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Old 17th September 2010, 11:43 AM   #1
Zanthus is offline Zanthus  Australia
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Default Power consumption

Hi there,

I have a pair of Nady powered monitors. The RMS wattage is 50 W per speaker (2 per box). I am trying to determine the power consumption so I can protect them with a UPS. but i need to know the max power it will take in Watts.

Can anyone help me understand how RMS differs from what power is drawn from the AC supply.

Any help with this would be greatly appreciated.

Thanks
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Old 17th September 2010, 12:29 PM   #2
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There is no direct relationship between the RMS wattage of an amplifier and the power it consumes. This is because there are many different types of amplifiers, some of which are more efficient than others.

Your best bet is to look at the user manual for the device, or sometimes there is a back plate which shows the power consumption. If you can't find out any other way, you can always use the fuse rating as a maximum value, e.g. a 110 volt supply with a 6A fuse will require a 660W UPS.

w
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Old 17th September 2010, 08:33 PM   #3
Zanthus is offline Zanthus  Australia
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Thanks for your help.

all it says on the back is:
input power: 115-230V 50-60hz
fuse: T2A/250V (115VAC), T1A/250 (230VAC)
each speaker is split 50W RMS for High freq and 50W RMS for low freq.

I could not find my copy of the manual, but I found a pdf on the nady site http://www.nady.com/manuals/audio/sm250a.pdf but this doesn't seem to have anything either.

It may help to know I'm in Australia where we run at 240V (230V) power supply.

Thanks for your help. Not sure if any of this extra information makes a difference??
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Old 17th September 2010, 10:32 PM   #4
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Why would powered monitors need to be protected with a UPS?

With the possible exceptions of units with computer processors and video projector bulbs (let's not go deeper with this) the UPS section of the UPS box doesn't protect equipment.

But if you must have a UPS on a power amp get a real big one.
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Old 17th September 2010, 10:41 PM   #5
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Quote:
Originally Posted by Zanthus View Post
input power: 115-230V 50-60hz
fuse: T2A/250V (115VAC), T1A/250 (230VAC)
Well taking things very simplistically and over-speccing a bit, power = volts x amps so you got 230 x 1 = 230 watts.
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Old 18th September 2010, 10:24 PM   #6
Zanthus is offline Zanthus  Australia
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a fully line interactive UPS protects everything connected from all power irregularities. when certain appliances get switched on in my house (IE: the Rangehood) i get spikes sent through to my monitors. A UPS would eliminate these. and regulate the voltage therefore protecting the monitors which I spent quite a bit of money on.

Thankyou ritchieboy. your answer actually helped me.. looks like i'll need to allow 500W for each monitor. even though they probably wont draw that much power constantly.

Thanks for your help.
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Old 19th September 2010, 12:20 AM   #7
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Some power amplifiers with modern power supplies get very unhappy when feed from a UPS. They draw a huge current spike for a small fraction of each power line half cycle. The UPS often isn't capable of sourcing these large current pulses that are way above their continuous current rating.
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Old 19th September 2010, 10:04 AM   #8
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Quote:
Originally Posted by Zanthus View Post
looks like i'll need to allow 500W for each monitor. even though they probably wont draw that much power constantly.
Have you got 4 speakers in total then? My calculation was for a stereo pair, which a 250W UPS would be more than enough for as you will never draw the same current as the fuse rating in normal use.
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Old 19th September 2010, 10:15 AM   #9
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by Zanthus View Post
a fully line interactive UPS protects everything connected from all power irregularities. when certain appliances get switched on in my house (IE: the Rangehood) i get spikes sent through to my monitors. A UPS would eliminate these. and regulate the voltage therefore protecting the monitors which I spent quite a bit of money on.
suppress the interference at source.
Then add interference suppression to any of your equipment that does not already have it.

Is it possible that the interference is airborne?
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Old 19th September 2010, 11:42 AM   #10
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Agree with Andrew. It's cheaper and more effective to sort the problem rather than cover up the effects.
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