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Electronics Question - Am I being "had"?

Discussion in 'Pro Audio Equipment' started by TC3, Mar 23, 2005.

  1. TC3

    TC3 Guest

    Right to the point: Is it OK to use a Power Supply rated at 9VAC / 800mA on a device that calls for a Power Supply rated at 9VAC / 500mA ?

    The long version: I just purchased a used RNC1773 Compressor. When it arrived I noticed that the wall-wart type Power Supply provided is rated at 9VAC and 800mA, and is made by ART. Looking on the back of the compressor near the power supply input I see 9VAC and 500mA. Looked fishy.

    I asked a buddy who recently purchased a new RNC1773 to look at his power supply. It shows 9VAC and 500mA - made by GlobeTec.

    So it appears the Power Supply I was given is not an original.

    Not wanting to fry the unit, I contacted the seller and asked them if they had made a mistake and sent the wrong power supply. Their reply was: "That should be the power supply I had with it, and it's fine to use. As long as the voltage is correct, any power supply with MORE milliamps than is required is safe to use. A power supply with less milliamps than required cannot be used. Thanks."

    So before I plug this thing in, I'd like to know from a disinterested (hopefully authoritative) third party...is what the seller wrote accurate? Is it really OK to use the power supply he provided?

    Thanks a TON !
     
  2. zemlin

    zemlin Well-Known Member

    I agree 100% - no fish. They may have changed supplies for the wall wart, or consolidated parts to increase puchasing power on a single model, etc -

    Any number of reasons they may be using a power supply with excess current, but no harm will come from it.
     
  3. phulden

    phulden Guest

    Yes it is definately safe to use the 9V/800mA. This means that the the power supply is capable of delivering 800 mA keeping the voltage at 9V (+/- some tolerance) without being affected.

    Since your unit will consume at max 500 mA the 800 mA power supply will handle this with margin.

    A unit rated 9V/500 mA will be able of keeping 9V up to 500 mA. What happens above that is design dependent, either the power supply may switch off or the voltage will start to drop leading in worst case to power supply overheat.

    However there are other things that might be of issue to consider which more has to do with the performance of the unit being powered. Examples of these are power quality and (dynamic) output impedance.

    Power quality may be a concern if the 9VAC (alternating current) is very noisy with spikes and/or high frequency ripple.

    Output impedance is of concern if your unit makes really fast load steps, that is the current consumption increases suddenly from say 50 mA to 500 mA.

    These are parameters that could differ from different power supplies even though their output voltage and current rating are identical.

    However I hardly believe this should be a problem. At least it should not be able to damage your hardware, so just plug the power supply in and listen how your compressor sounds.

    I've been working as an engineer for more than 5 years with issues like power supply design for a space electronics company so I hope you trust me on this.
     
  4. TC3

    TC3 Guest

    Thank you both ! I'll plug it in and give it a whirl.
     

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