640 amps inrush current

snipped-for-privacy@ipal.net wrote in news: snipped-for-privacy@news4.newsguy.com:

Hehe...I wonder if they have a typo there...maybe 64A@115v / 10A@230v?

I agree with Anthony, that's just *got* to be a typo. 640 amp inrush would trip almost any residential service feed. Much more likely 64.0 But even that sounds pretty high.

Since it's rated for 400W and >70% efficiency, the RMS current would have to be...

400/(0.70*115) = ~5. amps

daestrom

Check out this for a similar 480W unit:

It shows 60A inrush current. Most ATX supplies use a voltage doubler front end, charging up to 550Mfd in series. You do the math. :-)

The similar unit shows 9A/5A, not too far off.

Virg Wall

On Sun, 23 Jan 2005 18:04:28 GMT VWWall wrote: | snipped-for-privacy@ipal.net wrote: |> This PC power supply is spec'd at 640 amps inrush current at 115v |> (100 amps at 230v): |> |>

|> |> That would definitely blink the lights. I wonder how long that lasts. |> Any idea how much energy storage one of these beasts has? | | Check out this for a similar 480W unit: | | | | It shows 60A inrush current. Most ATX supplies use a voltage doubler | front end, charging up to 550Mfd in series. You do the math. :-) |> |> And then it says 12 amps input at 115v or 6 amps at 230v. Are they referring |> to the peak current in each cycle, or RMS? If RMS, that's over 1300 watts. | | The similar unit shows 9A/5A, not too far off.

It still seems like a lot of wasted power if that amperage figure is for RMS. But if it is for just the peak during each half-cycle, then I can see that as making sense. They are claiming efficiencies on the order of

60 to 70 percent, so it needs to be less than that for RMS.

115v

the numbers are all screwed up... nothing rated at 110 is going to ever draw remotely close to 640 amps... even a hundred amps is stretching it to the max and thats usually for the old style 110vac motors..2 hp.. maybe 50 locked rotor amps.. and that lasts for about 2 seconds, tailed off as the motor comes up to speed.

The wire size necessary to support 640 amps at 110 even just inrush would be larger than your thumb... so its fishy numbers or a missed decimal point or whatever.... maybe as you suspect its the inrush for the first millisecond.

Would it dim the lights? Doubtful. As the lights come off the main feeders and that millisecond of 600 amps, down line on a different breaker, on light wire would not drop the voltage significantly in the feeders... any lights that were on the same breaker as the unit you are installing might dim for a fraction of a second, not enough to be visible, since with incandescents the element keeps glowing .. florescents might blip.

Phil Scott

that lasts.

Are they referring

over 1300 watts.

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Most switching power supplies, which these are, have poor power factors. In other words, some of that amperage is in VAR's not Watts. The amperes mentioned are that which you'd read on a RMS ammeter.

Virg Wall, P.E. (K6EVE)

| snipped-for-privacy@ipal.net wrote: |> On Sun, 23 Jan 2005 18:04:28 GMT VWWall wrote: |> | snipped-for-privacy@ipal.net wrote: |> |> This PC power supply is spec'd at 640 amps inrush current at 115v |> |> (100 amps at 230v): |> |> |> |>

|> |> |> |> That would definitely blink the lights. I wonder how long that lasts. |> |> Any idea how much energy storage one of these beasts has? |> | |> | Check out this for a similar 480W unit: |> | |> | |> | |> | It shows 60A inrush current. Most ATX supplies use a voltage doubler |> | front end, charging up to 550Mfd in series. You do the math. :-) |> |> |> |> And then it says 12 amps input at 115v or 6 amps at 230v. Are they referring |> |> to the peak current in each cycle, or RMS? If RMS, that's over 1300 watts. |> | |> | The similar unit shows 9A/5A, not too far off. |> |> It still seems like a lot of wasted power if that amperage figure is for |> RMS. But if it is for just the peak during each half-cycle, then I can |> see that as making sense. They are claiming efficiencies on the order of |> 60 to 70 percent, so it needs to be less than that for RMS. |> | Most switching power supplies, which these are, have poor power factors. | In other words, some of that amperage is in VAR's not Watts. The | amperes mentioned are that which you'd read on a RMS ammeter.

I'm wanting to know how many of these I can put on a 15 amp or 20 amp circuit, either at 120 volts or at 240 volts. Given that the voltage drop on building wiring, and the circuit breaker thermal element, is in proportion to the current, the power factor will certainly make it worse. But the duty cycle of the current is also a factor. If the current were sinusoidal, this would be easy. But what I don't know is whether the amperage rating is the peak current at some unknown duty cycle, or if the rating is the time averaged equivalent in terms of a sinusoidal load. For that 9 amp rating, if I insert a 0.1 ohm resistor in the circuit, will I get the heating of 8.1 watts because the current is equivalent to 9 amps RMS, or will I get less because it's 9 amps for short duty cycle (and the resistor gets to cool off in between the half cycles)?

The point here is not the peak RMS amps drawn by the supply, but the amps actually used by the supply on the particular computer(s) you have connected. I suggest making up a computer supply line cord with 1 ohm resistor in series with the hot line. Measure the voltage across this with the computer at maximum usage, and calculate the amps used. I think you'll find it much less than the values shown, unless you are running a game with a high end video card or doing full time CPU/video card intensive computations. They will not *all* be running full tilt all the time.

If you post a list of a typical computer's hardware and usage, we can probably give a good estimate of power needed and maximum line current expected.

I'll try to answer your other questions in your other posts.

Virg Wall, K6EVE

| The point here is not the peak RMS amps drawn by the supply, but the | amps actually used by the supply on the particular computer(s) you have | connected. I suggest making up a computer supply line cord with 1 ohm | resistor in series with the hot line. Measure the voltage across this | with the computer at maximum usage, and calculate the amps used. I | think you'll find it much less than the values shown, unless you are | running a game with a high end video card or doing full time CPU/video | card intensive computations. They will not *all* be running full tilt | all the time.

Measuring that way will require a voltmeter that responds to the waveform correctly. I don't know which ones do.

| If you post a list of a typical computer's hardware and usage, we can | probably give a good estimate of power needed and maximum line current | expected.

They all vary. I'm wanting to get an idea of the reactive power as a function of the real power. I can add up the power used by the parts inside. The P/S then complicates that.

You would need a true RMS voltmeter. In practice any VM will be close enough for a good estimate. You may be surprised by how little power is used.

Don't worry too much about VAR's. I only mentioned this to explain the peak amperage use specs. They may also include fan(s) which are not included in the efficiency rating.

The things that use most power are CPU's, (varies with CPU usage), and maximum performance video cards. The HD's can use ~35W each at startup, but require ~13W when active after start-up. When idle, ~8W typical. Fans run a couple of watts each. Add up all the power consuming devices and use an efficiency of 65% to determine input wattage and current.

At 240V, 20A, you'll have 4800VA available. This should handle at least

8-10 power hungry computers, (with monitors on a different circuit).

Virg Wall