Alan Sledzieski wrote on Thu, 22 July 2010 17:35 |
Bob Lee (QSC) wrote on Thu, 22 July 2010 18:07 |
Alan Sledzieski wrote on Thu, 22 July 2010 14:31 |
As voltage drops, current goes up.
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Only if you use one of those voltage regulators that the pros here have advised you not to use on power amps.
Quote: | If voltage is low would a amp tend to run hotter because of increased current?
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No, because the current will decrease.
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Interesting.
P = V x A
1200 watts = 120 volts x 10 amps
1200 watts = 100 volts x 12 amps ?
Still confused why someone would want to run at 100 v when you could run them at 120 fairly cheap for a small system like mine.
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In the case of most unregulated amps: The input voltage charges the voltage rails of the amp. If the input voltage of the amp is lower, there is less voltage in the amp's power supply to create output voltage. Less output voltage into an unchanging load impedance equals less current. Amps running on lower mains voltages produce less waste heat too for the same reason - there is less spare power to be dissipated in the output stage.
There are a few models of amps (Itechs, Powersoft I believe, and probably a couple of others that have internal regulation and can produce full rated output at voltages as low as 90 or 100 volts, which do indeed work the way you expect. Your Crests do not fall into this category.
As far as your question about why not use a voltage regulator - first of all you haven't really defined if your 100 volt spec is an "unloaded" voltage, or if this is what you are imagining the circuit does when the amp pulls a bit of power. Any branch circuit that has lost 20 volts by the time it gets where you are using it is going to be so spongey that even if you prop it up to 120 volts using a regulator, you're going to knock it down a whole bunch more when you ask for 50 amps of instantaneous current, which is not untypical for a non power factor corrected amp of the sizes we are discussing.
For those peak hits, they happen faster than your regulator can switch taps, so you're not really even catching them, short of permanently setting up your VR as a boost transformer.
A power factor corrected amp is able to draw current over the entire waveform, which reduces peak demand, softens hits on the supply circuit, and just plain lets you get more usable power out of a limited supply.
In one of your other replies you said you can't damage a circuit due to heating because the breaker is protecting it - I would beg to differ. The same resistances that cause low voltage create heat. I have melted more than a couple extension cord plugs in my time. In my home breaker panel, the previous owners hadn't re-torqued the breakers probably ever, and the line to the washing machine got loose. The wire got so hot that the insulation melted about an inch and a half from the breaker.
There are two good solutions to the problems you have:
1. Figure out how to get better power - rent a generator, use a distro, find better circuits, and/or reduce your load.
2. Get more efficient amps that can better deal with the power you have to work with.