PSU Question

Uncorruptable

I am looking for guidance on this one please, the orange wires that exit a PSU are the ones that carry a +3.3v, what i need to know is if i want to utilise this power supply only for another use where do i get the neutrral from?

Are some of the orange wires + & -?

The black wires are grounding wires, but where do i get a neutral? (Image from wiki)

http://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Wiring_diagrams

Redisle

The black wires are your neutral. The only place you will find an actual ground/earth wire in a PC PSU is connected to the inside of the case.

If you are using the PSU outside of the computer it will need to be activated by bridging the PS-ON wire and a neutral wire and many modern PSU's will not power up correctly without a certain load connected.

Uncorruptable

So i will have to ground the case to an earth, yes?

Also, where will i find the PS-ON wire & how do i bridge it?

Redisle

Tbh I would recommend against using a computer PSU if you aren't very familiar with electricity. These things are capable of delivering very large currents and could be dangerous if used incorrectly.

If you need 3.3V you would be best off buying an adjustable wall adaptor or something like this. A much safer option.

What exactly are you trying to do?

But just for reference..

You don't to do anything with the case. When I say the case is connected to earth what I mean is that the earth coming in from the mains socket is connected to the inside of the case. This is a safety feature of the power supply. If something were to go wrong inside the power supply and the metal case became live the house RCD (Trip Switch) would blow. The PS-ON wire is one of the wires on the main motherboard power block. Usually some strange colour like purple. The colour code should be written on the side of the PSU. By bridge it I just mean connect a piece of wire between one of the black wires and the PS-ON wire.

Uncorruptable

Redisle wrote: »

Tbh I would recommend against using a computer PSU if you aren't very familiar with electricity. These things are capable of delivering very large currents and could be dangerous if used incorrectly.

If you need 3.3V you would be best off buying an adjustable wall adaptor or something like this. A much safer option.

What exactly are you trying to do?

But just for reference..

You don't to do anything with the case. When I say the case is connected to earth what I mean is that the earth coming in from the mains socket is connected to the inside of the case. This is a safety feature of the power supply. If something were to go wrong inside the power supply and the metal case became live the house RCD (Trip Switch) would blow. The PS-ON wire is one of the wires on the main motherboard power block. Usually some strange colour like purple. The colour code should be written on the side of the PSU. By bridge it I just mean connect a piece of wire between one of the black wires and the PS-ON wire.

I am powering a high intensisty LED, the LED need up towards 13 amps for max lumens, hence i have opted for a power supply, i pulled it out of an old PC & the 3.3v is rated at 10amps, theLLED will operate at differing intensities depending on the ampage.

Allso, advised by the manafacturers, that using the power from a PSU is more stable than any wall adapters & that the LLED's are very sensitive to any change in the current, a PSU provides a stable constant current.

I will connect my device, bridge the green wire to ground (i have been informed elsewhere this is accurate), conceal it in a wooden box for safety, turn on the power & if it does what i am attempting to do i will report back with pictures.

thanks for all your assisstance.

Redisle

Hope it comes with a good Heatsink and fan! 42W is an awful lot for an LED.

If you are planning on drawing the rated current from the power supply you can't just use one one pair of wires either. You need to connect all the 3.3V wires together and use an equal number of black wires as your + and -.

If the LED is capable of drawing 13amps and the power supply can only deliver 10 then the power supply may react badly and over-current protection may kick in. You might need a constant current driver instead.

Uncorruptable

Redisle wrote: »

Hope it comes with a good Heatsink and fan! 42W is an awful lot for an LED.

If you are planning on drawing the rated current from the power supply you can't just use one one pair of wires either. You need to connect all the 3.3V wires together and use an equal number of black wires as your + and -.

If the LED is capable of drawing 13amps and the power supply can only deliver 10 then the power supply may react badly and over-current protection may kick in. You might need a constant current driver instead.

Thanks for the tip, i need to use all the wires together, yes?

The spec of the LED says it will ramp up to what it is being provided amp wise & only emit a certain amount of lumens related to the amps.

If it doesnt work out, i will have to invest in a constant current driver but i was trying to get around this for free.

Redisle

Uncorruptable wrote: »

Thanks for the tip, i need to use all the wires together, yes?

The spec of the LED says it will ramp up to what it is being provided amp wise & only emit a certain amount of lumens related to the amps.

If it doesnt work out, i will have to invest in a constant current driver but i was trying to get around this for free.

Yes connect all the orange wires together and the same number of blacks together. Thing is though it sounds like the LED is expecting a constant current driver. The computer PSU provides a constant voltage up to a rated current. The current drawn is dependent on the load.

I don't know exactly what kind of LED you are driving but generally you would need to use a resistor in series with the LED to limit the current to a certain value. This would be a huge power resistor in this case too. Lots of calculators about like here.

Uncorruptable

The LED states on the data sheet that it has variable drive currents from 1amp through to 13amps.

Its this LED chip,

http://www.luminus.com/products/CST-90_5_1215300843.pdf

Redisle

Ok. It is somewhat unusual to connect an led straight to a power supply like this as normally a current controlled source is used. However, looking through the data sheet this LED is listed as having a current of about 3A with a forward voltage of 3.3V. (Graph on Pg 10). Hence it should light up when connected directly to the 3.3V but you won't be getting anywhere near the full capacity. I also get the impression that the light output may not be very stable in this way as the ripple from the power supply may be visible as variations in the light output. Some more discussion on that here. Don't try to run this LED without a good heatsink however.

Uncorruptable

Redisle wrote: »

Ok. It is somewhat unusual to connect an led straight to a power supply like this as normally a current controlled source is used. However, looking through the data sheet this LED is listed as having a current of about 3A with a forward voltage of 3.3V. (Graph on Pg 10). Hence it should light up when connected directly to the 3.3V but you won't be getting anywhere near the full capacity. I also get the impression that the light output may not be very stable in this way as the ripple from the power supply may be visible as variations in the light output. Some more discussion on that here. Don't try to run this LED without a good heatsink however.

Cheers, i will have a processer heatsink cemented to the rear orientated to the fan, with a bit of luck it might do what i am aiming for.

Uncorruptable

I have successfully powered the LED from the PSU, it is giving off a very good light but i think it can be improved on,

If i understand some basics of electronics, will the guage of wire used to carry current determine its effectivness?

The wires i used to feed the LED needed to go through the small holes, the wire is thinner than the wires leaving the PSU which i dont think is good idea.

I did this just to test it, should i upgrade the wire to the thicker guage yes? Will it increase the lumens being emitted?

One other unrelated question,

If i put a 100 watt bulb where there is a 150watt supply it is ok as it will only draw 100watts.

If i put a bulb that runs off 230v ac onto a 65vdc supply, will it just light up dimmer? Or does it have a negative consequence on the circuit providing the 65vdc?