115VAC or 230VAC???

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Thread: 115VAC or 230VAC???

  1. #1
    Great White Shark
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    115VAC or 230VAC???

    What is the difference between 115VAC and 230VAC-is it more power being drawn=more output for things like o/c? What setting should the average user use if this is not the case? Thanks.

  2. #2
    Old School OCer OS-Wiz's Avatar
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    We use 117vac in the USA. The difference between 117 and 220vac is that more power is AVAILABLE, not necessarily drawn at 220vac.
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  3. #3
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    Power(watts) = Voltage x current(Amps) so for the same power at lower voltage takes higher current flow rates(thicker wires)
    Voltage is electrical pressure. Current is the rate of flow.

    In australia we use 230/240v Our wires dont have to be as thick to provide the same power since the rate of flow is reduced but the insulation has to be thicker like the walls of a pipe must be thicker to keep it from bursting under higher pressure. And it bites harder down here
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  4. #4
    Not Wurm Isezumi's Avatar
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    Originally posted by GB_Cobber
    Power(watts) = Voltage x current(Amps) so for the same power at lower voltage takes higher current flow rates(thicker wires)
    Voltage is electrical pressure. Current is the rate of flow.
    To put it in Cobbers terms. You have switch the change how resistent to pressure your PSU can be.

    If its set to 110 and you plug it into a 220 line, dont be surprised if your PSU gives up the ghost.

    If its set to 220 and you plug it into a 110 line dont be surprised if nothing really bad happens.

    However you live in the states it is not recommended that you leave it on 220.

  5. #5
    Hammerhead Shark
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    Like GB_Cobbler said, Power = Voltage*Current. In most 110-120V countries, the max current rating is typically ~10A. In 220-240V countries, a given outlet is usually rated at ~5A. Thus, the max available power is the same. On the surface, you can see that 220*5=110*10, but calculating AC power is slightly more complicated then that when you have complex power comprised of real and apparent power.

    Leaving the technicalties aside, its suffice to say that the available power is a function of the current rating and the voltage rating.

    Also, you can't plug a 220V appliance into a US outlet and hope it'll work at a lower power! Most likely, the appliance will be designed to work at a lower current then the US counter part to have the same power output, thus the high current could and likely would damage the appliance. This is true since Voltage=Current*Resistance. When a device is designed to operate at a given voltage and current, it will have a given resistance (technically impedance in AC). If the voltage goes down (i.e. a 220V appliance in a 110V outlet), then the current HAS to go up if the resistance (impedance) remains the same.

    Note: Read my explanation in my next post regarding Adisharr's comments about the above paragraph. I didn't explain this correctly.

    In a computer PSU, what happens is you take the 110 or 220 V and convert it into a lower voltage with a transformer (which implicitly increases the current due to the conservation of power). This lower AC voltage is rectified (into DC), filtered and regulated to give you the desired voltages. With 220V input, you draw half as much current compared to a 110V input, thus power consumption and available power remain the same.

    Another difference is that most 220V systems are 50Hz, whereas 110V systems are usually 60Hz. This won't make much of a difference for purely resistive loads (light bulbs, heating elements etc.), but for inductive (motors etc.) and capacitive loads (electronics etc.), it'll throw off a balanced power factor, which means that you'll be drawing more apparent power. I hope that wasn't too confusing, AC power analysis by its nature isn't straight forward, so its hard to give say that P=IV IS absolutely correct (it holds, but the process is slightly more involved).
    Last edited by Ramuman; 12-04-2002 at 04:43 PM.

  6. #6
    Master of the obvious Adisharr's Avatar
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    Originally posted by Ramuman

    Also, you can't plug a 220V appliance into a US outlet and hope it'll work at a lower power! Most likely, the appliance will be designed to work at a lower current then the US counter part to have the same power output, thus the high current could and likely would damage the appliance. This is true since Voltage=Current*Resistance. When a device is designed to operate at a given voltage and current, it will have a given resistance (technically impedance in AC). If the voltage goes down (i.e. a 220V appliance in a 110V outlet), then the current HAS to go up if the resistance (impedance) remains the same.

    I'm surprised you said that when everything else you said is correct.

    A device designed to work on 220V will draw half as much current on a 110V source. It WILL NOT maintain the power draw. In order for the device to increase it's current draw its internal resistance or impedance must be reduced to 1/2 of what it was previously which just doesn't happen.

    Current draw is a function of a voltage source attached to a resistance / impedance.
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  7. #7
    Master of the obvious Adisharr's Avatar
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    Originally posted by OS-Wiz
    We use 117vac in the USA. The difference between 117 and 220vac is that more power is AVAILABLE, not necessarily drawn at 220vac.
    More power isn't necessarily available only a higher voltage. If I step up 100VAC (5A capacity) to 1000VAC does that mean I have more power available?

    No. My current capacity is reduced to .5A now.

    The power available stays the same (not counting losses in the transformer).
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  8. #8
    Hammerhead Shark
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    Originally posted by Adisharr


    I'm surprised you said that when everything else you said is correct.

    A device designed to work on 220V will draw half as much current on a 110V source. It WILL NOT maintain the power draw. In order for the device to increase it's current draw its internal resistance or impedance must be reduced to 1/2 of what it was previously which just doesn't happen.

    Current draw is a function of a voltage source attached to a resistance / impedance.
    You're right for fixed impedance loads . I was babbling about something then I sidetracked myself (scary I'm an EE isn't it? ).

    A 440W appliance (purely resistice) in 220V AC would be as follows:
    440W=220Vrms*2A=I^2*R=4*R, so R=110 ohms.

    Same appliance at 110V AC:
    110Vrms=1A*110ohm

    The same appliance at 110V AC thus only uses 110W of power.

    However, there are situations where the power is maintained despite a drop in voltage!. Fixed speed induction motors are a prime example. When you drive down the voltage trying to slow down a fixed speed induction motor, it'll seem to work for awhile, but then it'll start ramping up the current (and stalling) to maintain the power rating. That is to say, there are real world devices that keep power constant, despite the input voltage (thus changing the current and impedance as well). Discussing complex AC power is beyond the scope of this thread I believe, and I'm sorry for any confusion that my simplified (and incorrect) example caused.

    I guess what I'm saying is that in some cases, the characterisitc impedance can change dynamically with the input voltage. This could be an undesired effect as in the fixed speed induction motor case, or it could be intended in situations where you want to conserve power despite voltage (or current) fluctuations.

    Thanks for pointing that out Adisharr .

    P.S.: Also note that in a transformer, current and voltage have to implicity be inverses of each other (law of conservation of power), neglecting winding losses. If voltage is stepped down, current HAS to be stepped up. Take a transformer with variable turns ratios in a PSU. Say it converts 110V to 10V at one ratio and 220V to 10V at another ratio. Setting it to the 220V ratio for a 110V input will result in an output of 5V, but at twice the current, given that the impedance connected to the secondary side is fixed. Thus, by setting it to the 220V side for a 110V outlet, you'll be supplying the rectifier/filter/regulator with half the voltage and twice the current, and this doubled current likely will burn some of the coils. Similarly, if you set it to the 110V ratio in a 220V country, you'll supply 20V at half the rated current. In this case you could blow out some voltage sensitive component like a capacitor. This is another example of a sitution where the power simply isn't reduced because you cut the voltage.
    Last edited by Ramuman; 12-04-2002 at 05:40 PM.

  9. #9
    Great White Shark
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    I live in the US so i should put my power setting on my PSU at 115VAC right? Thanks for the posts.

  10. #10
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    Originally posted by speedstream5621
    I live in the US so i should put my power setting on my PSU at 115VAC right? Thanks for the posts.
    Absolutely, see the addition to my previous post.

  11. #11
    Master of the obvious Adisharr's Avatar
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    Originally posted by Ramuman


    You're right for fixed impedance loads . I was babbling about something then I sidetracked myself (scary I'm an EE isn't it? ).

    A 440W appliance (purely resistice) in 220V AC would be as follows:
    440W=220Vrms*2A=I^2*R=4*R, so R=110 ohms.

    Same appliance at 110V AC:
    110Vrms=1A*110ohm

    The same appliance at 110V AC thus only uses 110W of power.

    However, there are situations where the power is maintained despite a drop in voltage!. Fixed speed induction motors are a prime example. When you drive down the voltage trying to slow down a fixed speed induction motor, it'll seem to work for awhile, but then it'll start ramping up the current (and stalling) to maintain the power rating. That is to say, there are real world devices that keep power constant, despite the input voltage (thus changing the current and impedance as well). Discussing complex AC power is beyond the scope of this thread I believe, and I'm sorry for any confusion that my simplified (and incorrect) example caused.

    I guess what I'm saying is that in some cases, the characterisitc impedance can change dynamically with the input voltage. This could be an undesired effect as in the fixed speed induction motor case, or it could be intended in situations where you want to conserve power despite voltage (or current) fluctuations.

    Thanks for pointing that out Adisharr .
    I figured you knew what you were talking about - I just wanna sound smart now and then I'm glad you skipped discussing complex AC power issues as I'd probably get a headache
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  12. #12
    Hammerhead Shark
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    Originally posted by Adisharr


    I figured you knew what you were talking about - I just wanna sound smart now and then I'm glad you skipped discussing complex AC power issues as I'd probably get a headache
    lol...so would I . BTW, I added a part about transformers to my first post that should do a better job of getting at what I was trying to say the first time around.

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    Mako Shark muzikjunkie's Avatar
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    Re: 115VAC or 230VAC???

    Originally posted by speedstream5621
    What is the difference between 115VAC and 230VAC-is it more power being drawn=more output for things like o/c? What setting should the average user use if this is not the case? Thanks.
    i feel utterly sickened that you have to ask that kind of question, you don't need to be a computer expert to know that US uses 115 and 230 is for just about everywhere else in the world.
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    8 Wheels Move The Soul Ashpool's Avatar
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    Re: Re: 115VAC or 230VAC???

    Originally posted by muzikjunkie
    i feel utterly sickened that you have to ask that kind of question, you don't need to be a computer expert to know that US uses 115 and 230 is for just about everywhere else in the world.
    You didn't need to flame him about it. You probably asked questions just as simple as that one at one point in you're life.
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    Master of the obvious Adisharr's Avatar
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    Re: 115VAC or 230VAC???

    Originally posted by speedstream5621
    What is the difference between 115VAC and 230VAC-is it more power being drawn=more output for things like o/c? What setting should the average user use if this is not the case? Thanks.
    Where do you get off asking a hardware question in General Hardware?
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