How to calculate the amps drawn for OneAC??

0 Members and 1 Guest are viewing this topic. Read 5201 times.

8thnerve

How to calculate the amps drawn for OneAC??
« on: 11 Nov 2003, 09:24 pm »
I am trying some of the OneAC power conditioners and need to calculate the appropriate draw so that I can match the components with the proper unit.  How do I calculate the Amp usage of a component?  For instance, the Naim CD5 requires 25VA power.  The OneAC CP1107 puts out a max of 3.6 A.  How do I put these figures in the same units?

I apreciate any help on this embarrassingly basic question.

mgalusha

How to calculate the amps drawn for OneAC??
« Reply #1 on: 11 Nov 2003, 10:14 pm »
If the OneAC is capable of 3.6A @ 125V that is approximately 450 Watts. Watts = Volts X Amps.

Add up the wattage drawn by your equipment. It needs to be less than the maximum supported by the OneAC. You Naim requires 25VA. VA stands for Volt-Amperes and is nearly equivalent to Watts. So 25VA is very close to 25Watts.

Hope this helps.

Mike G.

8thnerve

How to calculate the amps drawn for OneAC??
« Reply #2 on: 11 Nov 2003, 11:03 pm »
Quote from: mgalusha


Hope this helps.

Mike G.


EXACTLY what I was looking for!  Thanks Mike.

Curt

How to calculate the amps drawn for OneAC??
« Reply #3 on: 12 Nov 2003, 09:57 pm »
Quote from: mgalusha
If the OneAC is capable of 3.6A @ 125V that is approximately 450 Watts. Watts = Volts X Amps.

Add up the wattage drawn by your equipment. It needs to be less than the maximum supported by the OneAC. You Naim requires 25VA. VA stands for Volt-Amperes and is nearly equivalent to Watts. So 25VA is very close to 25Watts.

Hope this helps.

Mike G.


V x A is exactly equal to watts. 25VA (VA = VxA) means 25 watts.

covermye

  • Jr. Member
  • Posts: 43
How to calculate the amps drawn for OneAC??
« Reply #4 on: 19 Nov 2003, 12:36 pm »
Ahhh... VA==W in the case of linear loads only.  Power supplies in computers are notoriously nonlinear, though, and the VA rating of the tranformer needs to be derated somewhat.  

I'm guessing that audio amplifiers are mostly linear, though, and that the only nonlinear loads you see on audio equipment are in the cases where you have DC power supplies (CD players, etc...).  I'm also guessing, then, that it might make sense to have the CD player (and any other piece of gear that has an AC-to-DC power supply on a seperate isolation transformer than the power amp in order to "isolate" this nonlinear load from the amplifier's input power...  Make sense?

Curt

How to calculate the amps drawn for OneAC??
« Reply #5 on: 19 Nov 2003, 03:13 pm »
Quote from: covermye
Ahhh... VA==W in the case of linear loads only.  Power supplies in computers are notoriously nonlinear, though, and the VA rating of the tranformer needs to be derated somewhat.  

I'm guessing that audio amplifiers are mostly linear, though, and that the only nonlinear loads you see on audio equipment are in the cases where you have DC power supplies (CD players, etc...).  I'm also guessing, then, that it might make sense to have the CD player (and any other piece of gear that has an AC-to-DC power suppl ...


There is no transformer in a computer switching power supply, unless it's a "Flyback" design. Ref: there are about 20 different switching power supply topologies and only the flyback has a transformer.

And if it is a flyback switcher the transformer doesn't come into the equation anyway, voltage regulation in a switching power supply is maintained by a feedback loop monitoring the supply's output (keeping it constant +/- Tol). The switching rate and /or duty cycle is thus servo controlled to keep the output constant within the desired tolerance.

Computer power supplies are spec'd by output and efficiency (Eff = Pout/Pin) and efficiency varies from 60%-96% depending on the type of switcher. I discounted power factor here for simplicity.

In audio we speak of the power (w=VA) delivered to the load. What the load gets and uses is usually our topic of interest. We can then calculate the power supplies efficiency if desired but most users don't care to.

Most audio loads are non-linear because their impedance (capacitiave and inductive elements) varies with the frequency and an audio program varies in frequency all the time. Loudspeakers are the worst case audio load because they need the most power.

BTW: By definition, watts = VA = joules/second ; this means that the true meaning of watts is the power in joules used in a one second period.

Curt

How to calculate the amps drawn for OneAC??
« Reply #6 on: 19 Nov 2003, 03:34 pm »
For a power conditioner I'd calculate all the components power as drawn from the wall, add them up, then add 50-100% for headroom and future changes.

Example--"Naim CD5 requires 25VA power" so 25/115 = 227mA or 0.227A

JoshK

How to calculate the amps drawn for OneAC??
« Reply #7 on: 19 Nov 2003, 04:08 pm »
OneACs are great for sources and preamps but don't use them for amps.  Just say no!

Curt

How to calculate the amps drawn for OneAC??
« Reply #8 on: 19 Nov 2003, 04:24 pm »
Quote from: JoshK
OneACs are great for sources and preamps but don't use them for amps.  Just say no!


I second that.

covermye

  • Jr. Member
  • Posts: 43
How to calculate the amps drawn for OneAC??
« Reply #9 on: 19 Nov 2003, 04:54 pm »
Quote from: Curt
There is no transformer in a computer switching power supply, unless it's a "Flyback" design. Ref: there are about 20 different switching power supply topologies and only the flyback has a transformer.

Right.  I wasn't insinuating that computer power supplies have transformers.  I was stating that when sizing a transformer, you need to derate its capability in the case of nonlinear loads.  For instance, we have a lot of 400 HP DC drives here where I work, and a 440KVA isolation transformer is what your "average" electrical guy would choose when sizing it.  However, these drive show a power factor in the 60's.  Typically, a standard isolation transformer would be derated about 50% in this case, meaning that we'd go with a 660KVA unit.

I've seen the same thing when isolation transformers are sized for large computer rooms.  The computer power supplies require that the isolation transformer for the main electrical service be derated and oversized due to the low power factors.

That's the point I was making:  that if you're sizing an isolation transformer in the case of the OneAC unit, the same principles apply.   If you really wanted to take care of the irregularities, each non-linear source should have its own seperate isolation transformer to isolate it (seperate OneAC units for each product?)

Right or wrong, that's just clarifying what I was thinking out loud...