Finally got me a clamp meter

[Flipx99 5,000+ posts]

You could but either way, speaker wires wont raise or lower impedence by a whole ohm.

I see, but couldn't you more accuratley set gains this way?

 

[johnson 10+ year member]

I see, but couldn't you more accuratley set gains this way?

Again, you wont have a voltage drop with 1' of speaker wire.

 

[Flipx99 5,000+ posts]

You only have one foot? I have about 15 foot. Does that make a difference?

 

[bjfish11 5,000+ posts]

i went out and tried to use my craftsman clamp meter, the one in the ebay auction that was listed. How exactly do i use it to meausre amps? I turned to to amps and clamped on the postive speaker lead from the amp and it showed like .02 amps. What am i doing wrong?

 

[Flipx99 5,000+ posts]

I would think that you would only measure watts and ohms on the speakers. I only wanted amps to see what was coming off the alternator, but then again I am in the same boat as you.

 

[bjfish11 5,000+ posts]

well from what i understand...to get your true rms wattage being put out by your amp, you take the volts your dmm reads multiplied by the number of amps your clamp meter reads and that gives you rms. Someone correct me if im wrong.

 

[jrz126 10+ year member]

Yes, Power=V*I But this is true for DC signals and AC signals with a pure resistive load.

Once you throw a speaker in there, (An inductive piece of equipment), You'll get some inductance which will then give a slight phase shift between the voltage and current.

When you have a phase shift, (caused by either capacitance or inductance) your power equation becomes V*I*cos(theta), where theta is the angle between V and I.

So the only accurate way to measure an amp's output is to use a power meter, or get some high power load resistors.

 

[Flipx99 5,000+ posts]

Is that extra value cos(0) negligble?

 

[jrz126 10+ year member]

the value of cos(0) is 1, therefore you get V*I*1

 

[Flipx99 5,000+ posts]

I meant cos(theta)

I have no idea how to calculate it. I was wondering if was a relatively large or small value.

 

[maylar 10+ year member]

Amp clamps are an electrician's tool intended for AC power wiring and have very little use in car audio. Most of them work at line frequencies only (50-60 hz). The Craftsman one apparently works on DC too, which could be very handy for checking alternators. But if the scale is 0-200 amps don't expect to do much else with it.

Speaker impedance does change with frequency, but for all practical purposes the nominal impedance spec is close enough for power calculations. Anything beyond a ballpark measurement needs a non-inductive dummy load.

 

[Moe Lester 10+ year member]

You should get the craftsman true rms meter off of ebay... It is what you want. I got mine for $47 shipped bnib off ebay.

 

[knukonceptz 10+ year member]

The Greenlee Model looks like it does amps in AC only. The Craftsman would check AC/DC. All you need to do is set it to the Amp setting and place the cables your checking into the "0" of the clamp. Double check your manual if all else fails.

Impedance is measured by Ohm (see the ohm symbol on your DMM ) The electrical load will be slightly lower then your expected load. 4 Ohm coils are usually 3.6-3.8 Ohm. Your 1 ohm load would be .7-.9 Depending on the coil.

 

[Flipx99 5,000+ posts]

Can I check voltage for gains?

 

[jrz126 10+ year member]

I meant cos(theta) I have no idea how to calculate it. I was wondering if was a relatively large or small value.

it will range from anywhere from 0 to 1, 0 meaning pure inductive (or capacitive load) and 1 being pure resistive load.