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Step 2Planning
Planning is the most important step of any successful project. To plan this project, I created a few images. I am going to be using four binding posts, a power switch, a fuse holder, a power resistor, and two light emitting diodes (LED's) with current-limiting resistors. The first image details the circuit connections inside the power supply, where everything will be connected
When the power supply is connected to the wall socket, but not yet turned on, it provides a +5v standby signal, that can be used by the motherboard for things like wake-on-LAN functionality. We use this signal line to indicate when the power supply is plugged in with a red LED and a 330 ohm resistor. On my power supply, this signal line has a purple wire, and is labeled "+5VSB" on the circuit board.
When the power supply is first turned on, it must go through a start-up sequence, to ensure that everything is working, and that it is able to provide stable power to the computer. When the start-up sequence has completed, it signals the motherboard by providing +5v on the "Power Good/Steady" signal line. We will use another red LED and 330 ohm resistor to indicate when the power supply is running. On my power supply, this signal line has a gray wire, and is labeled "PGS" on the circuit board.
The power resistor is a 10 ohm, 10 Watt resistor, commonly called a "sandbar", because they are usually coated with a material that feels like sand. Most power supplies need a minimum load to keep them running, so this sandbar resistor provides a constant minimum load between the +5V rail and Ground. I've heard that newer power supplies also need a load on the 3.3v rail, your mileage may vary.
In the second image, you can see the diagram for the front of the power supply. Here I have marked where the components will go, including the LED's, the binding posts, the fuse holder, and the switch.
The third image is what the power supply looks like without any modifications. You can see the various voltages I am going to use along the front edge.
When the power supply is connected to the wall socket, but not yet turned on, it provides a +5v standby signal, that can be used by the motherboard for things like wake-on-LAN functionality. We use this signal line to indicate when the power supply is plugged in with a red LED and a 330 ohm resistor. On my power supply, this signal line has a purple wire, and is labeled "+5VSB" on the circuit board.
When the power supply is first turned on, it must go through a start-up sequence, to ensure that everything is working, and that it is able to provide stable power to the computer. When the start-up sequence has completed, it signals the motherboard by providing +5v on the "Power Good/Steady" signal line. We will use another red LED and 330 ohm resistor to indicate when the power supply is running. On my power supply, this signal line has a gray wire, and is labeled "PGS" on the circuit board.
The power resistor is a 10 ohm, 10 Watt resistor, commonly called a "sandbar", because they are usually coated with a material that feels like sand. Most power supplies need a minimum load to keep them running, so this sandbar resistor provides a constant minimum load between the +5V rail and Ground. I've heard that newer power supplies also need a load on the 3.3v rail, your mileage may vary.
In the second image, you can see the diagram for the front of the power supply. Here I have marked where the components will go, including the LED's, the binding posts, the fuse holder, and the switch.
The third image is what the power supply looks like without any modifications. You can see the various voltages I am going to use along the front edge.
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Brilliant instructable I am new in electronic engineering and wanted a lab power supply will you please tell me that how Can we add a potetiometer(voltage regulator),rheostat, voltmeter and ammeter to calculate and vary voltage and current?
Thanks
You should be able to either modify an existing volt/ammeter to do what you need, or you could always whip up some sort of microcontroller + tiny current sampling resistor + 7-segment displays for your volt or ammeter. Good luck!
I get 5v to the purple (standby) wire, but when switched on the fan does not come on and I get no voltage whatsoever on the grey (power on) wire, or to any 3, 5 or 12v lines. I have a good ground, so I know it's not that. Is the power supply just dead? For whatever it's worth, I hear an odd clicking sound which sounds like it's coming from the area of the large capacitors. Bad sign I assume?
Scroll down on this page, and look at the pinout.
http://www.informit.com/articles/article.aspx?p=339053
Is this what yours looks like?
Hope this helps.
A good point to watch, when you turn on the supply, does the cooling fan power up to full? or partial, or just for a brief moment, then spin down, with absolutely NO load applied? If it spins up to full, there is some form of load already at work. If the later (slow, or spins down) there is no active load resistor, and will require the load resistor to maintain operation.
Here's my 400W supply, with one of the Drive power cables still installed. (which I can use to power external hard drives.)
you need to do some math , because AC amp and DC amp is not the same , and you will be using current on the 12V so the AMP ratting will be different on your 120V AC .
i will suggest that you put a 1Amp at fist , if you have problem switch to a 2Amp or more .
normaly 1amp on the 120VAC is enough for most DIY project .
1Amp X 120Volt = 120Watt . this is alot of power .
??? X 12Volt = 120Watt = 10Amp
so
you will need between 8-10Amp on the 12Volt for your 1Amp fuse to burn .
so , if you want to draw 17Amp , i sugest you a 1.5Amp fuse on your 120VAC .
The fans are not running either. Any easy way to figure out what is going on?
I don't want to mess with the high voltage in the board.
Thanks!
Does the fan 'twitch' when you plug it in, or when you flip the power switch?
http://www.circuitprotection.com/catalog/fundamentals/PSWFundamentals.pdf
The 10 ohm resistor is used to provide a small, constant load on the 5v line, which is frequently required to get the power supply's internal circuitry to work properly. With the 10 ohm resistor across 5v, it draws 500 mA, which is most likely way more current draw than is necessary. I would guess that 100 mA would suffice. As long as you draw more than some minimum current from 5v (maybe 100 mA?) you should be fine.
The resistor in-line with the LEDs are used to control how much current goes through the LED. Once the voltage across an LED exceeds its "forward voltage" (usually between 1.5 and 3v, depending on color) the LED will pretty much conduct as much current as it can. We use a series resistor as a simple method to restrict how much current can flow through the resistor and LED. Since you're talking about 6v leds, I don't think they would even work for the power on and standby LEDs, as those are only 5v signals, which isn't large enough to exceed the 6v LED forward voltage.
I could be wrong, however, as I've never seen or worked with 6v LEDs. Do you have a link to their product page on Digikey/Mouser/etc?
Good luck!
and I make mine work by shorting p-on and ground wire + the incandescent light on 5v + 80mm fan on 12v (because the internal fan connector was broken)
True! (Most of the time)
> Also, ... If a ground fuse ever blows, you'll find yourself with a circuit that could send way more than the required 5 volts to the microcontroller and will definitely fry it !
Yep, very true! But .., The fuse is not there to protect the circuit. It is there to protect ..YOU!
If the fuse on the ground line should blow, the whole situation changes, there will be a 7V difference between the +12V and +5V lines and even a 24V level between +12V and -12V! How much current will flow on the lines .. who knows?!
> Always put fuses on supply lines and always make sure that your ground connexions are solidly secured without any fuse.
Totally acknowledged.
> Same thing for a mains switch in a project: You may (and i suggest it) switch both LINE and NEUTRAL at the same time
YES! Use a dual pole switch (DPST or DPDT) and switch both, live and neutral lines! That way it doesn't make any difference which way the plug is connected (think about countries with symmetrical plugs, e.g. Germany) or if the socket is miswired.
> but NEVER put a switch (or a fuse) on the GROUND (green or green-yellow) line !
YES! YES! YES! The ground (earth) connection _M_U_S_T_ not be broken. I don't care that it is against the law to brake the connection - it's just f***ing damned stupid to do so. And it might kill you. 'nuff said.
And you are partly right...fuses/breakers are there to protect CIRCUITS not the operator. They taught us Earth grounds save lives (that is the only purpose) fuses save equipment.