Volts x Amps = Watts?

[kylelevi 10+ year member]

I just hooked up a dmm to my Kicker ZX460 to see what would happen. With the sub hooked up and a 50 hz. sine wave, the dmm read 8.58 amps (clamp style meter) and 34.9 volts. If you multiply these readings, it should give you the rms watts, right? So my little 30x4 Kicker is putting out 299.442 watts into a 2 ohm bridged load? If so, kick azz! If not, please school me. Thanks.

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[djeazie 10+ year member]

i dont think so.

 

[ryanj91 10+ year member]

I just hooked up a dmm to my Kicker ZX460 to see what would happen. With the sub hooked up and a 50 hz. sine wave, the dmm read 8.58 amps (clamp style meter) and 34.9 volts. If you multiply these readings, it should give you the rms watts, right? So my little 30x4 Kicker is putting out 299.442 watts into a 2 ohm bridged load? If so, kick azz! If not, please school me. Thanks.

you are correct http://ebtx.com/mech/ampvolt.htm

 

[bose301s 5,000+ posts]

i dont think so.

Wrong, P=IE, p=power in watts, I=current in amps, V=voltage in volts. I am an EE.

 

[kylelevi 10+ year member]

Sweet. Not bad for being rated at 180 watts for that configuration. Guess I don't need the 250/1 after all.

 

[Immacomputer 10+ year member]

Wrong, P=IE, p=power in watts, I=current in amps, V=voltage in volts. I am an EE.

In AC conditions, current time voltage is apparent power or VA (volt amps), not power. That is true only in DC conditions.

RMS Power equals RMS voltage times RMS current times the power factor to distinguish the real part of the power from the apparent power.

 

[RAM_Designs 5,000+ posts]

I just hooked up a dmm to my Kicker ZX460 to see what would happen. With the sub hooked up and a 50 hz. sine wave, the dmm read 8.58 amps (clamp style meter) and 34.9 volts. If you multiply these readings, it should give you the rms watts, right? So my little 30x4 Kicker is putting out 299.442 watts into a 2 ohm bridged load? If so, kick azz! If not, please school me. Thanks.

The voltage you need to be using is the charging voltag of your electrical system, which will be around 13.5-14.5 when your vehicle is running.

Then you also have to take into account that an amp is not 100% efficient, and that some of the amperage that is being drawn gets wasted. This depends on the amp topology(class d, class a, class a/b, etc.) and what ohm load the amp is running at(lower ohm loads make amps a little less efficient than what they'd be at higher ohm loads).

 

[bose301s 5,000+ posts]

In AC conditions, current time voltage is apparent power or VA (volt amps), not power. That is true only in DC conditions.
RMS Power equals RMS voltage times RMS current times the power factor to distinguish the real part of the power from the apparent power.

Well, yes, you are right, I didn't actually bother reading his thread, I just posted and answer tothe title. But, since DMMs measure RMS voltage and current for AC signals he is getting a decently correct rating. Like you said though, the one thing he does nto know is the phase angle of the power. That however does not matter as the amp delivers the apparent power, i.e. with a .75 PF load that is a 1 kW apparent load the generator will see a 1 kW load and be making one kW even though only 750 watts are actually being used.

 

[Haunz 10+ year member]

That however does not matter as the amp delivers the apparent power, i.e. with a .75 PF load that is a 1 kW apparent load the generator will see a 1 kW load and be making one kW even though only 750 watts are actually being used.

what ?

No... An amp does not deliver apparent power, thats why it's called 'apparent'... in your example even if the amp is only capable of delivering 750watts it would still seem to deliver 1000....

 

[Ed Lester 10+ year member]

I just hooked up a dmm to my Kicker ZX460 to see what would happen. With the sub hooked up and a 50 hz. sine wave, the dmm read 8.58 amps (clamp style meter) and 34.9 volts. If you multiply these readings, it should give you the rms watts, right? So my little 30x4 Kicker is putting out 299.442 watts into a 2 ohm bridged load? If so, kick azz! If not, please school me. Thanks.

That would be max.

you have to also multiply by .707 to find the RMS.

so 211.68994 watts RMS

 

[djeazie 10+ year member]

Just have the fvcker benchtested and you can end this.

 

[Haunz 10+ year member]

That would be max.you have to also multiply by .707 to find the RMS.

so 211.68994 watts RMS

I assumed he used true RMS meters...

If he did not then the meter already takes the peak value for current or voltage and multiplies it by .707.... problem is because it's not true RMS it's calibrated for 60hz and will only be accurate at 60hz.....

 

[Ed Lester 10+ year member]

I assumed he used true RMS meters...
If he did not then the meter already takes the peak value for current or voltage and multiplies it by .707.... problem is because it's not true RMS it's calibrated for 60hz and will only be accurate at 60hz.....

Yeah, I always measure while playing 60hz.

Just from my experience with that amp, it seems as though he did not use a true RMS meter.

Its been a while since I measured that amp but I remember it being around 210-220w at 2 ohm reactive load bridged with 14v DC input dropping to 13.2v

 

[Ed Lester 10+ year member]

Just have the fvcker benchtested and you can end this.

a bench test uses the same method he is using, difference is that he is using his reactive load (subs in his box) so his reading will be more accurate.

 

[kylelevi 10+ year member]

I did use a true RMS meter, it is an Ideal 61-766. And yes, I assumed that the most accurate readings would be under real-world conditions...installed in the vehicle with the subwoofer hooked up. I could tell that there was a fair amount of clipping during the test...does this express itself as a voltage higher reading? Would I want to take the measurements at the onset of clipping? Thanks for all of the input so far.