Why are you mixing notebook and desktop power supply problems which are almost unrelated?
I'm not aware of any notebook PC using a 12V supply rail. They are running optionally from a Li-Ion battery with design specific cell count, all regulated internal supply rails are 5V and below.
Different ATX connectors have different current rating which must not be exceeded. PC motherboards and cards with auxiliary power connectors have clear specifications regarding required power supply.
Think of the power rating of a desktop PC power supply, they typically range from 450W to about 1000W. Now look at the power rating of a typical notebook PSU, typically 45W to about 90W, in other words about 10% of the rating.
Look at the individual output current ratings of a desktop PC to see what you would have to replicate.
A notebook PSU is completely unsuitable for a desktop system. It's like running a car from an AAA battery!
Brian.
Still not sure if I understand the question completely. Standard ATX power supplies are multi voltage supplies, to supply a desktop PC from a notebook power adapter (or e.g. a similar 12 V adapter), it needs an internal power converter generating multiple voltages.
So first question is which input voltages are needed by your system?
19.5V is a compromise between needing high current and having enough voltage to charge the laptop battery. There has to be some overhead above battery voltage for the charge control circuit to operate. Bear in mind that the cells in a battery pack are usually 3.7V each so the next voltage down would be (19.5 - 3.7) 15.8V which might be too low to regulate down to 12V as the battery starts to discharge.
I disagree with your assumptions of power requirements, I'm using an i7 at 3.4GHz right now, it is fitted with 8GB of RAM and has a GT1050Ti graphics card. It 'ticks over' at around 360W but if I run highly intensive calculations, especially ones producing graphic output, it goes up to around 600W, about 40W of that in the cooling fans alone. I have a mains power meter in line with it to take the readings. Another i7 with similar configuration is used here exclusively for high-end video graphics production and editing, it regularly goes over 800W consumption (and keeps the room nice and warm too!).
Brian.
Its a new house and I wired it myself.
The figures are accurate. You didn't factor in the hard drives, Blu-Ray burners and several other interface cards.
Even so, it doesn't help your task of inventing electricity from thin air.
Brian.
Your "estimates" seem to be off...
http://www.buildcomputers.net/power-consumption-of-pc-components.html
If you add up the high end stuff in that list you end up right around 600 W, now if your finances restrict you to the technological backwater of PC components then if you add up the low/mid range of the scale then you end up with less than 300 W.
Now given that a PC can have any number of items switched out to high end components (specifically the video card) one might end up with a system that used to require 200 W (minus the video card power) that suddenly needs >400 W just for the video card alone ().
So unless you build your system as a walled garden (i.e like Apple) and offer no upgrade possibilities then you have to have a 600 W minimum ATA power supply to allow for the flexibility of changing out components (to something better than the run of the mill graphics card that came with the system), without having to also change the supply.
Laptops are for the most part already self contained walled gardens, which is why they can use a supply that has much less wattage. They also tend to use much less capable hardware overall to reduce power consumption.
Engineering workstations like the HP Z840 workstations draw a lot more than 600 W when loaded. They work very well as space heaters in a cold office
System Power Consumption
For this test we hooked up our power supply to a UPM power meter that will log the power consumption of the whole system twice every second. In order to stress the GPU as much as possible we used 15 minutes of Unigine Valley running on a loop while letting the card sit at a stable Windows desktop for 15 minutes to determine the peak idle power consumption.
so back to the main Q , Why all External power supplies used for PC outputs 19.5V and not 12V like in the internal ones ? it makes no sense.
They are running optionally from a Li-Ion battery with design specific cell count, all regulated internal supply rails are 5V and below.
My question is : If I use an external power supply of 12v outputs and plugged it into the Graphic cards direclty , would it work ?
or is it better to use the 19.5V notebook external power supply and add a DC to DC converter from 19.5 to 12V and then plug it into the card?[/qoute]
A definite NO. Simply because you need to reduce the 19.5V down to 12V, which in turn would require an extensive circuitry
i.e. Pass transistors, high value capacitors etc. and a fairly hefty heatsink. Also, you'll end up losing its current capability due to all the losses in the separate circuit.
It just wouldn't be practical.
In answer to Part 3 of your questions:
some ATX power supplies come modular , and my question is : lets say I use just one 12V plug and ignore the other plugs , can I use the whole wattage from that single plug ? or is there a limitation of each plug watt?
Yes, there are limitations of each plug, as PC PSU's are designed to output a certain amount of current for each voltage rail. This is mainly due to what wattage
rating of the output transistor/diodes within the supply that it can tolerate, as well as the wire thickness in any output inductors, also the circuit track thicknesses.
The 5V and 3.3V rails are more current hungry than the 12V rail, due to having to run the CPU, RAM, drives etc.
A 12V rail on average can deliver up to 12 Amps. Therefore you're looking at around 144W max output on a 450W PSU. Though the overall higher rating of the
PSU, the higher 12V wattage output you will be able to obtain.
They say it is single Rail (meaning watt is not divided between Vi)
I'm not 100% on what you mean by this question but if I'm reading it right, then even though the 12V volts is a rail in of itself, it still needs to share the overall wattage of the PSU
with all the other rails. Here it still boils down to what I've already said: wattage rating the output transistor/diodes etc.
No, see above...Example : I need to power a graphics card of 300 watts .. and I use an ATX power supply with single rail of 350 watts ... the power supply has the motherboard connectors that I will not use , and has only one PCIe 6 pin plug for card .. but since I am not using it for mother board , can I use one port for the whole 300 watts or do I need to take 12 V from the Motherboard plug ?
I can use thicker wires for 300 watts , if the plug on the power supply can stand 300 watts ..
more over , on the PCB of the power supply itself , does it stand 300 watts since it is a single rail or must also be divided between plugs ?
No need to use thicker wires, provided you use ALL the 12V wires together and their associated ground wires.
The 12V rail will not be delivering the 300 watts you desire. You'll only get what ever wattage the 12V rail is designed to deliver.
If you desire as much wattage for the 12V rail as possible from an external PSU, then consider purchasing a 1000 to 1200 watt unit and make the
modifications that will allow you to plug it into the rear of your new case and have it switch on at the same time.
I hope the above clarifies some of your questions. :smile:
Regards,
Relayer
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