Confusion over Power

[highfigh]

Thanks for the info, I think am catching on. Sometimes it take me a while. Amp runs almost as hot as an iron. Besides I don't know anything about wiring, but it makes sense.

Running really hot is a bad thing and it's also a symptom of voltage drop caused by conductors that are too small. to keep from damaging the amp, either use a fan to blow air on it or turn it down. If you crank it up and get it up to normal temperature (AKA, too hot), grab the plug at the wall and feel how warm it is. If it's warm at all, you need to upgrade the service to the amp. I would tell the electrician that you want 10ga, or two circuits run to that location (the breakers should either be directly across from each other or if they have to be on one side of the panel, skip a space instead of placing the breakers in sequential slots to avoid being on opposite 110 feeds). Again, if the amp can run on 240VAC, do that and have a separate circuit run just for the amp, using the appropriate plug & receptacle.

 

[jcmccorm]

We have been through with this many times before in this forum. You will not get 1800W from 120V 15A unless the load current is in phase with the voltage and that only happens if the load is 100% resistive such as a resistor with no inherent inductance and/or capacitance and if there is no voltage drop that depends on the length and size of the cable. An amplifier is not a resistive load and its current draw is not going to be in phase with the voltage

I agree! I was merely stating the theoretical maximum, which was still less than what the OP was expecting.

You *could* do power-factor correction in the amplifier to align the voltage and current but I have no idea if that's standard practice or not.

Cary

 

[Sylar]

this may sound a little dumb, but I know of 5A & 15A wall units. How can a 15A wall unit supply more than 15A.....30A???

 

[Sylar]

You got it.

You're not going to get more than 120V * 15A = 1800W from a single circuit. Considering that continuous loads should be limited to 12A, you won't get more than 120V * 12A = 1440W from a single outlet. Add the efficiency of the amp (the 70% number given is probably generous) then you're down to 1008W available for your speakers. Through the magic of capacitors you could get more for peaks but not for long and the overall average won't exceed 1008W.

Cary

So if I have a receiver like TH NR708 with rated power consumption as 570W or 750VA / ~600W @ 0.8 PF.

From this link - Post #5 Power consumption rating on receivers is usually not MAX figure. Its usually with 2 channels at full power and the others at 1/8th.
And this tells me,, Power (8ohms 20-20kHz 0.08%) /Ch 110W, (the receiver is capable of outputting 110W per channel with Max 0.8% THD at 8ohm).

So with the rated power of 570W, and an efficiency of around 70% gives total of 400W of available power at amps terminals.
But, with 2 channels @ full power gives 220W, & 1/8 for remaining 5 channels - 1/8* 110 * 5 gives ~70. Totalling - 290W.
Where did I miss out on the remaining 110W? (60% efficiency gives 340W still 60W unaccounted).
Or is it that, 110W is not the full power, it is the rated power at the given TDH?

Also, if an amp is rated at 2 channel like above, and if it is driven using 2 channels instead of 7, does it mean the remaining power of 5 unused channels is available at these 2 used terminals?

 

[TLS Guy]

So if I have a receiver like TH NR708 with rated power consumption as 570W or 750VA / ~600W @ 0.8 PF.

From this link - Post #5 Power consumption rating on receivers is usually not MAX figure. Its usually with 2 channels at full power and the others at 1/8th.
And this tells me,, Power (8ohms 20-20kHz 0.08%) /Ch 110W, (the receiver is capable of outputting 110W per channel with Max 0.8% THD at 8ohm).

So with the rated power of 570W, and an efficiency of around 70% gives total of 400W of available power at amps terminals.
But, with 2 channels @ full power gives 220W, & 1/8 for remaining 5 channels - 1/8* 110 * 5 gives ~70. Totalling - 290W.
Where did I miss out on the remaining 110W? (60% efficiency gives 340W still 60W unaccounted).
Or is it that, 110W is not the full power, it is the rated power at the given TDH?

Also, if an amp is rated at 2 channel like above, and if it is driven using 2 channels instead of 7, does it mean the remaining power of 5 unused channels is available at these 2 used terminals?

You are forgetting the power to drive the DACs, microprocessors and analog circuits etc. That will be 85 watts at least.

 

[highfigh]

this may sound a little dumb, but I know of 5A & 15A wall units. How can a 15A wall unit supply more than 15A.....30A???

"Wall units"- what is that? If you mean receptacles, they come in 15A, 20A, 40A and above that, they're twist-lock. A true 20A plug won't work in a 15A receptacle because one tab is at a right angle to the other.

 

[PENG]

From this link - Post #5 Power consumption rating on receivers is usually not MAX figure. Its usually with 2 channels at full power and the others at 1/8th.
And this tells me,, Power (8ohms 20-20kHz 0.08%) /Ch 110W, (the receiver is capable of outputting 110W per channel with Max 0.8% THD at 8ohm).

The key word is 'usually'. Some do provide a 'maximum' power rating for their models. Examples are Harman Kardon and some Yamaha RX-V models, just checked out their manual. If I remember correctly, those particular Yamaha models even provide the THD at that 'maximum' number.

 

[Sylar]

"Wall units"- what is that? If you mean receptacles, they come in 15A, 20A, 40A and above that, they're twist-lock. A true 20A plug won't work in a 15A receptacle because one tab is at a right angle to the other.

Where we live the ac power supply has only 5A & 15A.

 

[Sylar]

Also, if an amp is rated at 2 channel like above, and if it is driven using 2 channels instead of 7, does it mean the remaining power of 5 unused channels is available at these 2 used terminals?

I understand that if it is not the max rating (usually not), so which means there is room to push further (but with a lot more distortion now).
Trying to understand how input to output power works here. How much further than the rated power (with the rated TDH) can one push the amp? Is it a direct relation to total available input power (Lets assume that impedance variations are negligible)? Anyone?

The key word is 'usually'. Some do provide a 'maximum' power rating for their models. Examples are Harman Kardon and some Yamaha RX-V models, just checked out their manual. If I remember correctly, those particular Yamaha models even provide the THD at that 'maximum' number.

So If i have a receiver rated at 110 W/ch @ 8 ohm, it would mean with a 4 ohm load, it would be around 170W/ch. 340W for fronts alone. Does it mean that it is much easier to drive 8 ohm loads, as now you have lesser power for remaining channels?
I am unsure if I am right here or totally off with power.

 

[tjf120]

For your typical 15 A breaker, it wont trip at 15.1 amps, typically it needs some amount of heat build up or similar mechanism to cause a trip. So you can pull more than 15 A out of a circuit for short periods of time with no issue.