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Help with reading power supply

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#1 JLi519


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Posted 28 November 2008 - 06:26 PM

I want to figure out how many amps and voltage my power supply is. Since I'm using AC my AC Input is:
AC Input: 115V/8A; 230v/5A; 60 Hz/ 50 Hz.
Which voltage and amperage number should I take? This is 350 W power supply.

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#2 garmanma


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Posted 28 November 2008 - 06:36 PM

Do you mean you want to check the different voltages?

Caution: There are electronics inside the case that are very susceptible to electrostatic discharges. To protect your computer, touch the metal of the case to discharge yourself of any electrostatic charges your body may have stored before touching any of the components inside. As a safety precaution you should unplug the computer to avoid electrical shock.
The purpose of this procedure is to bypass the motherboard to test the PSU.

This procedure will involve working with live 12VDC electrical potentials which if handled improperly may lead to electrical shock. Proper precautions should also be taken to prevent electrostatic discharges (ESDs) within the case of the computer. For safety purposes please follow the instructions step by step.

First, shutdown your computer. Then unplug the power cable going into your computer.

Once you have opened the case, touch the metal of the case to discharge any static electricity.

The connector of the PSU which connects to the motherboard is readily recognizable by the number of wires in the bundle. To disconnect it you will need to press on the plastic clip to disengage it and then pull the connector up and away from the motherboard. Please take notice of the location of the locking tab and the notch on the socket of the motherboard, this will only connect one way as it is keyed. This wire bundle will have a memory of the way it has been installed and will want to bend back that direction, you may have to play around with it to find a position that the connector will stay in the same position while you run the test.

Posted Image

From the top left to right the pins are 13-24, the bottom from left to right are 1-12.

Please notice that there are PSUs with 24 pin and 20 pin connectors, the location of the green wire in the 24 pin connector is #16, and the green wire in the 20 pin connector is #14. If you look at the connector with socket side facing you and the clip on the top the number one pin will be on the bottom left corner. This makes the pin out for the 24 pin connector from left to right 13-24 on top, and 1-12 on the bottom. The pin out for the 20 pin connector from left to right is 11-20 on top , and 1-10 on the bottom. If you look at the connectors you notice that these are sockets that fit over the pins on the motherboard where the PSU cable attaches, this is where you will place the jumper. For a jumper you will need a piece of solid wire about the size of a paper clip (20-22 awg), preferably a wire with insulation. It will need to be large enough to fit firmly into the socket so that it will not need to be held in place while testing. You are at risk of electrical shock if you are holding the jumper when you power up the PSU. Insert one end of the jumper into the socket of the Green wire, and insert the other end into the socket of any Black wire.

Once the jumper is in place plug the cord back in. If the PSU is working properly the case fans, optical drives, hdds, and LEDs should power up and remain on. I would suggest that you not leave this connected any longer than is necessary for safety purposes.

To reconnect the 20/4 pin connector unplug the power cord, remove the jumper, and reconnect the connector. Take a moment at this time to make sure that nothing has been dislodged inside the case.
At this point you can use a DC Voltage meter to read the different rail Voltages. You will want to insert the black probe into any of the Black (-) sockets, and insert the Red (+) probe in the five different colored sockets, one at a time. Below are the five different colors and their corresponding rail Voltages. The Voltages should be within about ten percent of the given values.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC
Posted Image
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#3 JLi519

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Posted 28 November 2008 - 07:30 PM

Thx for trying to help but im doing this thing for school for an electricity assignment. I jsut want to know the total voltage and amperage it uses and i'm supposed to read the sticker on my power supply. For example my lightbulb uses 60 W, 120V and 0.5 amps. But the stuff on the sticker confused me so...

Edited by JLi519, 28 November 2008 - 07:32 PM.

#4 skiplc


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Posted 28 November 2008 - 08:21 PM

Why would the label confuse you? Ohm's law is only concerned with Volts, Amps, and Wattage...doesn't make any difference if it's a lightbulb or a toaster.


If V x A = W

What does

120 x 0.5 = ?

and what does

115 x 8 = ?

#5 Dennis the Menace

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Posted 29 November 2008 - 06:24 PM

I want to figure out how many amps and voltage my power supply is. Since I'm using AC my AC Input is:
AC Input: 115V/8A; 230v/5A; 60 Hz/ 50 Hz.
Which voltage and amperage number should I take? This is 350 W power supply.

You would either have to take the readings of each of your devices and compute and add them together using
ohm's law or use a Fluke multimeter or the like and take the amp reading to see the total draw on the
power supply. If that is what you are trying to determine ... i gather from your lightbulb example ... if you put 2 bulbs
in you have twice the draw.

#6 Platypus


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Posted 30 November 2008 - 03:25 AM

With regard to an electrical rating label including more than one voltage rating, you use the figure which matches the mains supply voltage you are using, as you've done for your 120V 60W lamp.

Actual voltage ratings given can vary slightly depending on the device manufacturer, and the primary market a product is specified for. So the rating you'd look at if your mains voltage is 120V, would be the 115V figure on your power supply. Some power supplies might be labelled 110-120V, with the same meaning.

Where I am in Australia, the nominal mains voltage is 240V, so I would use the 230V rating figure here.

Also, how much current (and therefore how much power) a computer power supply draws from the mains is not as simple as for something like a lightbulb or a toaster. Such a supply only draws as much power as it needs to run the computer, so as Dennis has said above, to know how much current a power supply is actually using, it has to be measured. The 8 Amp current rating on the label is the maximum current the supply can ever be expected to draw under normal operation, and tells, for example, what line fuse rating it needs.

It might be more information than you need for your assignment, but if you want to research more about computer power supplies, search for information about Switched Mode Power Supplies (SMPS).
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#7 dc3


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Posted 30 November 2008 - 04:42 AM

Most all PSUs have a label which will include the different rail voltages and their current ratings, is this what your instructor is asking for?


VAC Input Voltage 115V/230V Current 7A/4A Frequency 60/50Hz

Max DC Output +3.3V/14A +5V/30A +12V/10A -12V/0.5A -5V/0.5A +5V/2.0A

If the instructor wants you to show how the figures are derived you can use Ohm's law as previously posted.

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