaker still connected). Crank it up as loud as you like, take the highest voltage reading you get (the meter reading will be bouncing up and down here). Now square the voltage reading and divide it by 9. This will give you the power output in Watts.

FYI. Listen carefully here, WATTS ARE WATTS AND NOTHING ELSE!! There is no such thing as Watts RMS. This has been so misleading that many manufacturers now use the term "Program Power" instead of Watts RMS to determine power ratings. RMS is a term that only applies to voltage and current. Although voltage times amps equals watts, RMS does not apply to power disapation. Even though its stamped on the back of most amplifiers and bragged about by many a sales person its a misnomer.

Comment

As the original answer states, there is no such thing as 'r.m.s. watts'; it is simply the product of an r.m.s. voltage and an r.m.s. current. It is used by hi-fi amplifier companies to give a meaningful value to the output power of an amplifier. Cheap and nasty amplifiers are rated in 'maximum watts', which are quite meaningless.